Significant Snow Risk This Weekend - General Discussion

[MKN]

Amber Alert of Snow04 Feb 2012, 12:00

Amber Alert of Snow

Valid From: 04 Feb 2012, 12:00

Valid To: 04 Feb 2012, 23:59

Issued at - 03 Feb 2012, 12:07

Valid from - 04 Feb 2012, 12:00

Valid to - 04 Feb 2012, 23:59

A band of wet weather over Northern Ireland and western Scotland early Saturday will move slowly east and southeastwards across the United Kingdom during the day. As it does so it will readily turn to sleet and snow away from western and southwestern coastal areas giving accumulations of 2-5cm in places and 5-10cm widely in the amber warning area. The snow is expected to turn to rain over some northwestern areas later. As skies then clear in this area after dark, icy patches will develop. The public are advised that this is likely to lead to some travel disruption, and it is recommended to keep up to date with forecasts as the event approaches.

Should cheer many of you up

Edited February 3, 2012 by SnowTornado

[Heisenberg]

It was originally posted in the London and SE thread so that's all I looked at!!! It's not to the exclusion of any other possibilities, just for a specific regional set. I suspect it will get up as far as Lincolnshire, but our 'local reporter' TEITS is the man to ask about his thoughts for that part of the World.

Weather and particularly snow isn't IMBYish, it falls where it likes and it's just lucky or not for whoever happens to be under it!!! :lol:

Fairy nuff mate. Lets hope we all get a good pasting this weekend. Weve all been so patient this "winter". We deserve it

[ITSY]

excellent Meto update there - my two towns, Leeds and Cambridge, both expected to get at least 5-10cms so if that happened i'd be happy!

[The Enforcer]

To give an example of how difficult this level of detail is to pin down at close range, I will cite my recollections of the last significant snowfall here, Saturday 18th December 2010. At around T+24, the BBC graphics forecasts were revised to show the northern limit of the snowfall along the M4 corridor, having previously been extended to cover most of the midlands. By T+15 this was still being shown on the graphics, but Rob McElwee was making references to "perhaps M40 corridor", which by T+12 had become "probably M40 corridor" and eventually the graphics were revised by T+9. [Note T+0 is when it started snowing here, approximately 9am]. The variables in that situation concerned only frontal position. In the current situation we're also looking at upper temps, surface temps and dewpoints. On this basis I think snowfall patterns will continue to move about until at least T+6 or closer.

EDIT - The situation is further complicated, by the fact we are not just looking at mild pushing against cold. There is a cold front catching up with the warm front and eventually resulting in an occlusion. Naturally, when and where this happens would limit the scope of the warm sector (bearing in mind 850s not getting above 0C in the SE quarter of the UK) to override the variables required to keep snow falling at surface levels. Too much uncertainty at this range.

Edited February 3, 2012 by The Enforcer

[dubmuffin]

Amber alert right over the top of me! Beautiful

[Snowstorm1]

Damn! Im just outside the amber alert hope that changes....

[NickyB]

Snow-Forecast keeping things for the majority of the UK, the new 4-6 day charts has 10-25cm of snowfall across northern parts of Wales most likely in association with the cold front behind this, much talked about, warm front.

I guess I should throw a link in there aswell for that http://www.snow-forecast.com/maps/dynamic/uk

That look very promising over the next week - any chance of re-posting this in the North West thread to cheer us all up ? :-)

[dave79]

Damn! Im just outside the amber alert hope that changes....

If you go into the breakdown of the towns and citys Snowstorm, it now has the teesside area to have snow saturday and sunday, only yesterday it was saying rain and sleet, so its changing all the time, dont think we will know for sure till its more or less on top of us!!!

[Don]

To give an example of how difficult this level of detail is to pin down at close range, I will cite my recollections of the last significant snowfall here, Saturday 18th December 2010. At around T+24, the BBC graphics forecasts were revised to show the northern limit of the snowfall along the M4 corridor, having previously been extended to cover most of the midlands. By T+15 this was still being shown on the graphics, but Rob McElwee was making references to "perhaps M40 corridor", which by T+12 had become "probably M40 corridor" and eventually the graphics were revised by T+9. [Note T+0 is when it started snowing here, approximately 9am]. The variables in that situation concerned only frontal position. In the current situation we're also looking at upper temps, surface temps and dewpoints. On this basis I think snowfall patterns will continue to move about until at least T+6 or closer.

EDIT - The situation is further complicated, by the fact we are not just looking at mild pushing against cold. There is a cold front catching up with the warm front and eventually resulting in an occlusion. Naturally, when and where this happens would limit the scope of the warm sector (bearing in mind 850s not getting above 0C in the SE quarter of the UK) to override the variables required to keep snow falling at surface levels. Too much uncertainty at this range.

Obviously subject to change but looking at those warnings for Saturday and Sunday it does suggest a snow to rain event for most eventually. However for a mild Winter overall this spell hasn't been bad.

Edited February 3, 2012 by Don

[Zakos]

To give an example of how difficult this level of detail is to pin down at close range, I will cite my recollections of the last significant snowfall here, Saturday 18th December 2010. At around T+24, the BBC graphics forecasts were revised to show the northern limit of the snowfall along the M4 corridor, having previously been extended to cover most of the midlands. By T+15 this was still being shown on the graphics, but Rob McElwee was making references to "perhaps M40 corridor", which by T+12 had become "probably M40 corridor" and eventually the graphics were revised by T+9. [Note T+0 is when it started snowing here, approximately 9am]. The variables in that situation concerned only frontal position. In the current situation we're also looking at upper temps, surface temps and dewpoints. On this basis I think snowfall patterns will continue to move about until at least T+6 or closer.

EDIT - The situation is further complicated, by the fact we are not just looking at mild pushing against cold. There is a cold front catching up with the warm front and eventually resulting in an occlusion. Naturally, when and where this happens would limit the scope of the warm sector (bearing in mind 850s not getting above 0C in the SE quarter of the UK) to override the variables required to keep snow falling at surface levels. Too much uncertainty at this range.

Ah yes, I remember that event all to well. My area was just north of the snow band.

However, this was not a frontal snowfall, this I believe was a shortwave bringing an unstable flow which brought in snow. This was poorly modelled before the event.

However frontal ppn tracks are easier to predict, and this one has been modelled well. The uncertainty arises as to where will see heavy snow, and where will see a snow- rain event. This, as you quite rightly point is subject to change.

The track of the ppn itself not going to change significantly at this range. The area of snow may well change. for example, If your location is just west of the met office amber warning, you may be well end up seeing mostly snow. Those just east of the western border of the warning area may end up seeing mostly rain.

My location is close to the centre of the warning area and hence I deem it highly unlikey that I and areas east of me wont see a dumping of snow.

Edited February 3, 2012 by Zakos

[Snowy Easterly]

Ah yes, I remember that event all to well. My area was just north of the snow band.

However, this was not a frontal snowfall, this I believe was a shortwave bringing an unstable flow which brought in snow. This was poorly modelled before the event.

However frontal ppn tracks are easier to predict, and this one has been modelled well. The uncertainty arises as to where will see heavy snow, and where will see a snow- rain event. This, as you quite rightly point is subject to change.

The track of the ppn itself not going to change significantly at this range. The area of snow may well change. for example, If your location is just west of the met office amber warning, you may be well end up seeing mostly snow. Those just east of the western border of the warning area may end up seeing mostly rain.

My location is close to the centre of the warning area and hence I deem it highly unlikey that I and areas east of me wont see a dumping of snow.

i got very lucky with the snow on the 18th dec 2010 the snow line stopped about 5 miles to the north of me, wonder if i will get lucky again

new bbc graphics are out and it shows snow at 6pm for a lot of the midlands then maybe it turns back to rain later

Edited February 3, 2012 by Snowy Easterly

[Liam J]

High res HIRLAM modelling a stronger fast moving front mixing out the coldest 850 temps as it moves through clearing the SE of the UK before fizzling out over France. Temps of +4 to 6c by Sunday.

12z runs should start to firm up on the specific detail later.

http://www.meteociel...&mode=6&carte=0

Edited February 3, 2012 by Liam J

[patrickshere]

High res HIRLAM modelling a stronger fast moving front mixing out the coldest 850 temps as it moves through clearing the SE of the UK before fizzling out over France. Temps of +4 to 6c by Sunday.

12z runs should start to firm up on the specific detail later.

http://www.meteociel...&mode=6&carte=0

If that happens, it would pretty much sum up this winter.

[Liam J]

If that happens, it would pretty much sum up this winter.

I know tell me about it dreadful so far but things are looking promising for further cold and snowy periods during February. Anyway tomorrows events aren't yet set in stone plenty of time for minor adjustments which could make a big impact over out small island. You're in a good location for this event even if it does turn to rain eventually, you should still witness a nice snowfall.

[Nick F]

High res HIRLAM modelling a stronger fast moving front mixing out the coldest 850 temps as it moves through clearing the SE of the UK before fizzling out over France. Temps of +4 to 6c by Sunday.

12z runs should start to firm up on the specific detail later.

http://www.meteociel...&mode=6&carte=0

I don't there will be too much mixing out at the surface for eastern and southeastern areas - with winds very light or calm when the band of snow arrives across theeast. Though as you say, temperatures aloft wwill probably mix out more as the flow will a little stronger aloft. The front slows late Saturday and overnight into Sunday morning as arrives across the east, so a window for persistent and heavy snow, occluding out as it does so, before snow fizzles out by Sunday afternoon.

[Kentish Kiwi]

In the model discussion thread, GP mentioned the potential for a 'big easterly to end the month'. Are there any examples people can think of where easterlies at the end of February/start of March have delivered significant snowfall to the UK? I'd be worried convection from the North Sea would be limited due to colder SST's and potentially less cold upper air temperatures...

Edit: Intended for this to be posted in the regional South-Eastern thread but it would still be interesting to here about UK wide examples of late winter easterlies. If it is considered off-topic, apologies Mods and feel free to delete...

Edited February 3, 2012 by Kentish Kiwi

[Liam J]

I don't there will be too much mixing out at the surface for eastern and southeastern areas - with winds very light or calm when the band of snow arrives across theeast. Though as you say, temperatures aloft wwill probably mix out more as the flow will a little stronger aloft. The front slows late Saturday and overnight into Sunday morning as arrives across the east, so a window for persistent and heavy snow, occluding out as it does so, before snow fizzles out by Sunday afternoon.

If the upper air profiles manage stay on the right side of 0c then it should stay as snow given the conducive surface conditions at the time of arrival. Perhaps a slow thaw setting in by Sunday but this also depends on which model you are viewing, things don't want to be going to far east as more people will be at risk of seeing a snow to rain event.

Edited February 3, 2012 by Liam J

[kold weather]

Yeah nick, thats actually not a bad run. It does suggest a milder set-up afterwards on Sunday but I'd be amazed if there was much mixing of the airmasses at all, the models tend to do a shocking job when it comes to these sorts of set-ups, nearly always over-egging any mixing out that does occur. Thats resulted before in snow-rain events actually turning out to be pure snow events.

Met Office warning looks decent, though wouldn't shock me if its underdone a little in parts, especially as the 06z suite seemed to strengthen the front.

Obviously places further west were always going to need big shifts westwards, but thus far not seen that happen, and frankly despite what people have aid I think there will be little shifting now, maybe a tiny bit east or west depending on the exact strength of that small low.

With that small low in place now on the models, not much chance of any major shift west.

[leicsnow]

In the model discussiopn thread, GP mentioned the potential for a 'big easterly to end the month'. Are there any examples people can think of where easterlies at the end of February/start of March have delivered significant snowfall to the UK? I'd be worried convection from the North Sea would be limited due to colder SST's and potentially less cold upper air temperatures...

Well there was February/March 2004 and 2005, and also March 2006 which was a very good March for cold and snowy weather.

[Heisenberg]

Well there was February/March 2004 and 2005, and also March 2006 which was a very good March for cold and snowy weather.

Oh no snow in March. Im going to Centre Parcs.....need sun and warmth like last year....

[Buzzard]

i got very lucky with the snow on the 18th dec 2010 the snow line stopped about 5 miles to the north of me, wonder if i will get lucky again

new bbc graphics are out and it shows snow at 6pm for a lot of the midlands then maybe it turns back to rain later

Remember that day in 2010 - crazy 2 hours of snow saturday afternoon and an interesting drive from ours to Kempston on the Sunday morning!!!

Famous last words...'Oh they will have cleared the new A421 by now' LOL....

[Kentish Kiwi]

Well there was February/March 2004 and 2005, and also March 2006 which was a very good March for cold and snowy weather.

Thanks for the reply. I'm unsure of February/March 2004 and 2005 but I was under the impression March 2006 was cold due to northerlies? I'm looking for specific examples of easterlies...

[Nick F]

If the upper air profiles manage stay on the right side of 0c then it should stay as snow given the conducive surface conditions at the time of arrival. Perhaps a slow thaw setting in by Sunday but this also depends on which model you are viewing, things don't want to going to far east as more people will be seeing a rain to snow event.

I think the snow will have fizzled out by the time less cold air moves in aloft, even if 850s creep above 0C, temps at the surface maybe close to 0C, keeping any snow cover. GFS keeps the 850mb temps below 0C until mid-week at least and we may see a revison in the models later to back the colder air further west again. But anyway, surface high pressure looks to build across the UK by mid-week, so will trap cold air at the surface away from the NW, so perhaps some retention of lying snow.

[woldsowl]

Thanks for the reply. I'm unsure of February/March 2004 and 2005 but I was under the impression March 2006 was cold due to northerlies? I'm looking for specific examples of easterlies...

Try 1979 if memory serves.

[arni]

Hi,

Any chance for the snow settling in London tmr night?