Model Output Discussion

[Iceberg]

Well this is how much the UKMET has changed and shifted southwards over night, even as early as Monday.

I really would caution anybody predicting from a model that is capable of this in the last 2 runs to wait, the GFS is reluctant to take the LP very far north at all on Monday, the GEFS has not performed well as it seems the lower resolution is struggling with the dual low interaction.

[Frosty.]

I think the 00z runs have moved a step closer to unlocking even colder air to the north and north east by later next week and the mild breakdown is less likely than it was showing yesterday thanks to the lows tracking further south as they move east, good news if you love cold weather :unsure:

[TEITS]

Huge scatter early on in the ensembles ranging from +4 to -9C!

http://charts.netweather.tv/ensimages/ens.20100220/00/t850Cambridgeshire.png

There is less scatter further N which suggests much uncertainity with regards to the track of the LP.

Interesting for Monday the track of the LP (Fax chart) is almost a carbon copy of the LP that bought snow for my region on Thursday. Worth mentioning that I discovered yesterday that whilst I enjoyed 7cm of snowfall only 20miles S of Peterborough they had rain. Just shows how localised the weather can be in these situations.

[Nick F]

Track of Monday's low looks fairly certain now as it did yesterday, tracking NE across SE England, though I wouldn't get hopes up of too much snow across Wales and Midlands as rain bumps into colder air, as it looks from NWP like the heaviest precipitation will be over southern counties where it will be raining.

The second low heading NE for Wednesday looks a somewhat deeper feature, and looks to bring heavier precipitation across central and northern England and parts of Wales which will likely be snow wherever the northern and northwestern flank of the low ends up, so could be a proper snow storm. 00z GFS track of this low on Wednesday looks rather dubious by taking it round in circles over Northern England, ECM looks more plausible with a straight NE track into the N Sea. be interesting what the 06z run does with the mid-week low.

[Tom D]

Huge scatter early on in the ensembles ranging from +4 to -9C!

http://charts.netweather.tv/ensimages/ens.20100220/00/t850Cambridgeshire.png

There is less scatter further N which suggests much uncertainity with regards to the track of the LP.

That's a quite confusing ensemble there; the operational and mean are dead on the mean for the Monday event but then afterwards each one introduces milder uppers at different times. Doesn't that mean the track for the Monday low is fairly set, whilst the Tuesday/Wednesday one is still up for big changes?

[kold weather]

Yep models now fairly sure of the general evolution of the low on Monday however they have somewhat downgraded thre snow risk, still time for the risk zone to shiftr as much as say 50-70 miles but southern Midlands still looks most likely.

The 06z is a little further north with the frontal system however the heavier pluse still runs across the south coast much like yesterdays 12z ECM, sadly the time of day this heavier pluse comes up really doesn't help, being right at the heart of the day, if it came up during the overnight hours things would be a little different. Still Nick's right, the 0z set of the models are not nearly as condusive for snow as the 12/18z last night for Monday as the warm front decays very rapidly compared to yesterday, plus the low is a lot weaker.

Still at least now there is increasing confidence on another system coming up after this low as well...

[Iceberg]

the 06Z doesn't really take the precip north of a line from the Severn to the lincs for Monday. However it does produce less cold for the SE as the closed circulation pulls down less cold.

[kold weather]

Yep 06z is a much milder run with regards to the 850hpa temps, a worse run all round I think. We need the low to seperate and remain a stronger system, if it doesn't then the cold air will not come down behind it and the next system will be a rain system rather then snow...

Very poor run for snow indeed, MUST keep that low a seperate system, if not then its curtains!

[conor123]

I find with these lows is that the models can never decide until the day before usually and the majority of times they end up further South so i expect everything will end up about 100 miles further south than currently shown though could be wrong.

[Nick F]

Interestingly, the low moving up from the SW late Tues/early Weds seems to have its energy taken away by a secondary shortwave on its southern flank swinging east into western France, so not looking like the deeper feature shown by 00z ECM, it does spread rain further north than Monday's low which would see snow across northern England this time, which could get quite a dumping as the low is slower to clear into the North Sea.

[KTtom]

Yep 06z is a much milder run with regards to the 850hpa temps, a worse run all round I think. We need the low to seperate and remain a stronger system, if it doesn't then the cold air will not come down behind it and the next system will be a rain system rather then snow...

Very poor run for snow indeed, MUST keep that low a seperate system, if not then its curtains!

I'm afraid the above post is once again very misleading and is obviously a IMBY post. For Wales its the best run in terms of snow potential I think i've seen this year. With temps on the GFS predicted to be no higher than 2c from Monday to Wednesday there would be plenty of snow around, especially Tuesday. Yes, the temps rocket to 7c in the southeaster third, but we don't all live there.

[kold weather]

06z is quite horrid for the double low pressure set-up with very little snow hope south of the North of England until Wednesday eveing, hopefully if that evolution comes off the whole lot gets shunted away from the UK totally because it would just be cold and damp once the intial snow has gone...

So whilst the low may have adjusted southwards, because of the evolutionary changes of the low, ironically those further north have more chance of snow then the Midlands now...indeed Wednesday looks rather snowy for the north on the 06z run!

KTtom, yes your right its good enough for Wales as well...however Wales always was going to be a hotspot because of the exact track, and you clearly couldn't have seen the 18z last night mate, it was an insane run, parts of Wales would have got 30-40cms easily from that run...

Saying all that, looking again, Tuesday would be mainly rain for all of Wales as well...away from the far north-west of the region.

BUT that was a general comment, and don't you even dare accuse me of being IMBY, I don't think you'll find many more people on this forum who spends times in the regional forums discussing things that will effect them then myself...

Edited February 20, 2010 by kold weather

[TEITS]

On a different note the jetstream pic Mr D posted I noticed the below average SSTS running from the gulf of mexico across the Atlantic into the Med/UK.

http://weather.unisys.com/surface/sst_anom.gif

I wonder what effect these below average SSTS will have on the tornado season this year?

Latest NAE for tomorrow.

http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/02/20/basis06/ukuk/prty/10022112_2006.gif

[Iceberg]

Interestingly, the low moving up from the SW late Tues/early Weds seems to have its energy taken away by a secondary shortwave on its southern flank swinging east into western France, so not looking like the deeper feature shown by 00z ECM, it does spread rain further north than Monday's low which would see snow across northern England this time.

Key post IMO, it wouldn' take much to see that extra energy from the secondary SW, develop into a new low IMO. The centre of the main low isn't well defined anyway, you would then probably see what was the main low swing down back south again, keep the whole lot much further south. IT will be interesting to watch out on the 12Z

[KTtom]

KW- I wasn't accusing you, I was suggesting the post was! as, unless I'm reading the 06z extremely wrong there are 3 possible fairly large snow events this week. Not all in the same area, but in general IMHO I think next week could well see more cummulative snow than in any week so far this year.

[MKN]

On a different note the jetstream pic Mr D posted I noticed the below average SSTS running from the gulf of mexico across the Atlantic into the Med/UK.

http://weather.unisys.com/surface/sst_anom.gif

I wonder what effect these below average SSTS will have on the tornado season this year?

Latest NAE for tomorrow.

http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/02/20/basis06/ukuk/prty/10022112_2006.gif

The NAE looks good for our area on monday, shame the gfs isnt consistant with the 18z outputs at the minute. The ensembles should be interesting

[kev238]

For the Midlands area,I would think chances are a little lower this morning than they were yesterday morning of a major snowfall event in the next 5 days.

However, I think at some point there will be a battle which will lead to a heavy snowfall event and that this will then herald the beginning of spring and the end of Winter!

The models are lurching around a lot with shapes of low pressures making a great deal of difference-- it will be interesting to see if the Met Office update their warning for Monday and if they change the areas marked in yellow.

[stratty]

On a different note the jetstream pic Mr D posted I noticed the below average SSTS running from the gulf of mexico across the Atlantic into the Med/UK.

http://weather.unisys.com/surface/sst_anom.gif

I wonder what effect these below average SSTS will have on the tornado season this year?

Latest NAE for tomorrow.

http://expert.weatheronline.co.uk/daten/proficharts/en/nae/2010/02/20/basis06/ukuk/prty/10022112_2006.gif

On that anomaly chart - why on earth do they have the same colours on that key representing totally fifferent things? eg pink= -3 & +9 Anyone???

Great winter chart viewing continues this week!

ps not much talk about the covering of snow likely overnight for most places?!

Edited February 20, 2010 by stratty

[kold weather]

KW- I wasn't accusing you, I was suggesting the post was! as, unless I'm reading the 06z extremely wrong there are 3 possible fairly large snow events this week. Not all in the same area, but in general IMHO I think next week could well see more cummulative snow than in any week so far this year.

The key is exactly how this evolves, the 06z strongly favours the north on this run, which would probably get 2-3 decent snow events, as would Ireland and at times N.Wales, further south then that and this run has mainly either front edge snow or back edge snow....

This run is in many ways the North's version of the 18z last night for the Midlands, very snowy from a line from say Hull WSW through N.Wales and into Ireland, south of that and as I said its not really a great run at all. Still would see some exceptional falls though from the 06z thats for sure, but I think it'd be better for it to start a little further south, give others further south a shot before any fun transfers northwards.

Somewhere is going to get nailed though I'm pretty confident about that...

Edited February 20, 2010 by kold weather

[TEITS]

I'm afraid the above post is once again very misleading and is obviously a IMBY post. For Wales its the best run in terms of snow potential I think i've seen this year. With temps on the GFS predicted to be no higher than 2c from Monday to Wednesday there would be plenty of snow around, especially Tuesday. Yes, the temps rocket to 7c in the southeaster third, but we don't all live there.

KW is spot on with his comments.

The LP during Monday needs to become seperate so it pulls down colder air from the N prior to the next LP coming up from the SW. The run might be okay for your location but trust me it could be a whole lot better. Worth mentioning that when members comment on the models we don't have time to focus on each region so KW was correctly taking the whole of the UK into account.

During next week a domino effect could take place. What I mean by this is if your location is on the NW flank of the LP then chances are the next LP will also bring you more snowfall. This is due to the LP bringing colder air S but also your existing snow cover will also have an effect on the temps. This occured during Feb 09 in my region.

On that anomaly chart - why on earth do they have the same colours on that key representing totally fifferent things? eg pink= -3 & +9 Anyone???

Great winter chart viewing continues this week!

ps not much talk about the covering of snow likely overnight for most places?!

Based on the NAE I would say Wales/W Midlands are favoured for around 5-7cm of snow. Im excluding regions further E mainly due to the timing of this arriving.

[Nick F]

Key post IMO, it wouldn' take much to see that extra energy from the secondary SW, develop into a new low IMO. The centre of the main low isn't well defined anyway, you would then probably see what was the main low swing down back south again, keep the whole lot much further south. IT will be interesting to watch out on the 12Z

Yes, expect more changes with Wednesday's low evolution, could end up further south like you say.

Hot on the heels of Wednesday's low, yet another low comes up from the SW late Thurs, spreading rain into Wales and the SW ... edging the snowline that bit further north this time. Looking like curtains drawn on snow for those south of the Midlands/Wales beyond the weekend.

On the subject of SSTs in the GoM and the effect on the tornado season. I think cold weather being unusually far south over the mid-west this winter, with a foot of snow in Dallas recently, has certainly manifested itself in colder SSTs over the GoM, but I believe the waters off the southern States are fairly shallow, like the N Sea, so should respond quicker to a warm-up as the jet pattern shifts north again. Though I do think there could be a delay to the northward shift of the severe storm season there this spring. Btw, we are having a storm-chasers' gathering next weekend in Manchester, so not too much snow up there please!!

[kold weather]

Eye, I agree synoptically it makes perfect sense for that to happen given the flow is so active at the moment.

Last nights 18z had the gravy chain for the Midlands, this run has shifted the main risk zone further north at the expense of Monday's event evn though the low is ironcally further south, once more proof that we need the low to stay seperate, even if its only slightly...

Still the 06z is a VERY snowy run for places like Manchester, esp from Tuesday afternoon onwards and I'm still confident somewhere will get utterly nailed in this set-up, I just hope as much of the country can get in on the act.

[TEITS]

Eye, I agree synoptically it makes perfect sense for that to happen given the flow is so active at the moment.

Last nights 18z had the gravy chain for the Midlands, this run has shifted the main risk zone further north at the expense of Monday's event evn though the low is ironcally further south, once more proof that we need the low to stay seperate, even if its only slightly...

Still the 06z is a VERY snowy run for places like Manchester, esp from Tuesday afternoon onwards and I'm still confident somewhere will get utterly nailed in this set-up, I just hope as much of the country can get in on the act.

Yep someone is going to get a right hammering next week, if I only knew where!

Based on the mean of all model runs these past 48hrs im going to continue suggesting N Wales, N midlands, S parts of N England. However this means very little because the reality could be quiet different.

Thanks for the reply Nick F. My knowledge of how SSTS affect our weather patterns is incredibly poor so I appreciate your reply.

[kold weather]

The problem for the Midlands now is its a catch 22 situation, if we want to get the cold dragged down we need a stronger low, but a stronger low is more likely to head northwards further west, which will result in much the same outcome as the orginal solution from the 06z. Therefore they need almost the perfect balance, we got that in the 18z run yesterday, today we've edged too much the other nway and it now favours the north IMO, as I said though if you draw a line from the Humber WSW across the more northerly parts of Wales and out towards Ireland, that will be a good line for where snow will stay snow, further south in the Midlands and a good chunk of Wales, looks like one of those set-ups that may flip several times.

[kev238]

To back up what you say the Met Office have issued a early warning for Wednesday in the exact locations you name Kold Weather!

I think the GFS 6z yesterday was the least favourable run so will be interesting to see what happens later!

Edited February 20, 2010 by kev238