ghoneym
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Posts posted by ghoneym
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@sausage Have a read.....
North Sea temps may not be a problem if the Easterly does come.
Essentialy what this study found was that split start vortex events had a quick response downward porpogation which effected both land and sea temps. Vs a displacement event which did not have the net overall effect. Also mention was a 30 day -ve AO state (NAM in document) During a split vortex event.
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Just done an official measure and can confirm 5cm in leven, on ma car roof ?
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Snaw! Falling light but I've got my 1cm hawsey predicted, anything else is a bonus ?
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29 minutes ago, Mattias said:
Nice to see the great action in the stratosphere! Will be interesting to see the tropospheric response. Could also be fun to compare with previous events and to make the comparison easier we have added a new product to weatheriscool.com that might be of interest. The product can be found from the website or following this link: http://weatheriscool.com/index.php/interactive-comparison-gfs-era-interim/ . The product will make it possible to plot charts with geopot. and temperature data at 10 hPa from the ERA interim record and compare it side by side with a chart from the latest GFS forecast. Both charts will have the same projection, colormaps and contour intervals to make the comparison as easy as possible. At the moment only January and February data from ERA Interim is available, but December and March will be added as soon as possible. The product might also have some bugs but hopefully someone finds it useful anyway. For each GFS forecast timestep we have also tried to calculate the most similar geopotential field in the ERA interim record (based on a simple Euclidean distance calculation) and the corresponding date is written out in the box at the bottom of this images: http://weatheriscool.com/index.php/stratosfaren-temp-geopot-height-10hpa/ . The calculation is very simple, just comparing the snapshot of the predicted geopot. field for each timestep, and does not take the dynamical background and so on into account so the result is of course far from perfect but maybe it could give some hints of analouge events.
This is cool Mattias, thanks!
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Current radar pic & current temps via my Netatmo map. Doesn't quite look cold enough yet out west for that band to be of the pink variety?
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Operation runs of 12z available models from meteociel up to +144 (to keep them in line with what we can get from UKMO) and also the 10mb strat for +144
UKMO
GFS ECMWF GEM JMA
Navgem
CMA CPTEC ICON GFS
The main trop vortex segment is similar in structure to me anyway, on UKMO, ECM & GEM. The pacific ridge is played out slightly differently in most models however the most detailed look to this is from the American GFS and NAVGEM. A fair difference in heights and navigation of the AZ high especially in the main 3 with the UKMO maintaining it east at this timeframe, whilst the GFS and ECM have began retreating Westward. All models show an Atlantic influnece on our shores, typically NW /W flows with a strong vortex still present. For how much longer?
Overall broad-scale patterns appear similar across the board with split trop vortices, the main vortex Straddling the USA /Canada / Greenland. The Strat vortex split in two and being tag team blowtorched.
What comes next? The teleconnections are favourable, the split and warming location is apparently favourable, solar activity is minimal and the experts (twitter & netweather) are excited. All looks tilted in the favour of a notable cold spell post mid month. Of course the alternative would be a slower trop response and with the days of winter ticking down could just be a somewhat expected cold winter period with interludes of mild conditions.
On a knife edge indeed.
P.S apologies to the seasoned enthusiasts and the like on here for using some of the lesser known models that are typically ignored but I think it will be interesting to see how they each individually handle the SSW in their outputs. Soon see
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10 minutes ago, bluearmy said:
Need to bear in mind that all the models go up to the upper reaches of the strat in the same single dynamic representation
They all ‘take the strat into account’ as it’s part of the same model run! They may, however, not be so good at modelling an SSW and it’s possible quick downwelling
I suspect the ec op should be the best on this high up so the Berlin zonal windflow charts should give us a good idea of what’s happening
I think the Models will have ways of coping with 'polar convergence' - the physical distance for a given degree of longitude will vary from equator to pole - not only at the surface but aloft as well. Some centres will skew the grid they use to make sure that the primary area of interest is over them, so 'notional' poles will result which may affect, even if only slightly, the forecast over the domain further away. So I think that @warrenb will be correct in respect of MOGREPS vs what GFS would input as starting data.
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Thanks for including me @Hawesy
looking at the Arpege and Hirlam precipitation charts 12z update I'm hoping for more than 1cm, fingers crossed!
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Many times in the past week since the start of the mentioned SSW there has conflicting opinions and even arguments on occasion regarding NWP output and whether or not a certain model has a grasp on the background signals at starting conditions. I think it is worth remembering that the 3 big guns ECM, GFS, UKMO ( in the majority of opinion ) are considered low resolution models focusing horizontal grid spacing at 9-27km. (ECMWF 9km grid spacing, UKMO 10km and GFS 13km for the first 10 days) The GFS resolution moves out to 27km for days 10 to 16! These models are good at grasping "general patterns" and we must remember that pinpoint accuracy and detail of IMBY events is impossible for these models alone to predict. The same should be said for ensemble use as their resolution is even lower.
All that being said it is important to look at the ensembles of each model (where available) and interperate them correctly. (ECM ensemble horizontal grid spacing 18km up to day 15 &36km thereafter, UKMO 20km & GEFS similair).
note- all resolution figures are ballpark and may not be 100% correct, up to date but you get the idea.
Looking at the Ensemble mean first, this typically verifies better than the control forecast by most standard verification scores because it smoothes out unpredictable detail & simply presents the more predictable elements of the forecast. It can provide a good guide to the element of the forecast but should not be relied upon on its own, as it will rarely capture the extreme events. (SSW surely being one of these extremes)
Postage stamp maps. These allow us to take in the individual ensemble member contoured plots and asses the possible risk of extreme events. Cherry picking an individual pertubation is good for eye candy but rarely will it be correct.
An EPS best represents the uncertainty in resolved variables, upper air forecasts are generally more accurate than surface conditions at most ranges and for short range specifics thats why some on here use more convective models such as Arpege, Euro4 etc as their resolotion is of much lower range (0-2km )and detail.
An EPS is only as good as the model it uses. If a model is unable to represent an certain phenomena, the EPS will also be unable to represent it. (a good example would be that most models cannot represent properly convective storms, which is one of the reasons we have convective scale models)
An EPS will share any systematic bias that the model uses. A list of the models and their Bias from you guys would be appreciated.
A common thought when looking at an ensemble chart would be to ignore certain members or cherry pick a "best" member but is this realistic? Perhaps for certain aspects of the forecast over very short period forecasts and for local forecasts over a small area. Over a large area or the full model suite, the control run will always be the most skilful.
To decide on your forecast , and therefore the comments you carefully select to input on to the MOD thread
have a look at the ensemble and if there is a lot of uncertainty try and describe a small number of possible scenarios and outcomes based on the evidence, and try to highlight your thoughts on the most likely scenario plus a single alternative scenario.
Some of the more seasoned posters in the MOD thread can quite rightly use there experience to sniff out certain outcomes and alternatives and these points should also be closely and carefully considered when thinking about you own forecast or model output interpretation.
I Have been guilty recently of one liners, posting nonsense in the MOD thread and I can see why people get frustrated and the forum team have a hard time moderating. If we all try and think a little more before we post and analyse the data hopefully with a few of the pointers in this post it will make for a much more pleasant experience and informative thread for everyone.
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Reading about the varying trop responses associated with SSW's. This article separated SSW's into two types. Reflecting (characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves) and absorbing (longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere.)
It appears to me from what I have read and what we are currently seeing, is that we are looking at a reflecting type of SSW which is not what we seen in 2010's SSW's ? (which most of us remember as being a recent strat/trop event for UK wide cold / snow)
A wee extract from the document.
For the absorbing type (such as the SSWs in February 1999, January 2009, and January 2010), the deceleration
of zonal winds starts in the subtropical upper stratosphere. The decelerating zone shifts poleward from the
subtropics and then the warming descends in the polar region. The poleward and downward penetration
is similar to the polar night jet oscillation. In this respect, it is also noticeable that
a cooling occurs prior to the SSW in the polar stratosphere in association with the strengthening of the polar
night jet. The tropospheric response associated with this type of SSW appears through changes in the polar
night jets, and thus appears as a negative AO-like pattern.
For the reflecting type (the SSWs in February 1979, December 1998, February 2007, and February 2008.), the
deceleration of stratospheric zonal winds is confined mainly to the polar region. Warming is rapidly terminated
by reflection of planetary waves, which induces downward propagation of the wave packets.
Fluctuations, including intermittent warming periods, precede or follow the major warming. The tropospheric
response of this type of SSW appears as an amplification of the tropospheric planetary wave in the
recovery phase of the SSW. In particular, a deepening trough over the North Atlantic and an enhancing ridge
in the North Pacific sector are evident. The latter enhancement provides a favorable condition for a blocking
formation over the North Pacific.
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Similar to above but this time influences of ENSO and its pathways to the Stratosphere & how important they are to Northern Hemisphere winter climate variability
In summary the conclusions are.....
- Tropical pacific SST's are NOT the sole nor the largest source of climate variability for the North Atlantic/Eurasia winter. The stratosphere is a MAJOR source of variability.
- The upward pathway of ENSO influences the tropical and polar Stratosphere in important ways....
- But, SSW's (the downward pathway) largely occur independently of ENSO.
- Models suggest 30% increase in SSW's during EL NINO which could contribute to seasonal predictive skill in the extra tropics.
Again an up to date study presented by Amy Butler ( 9th January 2018 )
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Up to date study (January 11th 2018) on the joint influences of the MJO and the Stratosphere polar vortex on the northern hemisphere extratropical circulation.
In summary the conclusions are....
- The stratosphere polar vortex maintains control of the North Atlantic and Europe
- MJO/Vortex adds valuable information that is not present through only the MJO or the Stratosphere polar vortex separately
- Significant differences in surface temperature when using MJO/Vortex compared to MJO / Polar vortex alone
- The MJO / Vortex events are not necessarily linearly additive
The presentation uses phases 3 and 7 of the MJO in its examples.
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Latest Meteogroup updates from midnight +24 then + 48
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A study into the relationship between the MJO and a SSW. I have inserted the summery of the linked document and associated charts mentioned in the summary. A link to the full document is attached also.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5699436/
MJO‐Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models
Stratospheric variability has important implications for surface climate (Baldwin & Dunkerton, 1999; Limpasuvan et al., 2004; Polvani & Kushner, 2002), and hence, it is crucial to understand the time scale over which stratospheric variability can be predicted. Here we have examined whether tropical convective anomalies associated with the MJO modulate stratospheric variability in operational subseasonal forecasting models, and to consider the duration over which this association can potentially lead to enhanced predictability of stratospheric variability at least in a probabilistic sense. For two different operational models and for nearly all SSW events, reforecasts which maintain anomalously strong MJO‐related convection simulate more realistic stratospheric variability up to 4 weeks later. Furthermore, stratospheric variability is more predictable for SSW events that were preceded by a phase 6/7 MJO event as compared to SSW events not preceded by a strong MJO event.
It is interesting to note that the BoM model has a model top at 10 hPa yet is still capable of capturing the relationship between the MJO and SSWs (as in the low‐top model considered by Garfinkel et al. (2014)). However, the BoM model struggles to capture SSW (cf. Figure Figure2),2), similar to the low‐top models contributed to the Coupled Model Intercomparison Project phase 5 (Charlton‐Perez et al., 2013). Furthermore, we note that in Figure Figure4,4, the BoM model captures weakening of the vortex over the 20 day period preceding a SSW even for SSW events not preceded by a strong MJO, though the weakening is significantly larger for SSW that were preceded by a strong MJO. This suggests that weakening of the stratospheric vortex may be predictable in a probabilistic sense even without anomalous MJO conditions.
We note the caveat that while reforecasts with strong MJO‐related convection simulate stratospheric variability closer to reality, the reforecasts examined in this study generally do not simulate an SSW: Only the tail of the probability distribution function for enhanced convection in Figure Figure2c2c extends to negative zonal wind values at 10 hPa, 60°N. Second, we have not yet addressed whether knowledge of a developing MJO actually contributes skill toward forecasting a SSW, though we plan to explore this question for future work. However, results of this work, combined with that of Garfinkel et al. (2012), Liu et al. (2014), and Garfinkel et al. (2014), suggest the potential for predictability of SSW events at least in a probabilistic sense up to 4 weeks in advance given that the evolution of the MJO can be predicted with some skill up to a few weeks (Marshall et al., 2016; Vitart, 2017).
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5 minutes ago, lottiekent said:
I love Scotland, the weather is beautiful, the scenery amazing - my great grandad grew up in the Highlands so I agree it is lovely.
I just don't get the need for digs at each other. And yes, I know that's what I did coming on and commenting in "your" thread, but the digs at other areas are uncalled for. No wonder the world is going to pot if we can't play nice on a forum created for people to share their love of the weather.
Sorry but I love the competition and find "digs" just part of the fun, it's not personal, it's not malicious, it's weather. Peace
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8 minutes ago, Hairy Celt said:
It's the folk who get reliable snow in winter as well as reliable heat and sun in summer that we're jealous of. Alps - French, Swiss, Austrian, Italian. Bloody EU, stealing the best weather.
Dunbar seemingly the sunniest place in scotland, whilst aviemore has most snow, I'd settle for somewhere in between, pitlochry maybe? Best of both worlds, best seasons? Travel distance to both ?
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11 minutes ago, lottiekent said:
Ah well, you enjoy your protracted winter why we in the south east enjoy our warm spring evenings, +25c sun and overnight thunderstorms in the summer
We just go on holiday for that then return awaiting the next snow fest ?
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The Azores high coming to Scotland favour in more ways than one this winter, it's repeated push from a s/w to n/e position, pressing out the flow from Europe/East has allowed the polar maritime flows to bring in the cold uppers along with the precip that's given us the snow so far. Looking ahead to next week I see more of the same, Scotland in for a cracking week once again hopefully.
Regarding the SSW, I think the after effect at troposphere level 7-14 days later (looking more and more like an extended response from the 15th onward) I think it will be too late in winter to have an effect for the MOD / SE forum englandshire contingent. Oh well ?
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Latest Meteogroup short range charts
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6 hours ago, RAIN RAIN RAIN said:
Do SSWs ever happen in the southern hemisphere?
https://link.springer.com/article/10.1007/BF02980093
2002 Antarctica sudden stratosphere warming caused by southern hemisphere rosby waves, splitting the ozone hole in 2, never happened since, I believe
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I think I upset Optimus slime earlier........
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GFS sea surface temperature anomaly. I would say from this that the majority of the North Sea off the east coast of mainland UK is slightly warmer than average which will allow for some unstable conditions giving heavier snow showers in a E to NE wind.
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Meteogroup use Ecm, ukmo, gfs, hirlam & wrf plus some of their own input based on their experts knowledge etc. That being the case why hasn't the potent cold / snow potential translated on to the BBC forecast yet? It's been spotted on here for 3 days now almost
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19 minutes ago, Gael_Force said:
P7 in cold ENSO looks quite similar to what is modelled in the charts but the diagram is not reflecting a monthly or seasonal differential.
https://journals.ametsoc.org/doi/full/10.1175/2010JCLI3446.1
zoomed in a bit.
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Teleconnections learning
in Spring Weather Discussion
Posted
Couple of questions folks....
First thinking about AAM and its phase shift from negative to positive then back again, and then also the MJO cycle from start to finish. are these two constantly in sync? / linear?
Secondly, Ive got a basic grasp now of Frictional and Mountain torque and there effect on AAM but I can't quite get my head around AAM fluxes and their part in all of this. Wee bit help would be appreciated thanks.