Model Output Discussion

[lukemc]

It still doesn't take away the fact that the set-up is much more marginal than it could be. I don't mean comparing it with as something severe as Feb 1947 necessarily, which was a really proper cold version of what we are seeing atm, with that winter culminating in a a series of non marginal disruptive snow storms (until mid March) - but back to the here and now, relying as we are on heavy ppn from core low pressure areas to produce heavy transitory snow is not quite what it could be (without having to compete with 1947) Indeed just a rather colder version of 2005 would be better.

So why do you think that this set up is a lot more marginal with a lot of factors in our favour (Like a very negative AO/NAO etc.)? In fact it is getting cold outside now and now I am near to the coast. But was it true that similar events that brought lots of snow like February 1996 in the northwest etc. where also marginal like next weeks setup (as a matter of interest - what did the south get out of that event - was it mainly rain thier? Or just dry?)

Luke

[Thundery wintry showers]

The main thing with this setup is that you always have a four way split in the weather:

South of the band: dull and damp with rain

North of the band: lots of snow

Just to the north of the band: dry, sunny, frontal cloud to the south

Further north still: sunshine and snow showers

There is also the issue that the further north the band, the greater the extent to which relatively northern locations get snow, but the greater the likelihood of it turning back to rain in southern areas. Perhaps the "snowiest case scenario" would be for a few days of frontal battleground, with big snowfalls across the Midlands and N England, with snow showers in the meantime over Scotland and rain over S England, followed by the whole lot buckling southwards and introducing a showery north-easterly. However this scenario looks unlikely as the negative NAO looks set to remain "west-based".

I must admit to a preference for convective snowfalls and lack of marginality over the current setup but that's just personal opinion, it is true that really big snowfalls are more likely to happen over a wider area with this setup than with snow showers firing in from the North Sea, I think it's just a question of taste.

[Guest North Sea Snow Convection]

I somehow feel this post above may have a little bit of bitterness as Kent might not be in the firing line but i do agree with you in a sence, i prefer a nice convective Northerly/easterly than having this sort of set up as snow will be more reliable whilst in this set up, its either heavy snow/rain. I'm sure for those who are fortunate to get the snow, they won't care and who can blame them, i know i won't.

I like you, hope we get at least one more proper cold set up before the main attention goes to more warm weather.

Anyways, whatever the set up, somewhere could see huge amounts of snow and Scotland could easily be the place to be on some runs, whilst on other runs, it may be further south etc. 18Z is probably one of the more extreme runs hence the term "pub run"

Interesting period coming up however i feel.

No bitterness at all and it is disappointing that you put the model thread north/south divide bit back again. If you have read any of my general posts then you will see that I go out of my way to be pleased for other regions that get snow. I even post on those threads to that effect.

I did say that what I said would be unpopular, on the basis that I regretfully anticipated posts like yours, but I had hoped that people would read between the lines as to what I was trying to say and why I was saying it. Not on an IMBY basis but on a Uk one.. Unfortunately not I should have known better.

Northants snow and anyone else - ditto same reply.

Edited February 19, 2010 by North Sea Snow Convection

[kent]

It still doesn't take away the fact that the set-up is much more marginal than it could be. I don't mean comparing it with as something severe as Feb 1947 necessarily, which was a really proper cold version of what we are seeing atm, with that winter culminating in a a series of non marginal disruptive snow storms (until mid March) - but back to the here and now, relying as we are on heavy ppn from core low pressure areas to produce heavy transitory snow is not quite what it could be (without having to compete with 1947) Indeed just a rather colder version of 2005 would be better.

This post is a balanced description of the present synoptics concerning the latest output and current conditions and should not be met with comments of bias and bitterness. It seems that some people are looking through snow tinted glasses and refuse to accept other than what they prefer to see.

[NorthantsSnow]

It still doesn't take away the fact that the set-up is much more marginal than it could be. I don't mean comparing it with as something severe as Feb 1947 necessarily, which was a really proper cold version of what we are seeing atm, with that winter culminating in a a series of non marginal disruptive snow storms (until mid March) - but back to the here and now, relying as we are on heavy ppn from core low pressure areas to produce heavy transitory snow is not quite what it could be (without having to compete with 1947) Indeed just a rather colder version of 2005 would be better.

Is it really that marginal though? Even taking the notoriously unoptimistic snow risk %s offered up by the GFS for this run, my location would have about a 30-50% chance of ppn being of snow on Monday, a 20-40% chance on Tuesday, a 45-80% chance on Wednesday and a 50-80% chance on Thursday!

EDIT: To add a graphic to illustrate my point, what's marginal about this for example?

http://charts.netweather.tv/gfsimages/gfs.20100219/18/108/uksnowrisk.png

Edited February 20, 2010 by NorthantsSnow

[Guest North Sea Snow Convection]

Is it really that marginal though? Even taking the notoriously unoptimistic snow risk %s offered up by the GFS for this run, my location would have about a 30-50% chance of ppn being of snow on Monday, a 20-40% chance on Tuesday, a 45-80% chance on Wednesday and a 50-80% chance on Thursday!

Ok - let me put it another way. The model suggestions are infinitely better than they have suggested in terms of cyclonic low pressure set-ups in many years - but relative to what could be (nothing to do with even larger teapot restrictions or any other psuedo voodoo winter curse) I am simply stating that much better is possible. And I am not the first to say that tonight.

For sure there will be snow, and that is of course good - and if you get snow, or I do, or anyone in Scotland, Ireland, Wales etc get snow then that is good.

I am just looking at the bigger picture as to what could be possible - but not trying to be a killjoy for any short lived snow events that undoubtably will crop up in the days ahead .

I am the first to usually suggest take what is on offer - I just see more that could be on offer that is all.

[mountain shadow]

For those arguments about whether it will be snow or rain based on the model output, at least take comfort in the fact you have those options.

For me the 18z GFS has zero precip until T+141, which massively downgraded the 0z snowfest promised.

[LomondSnowstorm]

Ok - let me put it another way. The model suggestions are infinitely better than they have suggested in terms of cyclonic low pressure set-ups in many years - but relative to what could be (nothing to do with even larger teapot restrictions or any other psuedo voodoo winter curse) I am simply stating that much better is possible. And I am not the first to say that tonight.

For sure there will be snow, and that is of course good - and if you get snow, or I do, or anyone in Scotland, Ireland, Wales etc get snow then that is good.

I am just looking at the bigger picture as to what could be possible - but not trying to be a killjoy for any short lived snow events that undoubtably will crop up in the days ahead .

I am the first to usually suggest take what is on offer - I just see more that could be on offer that is all.

I have to say that I agree fully with you Tamara. This setup is potentially very snowy for some, but it looks less likely to be widespread across the whole of the UK as the south is always more prone to marginality and anywhere north of the border is always going to be at risk of not getting the precipitation. In fact, if the latter is not true then the former applies not only to southern England but also to most of central Britain, whereas marginality would be lessened hugely by the setup you described, even in late February. I can't possibly sniff at the outlook really (other than the 18Z which I would feel most entitled to getting a bit annoyed about it if it came off!) but people forget how good that spell could have been had the source been as cold as it is now - I'm sure a foot or two would definitely be possible down the east coast.

For those arguments about whether it will be snow or rain based on the model output, at least take comfort in the fact you have those options.

For me the 18z GFS has zero precip until T+141, which massively downgraded the 0z snowfest promised.

I know how you feel, but this just shows not to trust the models at even 48 hours out at the moment.

[Guest North Sea Snow Convection]

For those arguments about whether it will be snow or rain based on the model output, at least take comfort in the fact you have those options.

For me the 18z GFS has zero precip until T+141, which massively downgraded the 0z snowfest promised.

That illustrates my point. If we we were to take each of the individual outputs atm in terms of this chaotic very marginal cyclonic pattern, in terms of tracking all these suggested shortwaves, we could see upgrades.downgrades and back again for the whole of the UK.

Even if I was in line for one of these potential modelled channel lows, if what preceeded it in terms of snow potential,, and what came immediately after it was a rainfest then in all honesty that is not much appeal at all.

I would prefer it to stay dry and fine with some frost.

I do respect others may feel different though and the mix in itself might provide some excitement. If it was late March I might too

Edited February 20, 2010 by North Sea Snow Convection

[kold weather]

Ok - let me put it another way. The model suggestions are infinitely better than they have suggested in terms of cyclonic low pressure set-ups in many years - but relative to what could be (nothing to do with even larger teapot restrictions or any other psuedo voodoo winter curse) I am simply stating that much better is possible. And I am not the first to say that tonight.

For sure there will be snow, and that is of course good - and if you get snow, or I do, or anyone in Scotland, Ireland, Wales etc get snow then that is good.

I am just looking at the bigger picture as to what could be possible - but not trying to be a killjoy for any short lived snow events that undoubtably will crop up in the days ahead .

I am the first to usually suggest take what is on offer - I just see more that could be on offer that is all.

I'm not sure thats really true though, we could have done better with the orginal cold spell IMO but given what the models were showing we've come so far...Its the orginal cold spell that could have been better BUT we have probably a 40-50% of a memorable snow event happening for somewhere north of Midlands, and I'd say a 15-20% of a historic set of falls. The thing to watch is the intial marker...what tended to hpapen in the past in these set-ups is the first runner dumps snow, then the 2nd and sometimes even 3rd set-ups will not be marginal at all simply because the snow on the ground freezes and temps overnight drop a lot in clearer skies, then they stay that bit lower and less marginal then the first band.

Worth also mentioning you do rather assume it'd be only the briefest of falls, I think the models at least offer the risk in the wes tof it staying as snow the whole way through several events...I just think your rather under-estimating the chances, esp considering our location will be just a rainfest...

Also worth noting the 12z ECM is a good un between 0-72hrs for the Midlands, with Sundays snow roughly the same as the GFS and also the set-up for Monday suggests snow for the Midlands, Wales and the north of England, it would become marginal in the eastern parts but it covers a decent swathe of England overall...

Edited February 20, 2010 by kold weather

[TEITS]

Wow only just seen the 18Z and I can safely say for some regions this is the best model run of the winter so far. The blizzard during Tues/Wed would paralyze parts of the Midlands/W parts of E Anglia. The precip totals for E Midlands where snow would occur are in excess of 40mm!

Despite all the model uncertainity there is one pattern that is clearly emerging. Despite the models predicting mild SWlys at +168 this always remains in this timeframe. What is basically happening is once these LPs appear within +96 the track is much further SE than initally progged. Now considering the current track projected I would say this might even be further SE than what we are seeing.

Certainly going to be mixed opinions in this thread because whilst some are experiencing heavy rain others could well witness very severe snowfalls. Those too far N from the LPs will only see a continuation of dry, cold weather.

From a personal perspective im not bothered if the snow events are marginal. Already seen plenty of bitterly cold, frosty days with lying snow. Now im seeking a severe snow event and thats exactly what the 18Z is showing for my region.

I will add that yesterday my max temps only rose to 0C. I witnessed 7cm of snowfall with no rain or sleet prior to this. Amazingly the upper temps were only -3C!

Edited February 20, 2010 by THE EYE IN THE SKY

[Guest North Sea Snow Convection]

I will be more than happy sometime next week to retract what I have said tonight. If I am wrong - then bring it on! It is always intriguing when the weather proves you wrong anyway!

The details regarding these rain/snow events are still uncertain - lots of daily nowcasting to come. And that is certainly more interesting than watching stratus coming in off the atlantic and 12C

LS - you and your folk countrywide look well positioned to me in terms of some bright weather - but any ppn that may come along,, even if it is less widespread than further south, is more likely to be snow than not. However much or little that might be. I would be happy with that

[LomondSnowstorm]

I will be more than happy sometime next week to retract what I have said tonight. If I am wrong - then bring it on! It is always intriguing when the weather proves you wrong anyway!

The details regarding these rain/snow events are still uncertain - lots of daily nowcasting to come. And that is certainly more interesting than watching stratus coming in off the atlantic and 12C

LS - you and your folk countrywide look well positioned to me in terms of some bright weather - but any ppn that may come along,, even if it is less widespread than further south, is more likely to be snow than not. However much or little that might be. I would be happy with that

That's true. Any fronts or convective showers that might make it this way WILL fall as snow on most likely frosty ground and I do forget how nice sunny, frosty days with some snow is - that pretty much summed up that amazing spell earlier in the winter, except with one or two bigger dumps from time to time. Perhaps some -20C minima in the highlands to look forward too also, which is another reason to be happy with this outlook. I do hope though that everyone sees at least some snow at times, just perhaps not quite to that extent http://expert.weatheronline.co.uk/daten/proficharts/en/2010/02/19/basis18/ukuk/weas/10022518_1918.gif

[TEITS]

I have just worked out that between Tues and Thurs I would see 45cm of snowfall!!

For members who don't understand the charts I have posted one below so you know what to look out for in tomorrows runs.

Basically you don't want to be on the S or E flank of the LP or even in the centre. Ideally you always want to be on the N/W flank of the LP. Here you're likely to see it start and remain as snow. However those away from this area may see rain turn to snow but it depends if the cold air can catch the precip and undercut this before moving away.

So just based on that chart for 3am Wed, E Midlands/W parts of E Anglia would be experiencing a severe blizzard.

[Weathizard]

I have just worked out that between Tues and Thurs I would see 45cm of snowfall!!

For members who don't understand the charts I have posted one below so you know what to look out for in tomorrows runs.

Basically you don't want to be on the S or E flank of the LP or even in the centre. Ideally you always want to be on the N/W flank of the LP. Here you're likely to see it start and remain as snow. However those away from this area may see rain turn to snow but it depends if the cold air can catch the precip and undercut this before moving away.

So just based on that chart for 3am Wed, E Midlands/W parts of E Anglia would be experiencing a severe blizzard.

How would my area do? not getting IMBY just wondering because I'm really not good at reading the charts.

[kold weather]

Yep TEITS the 18z was a historic run no matter what way you cut it IMO.

What I like best is the amount of cold air that comes flooding back down the western side of the low on Wednesday morning, not only does it really raise the risk of backedge snow for places further south but also means we are well set-up for another event.

My big fear is the 0z GFS is a big shift, the 18z ensembles are nearly all with the UKMO solution, and I've seen times where the GFS has flipped to agree wit hthe ensembles, but equally we've seen it the other way round.

The ECM is somewhat a middle ground run with the track, which would make your location for example marginal but further west would still get avery good set-up.

[Paul T]

18Z has focused far to much on channel lows....it brings in the colder air around them far to progressively, notible on the third or forth one...i lose count.

The run is a waste of time from t72.

lets see what the 06z shall bring, thats the most progressive sw'rly run at the mo....will be interesting if it sticks to a strong atlantic flow; if not then mon/tue will be very much more odds on.

Paul

[Iceberg]

Well I think as kind of expected the METO has backtracked to be more in line with the ops GFS, ECM and NAE in the much shorter timeframe.

Instead of exiting the LP over Scotland, it now leaves over Norfork, the assocaited consequences of much colder air for the UK, more snow etc duely follows. Probably not good news for Scotland but...

We are back firmly to the dual low pressure systems at T48, with the first LP becoming increasingly downplayed (GFS has it skirting the far south, METO upto the north midlands and ECM, probably taking monday precip to Birmingham).

The second LP for Wed then brings precip probably upto the scottish borders, but tbh this is so far away we really just need to consider that an second LP will move across England, bring snow to some places. The exit strategy for the LP is a mess and must generally remain unknown at the present time.

Moving closer in METO makes more of the precip for Sunday than the NAE, if right Birmingham southwards could see a fresh covering of snow, but I can't but feel that this is being over progged.

Anyway some good news in the models this morning, still disagreements re developments, but not quite the joke of yesterday and I generally favour the more southern solutions.

[Weather-history]

I'm not an expert on the jet stream but is it unusual for the jet stream to be this far south generally? Normally if it is meridonal then the jet stream is up and down like a roller coaster ie ridges and trough but to me it just looks generally as though it just south almost everywhere.

[bluearmy]

Well I think as kind of expected the METO has backtracked to be more in line with the ops GFS, ECM and NAE in the much shorter timeframe.

Instead of exiting the LP over Scotland, it now leaves over Norfork, the assocaited consequences of much colder air for the UK, more snow etc duely follows. Probably not good news for Scotland but...

We are back firmly to the dual low pressure systems at T48, with the first LP becoming increasingly downplayed (GFS has it skirting the far south, METO upto the north midlands and ECM, probably taking monday precip to Birmingham).

The second LP for Wed then brings precip probably upto the scottish borders, but tbh this is so far away we really just need to consider that an second LP will move across England, bring snow to some places. The exit strategy for the LP is a mess and must generally remain unknown at the present time.

Moving closer in METO makes more of the precip for Sunday than the NAE, if right Birmingham southwards could see a fresh covering of snow, but I can't but feel that this is being over progged.

Anyway some good news in the models this morning, still disagreements re developments, but not quite the joke of yesterday and I generally favour the more southern solutions.

to be fair, sundays trough now has a shallow pressure centre which justifies the larger precip shown on recent NAE runs. however, my take on the 00z's is that despite ukmo going further south on the initial shortwave, the models are generally trending north with the overall pattern. mondays shortwave seems likely to bring uppers above 0c into much of the se quarter of the country and make the snowfall area to the nw of the front quite sharp. all the output seems to indicate that the 'snow zone' over the next week will be north of watford gap. there are plenty of historical precedents for this. 30 years ago, it was not usual for somewhere in the midlands to be the dividing zone green/white. cant really remember the opposite being true without the atlantic battling against a cold block to the northeast. warm lows phasing into a cold trough is a rather different situation. in conclusion, it seems very unlikely that the action will be suppressed to our south. hence, there will be plenty of delighted posters this week and probably a few more frustrated ones.

[Frosty.]

That's true. Any fronts or convective showers that might make it this way WILL fall as snow on most likely frosty ground and I do forget how nice sunny, frosty days with some snow is - that pretty much summed up that amazing spell earlier in the winter, except with one or two bigger dumps from time to time. Perhaps some -20C minima in the highlands to look forward too also, which is another reason to be happy with this outlook. I do hope though that everyone sees at least some snow at times, just perhaps not quite to that extent http://expert.weatheronline.co.uk/daten/proficharts/en/2010/02/19/basis18/ukuk/weas/10022518_1918.gif

The 00z runs again look great for our friends in scotland with cold air becoming even more firmly entrenched during the coming week (minus 12c this morning in places), there are even signs of deeper cold pushing south into scotland later next week as the lows further south push east so a very frosty icy spell, a mix of sunshine and snow showers and occasionally longer periods of heavy snow with no danger of milder air with the jet so far south. For the rest of the uk it also looks cold but less cold at times in southern england although a few inches of snow tonight are likely but on monday it will be heavy rain in the south turning to snow across central and northern england & wales and the coming week will maintain a wintry mix but with milder air getting closer to the south.

Edited February 20, 2010 by Frosty039

[LomondSnowstorm]

http://212.100.247.145/viewimage.pbx?type=gfs;date=20100220;time=00;ext=117;file=h500slp;sess=90dd181fad69d031b595259851a31be7;

http://www.meteociel.fr/ukmo/run/UW120-21.GIF?20-06 http://www.meteociel.fr/modeles/ecmwf/run/ECM1-120.GIF?20-12

Now that's more like it! I think (just judging by the position that low pressure gets to) that these runs probably suit everywhere north of the M4 at some point. Starting with this http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/02/20/basis00/ukuk/prty/10022106_2000.gif

LS

[Frosty.]

And south of the M4 looks wet rather than white sadly although snow tonight across england & wales looks widespread with 3-6cm generally, this snow then clearing tomorrow but with heavy rain on monday turning to snow north of the M4. The ECM 00z seems an upgrade for the north later next week, as does the gfs.

Edited February 20, 2010 by Frosty039

[cooling climate]

Ok - let me put it another way. The model suggestions are infinitely better than they have suggested in terms of cyclonic low pressure set-ups in many years - but relative to what could be (nothing to do with even larger teapot restrictions or any other psuedo voodoo winter curse) I am simply stating that much better is possible. And I am not the first to say that tonight.

For sure there will be snow, and that is of course good - and if you get snow, or I do, or anyone in Scotland, Ireland, Wales etc get snow then that is good.

I am just looking at the bigger picture as to what could be possible - but not trying to be a killjoy for any short lived snow events that undoubtably will crop up in the days ahead .

I am the first to usually suggest take what is on offer - I just see more that could be on offer that is all.

Fully agree with what you are saying, I said pretty much the same myself in a earlier post.

Because of these spawning slow moving shortwaves that are developing off of the low to the west of

Norway they are blocking what could be some bitter true Arctic air from reaching our shores where

we could well be looking at powder snow and maximum temperatures widely across the country

into the negative digits.

Several days ago when the shortwave developed around Iceland if that had moved south down the

north sea we would then have seen the start of a prolonged freeze but for some reason that I can

not fathom out (apart from perhaps sea surface temperatures ) it decided to anchor off of the coast

of Norway leaving the UK in this rather coldish type of weather.

It has been a very frustrating couple of weeks knowing the UK was so close to seeing a prolonged

freeze that could have rivaled the likes of February 1986 perhaps.

As far as the models go this morning I would not start thinking of a snow event for any particular area

until you are only at a maximum 12 hours from a possible event due to the uncertain tracking of these

lows pressure systems.

[chionomaniac]

I'm not an expert on the jet stream but is it unusual for the jet stream to be this far south generally? Normally if it is meridonal then the jet stream is up and down like a roller coaster ie ridges and trough but to me it just looks generally as though it just south almost everywhere.

That is a great chart illustrating the position of the jet stream. Of course one of the factors that may influence this could be the weakness of the stratospheric vortex following the MMW. It shows the lack of direction that the current troughing over the UK is receiving from up above and that in turn helps explain why the models are having trouble modeling the mishmash of upper and lower weak troughs. As long as the jet stream persists this far south without any meridionality, then I think that the longer this pattern persists.

I believe that what Tamara last night was suggesting was that the current set up has the potential for deep cold across the whole country without marginality at all. However we are seeing a watered down version of the blocking that is centered over the pole which is giving the marginility. Good luck to those that see snow is what I say. Perhaps it is the lack of meridionality from the jet stream that is responsible for this.

c