Vorticity0123

For this question there is more than just one way of interpretation of how this can be answered. In one way, one can think about the results from an SSW (sudden stratospheric warming), and how this may transition in high latitude blocking etc. by various feedback processes. On the other hand, one can also just plainly look at the shape of the polar vortex in the stratosphere (pressure-wise) and compare this with tropospheric pressure patterns. Effects of a sudden stratospheric warming on tropospheric conditions A sudden stratospheric warming can result in an increase of high latitude blocking in the troposphere a few weeks after the SSW has occurred. This is basically where my knowledge ends, and therefore a quote from the excellent stratospheric introduction from Chionomaniac earlier this year (who is much more knowledgeable on this subject): To try to remain a little on topic, more about SSW's and so on can be found here: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ Comparison of tropospheric and stratospheric pressure patterns The second option is to compare tropospheric and stratospheric pressure patterns, and then see whether there is any match. For this purpose, I will use the ECMWF stratosphere charts from FU Berlin and ECMWF surface output from wetterzentrale. First, check the ECMWF output for 100 hPa level (stratosphere, equalling about 16 km height1): ECMWF 100 hPa heights (12 UTC 26-12 run, T+96) From the image, one can see there is a clear ridge (higher heights pointing toward the pole, meaning high pressure) present over Western Europe toward Scandinavia. Furthermore, a ridge is present just to the west of California. On the other hand, a sharp trough (lower heights pointing equatorward, meaning low pressure) is located over central US. For comparison, check the ECMWF surface level pressure map at the same timeframe: ECMWF surface level pressure and 500 hPa heights (12 UTC 27-12 run, T+72) The ECMWF run given above is from one day later, but in general it can be assumed that at 3 to 4 days out, the large scale features between two model runs do not vary that much. As can be seen from the chart, the 500 hPa and surface features match the stratospheric height chart almost entirely in the way of patterns (neglecting that there is no real polar vortex present at the surface). Once again, there is a 500 hPa ridge present over Western Europe (edging northeastward), along with a surface high. A very large 500 hPa trough exists over the central US with a complex area of low pressure. Finally, the high to the west of California is present here as well, at the surface as well as at 500 hPa. This connection might imply that the stratosphere has some direct predictability over the troposphere and vice versa. For example, one can immediately deduce from the stratospheric chart at 100 hPa at the timeframe used above that there is some kind of ridging present over Western Europe, which is coincident with settled weather. Note that this way of predicting might not always work, but it could be a good first guide. Conclusion Regarding SSW's, the time it takes before possible effects to the troposphere unveil itself is difficult to predict. However, there is a straight coupling between the troposphere and the stratosphere regarding pressure distribution, this kind of 'effect' is immediately visible. It is difficult to assess, though, whether this is caused by tropospheric effects or whether stratospheric effects cause this, a bit of the chicken and the egg story. There are of course quite some people at this forum more knowledgeable than me who can perhaps give a better answer to this question, if so feel free add some content or to correct me! Hope this answers your question to some extent Sources: 1: http://www.meteociel.fr/modeles/sondagegfs/sondagegfs_6.694244534188226_51.20863715175564_6_0.png http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ http://www.wetterzentrale.de/topkarten/fsecmeur.html http://www.meteociel.fr/modeles/gfse_3d.php?lat=49.75&lon=-0.5&ech=6&zoom=6

After the tour across the UK, the low pressure area currently located somewhere close to London is bound to bring some quite significant amount of rain and snow for the Benelux. As has been observed over the UK, the Benelux is also going to experience a north-south split in the type and amount of precipitation, with the Netherlands (especially the middle- and southern parts) will be experiencing quite some snow, while Belgium will see a mix of rain and snow (probably more snow to the north and east in Belgium). Low pressure tracks toward the Benelux To place this into perspective, below is the wind and surface level pressure chart of tomorrow morning from the Harmonie model (Dutch mesoscale model): Harmonie 10 m wind and MSLP 18 UTC run, T+14 h. The core of the low pressure area is located directly over the center of Belgium at 09:00 local time (08 UTC). The low pressure area also contains quite a strong wind field, with the northwestern edge of France probably having a sustained 8 BFT for some hours. Over land, winds could also edge up to 5 BFT, about 200 kilometres north of the center. Temperature structure of the system Furthermore (perhaps more interesting) is that the wind blows from land north and east of the low pressure area, while winds from sea are being experienced on the western and southern half of the system. This has also some consequences for the temperature, and more importantly (for snow), the dewpoint. Therefore, the dewpoint temperatures forecast at the same timeframe is given here: Harmonie dewpoint temperatures 18 UTC run, T+14 h. Over the whole Netherlands, and over extreme eastern Belgium, the dewpoints are just at the edge for snow/rain, being at 0*C. On the other hand, the dewpoints over the central part of Belgium are much higher, up to 5*C (as a result of the winds from sea and the influx of warmer at the center (?) ). Yet they are lower again over the western part of Belgium (about 0*C again). This difference is better visible when taking a look at the 850 hPa temperatures at the same timeframe (the chart is from Meteociel, because the Harmonie model does not have the 850 hPa temperatures): WRF NMM 850 hPa temperatures 18 UTC run (T+14). For the time being, I assume that the position of the low pressure system is identical (which is not exactly the case, but does fulfil the conditions to make comparison possible). As can be seen from the image, sub -4*C 850 hPa temperatures encompass the northern, southern and western extent of the low pressure area. However, the center of the low pressure area does contain somewhat higher 850 hPa temps (even higher than -2*C just to the west of the center, check the Harmonie output at the first image). The reason for this is unknown to me, but most likely it has something to do with the frontal structure of the low. If anybody knows the answer, it would be greatly appreciated! Precipitation analysis Then, finally, to what it all comes down of course: the snow itself. Check the Harmonie output for the precipitation amounts of the same timeframe as given above: Harmonie 10 m precipitation amount 18 UTC run, T+14 h. The main precipitation zone lies over the southern half of Holland. There is also some scattered precipitation over Belgium. However, a few hours prior to this, the precipitation zone was lying over Belgium as well. As the dewpoints are around zero over Holland and over the extreme eastern part of Belgium, and considering that the precipitation expected is going to be pretty intense (more than 1 mm/h at many places in the Benelux), this will be mainly snow at the areas mentioned before. The Harmonie model can also indicate where the precipitation will be wintry and where rain. For that forecast, check the link below: http://www.weerplaza.nl/gdata/weerkaarten/harmonie/charts_harmonie_pcptype_bnl_15.png (Harmonie 10 m assessment of kind of precipitation, 18 UTC run, T+14 h.) The red dots indicate wintry precipitation, while the blue dots indicate rain. This image agrees with the statement given above. Conclusion Ultimately, summing this all up, snow amount are forecast to vary between 0 in the north of Holland, up to more than 10 cm in the center and south of Holland and eastern Belgium. However, any change in the track of the low pressure could completely change this forecast, especially with such a precarious situation. Very exciting times lie ahead! Sources: http://www.weerplaza.nl/weerkaarten/harmonie/?tau=15&element=pcptype http://www.meteociel.fr/modeles/wrfnmm.php?ech=3&mode=21&map=0 1:https://twitter.com/weerplaza

With Christmas now on the doorstep, the weather charts are turning interesting from a cold perspective. This all seems to begin with a very small scale low pressure system which is expected to pass this Friday or Saturday. How will this small-scale feature influence our weather, and what are the long-term trends after this passage? To answer these questions, I will give a look at what various models are showing. Current synoptic situation For the first 96 hours, I will use the GFS charts as a guide for the synoptics. The current synoptic situation is given below: GFS 18Z surface pressure + 500 hPa heights (colours) T + 0h. As of speaking, we are experiencing a zonal flow (red arrow), with relatively high pressure located over central Europe, and low pressure activity located near Scandinavia. This complex area of low pressure is associated with some weak troughing (indicated by the blue colours on the map edging slightly southward over the southern tip of Scandinavia). The zonal flow over the past few days has led to anomalously mild conditions, with average temperatures about 1 to 3 degrees above average last week1. There is also a notable cut-off trough present to the southeast of Newfoundland (green colours, emphasized by the blue circle), associated with a remarkably strong low pressure area there. However, the main focus for the short-term weather will lie in the area blue-encircled to the west of Greenland. If one looks very closely, a dip in the 500 hPa heights (indicated by the blue colours) can be observed. This dip is in part responsible for the formation of the low pressure area affecting the UK on Friday or Saturday. Short-term developments 24 hours later, the 500 hPa trough has moved east and extended somewhat southward, as can be seen in the link below: http://www.wetterzentrale.de/pics/Rtavn241.gif (GFS 18Z surface pressure + 500 hPa heights, T+24h.) The trough can be seen just to the northwest of Iceland (blue colours). Also, a surface low is located at the position of the trough, but this is not the surface low that will move over the UK. The low of interest is located to the west of Ireland, as a sub-1025 hPa low pressure area (if one can call it as such). Another 24 hours later, the low pressure has deepened somewhat into a sub-1010 hPa low pressure area now located near London. http://www.wetterzentrale.de/pics/Rtavn481.gif (GFS 18Z surface pressure + 500 hPa heights, T+48h.) Note that the minor 500 hPa trough previously located near Iceland is extending toward the low pressure area located over London. On the 850 hPa temperatures chart of the same time, the low pressure area is also beautifully visible, with relatively warm subtropical air flowing into the storm from the south, and cold 850 hPa temperatures moving in behind the low from the region near Iceland. (GFS 18Z 850 hPa temperatures, T+48h.) What is also remarkable is that there is a large pool of rather cold 850 hPa temperatures located over and to the east of Scandinavia. For the long-term prospects, it is important to focus on the low pressure area located over Nova Scotia. On the southeastern side of the system, a significant stretch of warm 850 hPa temperatures is being advected northward. If one combines this with the 500 hPa pressure chart, one can see that at this position, ridging starts to edge northward as well (just to the east of the warmest 850 hPa temperatures). Looking at another day later, the low pressure system has moved well into Europe, which can be seen in the following link: http://www.wetterzentrale.de/pics/Rtavn721.gif (GFS 18Z surface pressure + 500 hPa heights, T+72h.) The system may deliver some harsh conditions in the Benelux, with snow and a northeasterly storm all within the range of possibilities (currently, there is too much uncertainty to say anything specific about this). More notable is the warm air advection (WAA) that has continued to the east of the low (500 hPa and surface) over Nova Scotia. This can be seen by the orange colours edging northward toward Iceland. Furthermore, this WAA has shifted somewhat to the east. As a result, high pressure at the surface starts to build in the vicinity of Iceland. In the days following, this high pressure activity will become established near the UK. Medium-term (un)certainty As a result of the warm air advection advertised above, a settled spell seems to be becoming more prevalent over the UK. There appear to be developing some minor discrepancies between the models then. For comparison, the links to the GFS and the ECMWF 5 days out will be given: http://www.wetterzentrale.de/pics/Recm1201.gif (ECMWF 12Z surface pressure + 500 hPa heights, T+120h.) http://www.wetterzentrale.de/pics/Rtavn1141.gif (GFS 18Z surface pressure + 500 hPa heights, T+114h.) The main feature that can be observed is that the GFS has the center of the surface high pressure area over the border between France and Germany, and the ECMWF has it around Normandy (much more to the west). If one looks at the 500 hPa heights (which are probably a better guide here), the GFS is somewhat more progressive in terms that it has the 500 hPa ridge (orange colours) moved further to the east than the ECMWF has. However, these differences at the 500 hPa level are not very significant (on the basis of large-scale patterns, not what will be experienced at the surface). To show this, take a look at the spaghetti diagram of 120 hours out of all GFS members: (GFS 18Z spaghetti contour lines of 516, 552 and 557 hPa height, T+114h.) A short explanation: the lines above originate from all GFS members from the 18Z run. These indicate lines of equal pressure (being 516, 552 and 557 hPa height). When the lines are close together, it means that all members agree on a significant kind of pattern. When the lines are all over the place, the uncertainty is large. As can be seen, clear patterns can be seen in the diagram, with the 500 hPa ridge extending toward Scandinavia from the southwest (northward-edging lines). On the other hand, a very deep trough is located over central Europe (southward-edging lines). The trough is partly caused by the low which will over the UK in about 2 days' time. This is a good indication that the spread for 5 days out is relatively small. Only the orientation of the (500 hPa) ridge over the UK seems to vary some. Given that there is quite some certainty that a ridge will be present over the UK (at 500 hPa and at the surface) it seems that a more settled pattern will start to emerge after Christmas with also somewhat cooler temperatures than we have been used to. Long-term trends Looking at the long-term trends, uncertainty (logically) increases significantly. The NOAA 8-14 day 500 hPa anomalies show that some kind of a ridge is likely to be present over Scandinavia, but one needs to see more consistency to be certain for this. They can be seen in the link here: http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php The ensembles from the GFS and ECMWF at day 10 (not indicated here) generally agree on the idea of some kind of high pressure activity remaining over northern Europe, but it is uncertain to which extent this will be. Also, the ECMWF ensembles for De Bilt, the Netherlands, show that after about 8 days, there is a range of about 15*C in maximum temperature between the warmest and coldest member, showing there is a large degree of uncertainty after that period. They can be found here: http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim Conclusion After the passage of the low pressure area in about 2 days' time, it seems that a dry period will emerge influenced by high pressure activity, with some frost at night also a good possibility. How long this high pressure activity will be able to sustain itself is still up to debate, but there are indications that this period may last more than just a few days. Finally, what rests is to wish a merry Christmas to you all :smiliz19: . Sources: 1 http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/wctan1.png http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php http://www.wetterzentrale.de/topkarten/fsenseur.html http://www.weerplaza.nl/15daagseverwachting/?r=midden&type=eps_pluim

Hi Lorenzo, thanks for the reply. It seems I was thinking too narrow on the GWO, there is much more to the GWO than I realized at the time of creating the post above. My understanding of the physics on the GWO is only very small, imagining what transport of angular momentum 'looks like' is already a challenge. A challenge that is not easily solvable, it seems. Going back to the basic principles of physics, the first thing that I have realized is that angular momentum is a measure of rotation in the atmosphere, analogous to vorticity (coincidently my profile name ). So, in simple terms, angular momentum (vorticity) indicates the 'tendency' of a particle to rotate. Physically, the definition is the gradient of the velocity of the air (wind speed). Yet, upon knowing this, it is hard to be able to 'visualize' this in terms of high- and low pressure areas, let alone what the effect is of increased/decreased angular velocity transport poleward or equatorward. Another thing I probably overlook was the assumption that the GWO phase space diagram (given in my post above) indicates angular velocity values at the midlatitudes. What the definition is, is uncertain to me. Concluding, I do agree that the GWO remains something of a puzzle (a very complicated one), which is very difficult to understand physically. Probably experience is a good tool to get an indication of what it all indicates, rather than try to get a full fundamental understanding. Sources: http://journals.ametsoc.org/doi/abs/10.1175/2008MWR2686.1 http://www.theweatherprediction.com/charts/500/basics/ http://www.wetter3.de/animation.html http://en.wikipedia.org/wiki/Madden%E2%80%93Julian_oscillation

After a week of (global) inactivity in tropical cyclones, a new one appears to be on the verge of forming. 04U has a large area of deep convection over and to the south of the center, as well as some banding features (especially in the south). The low is located to the southwest of Indonesia, just to the north of Cocos Island. The Bureau of Meteorology (BOM) expects the cyclone to intensify into a category 3 cyclone (Australian scale, about equal to a category 1-2 hurricane on the Saffir-Simpson hurricane scale). Regarding track, 04U will move southeastward intially, before curving back to the southwest possibly impacting Cocos Island in about 3 days. Track forecast of 04U (as of 23-12-2014, from the BOM) Sources: http://www.usno.navy.mil/JTWC/ http://www.bom.gov.au/cyclone/index.shtml http://en.wikipedia.org/wiki/Tropical_cyclone_scales

For anyone interested, an in-depth post about some indices (GWO, being the global wind oscillation, and the MJO), and their relation with the weather at our latitude and longitude, can be found in the In Depth model discussion part: https://forum.netweather.tv/topic/76236-in-depth-model-discussion-and-summaries/page-11

Now that the models are showing some interesting synoptics in the long term (i.e. a Greenland block), it seems that a pattern change is possible in the near future (about 10 days away). I will try to give an in-depth look on what indicators point toward a pattern change. Given that I am covering some unexplored terrain for myself in this post, any corrections/comments would be very welcome. GWO The first thing that will be discussed is the GWO (Global wind oscillation). A very good description in what it exactly is, can be found in the Netweather guides, with the link given below: https://forum.netweather.tv/topic/52083-gwo-and-global-angular-momentum/ In short, a GWO in phase 6 to 7 indicates a westerly wind tendency at the midlatitudes (in other words: the winds are flowing more from the west than usual, giving rise to a more zonal pattern). On the other hand, phases 2 and 3 indicate an easterly wind tendency at the midlatitudes (the winds do have a tendency to be less westerly than usual, which often goes along with blocked, highly amplified jetstream patterns. As mentioned by Tamara in the MOD thread, the GWO is currently trending toward phase 2 and 3, which indicate that zonal westerly winds are less likely in that period. Therefore, a trend to more blocking is plausible, given this forecast. The GFS agrees with this forecast, as can be seen in the phase diagram below: GWO trend over the past few days and GFS forecast (green colour), as of 16-12-2014. What can be seen is that, after about 20 December, the GWO starts to become active, cycling toward phase 2 and 3. A more in-depth explanation of the GWO can be found in the link below: http://www.esrl.noaa.gov/psd/map/clim/test_maproom.html MJO The MJO (Madden-Julian oscillation) is, in short, a measure for the amount and distribution of convection anomalies near the equator. The placement of these anomalies over the equator tells us something about the weather which occurs, or is likely to occur in the future, in the midlatitudes as a result. A more extensive explanation can be found in the link below: http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/mjo.html Currently, the MJO is not active at all, giving little aid to the predictability of the weather over the midlatitudes. However, in a week or so, the MJO is forecast to enter phase 3, as suggested by the GFS ensembles: MJO trend over the past few days and MJO forecast (green lines) as given by various GFS ensemble members, as of 16-12-2014. The MJO 'travels', like the GWO, counterclockwise around the diagram given above. Currently, there seems reasonable certainty that the MJO will enter phase 3, but there remains a lot amount of uncertainty as whether and how fast the MJO will continue toward phase 4, or whether it will weaken back to a state in which the convective anomaly patterns over the equator caused by the MJO are negligible. The Climate Prediction Center states this, in their discussion, as follows: If the MJO would trend into phase 3, the following 500 hPa anomalies would be observed: 500 hPa anomalies caused by a MJO signal of greater than 1 (out of the inner circle as given in the phase space diagram). This is phase 3. Note that these anomalies are no guarantee that the pattern will look exactly like that; they are only a general guide. Furthermore, these charts indicate anomalies, no real 500 hPa heights. This means that positive anomalies may still be associated with a 500 hPa trough, with it being only weaker than it usually is. What can be seen is that there is indeed some kind of a positive 500 hPa anomaly noted to the south of Greenland, which kind of coincides with the Greenland block which has been advertised by some models. However, there are also positive anomalies forecasted over Scandinavia, which do not seem to be very likely at the moment. This can be seen in the GFS ensemble 500 hPa anomalies anomalies forecasted for 26 December, which can be found in the link below. http://www.wetterzentrale.de/pics/Rnaa2401.gif All in all, it seems that a pattern change is plausible given the various model output, the negative GWO and the MJO becoming more dominant again. To what this will lead is still up to debate, though. It will be a good watch, that is for sure . EDIT: For the GWO forecasts, there is a great link available which does show the trend and forecast of the GWO by the GFS. It can be found in the link below: http://mikeventrice.weebly.com/misc-oscillations.html There is much more to find on this link in terms of MJO, GWO, waves etc., hope it helps! Sources: http://www.americanwx.com/raleighwx/MJO/MJO.html (MJO anomaly composites) http://www.esrl.noaa.gov/psd/map/clim/test_maproom.html (GWO circle explanation, also showing more in-depth mountain torque events associated with the GWO) http://www.esrl.noaa.gov/psd/psd1/review/Chap04/sec3.html (Explanation of GWO) http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (GFS MJO forecast) http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/ (Tropical convection and MJO uncertainty analysis) http://www.wetterzentrale.de/topkarten/fsenseur.html (GFS ensemble forecast of Europe) http://mikeventrice.weebly.com/misc-oscillations.html (Various oscillations and their current strengts)

That was a sudden and quick demise from this cyclone, what shear can do to such systems. This cyclone reminds me of TC Omar in 2008 (Atlantic), with which it took only 6 hours to get from a category 4 tropical cyclone to having an exposed LLCC (low level circulation center). Bakung is not dead yet, though, The system keeps firing some convection, but it is also in a region of very strong shear (20-30 kt as analyzed by CIMSS, as of 10:00 UTC). However, just to the south of the cyclone, there is a pocket with almost no shear, so it takes just a little southward drift for this cyclone to find itself in a more favorable environment. Looking at ASCAT imagery from yesterday afternoon, one can see that the center is not well defined. It is given below: ASCAT pass of Bakung (15-12-2014 15UTC) The center is indicated with the black cross (center position analyzed by CIMSS, assuming little movement has occurred since yesterday). What can be seen is that there is a wide line of convergence (winds blowing toward a certain area from the north as well as from the south) oriented ESE-WNW from at least the center of Bakung up to the west. This means that the center of Bakung is very elongated at best. In fact, it seems that the cyclone is entangled with the ICTZ (intertropical convergence zone). The GFS is suggesting that the cyclone will develop in a few days, but it has had a positive bias for most of the lifetime of Bakung (indicating development where it did not occur). Unless Bakung is able to escape the shear and the influence from a possible ICTZ, chances for development seem not very high, at least in the short term. Sources: http://en.wikipedia.org/wiki/Hurricane_Omar_%282008%29 http://www.knmi.nl/scatterometer/ascat_osi_25_prod/ascat_app.cgi?cmd=showimage&ascending=yes&day=0&flag=yes&coord.x=374&coord.y=214 http://www.acmad.net/new/?q=en/pages/itd-itcz-positions http://www.usno.navy.mil/JTWC/ http://tropic.ssec.wisc.edu/# http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14121600/13.html

For the ones looking for a nice new way of analysing weather synoptics (or charts), Meteociel has a chart viewing option which enables one to 'visualize' the flow in the atmosphere by means of an interactive 3D viewer (somewhat similar to earth.nullschool.net viewer, but then with a few more and different features). The link is given below: http://www.meteociel.fr/modeles/gfse_3d.php?lat=49.75&lon=0.5&ech=138&zoom=6 A really nice example of this visualization can be found by checking the 'temp 2m + vent 10m' (2 meter temperatures and 10 meter wind), at Wednesday, 17 December, 19Z. As an illustration of what can be seen there, below is the 850 hPa temperatures forecast of the GFS for the same date, but then from the standard Wetterzentrale view (the Meteociél images cannot be uploaded in this way as far as I am aware). GFS 850 hPa temperatures and surface level pressure, 18Z run, T+120 H. From the chart given above, it can be seen that the south of the UK is located between two fronts, with the warm front being located over Germany (red line). Furthermore, a cold front is oriented ESE-WNW just to the north of the UK (which can be seen by the very sharp temperature gradient there, blue line). The southern part of the UK itself is therefore located in the warm sector. This is made evident by the fact that the southern part of the UK is located in very warm 850 hPa temperatures for the time of the year (over 10*C in the extreme south). On the Meteociel charts given in the link above, this weather pattern is beautifully evident. This is definitely the case at the cold front, where the temperature gradient is very large (large change in temperature over a small distance), and there is also a pronounced wind shift (the wind blows from the northwest north of the cold front, and from the southwest south of the cold front). With the Meteociél link, it is also possible to view ensemble forecasts from the GFS at any location. Also, GFS sounding forecasts can be accessed at any random location. This can all be done by clicking with the right mouse button on any location one wishes to analyse. Hope you like it . Sources: www.meteociel.fr/modeles/gfse_3d.php?lat=49.75&lon=0.5&ech=138&zoom=6 http://www.wetterzentrale.de/topkarten/fsavneur.html http://www.atmos.illinois.edu/~snodgrss/Midlatitude_cyclone.html

This is quite odd, TCWC Jakarta did not mention anything about the system yesterday, and now they have upgraded it to a 50 kt tropical storm! Probably they were not aware of the system? Could it have anything to do with the lack of observations in that area? Regardless of this, Bakung does look like a healthy tropical storm. Even though banding features have diminished some over the past few hours (as of 18:00 UTC), the central convection has been on the increase, both in magnitude and intensity. This can be seen in the Rainbow loop from NOAA given below: Rainbow satellite image loop of Bakung. It can be activated by clicking on it. Note that the image does not auto-update itself. The forecast from TCWC Jakarta suggests the system will intensify into a category 3 cyclone (Australian scale), with an intensity of 70 knots. This track forecast can be seen below: Track forecast of Bakung. If the cyclone tracks as forecasted, it may pass three basins in just three days, being Jakarta area of responsibility, Australian area of responsibility (once it moves below 10S), and in La Reunion area of responsibility (when it tracks west of 90E). Sources: http://en.wikipedia.org/wiki/Tropical_cyclone_basins http://www.usno.navy.mil/JTWC/ http://www.bom.gov.au/wa/forecasts/nwcyclone.shtml http://meteo.bmkg.go.id/siklon

It looks like this option will not occur, as the JTWC is no longer indicating this possibility. However, still a few models are going for a track very near the coast. This can be seen in the track guidance given below: 0 06 UTC 11-12-2014 tropical cyclone model forecasts. Note that the GFDN is still indicating a track just to the south of Vietnam. Regardless of whether Hagupit will track over Vietnam or not, wind shear over Hagupit is currently about 20 kts, and will probably only increase over the forecast track of the tropical cyclone. Therefore, dissipation in the next few days seems to be unavoidable. A shear analysis of the Western Pacific, with TC Hagupit indicated on it, can be found in the link below: http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=westpac&sat=wgms∏=sht&zoom=&time= Sources: http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=westpac&sat=wgms∏=sht&zoom=&time= http://www.usno.navy.mil/JTWC/ http://www.ssd.noaa.gov/PS/TROP/floaters/22W/22W_floater.html http://www.ral.ucar.edu/guidance/realtime/plots/northwestpacific/2014/wp222014/

With western Europe now being entrenched in a quite strong westerly flow, the weather looks to be unsettled over the UK over the next couple of days. How will the general surface pressure and 500 hPa pressure patterns evolve over the next few days, and are there any indications for changes in the large-scale pattern? A broad insight in the weather pattern (focussing mainly on the tropics on the long term) will be given in order to answer these questions. N.B. No direct translation of the synoptics to surface conditons in the UK will be given. Current situation For the description of the near-term weather, the GFS 18Z run of 9-12-2014 will be used. First, the current synoptic weather map looks as follows: GFS surface level pressure + 500 hPa heights (colours) 18Z run, T0. What can be seen is that there is a large 500 hPa trough (purple colours) near Iceland. This trough has been influencing our weather over the past few days, and currently a very deep surface low pressure area (sub 950 hPa low) is located near Iceland as well. This low will bring gales to the UK tomorrow, as discussed by others before. Furthermore, the Azores high (at the surface as well at is also quite strong, located over sea to the west of Spain. This is helping to create a very sharp gradient in pressure (read: strong wind field) south of the low pressure area over Iceland. The Russian high pressure is located in the far east, too far away to exert any influence on the weather near the UK. The same accounts for the cut-off 500 hPa low (green colours) over the central Mediterranean. Mid-term outlook If one looks 48 hours away from today 18Z, the pattern seems to become more amplified, as can be seen in the link below. http://www.wetterzentrale.de/pics/Rtavn481.gif High pressure appears to be edging toward Greenland from the Azores high (both at 500 hPa and the surface), and the trough over Iceland has become elongated in a North-South direction. However, 2 days later (so 4 days later from now), the pattern has returned to a more zonal flow: http://www.wetterzentrale.de/pics/Rtavn961.gif The high pressure area toward Greenland has weakened, and a new low pressure area has developed near Iceland (at the surface), causing the flow over the UK to reorient more in an East-West direction. Thereafter, the pattern is forecast to stay mainly zonal (being weakly wavy, or in other words the flow is not completely straight but modestly amplified). The NOAA 6-10 day forecasted heights and anomalies (as suggested by John Holmes) show this: http://www.cpc.ncep.noaa.gov/products/predictions/610day/610day.03.gif Note that the green contour lines are very close together over the Atlantic between the UK and Canada, indicating a strong pressure gradient. Furthermore, there is also a very dominant trough at 500 hPa near Iceland, as indicated by the below-average heights (which tend to be low at this time of the year on average as well). Long-term analysis and trends The 8-14 day 500 hPa heights and anomalies from NOAA suggests that the westerly flow is going to continue, with a deep 500 hPa trough over Iceland and a dominant Azores high just to the west of Spain: http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif This signature is also indicative of a positive NAO (North Atlantic Oscillation). Tropical-extratropical interactions The interesting part comes when one checks the MJO forecasts, or more physical, the evolution of the tropical convection anomalies. These anomalies (which are partly explained by the MJO) tend to influence the weather in the midlatitudes (e.g. the UK). Note that this relationship is in both directions (i.e. the tropical convection anomalies influence the extratropical synoptics, but also vice versa). A good read about this can be found in the link below: http://www.atmos.albany.edu/facstaff/roundy/convection/Walich14.pdf (scientific article about the interaction between the pressure pattern in the extratropics and the tropical convection anomalies). From the weekly discussion from the Climate Prediction Center (from the NOAA, given in the link below), it appears that the uncertainty in the weather pattern is very high in the tropics: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/ I will try to give a short summary, using quotes from the discussion in the link given above. Lack of Atmospheric El Niño response The first thing that comes to mind is the lack of coupling of atmospheric conditions with the El-Niño like conditions in the ocean. Usually, an El Niño event tends to influence the general weather pattern quite a bit, but this does not seem to be the case at the moment. From the discussion: A link to very brief information of what the influence of an El Niño event on the weather patterns in the midlatitudes can be found in the link below: http://www.wmo.int/pages/themes/climate/significant_natural_climate_fluctuations.php MJO evolution uncertainty The next thing that is notable is the uncertainty regarding the evolution of the MJO (madden-julian oscillation). A few days ago, it seemed that the MJO could move into phase 7 or 8. Without going into too much detail, this phase tends to coincide with positive anomalies (higher than average 500 hPa pressure, or in other words, a ridge) near Scandinavia. A whole set of composites can be found in the link below: http://www.americanwx.com/raleighwx/MJO/MJO.html However, for now, some models are forecasting the MJO to weaken (i.e. decrease in amplitude), which would result in its influence being negligible over the weather over the midlatitudes. It has to be stressed, though, that uncertainty associated with this forecast is very high. This is also noted in the discussion of the Climate Prediction Center: Long-term summary Given the all above, it appears that uncertainty is very high regarding the weather in the tropics. This could have implications on the predictability (read: a decrease in predictability) of the weather in the extratropics. This is nicely summarised by the CPC: Overall summary At first glance, the forecast for the next few days looks pretty straightforward, with slightly amplified (wavy) zonality continuing for the next several days. Thereafter, there are signs that the weather will not change (e.g. the 8-14 day anomalies from the CPC), but given the large uncertainty in the tropical weather, the predictability of the weather in the extratropics after about 7 days could be very uncertain, regardless of what the models are showing. And then the stratosphere, and the other hints mentioned by other members are not even considered in this post . So I would suggest an exciting period lies ahead in terms of model watching, which I will followed with interest! Of a final cautionary note: the uncertainty mentioned in the tropics does in no way gurantee any pattern change in the extratropics, it only shows that a pattern change is possible in the midlatitudes. Sources: http://www.americanwx.com/raleighwx/MJO/MJO.html http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/ http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php http://www.wmo.int/pages/themes/climate/significant_natural_climate_fluctuations.php http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf http://www.wetterzentrale.de/topkarten/fsfaxsem.html

Hagupit is currently in the process of making landfall. Unfortunately, the system has taken a southward, which increases the threat of the system to Tacoblan, which was hit hardest by Haiyan last year1. However, it seems that Tacoblan will remain just to the south of the most intense part of the system, as can be seen in the Rainbow satellite image below: Rainbow satellite image of Hagupit The area where Hagupit is currently located is fortunately quite sparsely populated. Furthermore, if one looks at the image above, it can be seen that no definite eye feature is present, which means that Hagupit at time of landfall is much less intense than Haiyan last year. However, it has to be mentioned that Hagupit remains a formidable category 3 typhoon, with sustained winds up to 110 knots (1 minute mean). The forecast track from JTWC for Hagupit indicates that Manilla may be receiving a direct hit from the system as well. The main threat will be heavy rainfall in that area, though the system is still expected to be a category 1 tropical cyclone by then. Let us pray for the people living there that they will stay safe! Sources: 1:http://en.wikipedia.org/wiki/Typhoon_Haiyan http://www.ssd.noaa.gov/PS/TROP/floaters/22W/22W_floater.html (image) http://www.usno.navy.mil/JTWC/ (intensity estimate)

Interesting way of thinking, seems to be quite a new, not well-understood (or unknown) part of science (tropical cyclone-stratosphere interactions). Reading through some articles suggested it could be related to gravity waves being emitted from the tropical cyclones vertically upward into the stratosphere. Here are some links to articles about this: http://onlinelibrary.wiley.com/doi/10.1029/95RG02097/abstract (stratosphere-troposphere exchange) http://onlinelibrary.wiley.com/doi/10.1029/92JD01679/abstract (evidence for gravity waves being emitted by TC's) http://www.sciencedirect.com/science/article/pii/S1364682614001667 (Gravity wave analysis at tropical cyclone Mahasen) If one looks at the latest cross section from the COAMPS-TC model (which can be found here), one can see that the cyclone does indeed exert influence very close to the stratosphere, up to about 150 hPa height. During the past few hours, the cyclone has bombed up to a category four cyclone with 130 kt winds. The JTWC is expecting the cyclone to become even stronger, reaching 160 kt winds at its peak intensity. Unfortunately, the Philippines are possibly in the line of the track of Hagupit, probably the same area as Haiyan last year is going to be hit. To go not too far out of subject, more information can be found here: https://forum.netweather.tv/topic/81931-super-typhoon-hagupit/#entry3080170. Typhoon Nuri from earlier this year probably influenced the tropospheric circulation quite a bit, but i am uncertain if this also applies to the stratosphere. A source for doubt, though, is that Haiyan from previous year did not induce a SSW, though it might have contributed to some kind of wave activity (perhaps this can be verified by using the MERRA dataset?). To try to make a kind of a bridge (and hypothesis) on the processes: it is becoming evident that tropical cyclones can emit gravity waves up into the stratosphere (especially the more intense ones). Furthermore, there also seems to be a link between these gravity waves and stratospheric wave activity (an article about this can be found here) What that link is, or whether it exists at all, is still up to debate, but an interesting part of research nontheless. Sources: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ https://forum.netweather.tv/topic/81931-super-typhoon-hagupit/#entry3080170 http://onlinelibrary.wiley.com/doi/10.1029/95RG02097/abstract http://onlinelibrary.wiley.com/doi/10.1029/92JD01679/abstract http://www.sciencedirect.com/science/article/pii/S1364682614001667 http://www.sciencedirect.com/science/article/pii/S1364682611000733

This indeed has the possibility to become a real catastrophe for the Phillipines, really wrong place wrong time... This is the last thing they could use, with such a monster approaching. Worrying to say the least. Back to the actual situation, Haiyan appears to be undergoing explosive deepening at the moment. In fact, it is looking like a full-fledged category 5 tropical cylcone. As an illustration, look at the Dvorak satellite image of Hagupit below: Dvorak satellite image of Hagupit as of 21:01 UTC 03-11-2014 (note that the image does not update itself) The most remarkable thing about Hagupit is the very strong eyewall convection that encompasses the system. The depth (intensity) of the convection is almost out of the scale. Also, some banding features exist on the western part of Hagupit, while the eastern part is devoid of any banding activity. Finally, note the nearly circular shape of the inner convection of Hagupit. Dvorak satellite images are not being able to keep up with the pace that Hagupit is currently strengthening, as noted by the JTWC in their prognostic discussion: Current satellite intensity estimates from CIMSS ADT are no higher than 103 kt, which is most likely far too low for the system in its current state. Whether Hagupit will hit the Philippines is still not entirely written in stone. The latest run from the GFS model (the 12Z run 03-11-2014) recurves the cyclone before it reaches the Philippines as can be seen below: GFS forecast track of Hagupit (12Z 03-11-2014). However, as noted by Somerset Squall, the official JTWC forecast does bring Hagupit very close to the Philippines, so a lot of uncertainty remains. The JTWC currently states the uncertainty as follows: One final complicating factor is the slow motion that may arise in about 5 days. If this would be correct, the Philippines could brace themselves for a huge rain event. But once again, confidence is very low. Wunderblogger Jeff Masters also wrote a blog about the system, when it was still a category 3 tropical cyclone. http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2871 Let us hope that the Philippines get spared on this one, they really cannot use another monster after Haiyan. Sources: http://www.ssd.noaa.gov/PS/TROP/floaters/22W/22W_floater.html http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/wp2214prog.txt http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2871 http://tropic.ssec.wisc.edu/# http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14120312/14.html

To give a first go for interpreting stratospheric figures, I will start with a rather difficult series of graphs, being the zonal mean winds and fluxes chart from FU Berlin. The graph (or better, set of graphs) is given below. Zonal mean winds and fluxes at 60N, as of 10-11-2014 (ECMWF-run) Due to the complexity of the lower three charts, and due to my very basic understanding of the stratosphere, only the two upper charts will be explained here. The explanation may not be without errors, so any comments or improvements would be greatly appreciated. To start with the first one, the chart shows the zonal mean wind at 1 hPa level (being at the top of the stratosphere) at 60 N latitude. The term zonal mean indicates that one measures a quantity at all points at a given latitude, essentially circling the earth, and averages these. For example, consider the wind at 60 N from 0E to 180E (the eastern part of the Earth) to be 10 m/s (westerly winds), and from 180W to 0W (the western part of the earth to be 20 m/s (westerly winds). This would result in a zonal average wind of 15 m/s. For anybody willing to learn more about zonal averaging, a good read can be found here: http://disc.sci.gsfc.nasa.gov/giovanni/additional/users-manual/G3_Zonal_Mean Note that a positive wind means a wind blowing from west to east. No meridional wind component (northern- or southern component) is being taken into account in the calculation of the zonal mean wind. The black line on the first two graphs shows the forecast for the zonal mean wind up to 10 days out. The zonal averaged wind at 1 hPa tells something about the strength of the stratospheric polar vortex. When the zonal mean wind is very high and positive, it means that the stratospheric polar vortex is rather strong (deep). However, when the zonal mean wind is very low or even negative (easterlies), the stratospheric polar vortex is in a much weakened state, and is highly susceptible to wave breaking activity. The second figure shows the zonal mean wind at 10 hPa and 30 hPa levels, which are closer to the surface than the 1 hPa level. In short, the same rules apply as indicated in the 1 hPa zonal mean wind profile, except for the fact that one is looking at a lower altitude. Finally, for an interpretation and intercomparison of these zonal average winds between this and last year, please take a look at the post from Chionomaniac below: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/page-29 Hopefully this information can help some to gain a little understanding in what all these mysterious stratospheric charts mean. And please do not hesitate to correct me, because, as noted before, my understanding of stratospheric meteorology is very basic at best. Finally, any additions or new information to make it easier interpreting these charts is greatly appreciated . Sources: http://disc.sci.gsfc.nasa.gov/giovanni/additional/users-manual/G3_Zonal_Mean http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/page-29

21W is definitely a very good example of a sprawling system. Such large and disorganized sprawling systems usually tend to develop rather slowly. Given it short time over water from now on, along with the sprawling nature of the system, this system might have a tough going becoming a tropical storm at all. However, more recently, the system has developed some quite intense central convection, as can be seen below: Visible image of 21W. Note that the image does not auto-update itself. Given that, if the JTWC is correct, the low level circulation center (LLCC) should be located somewhere in the circle, it does have a decent CDO (central dense overcast). This means that further organization may be more likely than the sprawling structure of the system would suggest at first hand. Time will tell. Finally, note the banding feature located all the way over the northern Phillipines associated with the system. This really shows the broad nature of the system. Sources: http://www.usno.navy.mil/JTWC/ http://www.ssd.noaa.gov/PS/TROP/floaters/21W/21W_floater.html

First of all, lots of thanks for putting up such an elaborate post. I was rather busy during the past few weeks, so that explains the rather late timing of my post, please forgive me for that. Agreed on the first comment, those charts definitely require some advanced knowledge, starting from the representation of a flux in terms of variances. And that only just explains what is indicated on one axis of the graphs, nothing more in detail yet. The point of view I was looking from was somewhat incomplete, as the part I only took in consideration in my initial post was the horizontal wave propagation. In other words, the transport of heat from the equator to the poles and vice versa while keeping the pressure level (or height) steady. But of course vertical wave propagation (thus the transport of heat toward higher/lower altitudes) is also a part of stratospheric meteorology. The combination of horizontal (East-West, North-South) wave propagation and vertical (altitudinal) wave propagation is quite a challenging subject to get my head around, let alone the figures on the FU Berlin site. This new insight does help me somewhat in getting the insight in what is meant with vertical wave propagation. So if I am correct, a flux of warm air toward the pole at, for example, 10 hPa over the USA translates into troughing in that position at the same position at a height of 500 hPa. Judging from simplicity, I would think it would be the other way around (WAA at 10 hPa causes WAA at the surface), but it is clear that this line of thinking is not elaborate enough. Also thanks for the cool plots from JMA, these plots do indeed give a nice insight. From the JMA profiles at the given time it does seem that the polar vortex is being pushed away from USA (given the continuous warming at that region). It is also interesting to see that the Western Pacific has been heating at 10 hPa over the past couple of weeks (given the image, if my way of reading is correct). About the Northern Annular Mode, it seems to be quite a difficult subject (never heard of it before), but I found a good article about it here: http://www.atmos.colostate.edu/ao/introduction.html One question about the NAM-part of your post: you mention that high heat flux activity leads to a stronger vortex. On the other hand, low heat flux activity relates to a colder vortex. But if the vortex is stronger (i.e. deeper), the polar vortex is also colder in general. Would high heat flux activity lead to a weaker (warmer) vortex instead? This polar vortex is definitely in a much different state compared to last year, great to watch it unfold this year. Furthermore, perhaps even better (from a personal point of view), is that, slowly but surely, the concept of stratospheric meteorology is slowly becoming more clear for myself. This forum provides an excellent place to build on this knowledge. Regarding winter prospects, let the polar vortex be quickly weakened by these atmospheric waves, and then we could well be facing a vastly different winter compared to last year. Hopefully this thread could turn into a very informative thread regarding stratospheric chart interpretation. I realize that a large part of the post is a little bit off-topic in that sense, but it appears to me that it is necessary to understand the concepts in order to be able to interpret the stratospheric charts in a reliable way. So probably when I have more time, I’ll try to give a more sophisticated look at these charts. Once again my gratitude for your very extensive post! And last but not least, any feedback from all sides is greatly appreciated!

Hi all, Now that winter is approaching, the stratospheric polar vortex is starting to take shape again. This also marks the time when the interest in stratospheric meteorology starts to increase again, due to its coupling with the weather in the troposphere etc. While looking at the stratospheric charts of the ECMWF from the Freie Universitat Berlin (or FU berlin in short), I came across a chart (heat flux charts) which I was so far unable to interpret. The type chart is given below: Heat flux wave 1 forecast of ECMWF, 12 UTC November 8 run, T+240. The chart is coincident with Wave 1 activity, which is expected to be present at the top of the stratosphere at around 70 N (zonal average). http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_ha1_f240.gif From what I could guess so far, I would say that the chart shows the covariance of horizontal, meridional wind with temperature. Assuming that the meridional wind is postive toward the pole, my guess would be that positive (orange) colours indicate transport of positive temperature anomalies toward the pole (in other words: a positive heat flux from lower to higher latitudes). This would in turn bring warm air from the midlatitudes toward the pole (in the chart above). Below is a representation of how this would look like at 1 hPa pressure level at the same timeframe: Geopotentials 1 hPa level, ECMWF, 12 UTC November 8 run, T+240. The black circle shows the line of 70 N around the pole. The arrows indicate temperature fluxes (if done properly). A possible interpretation would be that the heat flux in the first chart indicate a flux of warm air entering the vortex from one side (since it is only prevalent in 1 wave). This would then be from the Eurasian side (the arrow with a box around it), since the temperature gradient would be the most sharp at that area. My question is: is the way of reading the charts given above correct? Does the heat flux chart presented in the first image indeed represent the transport of heat poleward and vice versa? And is the way of application to the final chart also correct? Many thanks in advance for taking the time to answer these rather technical questions! Regards, Vorticity. *Edited to change thread tag.

Jeff Masters had an interesting blog about this "Medicane" on Wunderground: http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2854 Certainly an interesting system. The system developed quite unexpectedly (at least I hadn't heard of anybody expecting the system beforehand). According to phase diagrams from Florida University, the system was just shy of attaining a warm core, as can be seen below: Phase analysis of the low pressure area (Medicane) which made landfall in Sicily yesterday (as of 06Z). The C indicates the current position of the system. If the system would have crossed the border toward the red area, it could have been designated as a tropical or subtropical system. Sources: http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14110806/14.html http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2854

Currently, we are experiencing a rather blocked pattern, with low pressure areas moving from the Atlantic over the UK and getting cut-off toward the Mediterranean. This seems to be occurring due to a large high pressure area over eastern Europe, which is preventing the Atlantic lows from moving into Western Europe. Instead, the cut-off lows are causing large rainfall totals in the Mediterranean, with also some flooding taking place there (for example: see link below) http://www.euronews.com/2014/11/06/italy-swamped-by-flash-floods-/ The pattern can be seen in the GFS chart below: GFS surface level pressure and 500 hPa heights (colours) 06Z run, analysis (T0) One can see troughing (blue to yellow colours) dipping from the UK into the Mediterranean, which causes a continuous flow of low pressure areas moving along that line (blue line on picture). Furthermore, high pressure can be seen over eastern Europe, with warm air being advected toward Scandinavia (green colours edging northward, follow red line) There does seem to be a much advertised, though slight, pattern change on the way, with signs of high pressure becoming more prevalent to the north of the UK. To show the pattern change in general, take a look at the NOAA 6-10 day chart: NOAA 6-10 day 500 hPa heights (green lines) and anomalies (broken lines) forecast. The main difference is that the warm air advection (WAA) has reached a more westerly position, now reaching as far as Greenland (which can be seen by the green lines edging poleward toward Iceland from Scandinavia, red line). The elongated trough over the UK and the Mediterranean is still visible, though (see blue line). As a result of the further advance of the warm air advection, high pressure is more likely to establish itself between Scandinavia and Iceland (with the ususal precautions). Note that confidence in this forecast (mainly the upstream part) seems to be fairly high, with the CPC (climate prediction center) giving a score of 5 out of 5 regarding confidence level of the 6-10 day forecast1. However it is important to bear in mind that this high level of confidence in the American sector does not immediately translate to a high level of confidence over Europe. Sources: 1http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html http://www.euronews.com/2014/11/06/italy-swamped-by-flash-floods-/ http://www.wetterzentrale.de/topkarten/fsavneur.html

Quick weakening is continuing, as the intensity of Nuri has come down to 105 kt (according to the JTWC). It looks like the weakening is partially caused by an EWRC (eyewall replacement cycle). In fact, visible satellite imagery shows a small area of intense convection, surrounded by a convective-free zone, and that area is surrounded by a possible second eyewall, which is not completely circular (i.e. it looks more like banding features). Visible satellite loop of Nuri. Note that the image auto-updates itself. For now, it seems that the very small inner eyewall is able to sustain itself, as shown in MIMIC imagery: CIMSS MIMIC imagery of Nuri. Note that the image auto-updates itself. What can be seen is that a very small eyewall (indicated by red/yellow) exists, with a much bigger eyewall encompassing the cyclone at much greater distance. As of 20:00 UTC, the small inner eyewall has not yet dissipated, though. This indicates that Nuri still has a well-organized structure. With strong shear located to the north of Nuri, further weakening is likely, as suggested by the JTWC as well. In fact, the more north Nuri tracks, the further the shear will increase (up to 100 kt over Japan). Therefore, it looks like ET (extratropical transition) will occur very shortly. After the ET, the life of Nuri is not yet over. it seems like a major extratropical storm may arise from this system, as many models are expecting a sub-925 hPa low (!) to develop in the Alaskan Sea as a result of the typhoon. Confidence in that this is going to be a real bomber is quite high for the system. To illustrate this, GFS-charts are used for analysis of the Northern Hemisphere. First, check the chart below: GFS MSLP + 500 hPa heights (12Z, T+48h) Nuri is located just to the east of Japan as a ~985 hPa low. In this stage, Nuri will well be underway to becoming an extratropical system. However, the surprise comes if one looks at the surface pressure charts 2 days later: GFS MSLP + 500 hPa heights (12Z, T+96h) Nuri is in this case located near Alaska(on the top of the map). The minimum pressure associated with ex-Nuri is not even readable from the map! It should be somewhere around 930 hPa. Such explosive cyclogenesis from a tropical cyclone is rarely seen. This system could have some severe impact on Alaska. More information about this unusual occurrence can be read below: http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2851 Sources: http://www.ssd.noaa.gov/PS/TROP/floaters/20W/20W_floater.html http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/wp2014prog.txt http://tropic.ssec.wisc.edu/real-time/mimic-tc/2014_20W/webManager/mainpage.html http://www.nrlmry.navy.mil/tc-bin/tc_home2.cgi?ACTIVES=14-WPAC-20W.NURI,14-EPAC-21E.VANCE,14-IO-91B.INVEST,14-EPAC-95E.INVEST&SIZE=Thumb&PHOT=yes&NAV=tc&ATCF_BASIN=wp&ATCF_YR=2014&ATCF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/image_archives/2014/wp202014.14110406.gif&CURRENT_ATCF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/image_archives/2014/wp202014.14110406.gif&CURRENT=20141104.2101.mtsat-2.x.ir1km_bw.20WNURI.105kts-944mb-240N-1369E.100pc.jpg&CURRENT_ATCF=wp202014.14110406.gif&ATCF_NAME=wp202014&AGE=Latest&MO=NOV&BASIN=WPAC&STYLE=tables&SUB_PROD=rscat_save&TYPE=ssmi&YEAR=2014&YR=14&STORM_NAME=20W.NURI&ARCHIVE=active&DIR=/SATPRODUCTS/TC/tc14/WPAC/20W.NURI/ir/geo/1km_bw&AREA=pacific/southern_hemisphere&PROD=shear&AID_DIR=/SATPRODUCTS/TC/tc14/WPAC/20W.NURI/shear http://www.wetterzentrale.de/topkarten/fsavnnh.html http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2851

Lots of thanks a lot for this very elaborate and clear post! I am very grateful for the time you took to explain a rather complex variable. This is a great help to understand the concept of the OPI! It is also nice to see out of which elements the OPI is built upon (regardless of the exact positions of all features). It would also be really cool to see what the physical background of the index is . Just some speculation: the fact that height anomalies over Eurasia are taken into account in the OPI, might give a link to the SAI (snow advance index). Positive height anomalies above Eurasia seem to develop due to a high rate of snow accumulation over Eurasia itself. (check the post of Chionomaniac in the Stratosphere-thread to see what I mean). https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ If the epsilon factor (from http://app.til.it/opi/) is indeed directly related to the anomalies over the same part of Eurasia as the SAI is, then there might be a significant link between them. Once again, this possibilty is only speculation, and is in no way based on physical evidence. Therefore, this possibility is nothing near a certainty. And finally, once again, thanks for your elaborate post Crocodile23! Sources: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ http://app.til.it/opi/

One cans say that the OPI is a really interesting measure, especially given the very high correlation with the AO. However, it does raise some questions to me (sorry for asking a lot of questions, but I am trying to understands the concepts somewhat better ). Relation of AO-index to blocking First, as the OPI-index is actually an indicator of the AO-index (if I am correct), does a negative AO-index frequently relate to a cold winter in Western Europe? Or does it strongly depend on the regions where (in longitudinal sense) the cold air flows out toward (as related to blocking)? In other words: does a negative AO favor blocking over Scandinavia, for instance, which often leads to a cold easterly flow over western Europe (due to land-ocean positioning etc.)? Or are the blocks more or less randomly placed during a negative AO? SAI- and OPI-index Second (and last): Is there any relation between the OPI- and the SAI-index? Since both seem to be related to events occurring on the northern latitudes, and both are mostly being influenced by the month October, one could argue that some kind of a feedback or relation exists between them. The SAI-index seems to be related to the rate of increase of snow cover over Eurasia, giving the following feedback loop: Feedback loop occurring during a positive- or negative SAI. The left hand side of the image applies to a negative SAI, while the right-hand side applies to a positive SAI. More about it can be read in the excellent post from Chionomaniac in the Strat-thread: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ Since a negative OPI-index implies a negative AO-index, it generally also indicates a weak polar stratospheric vortex (correct me if I'm wrong). As can be seen from the SAI-feedback loop, a positive SAI-index also indicates a weakened polar vortex. A second piece of evidence (though not very strong) shows up when locating the origins of both indices. The theory used for the OPI-index is a piece of a post of Steve Murr in the same thread, given below: As can be deduced from the theory/suggestion given (in bold), the OPI-index itself possibly originates near the north pole (with all precautions applicable here). The SAI itself originates from the Eurasian part close to the north pole. These regions are quite close together, and do very likely influence each other as well. Many thanks in advance . Sources: http://en.wikipedia.org/wiki/Arctic_oscillation https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/

Indeed a very bizarre track, alongside with a very unusual second place of formation, this is definitely an odd cyclone to say the least! Unfortunately it is indeed so close to land that it could bring lots of flooding. Even though Hanna developed very close to land, forecast models give the possibility of the system emerging just to the east of the Yucatan Penninsula, after moving west-northwestward. Track model forecasts of Hanna. Source: http://www.ral.ucar.edu/guidance/realtime/plots/northatlantic/2014/al092014/