Model Summaries And Thoughts

[Paul]

As per the post in the discussion thread, this new thread is intended for members who want to post a more considered view, to perhaps summarise the models, a particular run, look a specific angle on the output, or just something a bit more in depth (doesn't have to be technical) which can be viewed by members in a quieter thread.

Members are more than welcome to copy and paste any of their own posts from the discussion thread should they wish so as to get the best of both worlds for a more considered post - eg discussion and reaction in the main thread + the opportunity for people to view over a longer period in a less fast moving atmosphere in the other thread.

We're keen to keep this thread to more considered posts etc, so please use the main thread for general discussion and chat.

http://forum.netweat...entary-1st-feb/

Thanks

Paul

[phil nw.]

Ok i will start us off.

It does seem that overall the 12z outputs have taken a small step back from pushing the cold away over the weekend.

Looking at the fax charts compare T84hrs. from 00z output with this evenings T72hrs.-both for the same time.

We can see now on the T72hrs the approaching Atlantic fronts slowing and buckling suggesting the possibilty of rain mixing with the cold air already over us and giving snowfall somewhere over the Central or Eastern part of the UK.This is a changing situation and tomorrow may well move things further west or back east pushing the milder air through.One to watch and at quite short range.

If we look at the models at T96hrs. we can see how the cold air is still near or over the East of the UK,which opens possibilities of a return of the cold further west towards the UK.

http://www.wetterzen...ics/Recm961.gif

http://www.wetterzen...cs/Rtavn962.png

http://www.wetterzen...ics/Rukm961.gif

http://www.wetterzen...ics/Rgem962.gif

Forecasting surface developments where there`s such large temperature differences over and near the UK is proving very tricky- as the daily changes in the Operation runs are showing.

Edited February 1, 2012 by phil n.warks.

[nick sussex]

The last week in the models has had more twists than an Agatha Christie novel with the Siberian high causing chaos in the models and this shows little sign of easing up as we head towards the weekend.

Certainly not a time for making concrete predictions about who gets snow and who ends up in the frustrating rain or dry zone!

The modelling of these battleground scenarios is the poorest in terms of detail, if you think about 100 miles on a global scale its nothing but this makes a big difference when you're dealing with the expected weekend set up.

It probably won't be until 24hrs before the event that we'll have a more narrowed down area at risk and even on the day this will still likely have some margin for error.

[The Enforcer]

To add to Phil's post, the preceding T96hrs Fax for Saturday here:

shows a slightly slower mild incursion initially, which the T84hrs Fax made more intense, but the slowing of the T72hrs is more evident when compared to both charts. This illustrates perfectly, the push and pull nature of each output that Phil was talking about.

Here are similar comparison charts for Sunday T120hrs and T96hrs respectively:

On this occasion I've spared everyone the crazy annotations, as the subtle changes in emphasis should speak for themselves. Also note the emergence of the front sneaking in from the east, enough time for that to move about a bit based on where it lies at 00hrs Sat T60hrs:

[West is Best]

Interesting cross-model 0z operational agreement in the medium term, with slight variatons having a big impact locally for the UK, specifically on the precise positioning of the high next week. There is no doubt that the developments for those against zonality have been vastly improved these past 18 hours, with the high holding the jet to our north and the current set up retaining some continental cold over the south-east of England under the high which is no longer a pure Azores one, but positioned close to the UK.

Of particular interest to me though is that despite the operational agreement there is still huge ensemble scatter in the short and medium terms, suggesting that there's little real resolution to this.

I still think the high will be pushed down by the jet but there's no guarantee that it won't go the other way. If so it would open all that cold sinking into southern France right up to the UK.

As a footnote it looks from these runs like a cold half-term for Alpine skiers.

[chionomaniac]

Interesting cross-model 0z operational agreement in the medium term, with slight variatons having a big impact locally for the UK, specifically on the precise positioning of the high next week. There is no doubt that the developments for those against zonality have been vastly improved these past 18 hours, with the high holding the jet to our north and the current set up retaining some continental cold over the south-east of England under the high which is no longer a pure Azores one, but positioned close to the UK.

Of particular interest to me though is that despite the operational agreement there is still huge ensemble scatter in the short and medium terms, suggesting that there's little real resolution to this.

I still think the high will be pushed down by the jet but there's no guarantee that it won't go the other way. If so it would open all that cold sinking into southern France right up to the UK.

As a footnote it looks from these runs like a cold half-term for Alpine skiers.

I think that it is best not to concentrate on the GFS solely for the output. However if you do , WIB you will note that the ensemble scatter is far more favourable to that yesterday. In fact from memeory the GFS ensembles were all keen on a 850hPa warm up from Sunday. But just look at that now, the mean stays well below -5C with some members keeping below -10C.

I suspect that any snow that lies may be around for quite a time yet!

Edited February 2, 2012 by chionomaniac

[johnholmes]

Not a detailed post just a few comments having seen this kind of scenario many many times.Models are not much better than human forecasters at very short time scales so bear that in mind when talking/looking/wondering about snowfall amounts. I do think the front will pose less problems in one sense. The air ahead of it is going to be pretty cold (dewpoints and upper air) that the problem snow or rain, away from western areas, will be less of a problem than it usually is in the UK. In another sense and its how much activity it will retain as it moves east/SE? I suspect that it will become fairly weak by the time its into Se'ern areas.

Complicating matters is what I raised in the model thread late last evening. The deepening cold air over the N Sea and increasing moisture, partly due to the cold pool/surface low (shown on Fax charts), will give decent snow showers from about Lincs southwards. The problem of that is how far inland before they run out of energy/moisture. I think the SE of East Anglia and Kent may see the most activity but also some places further west from that zone. This of course occurring before the frontal situation extends into those areas.

For a forecaster its both highly interesting and also highly complex. I don't envy either the Met forecasters on TV nor our own Nick and colleagues on Net Weather!

snow lovers enjoy if you are the lucky ones-others enjoy the piccs they will undoubtedly post for us.

Edited February 2, 2012 by johnholmes

[johnholmes]

In the longer term then the 500mb anomaly charts show no signs of any Atlantic type dominated weather, NOAA last evening 6-10 and 8-14 pretty similar to the EC-GFS issue this morning, see below; and all 3 have been consistent for days now on the likely upper air pattern. Detail of course will change but the overall idea of cold not mild seems pretty secure into mid Feb at least.

http://www.meteo.psu.edu/~gadomski/ECMWF_0z/hgtcomp.html

[TEITS]

A very short summary from me for the medium range follows on nicely from John H post.

http://cdn.nwstatic.co.uk/ensimages/ens.20120202/06/t850Cambridgeshire.png

Very little sign of any mild weather as we head into mid Feb with the mean around -4C.

Only difference from our current pattern is the cold in mid feb may come from the N instead of the E.

[johnholmes]

as promised to try and help new folk confused by the multitude of posts about this weekend

weekend of 3-5 feb-rain or snow.pdf

[alijoe]

as promised to try and help new folk confused by the multitude of posts about this weekend

weekend of 3-5 feb-rain or snow.pdf

Thank you John for the time spent on that, it was much appreciated.

[johnholmes]

as promised to try and help new folk confused by the multitude of posts about this weekend

weekend of 3-5 feb-rain or snow.pdf

blimey seems popular

I'll do the same tomorrow afternoon after the 12z comes out and by then we can look at how the closer models, fine mesh type, NAE (Met Office=T+48) and just about the NMM(Net Wx=T+36) are dealing with things.

[The Enforcer]

Latest evolution of Fax Charts for the weekend from left to right:

Saturday:

Sunday:

Reason for edit - to add T72hrs chart for Sunday.

Edited February 2, 2012 by The Enforcer

[Harsh Climate]

This is where I am currently expecting the heaviest falls of snow saturday/sunday

In the red zone I'm expecting widely 7-15cm. (Due to the marginalty of this situation heaviest accumulations will be restricted to above 100m)

In the orange zone 5-10cm. (Down to sea Level)

In the Yellow zone 1-5cm. (Down to sea Level)

I expect that narrow red strip to get the heaviest accumulations due to an abundance of moisture pushing in from the north west and marginal uppers, this will only aid precipitation and I would expect to see some locally huge flakes associated with snowfall at marginal temperatures (could be some good hourly snow rates ).

The orange zone should also see some intense periods of snow, less in the north east at first but as the front backs west on sunday and grinds to a halt, this area should be set for a good period of snow. With long periods of moderate snow in the linconshire area saturday/sunday.

The western part of the yellow zone will probably be too marginal for the highest totals of snow, the wet nature of it should restrict snow totals (But a shift west in the charts again could very well change this ; ).) And in the southern part of this zone I think the front should be weakening with mainly light perhaps moderate at times accumulations, so not expecting too much here.

Sorry about my map been a bit sketchy, was the only map I could find and had to use paint.

Edited February 2, 2012 by Harsh Climate

[OldMetMan]

It’s amazing how much model output can change in but a few days!

There is fairly broad agreement on maintaining the current block but for the 12Z ECM that is trying to bring in a NW flow late in the period. There are some variations in the location and intensity but HP is maintained over or near the UK, with a light flow off the near Continent or a high cell right over us.

The main area of interest at the moment is the LP forecast to move S over the country during the weekend. Again, there are slight variations but the general predicted path is down the middle of the country with snow on its E side. Once it is past, then pressure is expected to rebuild to the N.

It is going to be extremely difficult to assess snowfall in this situation. The projected path would certainly provide several hours of snow over the E Midlands, NE England and central and S/SE England, but with a slight fetch off the Channel coastal areas may escape. It is worth bearing in mind that the forecast is for a shallow LP that is unlikely to develop much so snowfall amounts could vary enormously from place to place.

That apart, the GFS shows another similar development next Wednesday, with the LP in this case heading S over the W of the country. It is hard to say at this stage how well surface temps will support snowfall with this event, if it happens, although with a mostly slack pressure field over the country and a pool of stagnant, cold air, there could certainly be some.

In the longer term, the models show a general trend of retrogressing the HP W, eventually leading to HP in mid-Atlantic. Upper air developments are showing some significant changes upstream with increasing meridional flow. Over the US/Canada, there is now a developing upper low over the W, moving E and amplifying, with a fairly strong ridge over the E Pacific. The upper low to our NW is moving little with the upper high holding firm over us, with an upper low covering much of Europe. This pattern has the look of a more stable wave pattern so the longer-term model depiction of a mid-Atlantic HP is a distinct possibility.

The jet is also showing some interesting changes. The is a complex split flow over US/ Canada with one arm heading NW towards us, and a more southerly branch which looks as if it will start to propagate on a much lower latitude. This raises the possibility of the UK being attacked on 2 fronts, with the development of an arctic front with LP heading down from the NW, together with the polar front displaced well south bringing systems in from the SW. If the cold air largely persists over the UK in the coming days with a light E or SE flow, this could provide some entertaining situations, especially if the HP over mid Atlantic extends W towards Canada – that’s the sort of pattern associated with prolonged cold spells.

I suspect the GFS may be first to indicate whether the above looks likely to happen. Meanwhile, the weekend will be very interesting!

[West is Best]

Will post in the other thread but some interesting synoptics at the moment, or at least we hope so. I'm not going to attempt to forecast what will happen the next 48 hours from the 0z runs as I'm poor with boundary snow events. All I would say is that despite the cold pool the angle of attack is unusual for a big snow event. Normally the rotation of this front would suggest to me sleet and snow turning readily to rain, but it may stall and therefore may be widespread. I'm not overly optimistic though.

Further ahead, and the models diverge. Looking at the 0z runs we have UKMO, GEM, NGP all pretty Atlantic dominated. The best hope is the slight delay that UKMO suggests at T60-T72, although it too eventually anchors the high over the Azores allowing a return of the westerly flow and it goes pretty full on zonal at T120 and T144. As the UKMO is, for me, the model of choice this is a concern.

Both the ECM and the GFS operational are very different, with the high anchoring over the UK prior to the FI retrogression in the GFS starting out at T240. The GFS pressure chart ensembles, however, show scant support for this high pressure to be over southern England and it could be called a true outlier:

However, the fact that the ECM backs that scenario adds considerable credence and the 850hPa ensembles continue to show a lot of scatter suggesting uncertainty and divergence:

In the meantime I hope everyone who likes cold can enjoy what we have, and hopefully some of you will see some snow, without worrying too much about next week. In terms of sustained cold we need to see if the GFS Greenland High in FI is the sign of a trend, or just another one of its guessing game scenarios. I'm not sure the GFS timeframe past T192 is a lot better than a game of Jack Straws. However, if that is indeed a trend then the key to unlocking true cold potential would be in the door.

[Harsh Climate]

The BBC weather site differs to your summary

yes latest models have pushed everything much further south east, remember my forecast was based on yesterdays 12z runs though. But I'm quite suprised as I really thought everything would be pushed further west .

[phil nw.]

With the next 48hrs. or so well covered in other threads i thought i would look beyond the weekend`s forecasted snow event and into the start of next week to see where we might be heading.

Tthe 00z runs suggest a rise of pressure across the UK as the block reforms,although the GEM seems less keen on this.

Yesterdays 12z `s runs all favoured some shortwave development further west around Tuesday which gave promises of undercutting and splitting the block with a return of an Easterly pattern.However GEM seems the only model still bullish about the undercutting this morning.We can see by around T120hrs. where the models suggest the energy may go.

We can see that GEM really digs that shortwave further west which would induce an Easterly quicker,the other runs seem to favour a more balanced split leaving the UK in a mid-latitude high.

GEM would retain the cold surface conditions for many with the SE still on the edge of the deeper cold from the nearby continent.

There would be a gradual warming from the north west on the other runs you would have to say.

Later output on the ECM,GFS and GEM show some form of Scandinavian High and weak Easterly pattern which suggests a return of some colder air off the continent.

So any slight warm up after the snow looks quite shortlived and the SE quarter of the UK looks as if it will remain quite cold for the next week at least and this cold spreading west again to other parts if the Easterly verifies as modelled.

Edited February 3, 2012 by phil n.warks.

[damianslaw]

My words are on the ECM model. This continues to suggest retrogression of heights NW towards greenland later next week and formation of scandi trough. It is a theme it seems to want to stick with and is in line with its ensembles. Is it picking up the amplification forecasted to hit NE USA just before mid month that tad a little too early? or is it bang on the money.. who knows. GFS suggests similiar evolution but way out in the fantasy land.

The background signals all point to northern blocking as we reach the middle of the month, and the for the second half of the month to be dominated by a north westerly to northeasterly airstream thanks to stubborn heights to our NW - the perfect synoptic for sustained long term cold and a much more conducive synoptical situation for snow - indeed a similiar pattern to what we saw in late nov 2010 early dec 2010 and also mid dec 09 - early jan 10.

Those who believe the second half of feb is too late to deliver bitter cold and snow shouldn't, such a synoptic would deliver widespread very sharp frost, quite easily the coldest conditions of the winter for the north, and much more widespread longlasting severe spells of snow compared to what we are going to get tomorrow. Indeed tomorrow looks like just a pre-starter.

[Zenarcher]

My thoughts on the weather models today,

GFS

First of all it must be said well done to the GFS last night most models tried to show a shortwave for mid next week but the GFS wasn't going for it now today we see most models moving over and agreeing with it. That's the thing right now we don't know who's right or who's wrong. So the GFS is showing really nice charts tonight in the long range with high pressure moving over Greenland giving us cold weather lasting well into mid February.

JMA

Still tries to bring a shortwave low in for Wednesday however doesn't really do the job to well. After this we do see it sending low pressure under the blocking letting high pressure build up in the Atlantic.

ECM

Shows the Russian high moving in over the UK for most of next week leaving the UK in settled weather and slightly warmer. After this once again the ECM is keen on building high pressure up in the Atlantic to give us a Northerly by next weekend. Its being showing signs of this for a few days now a good trend showing even the ensemble run shows high pressure building up in the Atlantic this is good we need to see the Atlantic weather ease off like this to give us our best chances for a good long spell of cold weather.

GEM

Bringing out some nice charts tonight as well it still seems very keen on sending low pressure down South and allowing high pressure build up over Greenland a somewhat similar trend to what the GFS and ECM show.

NOGAPS

Not showing great charts tonight with the Atlantic sending to much energy over our North not giving us good chances for high pressure to move up there.

UKMO

Not showing a shortwave tonight and that Azores high seems keen on moving up over the UK during next week so not excellent charts from it tonight thankfully it seems to have very little support on this.

Overall this weekend is looking very cold with Eastern England seeing the best chances of snowfall which is likely to be heavy at times. Currently we are unsure on how far in the cold will make it so look at the high res models like NAE and NMM for 24 to 48 hour ranges as they will give you a better idea. As for the longer term we are still unsure on things but there does seem to be a good trend in the GFS, ECM and GEM for a long lasting period of cold weather starting sometime next week this needs to be watched. For now those who are lucky enough down South enjoy the snow because its a rare thing this winter.

[leicsnow]

Ooh the 06z GFS keeps a rather sustained cold outlook, with northerlies (noreasterly) producing snow more widespread and including western areas in FI.

It is the 06z though, again the run with the lowest verification stats, but if 12z follows it will certainly be looking good.

Edited February 4, 2012 by Tellow

[phil nw.]

The 12Z models have come up with a full house for cold and snow fans by the seems of it.

Here are some images from the different runs at T144hrs. which show the onset of another Easterly as heights are shown to rise to the NE again.

Further on we see the trend for vortex splitting again with the likelhood of Greenland Blocking in week 2.

See the mean Ht.Chart here for days 8-10 from the 12z GFS/ECM runs.

If we also view the tropical MJO forecasts and the matching composite for it`s high amplitude and it`s placement in Phase 8 of it`s cycle then again we see a familar trend of Northern Blocking suggestive of a North or North easterly flow in the medium term.

If we consider the 12z outputs and those others i have shown along with Chiono`s.data in the Strato Thread there is good agreement that an Easterly and then a Northerly are the likely patterns to expect in the next 10-15 days.

Pretty good stuff for those looking for more cold and snow before Winters end. Indeed these outputs signal the strong chance of a very cold February.

Edited February 4, 2012 by phil n.warks.

[Zenarcher]

Thoughts on the weather models today,

GFS

One interesting thing about the models recently is we see low pressure tracking across the Atlantic around Tuesday and Wednesday they all come up with different ideas on this. The GFS shows a low pressure system move near the far West of the UK which then drops in pressure and heads up to Iceland. While this happens the UK is under high pressure with settled weather. An increasing trend is appearing after this on all models now. With high pressure building up in the Atlantic but with some low pressure systems in there as well. The GFS shows the Russian high move over to Greenland by next weekend and from then on it gives us a good solid Northerly not just a short cold spell. It shows this Northerly lasting well into the mid month. Very good charts tonight from the GFS and a trend that's still going strong.

JMA

Not the best charts tonight but still okay. It tries to build high pressure up in the Atlantic and over our North but it sends a large low pressure system over Greenland and Iceland stopping any blocking happening it would leave the UK under high pressure though.

ECM

Showing very nice charts as well tonight and agrees with the GFS although it makes the Northerly happen a bit quicker. We see the Atlantic weather coming pretty much to a grinding stop by Thursday. After this high pressure from the West and East join but we have a low pressure system in the middle of this all which actually helps us get the Northerly. The ECM solution tonight is a very complicated one and when you throw in a low pressure system that makes things extremely hard to handle because there are endless ways things could end up. But at least its still showing a cold outlook with a Northerly in place, a good trend from it and the GFS in the past few days.

GEM

Had us excited early on this week showing a possible shortwave for next Wednesday however most models dropped this idea last night and today the GEM seems to be the last one to drop it. Anyway its also giving us a nice outlook possibly not the best but still good. It has high pressure to our North East and in the Atlantic but a low pressure system over Greenland. That's what it shows up to 144 hours beyond that is unknown what it would show, I would think the low would go under the blocking helping us get a stronger blocking to occur in the North.

NOGAPS

Also agrees on this trend and actually the 144 hour chart looks similar to the UKMO. It has high pressure to our North East and high pressure out in the Atlantic. It then eventually leads to another Easterly later on.

UKMO

Its very good to see this model agree with a cold set up. Although its hardly surprising the ECM and GFS have been keen all week on a colder outlook and even the ensemble run was showing good signs. The UKMO shows high pressure to our East and West with a shortwave for next Friday to the West of the UK.

Overall not to much attention it seems on the weather models today with all the snow. So after this current cold spell its time to look for the next and the models are already showing us nice charts although they all differ in exact detail the trend is there for some sort of blocking to happen some time soon. Interesting model watching continues.

Edited February 4, 2012 by weathermaster

[damianslaw]

All models agree on blocking ruling the roost for the foreseeable future with the atlantic making only splashes into western parts before being forced to retreat mid-week thanks to a resurgence of those heights to our east nosing into the country. Indeed the outlook looks a carbon copy of the week just gone -slightly less cold uppers, but a predominantly dry outlook away from the west, frosty nights and cold days- keeping the CET well below average.

Longer term - the models picking up on upstream northern hemispheric changes - scandi trough being shown by both ECM and GFS, ECM a bit more progressive in its timing, heights quickly transferring to Greenland. So an easterly followed by a northerly/northeasterly and an unstable one meaning excellent chance of heavy widespread snowfalls thanks to trough/shortwave action and energy going into the southern arm of the jet.

I think there are going to many snow lovers happy in the next month.

[TonyH]

My take on the coming week from a regional perspective:

Weather guide Monday 6th to Sunday 12th February (west Wales and central MIdlands)

Headline: Becoming cold and mostly dry again

The battleground event happened on cue yesterday with 3- 5 inches of snow falling across Coventry and Warwickshire, while the milder air won out over west Wales. The continent has been bitterly cold of late, in Paris the temperature falling to -9c, and heavy snow in Rome for example. Llanwnnen got down to -10c Friday morning, this nowhere near as cold as the -17c recorded on Christmas Day 2010!

During the early part of this week we are in a 'No Man's Land' neither in cold nor mild air, being within a slack area between high and low pressures.

Messy weather too, some sun, some cloud, bits of rain or drizzle about, but dry in places too! Not cold enough for snow, but cold enough to freeze overnight with potential ice problems for morning commuters. Maxima on Monday and Tuesday between 4 and 8c, mildest over Pembrokeshire.

Rather debatable Wednesday onwards with the models showing some slightly differing trends, but with greater consequences in weather terms.

Strongest indications are for high pressure to reform over Scandinavia again with this ridging cold air back over England and Wales from Wednesday. During Wednesday itself though, a niggle, as Atlantic fronts may progress close enough to west Wales to bring some sleet or snow here, however this is a low probability at this stage, but don't be too surprised to see some wintriness this day perhaps. Cold easterly winds look likely again to end this week, with crisp sunny periods by day, but hard frosts overnight, and also freezing fog could linger well into the day in places. Maxima between 1 and 3c generally, although staying below zero locally, should freezing fog persist well into the afternoon. With the high pressure in control, snow is unlikely, apart from the odd rogue light flurry into the Midland perhaps.

Next weekend, as always at a distance, and greater doubts cast as to what may happen. It looks like the high pressure will be over or close to the UK by then, so it would still be cold and frosty, although should the high sink to our south-west, as GFS suggests, turning milder. However, I would bet on the cold holding on well into next weekend.

For supportive model charts see the Welsh thread:

http://forum.netweather.tv/topic/72450-wales-cymru-regional-weather-discussion-part-4/page__st__640__gopid__2255764#entry2255764