Vorticity0123

I'll try to give a short summary of today's output (mainly trends), regarding the 500 mb charts, and the surface charts in the mid- to long term. For the large scale, the 500 mb charts will be shown. Thereafter, I'll go in somewhat more detail. 500 mb trends First, the 500 mb forecast chart (6-10 day) with anomalies is given below: NOAA 500 mb heights and anomalies output for day 6-10 The first thing that shows up is a persistent 500 mb trough (as shown by the green isohypses) over northeastern Canada. This trough has been apparent for a long time now, and it is causing the numerous arctic outbreaks over central United States. Secondly, note the diffluent flow over Europe (isohypses flowing out of each other over central Europe). As a result, there is a 500 mb ridge over the western part of Russia. The position of the ridge is somewhat more to the east compared to earlier outputs a few days ago. Next, we will focus on the anomalies. Note the sharp negative anomalies over the UK, the Benelux and France, indicative of surface troughing being likely near that area. As a result, the Azores high is forecast to be deflected toward the south, as noted in Tamara's post above. Moreover, the anomalies become more positive toward the north. A synopsis like this would create southerly-positioned westerlies. Moreover, there will most likely be a sequence of lows diving into central Europe. As the sharp negative anomaly is also located over the UK, the weather there will most likely be wet as well. Next, the 8-14 day outlook by NOAA is given below: NOAA 500 mb heights and anomalies output for day 8-14 The general forecasted pattern is about the same when one looks at the 500 mb heights, but with the anomalies there are some subtle (and perhaps important) differences. Firstly, the negative anomalies over the UK have shifted to the west, now being concentrated just to the west of Ireland. This could induce a possibly more southerly flow over the UK, with some milder conditions, if this verifies. Moreover, the Azores high has moved somewhat more to the west as well, as can be seen in the positive anomalies. The Azores high will therefore most likely have very little direct impact on our weather. The wind direction "pluim" from De Bilt, the Netherlands confirms the trend in the long range, though there is a large scatter, as can be forecast in this timeframe. De Bilt wind direction "pluim", showing 50 members from the ECMWF. What can be seen is a trend for the "pluim" to veer toward the south from eastern directions (including Oper and Control), but there is indeed a wide scatter after T168. Detailed synoptic evolution (short range) For the detailed synoptic evolution, I'll use GFS charts from Wetterzentrale. Over the first few days, a general trend for lows to dive into central Europe can be seen, as also seen on T84: GFS T84 (12Z) The diving low scenario is mainly causing very wet weather over the UK, as consistent low pressure activity is located there. However, on the northern side of the lows, there is a risk of an easterly developing with possible snow chances on higher elevations. 850 hPa temperatures in this situation are generally near -4*C over the UK, giving rise to marginally cold conditions, as can be seen in the chart below: http://www.wetterzentrale.de/pics/Rtavn965.png The 144h surface pressure chart can be seen below: GFS T144 (12Z) What can be seen is a rather messy situation to the northwest, though generally low pressure is observed there. This is consistent with the 500 mb anomaly charts as given above (though I do think the GFS has somewhat more northerly troughing than I would expect with the 500 mb surface charts). Moreover, the high pressure over Russia has moved somewhat southward. The result is a southerly flow, but as usual, there are many uncertanities at this timeframe. Concluding, there will be a change in steering in the near future, possibly resulting in somewhat milder conditions. All models show a low pressure area to the northwest of the UK, though. It will be interesting to see how this situation plays out. Sources: http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php http://www.weerplaza.nl/15daagseverwachting/?type=eps_pluim&r=midden http://www.wetterzentrale.de/topkarten/fsavneur.html

Incredible... Such different extreme events at such short distance in Western Europe, this is truly amazing! I've rarely see such a wide variety of extremities in such a short distance from each other! I'll give a short summary of the extreme events in the UK, and especially the Netherlands, below: The KNMI (the Dutch equivalent to UKMET) has issued 3 consecutive warnings for parts of the Netherlands, creating a kind of "ring of fire". The map can be seen below: The yellow color indicates warning conditions are likely to be met at a short timeframe (2 days). What can be seen is a risk on snow in the north of Holland today and tomorrow, accumulation is forecast to be around 5 cm max. Moreover, there is a warning of strong winds in the western parts of the Netherlands (gusts up to 100 km/h are forecast). And finally, there is a risk of lightning in the southern parts of the Netherlands. This is an unique variety of events at such small scale! Synoptic situation The reason for all this hazardous weather is a low pressure area (currently a well-defined trough, i.e. the isobars are not closed yet), forecast to move from Scotland and the North Sea toward the central part of the Netherlands. The trough can be seen below: Hirlam T06 (12Z) Note the sharp dip in pressure over the central North sea extending northward. Eight hours later, the low pressure area is forecast to be located over the border of the Netherlands and Germany. Hirlam T14 (12Z) Squall line Associated with the trough is a squall line (the second in January), currently extending from London to the central North Sea. The squall line caused heavy precipitation, as well as lightning (very extreme for January), to Wales and central England. This line is now forecast to move along with the low toward the Benelux, while (seemingly) deactivating. Estofex has issued no warning about the system in advance, and the KNMI also didn't have this intense area in their forecast. Therefore, it appears to have become a surprise for many! A real-time image of the squall line can be seen on the link below: http://europa.buienradar.nl/images.aspx?jaar=2014&maand=01&dag=25&uur=18&minuut=15&c=&type= Wind The sharp trough is also having a rather strong wind field around it, as can be seen below: Hirlam T07 (12Z) The map above shows the average wind speed forecast (BFT). What can be seen is an 8 BFT emerging in the Cahnnel and near the southwestern part of the Netherlands. Also note the 10BFT just to the souheast of Norway. As stated in previous posts, numerous gusts have been recorded over England as well, though they aren't exactly linked to the trough. Snow As a result of the trough, there is also forecast to be some snowfall over the northeastern parts of the Netherlands and Scotland. The snowfall over Scotland is mostly over elevated regions and is a result of very cold upper temperatures. The snowfall over northeastern Holland has a different origin. It is caused by low level easterlies forecast to develop on the northern flank of the trough, as can be seen above. The northeastern part of the Netherlands lies directly in the battleground line between arctic air caused by a high pressure area to the northeast (over Scandinavia), and mild Atlantic air from the southwest. The trough is essentially activating the battleground frontal zones. Temperature gradient Finally, there is a very sharp temperature gradient located over the Netherlands. What can be seen is a difference of 8*C over just 100 km, as seen below: The temperature gradient is forecast to persist over the next couple of days, with an increasing likehood of cold conditions over the complete country in a few days. Of note is that a very small shift in the movement of the low pressure area can cause a major difference in the areas impacted by snowfall, the temperatures, the forecasted wind, and finally the southern extent and intensity of the squall line. It is, to keep it short, a very interesting situation, to say the least There is so much to tell about the current situation, that I think I would be able to write a full page about this event. But for now, I'll keep watching the situation with excitement, and just be surprised Sources: http://www.knmi.nl/waarschuwingen_en_verwachtingen/regio.php?pr=ZH http://www.weeronline.nl/vakman-index/130/0 http://europa.buienradar.nl/images.aspx?jaar=2014&maand=01&dag=25&uur=17&minuut=30&c=&type= http://www.estofex.org/ http://www.weerplaza.nl/gdata/10min/GMT_TTTT_latest.png

Thanks for the reply! Nice to hear that you are so enthousiastic about the study! I'll keep you updated on the progress!

Hello all, I'm Lars, a second year student at the university of Wageningen, studying Soil, Water and Atmosphere. Since I was a child, meteorology has always been my passion. In the third year of my study, there is an opportunity to do a minor (half a year) on a university in Europe. Because it seems very nice to go abroad for half a year, I would really like to take that opportunity. Moreover, I also hope to get a somewhat stronger (mathematically and physically) background in meteorology. The universities that are on my shortlist are Reading and ETH (Zürich). And therefore, my question is: does anybody have some experience with one of these universities or going abroad for a minor in meteorology? Many thanks! Vorticity.

Indeed, Lingling didn't like having a straightforward path, it was a very stubborn cyclone! Was because the last advisory has been issued by JTWC, as most of the convection has been sheared northwestward and the LLCC (low level circulation center) has become ill-defined. The very odd track of Lingling can be seen below: Moreover, the stubbornity of Lingling was also evident in the JTWC forecasts. The JTWC consistently forecasted Lingling to make landfall on the large southern island on the Phillipines, but it just refused to do so. Instead of the forecasted southwestward track, it continued moving southeastward up to its demise. The southwestward track forecasted by the JTWC was definitely not unreasonable, giving the strong northeastern surge evident from 1000 to 700 hPa height, as visible on earth.nullschool. Analysis on this site doesn't give a clear explanation for the southeastward track of Lingling. The demise of Lingling can be clearly attributed to the easterly shear, as seen in the GIF loop below: The convection can clearly be seen developing, moving rapidly westward and subsequently dissipating. Earth.nullschool shows this at the 250 hPa level, showing winds blowing from the southeast to the northwest (curving to the north later on). The 250 hPa level is around the height of the tropopause (approximately 10 km). Convective clouds reach up to about this height when they develop. Due to the present steering winds at that level, they are blown away to the northwest. Data from CIMSS does justify the (south)easterly shear, as can be seen below: More worryingly is the large amounts of rainfall being unleashed on the Philippines by the remnants of Lingling. Rainfall totals up to 900 mm have been recorded in the eastern part of the southern big island of the Philippines. Knocker posted a thread about this rainfall, and a short article about the extremity of the event. This can be seen below: http://forum.netweather.tv/topic/79121-phillippine-rainfall-and-flooding/ The very heavy rain is continuing, mainly because of Lingling. Convection from Lingling is being sheared over the southern island, giving a continuous renewal of rain at that location. Right now (at the time of writing) an impressive burst of convection is impacting the island. Let's hope people there will stay safe. Sources: http://www.usno.navy.mil/JTWC/ http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=-246.83,11.67,950 http://www.ssd.noaa.gov/PS/TROP/floaters/01W/01W_floater.html http://forum.netweather.tv/topic/79121-phillippine-rainfall-and-flooding/ http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=westpac&sat=wgms∏=shr&zoom=&time= http://www.csgnetwork.com/pressurealtcalc.html

Those are very impressive amounts of snow, especially near Denmark! Competing airmasses The meteorological situation causing this high amounts of snow is also very interesting. The snow is caused by a sharp temperature gradient (large temperature differences at a very short distance), caused by two competing airmasses. The temperature gradient can be seen below: GFS T0 850 hPa temperatures. Note the 10*C temperature differences just to the north of Denmark. As a result of the different airmasses competing with each other, a frontal zone (also called a winter front) has developed along the temperature gradient causing high levels of snow over these areas. Synoptic situation The synoptic pressure chart responsible for this snow can be seen below: GFS surface pressure chart (T0) What can be seen is a strong high pressure area over Scandinavia, as well as a large trough (a North-South elongated area of low pressure, also visible in the 500 hPa thicknesses, the color shading on the map) extending from Ireland to Spain. The high pressure area is sending frigid air from the east toward the area around Denmark. Moreover, the long-stretched trough is sending mild air from the Mediterranean toward the area around Denmark as well. (this can also be seen in the 850 hPa charts given above). As the synoptic situation is not forecasted to change much over the next few days, more snow will be likely for southern Scandinavia and Denmark. Mountainous effects The precipitation distribution for the next 72 hours can be seen below: GFS total precipitation amounts (up tot T72) Note the area of increased precipitation over the eastern part of southern Norway. This is caused by the hills just west of the precipitation spike. When the air from the east meets the hills over western Norway, the only way the air can go is upward. As a result, there will most likely be increased amounts of precipitation over that area. Concluding, it will be interesting to see how the battleground around Denmark will evolve. Most likely, they will see a white world in the next couple of days! EDIT: Of note is that the battleground area was forecast to be over the UK one and a half week ago! Sources: http://www.wetterzentrale.de/topkarten/fsavneur.html http://www.weer.nl/weer-in-het-nieuws/weernieuws/ch/e23c4b083d8d5bc9423437531b60521a/article/grote_tegenstellingen.html

Indeed, it looks like a pretty well-organized storm! However, a satellite loop shows that June has got some trouble sustaining central convection. The cyclone consists of a very well-defined band of convection extending all the way from the northeast to the south of June. Unfortunately, as New Calendonia will be located on the eastern flank of June, they will experience the most intense convection and precipitation. The intensity seems to be higher than the 35 kt as analyzed by JTWC, given the well-organized structure of the cyclone. Evidence for a higher intensity is an OSCAT pass, showing winds up to 50 kt to the south of the cyclone. The strongest winds are currently affecting New Calendonia itself. The 50 kt winds can be seen as the triangles over and to the west of New Calendonia. Current Water Vapor imagery shows that June is encircled by a vast area of dry air to its far south and west. Though the area of dry air is still pretty far away from the center of the cyclone, it could pose a threat to the intensification of the cyclone in the long term. Note the very dry air (black colors) to the west and south of June. What is also interesting to note is that the GFS has had the cyclone in its forecast for about 5 days ahead! The GFS has also been very agressive on the intensification of the cyclone, as shown in the image below: The actual position of the cyclone is given by the C on the map. The minimum surface level pressure (in its tropical stage) is forecast to be around 980 hPa, indicative of a category 1 cyclone. The cyclone is forecast to intensify rapidly once it reaches extratropical status. The GFS forecasts the system to deepen to a pressure of around 960 hPa at the end of the forecast. Moreover, the northern part of New Zeeland is also in the line of fire of the (extratropical remnants of) June. The JTWC forecast is somewhat less agressive. It shows maximum winds of up to 45 knots, which is lower than has been analyzed by the OSCAT pass I showed above. And therefore, I think the intensity forecast will be upgraded in the short term, given the OSCAT pass. It will be interesting to see wheather June will also be able to intensify rapidly, as many more cyclones before June have done so in the Southern Hemisphere this year. Sources: http://www.ssd.noaa.gov/PS/TROP/floaters/10P/imagery/ http://tropic.ssec.wisc.edu/real-time/austeast/images/wvgms.GIF http://manati.star.nesdis.noaa.gov/products/OSCAT.php http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14011712/8.html http://www.usno.navy.mil/JTWC/

Thickness is indeed the distance (in altitude) between two pressure levels. On the contrary, a chart of geopotential heights at 500 hPa., for example, gives lines of equal height (isohypses) at which the pressure is equal to 500 hPa. A good question it is. For the post itself, I used the surface pressure for the analysis, though I did, perhaps incorrect, interpret the troughing also with the geopotential heights (given in color). Searching for answers on the internet has given some contradicting results: From MetMonkey: From weatherfaqs.co.uk: The best information I have found came from a Netweather thread itself: http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/ I hope this helps a little. I'm sorry to have caused some confusion in my post. I'll try to be more clear in the future. Sources: http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/ http://weatherfaqs.org.uk/node/189 http://www.null.co.uk/

Indeed, it looks like the arrival of full on zonality will not be getting a chance for the next couple of days, perhaps even weeks considering the latest output. The difficulity in modelling seems to be a result of a split flow occuring directly overhead, as can be seen in the 500 hPa composites. 500 hPa analysis For the forecast, I've used the 500 hPa forecast from NOAA at day 8-14. The chart can be seen below: GFS geopotential heigts and anomalies forecast (500 hPa) The part to focus on are the streamlines (isohypses) near Europe. Note the very diffluent pattern (isohypses very far apart) over Europe. This is (correct me if I'm wrong) indicative of a split flow. In such cases, it is very difficult to predict the weather at the surface even at short timescales. Usually, the lines are somewhat parallel to each other (zonal westerly flow), making it a lot easier to predict which track lows may take than in the situation given above. For the situation above, it seems that a very small deflection in the latitudinal position of a low pressure area (when it is located for example near Newfoundland) could cause major differences in the track downstream. (north south differences) Moreover, there is an impressive blockade also visible at 500 hPa and the surface near Scandinavia ( it can be seen above in the northward curvature of the low heights in the figure above). The high pressure area prevents the low pressure areas from the west to enter Europe, making the situation even more difficult. Therefore, it looks like the atmosphere is very difficult to model, due to the split flow above Europe mentioned above. Surface charts For the surface analysis, I'll use GFS forecasts from Wetterzentrale. The 500 hPa situation given above reflects itself in the surface charts: GFS T72 (6Z) What can be seen on the surface charts is a trough extending all the way toward Spain, and a high pressure area above Scandinavia. We are under the influence of the eastern side of the trough, with mild air moving from the south toward NW Europe. This can also be seen in the 850 hPa charts: GFS T72 (6Z) 850 hPa temperatures Note the long stretch of warm upper temperatures extending up to the east of Scotland. The very cold air is not very far away, though. -10*C uppers are located over the southwestern part of Scandinavia. Next, below is the GFS chart for T144: GFS T144 (6Z) What can be seen is that the trough has moved somewhat to the east, now extending toward Italy. Low pressure is located to the west of Ireland. Moreover, the Azores high has also moved somewhat northeastward. This results in a kind of status quo, with none of the systems really having a dominant influence over our weather(though the northwestern part of the UK will most likely be under the influence of lows over the ocean). The wind forecast also shows this over the southeastern part of the UK, with barely any wind occuring around that timeframe. GFS T144 (6Z) The flow over the western part of the UK is clearly cyclonic. However, over the southeastern part, no definite flow mechanism can be found. The status quo (COL area) extends all the way southeastward. toward the Alps. The ECMWF shows a similar idea of synoptics like the GFS, though the phasing of the lows diving southeastward appears to have some differences. Concluding, even though the models generally agree on the overall synoptics, a very small shift on the charts could result in major implications for our weather. A slight deflection of the Scandinavian high westward would mean we are likely to see very cold conditons. However, a little shift toward the east of the same high pressure system would mean complete influence by the low pressure system over the UK and more wet conditions as a result. Sources: http://www.theweatherprediction.com/blocking/ http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php http://www.wetterzentrale.de/topkarten/fsavneur.html

Extreme temperature conditions It has certainly been an impressive set of extremes that have happened during the past year or so in Australia. It does make me wonder, though, as Australia hasn't had (as far as I can see) very extreme synoptic settings, with, for example, a highly amplified flow. To put the possible 3 days of 45+ temperatures (as Upgrade noted) in perspective, the Guardian stated that: The article (about last year's heatwave) is discussing the exceedence of 39*C temperatures, while we are currently dealing with a sequence of 45+ temps! Also worth noting is that extreme heatwave conditions (relatively spoken) are mainly forecast to develop over the very south of Australia, including Tasmania. This can be seen in the map below (from BOM): This chart indicates the forecasted heatwave extremity during the next 3 days, from the 14th onwards. Note that this is relatively spoken, as an "extreme heatwave" indicates extreme heatwave conditions only for the specifically indicated areas. It really makes me wonder what could actually be causing these highly extreme conditions mainly over Australia. It could be as a direct result of global warming, but the 1*C temperature increase wouldn't explain the full extent of the extreme warming events. Could it be a consequence of changed synoptic patterns (possibly as a consequence of climate change)? Tropical low over Australia Meanwhile, a tropical low has developed over the northern coast of Australia. The low is not forecast to develop into a tropical cyclone, as it is located too far over land. However, the GFS is actually indicating the low to remain quite vigorous (pressure of below 995 hPa during land passage) while moving west-southwestward over the Australian continent. The forecasted track of the low by BOM can be seen below: Meanwhile, the forecasted track and MSLP of the low, as forecasted by GFS, can be seen below: The light blue color indicates a pressure of around 990 hPa, while the dark blue indicates a pressure of around 1000 hPa. Note the pressure of the system oscillating between 990 and 1000 hPa over land, which is quite remarkable for a tropical system. General picture For a more general image, an infrared image of Australia is given below: What can clearly be seen is the convection associated with the tropical low mostly displaced over the sea, with some bursts just inland over Northern Australia. Moreover, a rather dark area can be seen over the southeast of Australia. In longwave images like the one above, very dark colors indicate high amounts of outgoing longwave radiation. This is a good indication for areas with high temperatures (Stefan Bolzmann's law). This illustrates that the impressive heatwave conditions over Australia can readily be seen in satellite images. In short, it has been a very impressive sequence of heatwaves currently occuring over Australia. This is in agreement with the prediction that more extreme weather would be more likely in the future. However, the reason(s) for this sequence of events have yet to be found. Sources: http://www.theguardian.com/environment/blog/2013/jan/21/what-is-causing-australia-heatwave http://www.bom.gov.au/australia/heatwave/ http://moe.met.fsu.edu/cyclonephase/gfs/fcst/index.html http://oiswww.eumetsat.int/~idds/html/product_description.html (for the explanation on the satellite picture of Australia).

It seems like the western part of the United States has seen a major change in weather during the past few days! 5 days ago, the maximum temperature recorded was below -10*C. Yesterday, the maximum temperature almost hit 16*C, which is a difference of 26*C in just 5 days! The historical temperature data of New York can be seen in the link below: http://www.wunderground.com/cgi-bin/histGraphAll?day=12&year=2014&month=1&ID=KNYC&type=1&width=614 Moreover, the 16*C almost broke the daily maximum record for the 12th of January (16.3*C)1 Synoptics change The reason for the drastic change in weather was a change in the overall weather pattern. For an analysis, look at the GFS chart of 8th of January below: GFS 8 January 500 hPa geopotential heights and surface pressure The white contour lines are the surface isobars, the black contours lines are the lines of equal geopotential at 500 hPa. The colors on the map also indicate geopotentials, but then corrected for topographical influences (correct me if I'm wrong on the last) What can be seen is a very distinct surface low pressure area (as well as at 500 hPa) over Northeastern Canada. Moreover, there is a surge of very low geopotentials (purple colors) flowing toward New York from the east. The low pressure area was very well stacked from the surface all the way to 100 hPa (that is where the connection to the polar vortex lies, will be discussed later). The low pressure area sent an area of very low 850 hPa temperatures from the pole toward New York (as the low pressure was in place for quite some time by then), resulting in the severe cold, as shown below: GFS 8 January 850 hPa temperatures The 850 hPa temperatures at New York were around -20*C around that time. 4 days later, the situation was quite different. Take a look at the GFS 500 hPa chart for 12 January: GFS 12 January 500 hPa geopotential heights and surface pressure A marked trough (noted in surface as well as in 500 hPa, it can be seen with the low geopotential heights dipping southward) can be seen extending all the way down to the Gulf of Mexico. The very low geopotential heights associated with the polar vortex moved nortwesttward away from Northeastern Canada. As a result of the trough to the (south)east of New York, the flow turned to the south, sending very warm air from the Gulf of Mexico toward the city. This can also be seen at the 850 hPa temperature charts: GFS 12 January 850 hPa temperatures Note the pool of very warm 850 hPa temperatures extending from the Gulf of Mexico toward the southeastern tip of Canada. New York had 850 hPa temperatures of about 10*C at that time, which is a 30*C increase in about 4 days. Stratospheric connection As the low pressure area the 8th of January was so well stacked, it was also visible at 100 hPa, as the polar vortex. This can be seen below: ECMWF stratosphere (100 hPa) geopotential heights of 8 January. Note the main center of the polar vortex was being located over Northeastern Canada, almost exactly where the low surface and (more important) 500 hPa heights were. This means the polar vortex was (in)directly connected to the cold in many parts of the US. Now take a look at the 100 hPa heights on the 12th of January: ECMWF stratosphere (100 hPa) geopotential heights of 12 January. The main lobe of the polar vortex has moved northwestward away from the east of the US. Still, the polar vortex hasn't moved that much, compared to 4 days ago. This indicates that the situation of a polar vortex being perfectly alligned with low surface heights at the bottom is not a very common situation. Therefore, 100 hPa heights shouldn't be used as a direct indicator wheather cold is coming or not. Concluding, it has been an impressive temperature swing in the west of the US. It is a nice example of how quickly the weather can change from the one extreme to the another. It will be interesting to see how the weather will develop in the western part of the US during the next week or so. For now, it seems like a return to normal temperatures will be the most likely, finally. Sources: http://www.wunderground.com/history/airport/KNYC/2014/1/12/MonthlyHistory.html#calendar http://www.weather.com/weather/wxclimatology/daily/USNY0996 1 http://www.wetter3.de/Archiv/ (for the GFS charts) http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ http://www.weeronline.nl/Noord-Amerika/Verenigde-Staten/New-York/3931993 (for the future weather prediction)

Colin is definitely looking very impressive right now! A real beauty it has become indeed! And without it affecting land, this is the best situation we hurricane fanatics can get! From the satellite imagery (CIMSS), It seems to be a category 4 hurricane (no full symmetry in Dvorak imagery, though it remains a very impressive cyclone). The best image showing this structure was from the whole Indian ocean (NHC imagery seems to be very ragged): What does make me wonder, though, is the big number of major hurricanes we have had so far in the Southern Hemisphere (2013-2014 season). So far, 5 out of 7 named systems in these basins have become major hurricanes (Saffir Simpson Hurricane Scale). Of the non-major systems, Christine also got very close to major hurricane status before making landfall. This all is in great contrast to the 2013 Atlantic hurricane season. Moreover, the forecasts of JTWC and La Reunion appeared to have been too conservative on much of the tropical cyclones, showing the general difficulty to forecast those rapid intensification events. It will be interesting to see the major intensity upgrade from JTWC and La Reunion in a few hours, with a possible >50 kt increase in 12 hours (!) Sources: http://tropic.ssec.wisc.edu/real-time/storm.php?&basin=indian&sname=08S&invest=NO&zoom=4&img=1&vars=11111000000000000000&loop=0 http://en.wikipedia.org/wiki/2013%E2%80%9314_Australian_region_cyclone_season

For the time being, I'll give a comparison of previous model output for today and the real output today (Johnholmes had some excellent pdfs about this comparison and forecasted pressure in the in depth model thread BTW), and the general trend in model forecasts for the far future. Verification of ECMWF and GFS It appears that the block over Scandinavia has been modelled somewhat too agressively during the past few days. For comparison, the ECMWF T168 from the third of January (this is today 12Z) and the analysis at the same time today is shown below: ECMWF 03 january T168 The model run showed a pronounced block over northern Scandinavia, and therefore easterly winds over the UK. ECMWF 10 January 12Z T0 As can be seen from the comparison, the block ended up much weaker than forecast at the same timeframe. Moreover, there also appeared no opportunity for the high pressure area north of Scandinavia to build between the lows moving eastward to the north of the UK. Note that the general pattern wasn't very far away from reality, with a trough over Spain (though it appeared to be weaker than originally forecast) and low pressure south of Finland (configuration was once again slightly different, which can be expected 7 days out). Also the GFS from the third of January is shown below: GFS 3 January T144 Note that the output from the GFS is one day earlier than the output from the ECMWF above. The difference is that the GFS at that time modelled the lows over the south of Scandinavia better compared to the ECMWF. However, the pattern over the US appeared to be less well forecast. Moreover, the GFS also had the trough over Spain right (though it was slightly too west) I have to admit that I don't have a reason for the differences in model output and result. Does anybody have a clue? Future general trend First, I'll start with the 500 hPa charts, as analyzed by the NOAA. The chart shows the 500 hPa heights (green lines) and anomalies (blue and red lines) forecast by NOAA in 6-10 days. What can be seen is a mainly diffluent pattern over Europe (the lines of equal geopotential are diverging over that area). Moreover, there seems to bea signal of a ridge over or to the north of Scandinavia, though the signal is weak. A stronger signal exists for a deep trough to extend over the UK toward Spain. Next, an analysis of the surface charts (comparison of the ECMWF and GFS) will be given. This will be at 8 days, to compare with the 500 mb chart above. First, the ECMWF: ECMWF 12Z T192 (8 days out) What can be seen is a trough (as well as a surface low) over Spain. This agrees with the 500 mb charts as analyzed by NOAA. High pressure is forecast to be located over eastern Scandinavia, which also agrees somewhat with the anomaly charts. The high pressure is located more to the east than anomaly charts would suggest (also the 500 hPa ridge). Next, the GFS: GFS 12Z T192 (8 days out) Looking at the chart shows that the GFS also agrees with the trough (low 500 hPa heights) and low surface heights between Spain and Italy (slightly more to the east than the ECMWF). However, the high heights at 500 hPa (as well as the surface high) are located much more to the east than on the ECMWF. Of a final note is that the troughing signal to the south and over the UK is also visible in the stratosphere (100 hPa) showing generally markedly low heights over that area. Concluding, there does seem to be a general agreement over the next couple of days, with troughing near the UK and the Iberian Penninsula. This will most likely lead to changeable and possibly wet weather over the UK, though no details can yet be given. The high pressure area appears to be too far east to provide cold air, along with easterlies, over the UK. The disconsistency in the exact position of the high will be worth watching, though, as it might provide more settled conditions if the exact position appears to be more to the west than shown by for example the GFS. I hope the post is of some value. However, because I'm still a beginner, there could be some mistakes in the post. Sorry for the possible inconvenience. Sources: http://www.wetterzentrale.de/topkarten/fsecmeur.html http://www.meteociel.fr/ http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

It appears like Ian has become the first major hurricane of the 2013-2014 season in the SW Pacific! (Saffir Simpson Hurricane Scale). What a beuaty it has become! Rapid intensification event and satellite presentation Satellite imagery shows Ian now has a well-defined eye embedded in a nearly circular area of convection. This shows a burst of Rapid Intensification has occured during the last few hours. The visible imagery also beautifully shows the development of a clear eye, along with the RI. On the Dvorak image below, the well-developed structure of the cyclone can be readily seen with the nearly circular and intense ring of convection surrounding the well defined eye, typical for major hurricanes. CIMSS ADT intensity estimates also show the rapid intensification of Ian, though their estimates continually underestimate the strength of the cyclone. As noted previously, this may be due to the small size of the cyclone. I expect the intensity to be increased markedly within the next few hours. Size of Ian The small size, as noted above, of the tropical cyclone can be seen below: This image is a Multiplatform Tropical Cyclone Surface Winds Analysis (MTCSWA). (an analysis of winds at the surface in cyclone Ian) This image is composed by integrating mulitple satellite intensity images near the surface1. The radius of tropical storm force winds is about 389 km2, which is pretty small for a major hurricane. Another image showing the small size can be seen below: Given above is a satellite loop of the whole South Pacific Basin, with Ian located in the center-left of the image. Note how small the system actually is! Environmental characteristics Data from http://earth.nullschool.net/ shows two large inflow channels at surface level. One wide channel originates from the equatorial Pacific (to the northeast and northwest of Ian, as well as one small channel from the southeast. The wide equatorial channel consists mostly of warm, humid air, as well as the one to the south. However, there is a sharp air mass gradient near the southwestern inflow channel. Just to the west, there is a line of very dry air, as can be seen in the water vapor imagery below: Water vapor imagery of the South Pacific. Note the dry air (black) to the southwest and west of Ian. As the line moves further eastward, the dry air could get entrained into the circulation of Ian. The result would be severe weakening of the system. http://earth.nullschool.net also shows Ian has a well-defined polar outflow channel, which aid in the ventillation of the system. (check 250 hPa for upper outflow analysis). What can also be seen at the 250 hPa height, are very strong upper winds to the south of the cyclone. As Ian is forecast to move south as well, it will experience much increased shear values in a few days, due to these upper level winds. All in all, Ian has proven to be a tenacious tropical cyclone! After hampering some in the beginning, it has become a formidable and beautiful system. Unfortunately, some islands are directly in the path of the major cyclone. Let's hope they stay safe! Sources: 1http://www.ssd.noaa.gov/PS/TROP/MTCSWA_UM.pdf http://tropic.ssec.wisc.edu/# http://www.ssd.noaa.gov/PS/TROP/mtcswa.html?storm=SH072014&id=IAN 2http://www.nhc.noaa.gov/gccalc.shtml (for calculating the tropical storm wind radius) http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html http://en.wikipedia.org/wiki/Tropical_cyclone#Size (for determining the average size of tropical cyclones. http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=-171.71,-20.83,1006

While the UK is currently in the mood of cold weather, Ian has continued to intensify. Last visible imagery shows a weak eye feature assoicated with Ian. The compact cyclone now consists of a circular ball of convection with some banding features to its north and south. Currently, the intensity During the last few days, forecasted intensities have been upped considerably, with top wind speeds up to 100 kt (major hurricane!) now forecast (as shown by CIMSS). Fiji Meteorological Center is indicating cat.4 intensity (on their own scale, this is equivalent with winds between 86 and 107 kt). This once again shows that much can still be learned about those tropical cyclones, regarding intensity as well as track. CIMSS ADT satellite estimates are currently at about 55 kt, but this might be related to the small size of the cyclone, possibly leading to underestimation of the intensity. The track forecast has become much more certain, now a well-defined steering mechanism has developed (the trough to the south of Ian). It looks like a few islands will be hit by the tropical cyclone, with much stronger winds than previously expected. However, as Ian is a small cyclone, a slight deviation in track could result in a major change in impact. Finally, CIMSS MIMIC imagery of Ian. Such images nicely show the internal structure of tropical cyclones. The loop is over 48 hours. Many structural changes can be seen in the loop, but the most important are the last few frames. They clearly show a circular eyewall developing, which could be an indicator of a burst of Rapid Intensification. It is very impressive to see a tropical cyclone evolving and organizing that quick. One thing that does make me wonder about such images is that most structural changes seem to be rather subtle. Does anybody know if there is any truth in that theory? Sources: http://tropic.ssec.wisc.edu/# http://www.met.gov.fj/aifs_prods/65661.html http://www.nhc.noaa.gov/

The main contributor to the forecasted corse change of Ian is a trough forecast to pass to the south of Ian in a couple of days, essentially reversing the steering winds around the tropical cyclone. The steering change can be seen below: (Sorry about the poor charts, but I unfortunately don't have access to better charts regarding steering mechanisms): GFS T0h (06Z) Ian is the 1000 mb low at the extreme western part of the map. For the steering influence, focus on the geopotential heights (colors) and not the surface level pressure (white lines). Note that the geopotential heights always decrease when one moves from the equator to the pole, because there is generally colder air located at high latitudes. Within this colder air, lower pressure levels are being reached lower up the atmosphere. (for example, 500 hPa pressures at 70*S are located at 4000 meters altitude, and at 40*S at 5000 meters) What can be seen is an increase in geopotential heights to the southeast of Ian, indicative of a high pressure area at higher altitude. The high pressure area blocks ian from moving toward the southeast. Moreover, because the high pressure area is not very close to Ian itself, the steering winds are generally very light. Looking 66 hours later: GFS T66h (06Z) The blocking ridge to the southeast of Ian has dissipated. in contrast, at T66 lower geopotential heights can be seen extending northward toward Ian. This is indicative of a trough (or low pressure). What happens is that the steering flow around that trough basically captures Ian and recurves it southeastward. In short, the drastic turn of Ian is mainly due to a high pressure area to its southeast dissipating and making place for a trough, which initiates a recurve scenario. There are many characteristics of a tropical cyclone. For instance, a tropical cyclone needs to have at least a low level circulation center (this causes turning of the clouds). Moreover, it shouldn't have frontal characteristics. And there are many more. Some more characteristics are in the link below: http://www.bom.gov.au/cyclone/about/ Well, it seems like a maximum intensity of 75 kt isn't as bad as it seemed to be 2 days ago! JTWC is also keying on 75 kt at the middle range of the forecast. Quite suprising! Also interesting to note is that Ian is basically tracking forth, back and, if the forecast verifies, once again forth over the same piece of sea! Visible imagery shows Ian is a very small cyclone, meaning it is susceptible to rapid changes in intensity. It also contains some banding features, and JTWC noted a mid-level eye feature. This means continued strengthening is most likely, concerning current signals. It will be interesting to see how Ian will evolve during the next few days! Source: http://www.wetterzentrale.de/topkarten/fsavnwt.html http://www.usno.navy.mil/JTWC/ http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html

To give a quick start, the polar vortex is a huge low pressure area mainly located over the poles. On the edges of the polar vortex, usually very strong winds are being reached higher up the stratosphere. This can be seen in the graph below, which shows the zonal wind mean: Zonal wind mean as analyzed from the ECMWF. On the x-axis, the latitiude is plotted. On the y-axis, the altitude (converted to geopotential heights) is plotted. The colors indicate the mean wind speed (m/s) averaged over the full longitude (or in other words completely circled around the earth) for each latitude. Red is winds from east to west, blue is vice versa. What can be seen here, for example, is the subtropical jet stream (200 mb, around 40N) but that is currently not the area of interest. The main area to focus on is the very strong wind belt (above 60 m/s) at about 60-70N, above 10 mb (stratosphere). The very strong winds (east to west) originate as a result of the temperature and isobarical gradient between the intense polar vortex (very low pressure and very cold air), and the higher pressure around it (coupled with 'warm' air). The polar vortex can be seen in the chart below: The chart shows the geopotential height (almost equivalent to pressure) at 100 hPa. What can clearly be seen is the polar vortex having 2 different lobes, the main one located over Northeastern Canada and the other over Siberia. I'll give a more complete explanation later tomorrow, if possible. I hope it helps to improve the general understanding of the polar vortex a little. EDIT: The main vortex lobe has been placed at Northeastern Canada instead of Greenland given BA's correct remark Source: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

During the last month or so, many different media resources have been talking about the "polar vortex". This has caused many confusion in the general public, as well as with some members here, as it seems. This caught my eye reading some of the posts on different places of the forum. Therefore, I thought it might be a sound idea start a new thread to help solving this confusion. For example, on Twitter, the following was posted: Courtesy to Lorenzo (for finding it) Moreover, many big news sites in the US have been hyping about this Polar Vortex, without actually explaining what it is. For example a link to a FOX article about this subject can be found below: http://www.foxnews.com/weather/2014/01/07/polar-vortex-spreads-into-eastern-southern-us/ Or an even crazier article, stating that the polar vortex is "dangerous": http://news.nationalpost.com/2014/01/05/dangerous-polar-vortex-expected-to-bring-record-setting-sub-zero-temperatures-to-more-than-half-of-the-u-s/ It seems like it is evolving toward a serious issue (if it has not already become one). To start with, some informative links about the Polar Vortex below: http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2604 http://en.wikipedia.org/wiki/Polar_vortex I'll try to give a basic explanation later today or tomorrow, if possible. Any new contribution for explanation of the Polar vortex is greatly appreciated! BTW: If this has already been discussed, or if it is in the wrong place, please remove or replace it to another subforum.

It seems like huge amounts of confusion are being caused by the Polar Vortex, which seems to be getting a hot topic in the last few months. Not without reason, though. Lorenzo posted something about this confusion in the stratosphere thread, stating that: Source: http://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/page-47 Things are really getting problematic, as far as I can see it...

That is certainly rather agressive, considering the state Ian is currently in and its organizational history. Though conditions will remain seemingly favorable during the next few days (apart from possible upwelling). By the way, the latest forecast from Fiji Meteorological Service only brings Ian up to 40 knots. That must have been a rather steep decrease in forecasted intensity. The graphical intensity forecast can be seen below: FMS graphical forecast Fiji meteorological service never brings the intensity above category 1 (wind speeds up to 53 knots1) The JTWC forecast has been increased in intensity in the latter parts of the forecast, with winds up to 55 kt being maintained at the end of the forecast. Moreover, the forecast has also shifted the short-term forecasted motion more toward the northwest, to become more in line with the GFS. As a result, Ian will be crossing slightly higher SSTS (up to 30*C) JTWC graphical forecast That's rather impressive to have (multiple) tropical cyclone(s) impacting land for so long. But to answer your question, there were multiple occasions of interactions between strong tropical cyclones in the past. The last one that comes to my mind was in the West Pacific, with Parma and Melor interacting with each other in 2005. They were both major hurricanes at the moment of interaction. The Fujiwara interaction between Parma and Melor in October 2009 About the frequency of such intense cyclones (in this case major) interacting with each other, I don't think it is a very common event, but I dont have access to any data for such interactions. It seems like it is something in the range of once every 5 years. And finally, (because I really like those images ) a MIMIC TPW (based on water vapor) loop of the Southeastern Pacific, in which Ian is also clearly visible (the spinning red color on the map): Source: http://www.met.gov.fj/aifs_prods/20032.txt 1= http://en.wikipedia.org/wiki/Tropical_cyclone_scales http://www.usno.navy.mil/JTWC/ http://tropic.ssec.wisc.edu/real-time/storm.php?&basin=seastpac&sname=07P&invest=NO&zoom=4&img=1&vars=11111000000000000000&loop=0 http://www.examiner.com/article/the-fujiwhara-effect-typhoon-parma-and-typhoon-melor http://tropic.ssec.wisc.edu/real-time/mimic-tpw/ausf/main.html

According to NOAA, more tropical cyclones develop in the South Pacific ocean during an El Niño event. However, less tropical cyclones develop in te Australian Basin due to an El Niño event. As stated from NOAA: http://www.aoml.noaa.gov/hrd/tcfaq/G2.html Concluding, there does seem to be some correlation between El Niño events and TC activity. Current state of Ian Ian itself appears to be less organized than it was yesterday, as it lost its banding features. It consists mainly of a distorted blob of deep convection, while still covering the low level circulation center. Moreover, a visible imagery loop shows the convection moving westward. I don't know wheather this is because of TC motion or upper level shear. Below a Dvorak image of Ian: Ian is currently under weak southerly shear (about 10 knots), as analyzed by CIMSS. This is generally favorable for development, though the analysis above could suggest stronger eastern shear setting up over Ian. Sea surface temperatures appear to be around 28*C, warm enough to support TC development (as seen below on the GFS track forecast and sst map). However, the forecasted slow motion of Ian may cause upwelling of cool water and possibly weakening if the tropical cyclone stays in its spot for too long. Track forecast of Ian As seen above, Ian is forecast to move very slowly toward the west for the next 3 to 4 days, before curving back toward the south-southeast, as it is being picked up by a trough. Because the UKMET and CMC models initialized the system only barely, they gave somewhat erroneous forecasts, and are not shown here. The official forecast of the JTWC mainly agrees with the GFS solution, though the initial motion is a tad more to the south: http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/warnings/sh0714.gif Track forecast from JTWC Overall, there seems to be reasonable agreement on the future track of Ian, though the quasi-stationary movement is usually very difficult to forecast. Intensity forecast of Ian The JTWC forecast slowly intensifies the system up to 50 kt, and then shows very modest weakening in the latter half of the forecast due to shear being caused by an upper level trough to the south of Ian. Moreover, they expect Ian to keep a steady intensity in the short term, which seems reasonable given the current cloud pattern. The upwelling of cold water could be a complicating factor in the intensity forecast. Sources: http://tropic.ssec.wisc.edu/# http://www.ssd.noaa.gov/PS/TROP/floaters/07P/07P_floater.html http://moe.met.fsu.edu/cyclonephase/gfs/fcst/index.html http://www.aoml.noaa.gov/hrd/tcfaq/G2.html http://www.usno.navy.mil/JTWC/

For the 12Z output of the models, I'll try to make a comparison between the ECMWF and the GFS and where I think the crucial difference lies upstream. First, GFS at T96 GFS T96 (12Z) Look at the low heights near Greenland (the purple colors) and not the surface pattern. The GFS shows the low heights edging toward the east slightly, which results in some low pressure areas moving toward that direction. Next, the ECMWF (T96) ECMWF T96 (12Z) Compared to the GFS, the ECMWF forecasts the low heights near Greenland (residual of the Polar Vortex) to edge more to the south, resulting in low pressure areas moving more toward the south. 24 hours later, the differences at the surface from the slight modelling difference above become clear. Once again, first the GFS (T120) GFS T120 (12Z) A long swath of low pressure (and low heights) can be seen stretching all the way from Newfoundland toward Scandinavia. This essentially blocks the opportunity for high pressure to set up over Scandinavia itself. Next the ECMWF (T120): ECMWF T120 (12Z) The Polar high has now got the opportunity to build in between the lows near Iceland and the Baltic States, providing more of a blocking scenario (Scandinavian high). As can be seen above, a very slight difference in modelling of the low heights near Greenland can make a huge difference in the eventual outcome of the weather in NW Europa. (westerly or easterly, zonal or meridional etc). It shows that this could be a very hard time for the models to give the right idea of what the weather will be in 5 days. In other words, uncertanity is very high beyond the 5 day mark. This is also shown in the temperature distribution forecast of The Bilt (credits to Nick Sussex for finding those): KNMI statistical maximum temperature forecast distribution (50 members) It shows that after 6 days, every maximum temperature category is possible, with equal likehood of occuring. Such spread indicates that no definitive things can be said about the exact weather in 6 days. Moreover, the wind direction forecast (new layout) also shows a large degree of uncertanity: KNMI wind forecast distribution (50 members) What can be seen is, for example, the main wind direction for the first 5 days will be from the southwest. At T196 most members (including Oper and Control) are keying on an easterly to develop. Thereafter, the spread is about 60% (South)westerly, 30% easterly. Concluding, wheather an easterly will develop in about 5 days is far from certain. A slight change can have a major impact even at just 5 days. It will be interesting to see what the final outcome of this situation will be. EDIT: the wind distribution and the temperature diagram forecast are outdated (run of yesterday), and therefore, check the link below for the actual wind and temperature forecasts. EDIT2: The temperature graph has been updated to the last output. The wind graphs haven't been updated yet. EDIT3: The critisism on Steve Murr's post has been removed as it wasn't valid (check reasoning below). http://www.weerplaza.nl/15daagseverwachting/?type=eps_pluim Sources: http://www.wetterzentrale.de/topkarten/fsecmeur.html http://www.knmi.nl/exp/pluim/

To add up on the nice list Sebastiaan1973 provided, there is also another feature to analyze wind directions, also found on the KNMI website. On those plots, the wind direction forecast of all 50 members can be seen (oper in red, control in blue). KNMI "windroos" ens (ECMWF 0Z) Every circle indicates 10 knots of wind strength. The circle is divided in 8 subparts, each containing a different wind direction. As with a usual "windroos", the upper part of the circle means northern winds (0 or 360 degrees), the extreme right means eastern winds (90 degrees) etc. Advantages are that the distribution of the wind forecasts up to 10 days can be seen much easier than in the usual "pluim". For example, the wind forecast at day 10 shows 50% giving southwestern winds, and about 40% winds with an eastern component (varying between NE and SE). Source; http://www.knmi.nl/exp/pluim/windroos.php

As the three main models have their (somewhat) reliable update time updated (T144), I'll give an attempt to highlight some interesting features that piqued my interest. General trends During the past week or so, many low pressure areas moved from Newfoundland toward Schotland while intensifying, to curve back toward the north and get absorbed by the next intense low pressure area. All low pressure areas were essentially blocked by the Russian High, which provided South-to-North steering currents on its western flank, as can be seen on the GFS charts below: GFS T24 (12Z). Focus on the low pressure area (or trough, was a 975 mb low at T0) just to the northeast of Iceland. It can be seen spiralling toward the dominant low (945 mb). GFS T30 (12Z) The low pressure area has moved southwestward closer to the main low's center. This has been the process that occured during the last couple of days. Moreover, the high pressure area over the pole is also barely visible to the extreme north. However, at T102, the parent low (945 mb low in the charts above) broke this trend, moving into Scandinavia to be located over Finland (in a weakened state): GFS T102 (12Z) As a result, the Russian high has moved southeast and weakened considerably. The polar high has also become slightly more visible. Differences in model output To me, it looks like this is a possible point of change. This is also the point where the main models start to diverge. I'll compare the T144 from all models. First, the GFS: GFS T144 (12Z) The GFS develops a weak high over Central Europe and Scandinavia, after the low has moved further eastward toward Siberia. However, the sitiuation is very fragile, with the Polar Vortex, along with very cold uppers, situated over Greenland This means that the increased heights could be short-lived. The cold uppers can be seen in the chart below: GFS T144 (12Z) The cold uppers provide an ideal breeding ground for deep low pressure areas, confirming the possible very bleak future for the Scandinavian high pressure area. Next: the UKMET model: UKMO T144 (12Z) The UKMO also shows a Euro high, but the other high is situated over the north of Scandinavia, as an extension of the Polar high. If the highs could connect (which is not very likely given the PV above greenland --> intensifying lows relationship), it could become an interesting situation. And finally, the ECMWF: ECMWF T144 (12Z) It once again shows the Euro high (the most southern position). The second high is a very poorly defined high to the north of Scandinavia. Also note the Polar high is no longer visible on this situation. FI "trends" The further progress of the ECMWF is a high to develop above Finland. However, it needs to be emphasized that this is too far out to tell anything sensible about it, as the GFS is showing a solution with a high pressure area quite some distance to the south of where the ECMWF is positioning it (T192). Concluding, it looks like the situation will provide a chance of a cold snap to develop or at least a change of synopsis. As the high above Russia will most likely be pushed away, the low pressure areas could finally take another course (toward mainland Europe). However, it will take some time before the result of this change in weather synopsis will be clear. EDIT: one thing that was also interesting is that the ECMWF develops the Finland low up to 974 mb toward Siberia (only visible on NH charts, but I won't post them because the post would then become slightly too long. The result of this is deep cold flowing out over the eastern part of Scandinavia. If, and a big if, a Scandinavian high would develop, it could bring very cold uppers toward NW Europe. The GFS doesn't show the low to be as deep as the ECMWF. Also, as Nick Sussex noted in the post below, the main fate for us will be upstream, where the PV is the main player. Source: http://www.wetterzentrale.de/topkarten/fsavneur.html

This was indeed a formidable storm for the third of January! Here in Holland, a wide swath of lighting strikes occured over the country, as seen in the above pictures. Moreover, there are also a few reports of possible tornadoes (EF0), though they have yet to be verified. And finally, some reports of hail (verified) have also been made. For a radar view of the possible squall line, check the radar image loop below: A clear intense line of convection can be seen from Luxemburg all the way to Amsterdam, which produced the lighting and very intense rain for a short period of time. What is also very interesting to see is the very sharp temperature drop which was accompanied by the system. The graph below shows a sudden temperature decrease of about 5*C (!) during the passage of the storm in Wageningen (Holland)! However, what is also interesting to note is that a maximum temperature of 11.9*C has been measured, about 6.7*C higher than average! Precipitation data from the same weather station also shows a maximum of 50 mm/h in that place, which is rather remarkable for mid-winter! When the line of convection was moving over SW Holland, a gust of up to 169 km/hr has been measured at that place. This data could be slightly too high, though a gust of 144 km/h has also been measured. There are currently still some features over England which might develop in new storms. EDIT: The sounding of Wageningen (WRF model) also showed something very remarkable during the storm (18Z). It showed the dewpoint decreasing to dramatically low levels during the storm. Does anybody have an explanation for this? Concluding, it has been an extreme event in many ways, it will therefore be a day here that won't be forgotten easily. And perhaps there is even more to come. Sources: http://weerwoord.be/ http://www.met.wau.nl/veenkampen/Graphics.html http://www.knmi.nl/ http://nl.wikipedia.org/wiki/Januari http://www.atmos.millersville.edu/~lead/SkewT_HowTo.html http://en.wikipedia.org/wiki/Dew_point http://www.met.wau.nl/haarwegdata/model/