Spring Model Discussion 21st March 2013 006z onwards...

[Coast]

New thread to discuss some potentially exciting weather prospects for the end of March.

The team would just like to stress that off topic posts, contributions with little or no analysis of the current models, questions about 'how much', 'where' and 'when will I get' snow or just moaning and whining may be moved, but if it gets too busy, will just be deleted. Can we also respect all other members views (even if you don't agree with them) just as you would ask the same respect and courtesy in return.

As you will be aware, many people reading this thread are looking for unbiased guidance on what the latest model output might give and not everyone has the depth of knowledge or understanding to differentiate between what the weather might actually turn out to be and what you want the weather to be....

If you do want to moan, whinge or ramp:

http://forum.netweat...n-ramp-go-nuts/

If you want to get an idea of where it may snow:

http://www.netweathe...l-it-snow;sess=

Enjoy this run-down to the next batch of crazy weather and let the roller-coaster continue!

Edited March 21, 2013 by Coast

[R.P. McMurphy]

Hi Steve, yes, the new run (Exeter happier now with NAE after corrections last night to match upstream imagery) takes some snow down to SE quite extensively by 06z Sat. The core totals (Amber upgrades expected this morn) remain in areas earlier discussed, with worrying 75cm snow accumulations in N Wales for example; Amber also ready to roll for Devon/Cornwall where locally 100-125mm rain raises flood concern significantly after discussions with FWC... chief stresses volatility with great scope for model errors in areal and accumulation sense, but even allowing for this, the signal for newsworthy severe weather - both white and wet - is well-set and the next 24-48hrs are going to be hellish for forecasters pretty much anywhere. Not good.

John McEnroe just said.... "You Cannot Be Serious"

Surely 75CM = Serious RED Alert from the Metoffice Warnings? NAEFS Progs a serious white picture for Northern England. 10-20CM Quite widely, at lower levels.

[Snowy Liverpool1]

John McEnroe just said.... "You Cannot Be Serious"

Surely 75CM = Serious RED Alert from the Metoffice Warnings? NAEFS Progs a serious white picture for Northern England. 10-20CM Quite widely, at lower levels.

Think about if this was an all rain event, hills in N. Wales would easily see 75mm from that. So 75mm wouldn't be out of the question for places like Snowdon surely.

[fergieweather]

John McEnroe just said.... "You Cannot Be Serious"

Surely 75CM = Serious RED Alert from the Metoffice Warnings? NAEFS Progs a serious white picture for Northern England. 10-20CM Quite widely, at lower levels.

Stress: these sorts of upland totals are progged in the output BUT as chief says: expect model issues currently with amounts and areal distribution. However the 75-100mm rainfall totals for parts of Cornwall/Devon have stronger support and have been a key component of PWS/FWC discussion this morning ahead of amber warnings being drafted. Expect issue of these soon.

[Severe Siberian icy blast]

The lates NAE brings rain tomorrow to southern midlands southwards , before readily turning to snow during Fridays evening night and Saturday day , so I feel Friday night is going to be the main concern for a much larger portion of England . Before that , we have tonight's snow which favours roughly Evashum (30 miles south of brum) , northwards , with alarming rates for Northern Ireland , north Wales , and north midlands , but Friday night Im sure other areas much further south will get a good 5-10cm , more on hills , with areas such as the Malvern hills , and the cotwolds seeing snow tomorrow day , but not as much as the north , followed by possibly 15cm Friday night . The lickey hills , the wasely hills into Stourbridge , upto Wolverhampton and Dudley (where ground is 600ft plus ) seeing up to 30cm . That's my take on things , I can't comment too much on areas I don't know , sorry.

[R.P. McMurphy]

Stress: these sorts of upland totals are progged in the output BUT as chief says: expect model issues currently with amounts and areal distribution. However the 75-100mm rainfall totals for parts of Cornwall/Devon have stronger support and have been a key component of PWS/FWC discussion this morning ahead of amber warnings being drafted. Expect issue of these soon.

Thanks Ian, we all appreciate your professional assessments on Net Weather & Twitter. I would expect potentially a Red Alert for the Cornwall/Devon area if 75-100mm is possible as this could cause serious flooding to an area that really does not need it again. What do Exeter think of the potential Shadow Pennine Effect showing on quite a few models ?

[Bobby]

Stress: these sorts of upland totals are progged in the output BUT as chief says: expect model issues currently with amounts and areal distribution. However the 75-100mm rainfall totals for parts of Cornwall/Devon have stronger support and have been a key component of PWS/FWC discussion this morning ahead of amber warnings being drafted. Expect issue of these soon.

Could there be similar rainfall totals in S. Wales? The ground is already fairly soggy here.

[Radiating Dendrite]

Wow.

Still wished I lived in North East Wales!

To be fair I witnessed 25cm of snow there in April 1998, so such totals are certainly possible.

My worry would be the marginality on very low ground, such as the Cheshire plain perhaps. If the precipitation is heavy though, evaporative cooling should help with this.

The real beauty with this event and what is unuasual for this late in the year is the fact that it is going to get COLDER after the snow. Usually at this time of year the snow would thaw straightway after it had fallen, but in this case it could be on the ground for a good few days, some very cold nights (-10c) could occur!

Very interesting.

[fergieweather]

Wow.

Still wished I lived in North East Wales!

My worry would be the marginality on very low ground, such as the Cheshire plain perhaps. If the precipitation is heavy though, evaporative cooling should help

Not in this set-up: low-level flow too strong and thus evaporative cooling influence very muted.

[SMU]

So then I feel full ramp mode could be apon us-

As Stratos Ferric used to say a veritable rampede....

In terms of IMBY its good to see a continual shift south- however that is of course at the expense of others - IE the NE & areas like this-

However they have done well lately.

IMBY aside we are 'possibly' on the cusp of something exceptional & historic-- one for the archives for sure.

We have cold air undercutting X2 fronts, the first staying as rain more in the south & SW but piling snow into the North/ North west & even South West midlands-

The NE part of the front will most likely make it towards yorkshire, however it will fragment & break up along the eastern end ( more likely east of the pennines.

All the while a secondary front will be chasing in from the SW & catching up the remenants of the first frontal zone.

The area where these 2 fronts allign together will possibly be the snowiest place & see snow on snow on snow for 36-48 hours.

This allignment is currently progged to be south wales & some of the SW shires out to Ireland up to North wales / the North west & out to NE Ireland - & of course stretching back into the Midlands-

Because I do a fair bit of Travelling up this way- Prone motorways look to be the M6, M5, M54, M42 - all the way up the A41 etc & possibly beyond- POSSIBLY up to Carlisle etc.Maybe just Maybe SW scotland-

To be under intense PPN for that amount time lets look at the numbers based on 42 hours of snow.

I would hazard a guess of rates INCREASING throughout the period.- starting out at a nominal 1:5 with the air being a little wet & marginal, increasing at the height to 1:10- especially over the hills-

So taking a net of that lot with a mean of 2MM an hour ( again this is for the BEST AREA ******)

you get 42X2 mm = 84 mm @ 75% ratio ( 1:7.5~)

= 63cm of snow.

Heres an image posted in the NE thread earlier- it feels spot on- especially for those areas close to wales ( Not forgetting Ireland !!!)

https://pbs.twimg.co...A1bMx.png:large

The GFS 00z was a tad more conservative @ 40cm.

So there we are, SNOW. Lots of it- as Francis Wilson said in 1991- Knee deep for a lot, maybe waste deep for the luckiest-

This isnt localised either, whilst the welsh hills etc will be the worst- surrounding areas maybe breech the 20cm Mark - with a more conservative line moving down towards london of 2-10cm.

If people ever wanted snow- its coming to you soon in an area that hasnt been that lucky this winter- so good stuff!!!!

S

Edited March 21, 2013 by Steve Murr

[Radiating Dendrite]

Not in this set-up: low-level flow too strong and thus evaporative cooling influence very muted.

Thanks for the reply Ian

Well you learn something all the time, so evaporative cooling is only really effective in relatively still air then. Makes sense, as I suppose the stronger the low level winds the more colder air could get mixed out.

Looking like my area could even get a bit of snow now also.........this winter really is going on and on. I think we really were a few hundred miles away from a classic winter/early spring period given the set ups we had in Jan and Feb.

[Cheshire Freeze]

Steve that big hole around Manchester/Cheshire amuses me greatly. Typical!

[SMU]

Steve that big hole around Manchester/Cheshire amuses me greatly. Typical!

could be a rain shadow ( or snow shadow)

S

[R.P. McMurphy]

could be a rain shadow ( or snow shadow)

S

Yes, its the Pennine Shadow Effect. Generally shows on these charts but we will see.

[A.J]

So then I feel full ramp mode could be apon us-

As Stratos Ferric used to say a veritable rampede....

In terms of IMBY its good to see a continual shift south- however that is of course at the expense of others - IE the NE & areas like this-

However they have done well lately.

IMBY aside we are 'possibly' on the cusp of something exceptional & historic-- one for the archives for sure.

We have cold air undercutting X2 fronts, the first staying as rain more in the south & SW but piling snow into the North/ North west & even South West midlands-

The NE part of the front will most likely make it towards yorkshire, however it will fragment & break up along the eastern end ( more likely east of the pennines.

All the while a secondary front will be chasing in from the SW & catching up the remenants of the first frontal zone.

The area where these 2 fronts allign together will possibly be the snowiest place & see snow on snow on snow for 36-48 hours.

This allignment is currently progged to be south wales & some of the SW shires out to Ireland up to North wales / the North west & out to NE Ireland - & of course stretching back into the Midlands-

Because I do a fair bit of Travelling up this way- Prone motorways look to be the M6, M5, M54, M42 - all the way up the A41 etc & possibly beyond- POSSIBLY up to Carlisle etc.Maybe just Maybe SW scotland-

To be under intense PPN for that amount time lets look at the numbers based on 42 hours of snow.

I would hazard a guess of rates INCREASING throughout the period.- starting out at a nominal 1:5 with the air being a little wet & marginal, increasing at the height to 1:10- especially over the hills-

So taking a net of that lot with a mean of 2MM an hour ( again this is for the BEST AREA ******)

you get 42X2 mm = 84 mm @ 75% ratio ( 1:7.5~)

= 63cm of snow.

Heres an image posted in the NE thread earlier- it feels spot on- especially for those areas close to wales ( Not forgetting Ireland !!!)

https://pbs.twimg.co...A1bMx.png:large

The GFS 00z was a tad more conservative @ 40cm.

So there we are, SNOW. Lots of it- as Francis Wilson said in 1991- Knee deep for a lot, maybe waste deep for the luckiest-

This isnt localised either, whilst the welsh hills etc will be the worst- surrounding areas maybe breech the 20cm Mark - with a more conservative line moving down towards london of 2-10cm.

If people ever wanted snow- its coming to you soon in an area that hasnt been that lucky this winter- so good stuff!!!!

S

If carlsberg did ramps.................

fingers crossed you're bang on the mark, otherwise you'll be a hunted man on here!.....lol.......but it looks like a pretty accurate analysis of what's likely to happen

[Cheshire Freeze]

could be a rain shadow ( or snow shadow)

S

Yep, annoying. Though might be overplayed as it's usually Greater Manchester that suffers this fate with the predicted wind direction, N Ches also. Mid and S Ches usually fares a little better.

[Mair Snaw]

So then I feel full ramp mode could be apon us-

As Stratos Ferric used to say a veritable rampede....

In terms of IMBY its good to see a continual shift south- however that is of course at the expense of others - IE the NE & areas like this-

However they have done well lately.

IMBY aside we are 'possibly' on the cusp of something exceptional & historic-- one for the archives for sure.

We have cold air undercutting X2 fronts, the first staying as rain more in the south & SW but piling snow into the North/ North west & even South West midlands-

The NE part of the front will most likely make it towards yorkshire, however it will fragment & break up along the eastern end ( more likely east of the pennines.

All the while a secondary front will be chasing in from the SW & catching up the remenants of the first frontal zone.

The area where these 2 fronts allign together will possibly be the snowiest place & see snow on snow on snow for 36-48 hours.

This allignment is currently progged to be south wales & some of the SW shires out to Ireland up to North wales / the North west & out to NE Ireland - & of course stretching back into the Midlands-

Because I do a fair bit of Travelling up this way- Prone motorways look to be the M6, M5, M54, M42 - all the way up the A41 etc & possibly beyond- POSSIBLY up to Carlisle etc.Maybe just Maybe SW scotland-

To be under intense PPN for that amount time lets look at the numbers based on 42 hours of snow.

I would hazard a guess of rates INCREASING throughout the period.- starting out at a nominal 1:5 with the air being a little wet & marginal, increasing at the height to 1:10- especially over the hills-

So taking a net of that lot with a mean of 2MM an hour ( again this is for the BEST AREA ******)

you get 42X2 mm = 84 mm @ 75% ratio ( 1:7.5~)

= 63cm of snow.

Heres an image posted in the NE thread earlier- it feels spot on- especially for those areas close to wales ( Not forgetting Ireland !!!)

https://pbs.twimg.co...A1bMx.png:large

The GFS 00z was a tad more conservative @ 40cm.

So there we are, SNOW. Lots of it- as Francis Wilson said in 1991- Knee deep for a lot, maybe waste deep for the luckiest-

This isnt localised either, whilst the welsh hills etc will be the worst- surrounding areas maybe breech the 20cm Mark - with a more conservative line moving down towards london of 2-10cm.

If people ever wanted snow- its coming to you soon in an area that hasnt been that lucky this winter- so good stuff!!!!

S

Cheers Steve for this very informative post and this is just the kind of post that this thread is all about.... it is certainly a very serious event especial for those of us that live as high up as i do it could be very serious indeed... im off to the supermarket to stock up as who knows the next time i will be able to go out after today?? Good luck to each and every member on here thats after snow that gets it.....

[fergieweather]

Steve that big hole around Manchester/Cheshire amuses me greatly. Typical!

The same void is also progged in EURO4 & UKPP in same area.... exact replica. Clear topographic effect there.

[Jason M]

could be a rain shadow ( or snow shadow)

S

Being from Crewe myself originally, I'd wager it will be a rain shadow :-)

Jason

[A.J]

Steve that big hole around Manchester/Cheshire amuses me greatly. Typical!

You see, even snow knows that it's best to avoid Crewe.....lol

hope springs eternal for parts of the SW/Central southern England from an IMBY perspective, as Steve M alluded to, GFS & NAE models suggest snowline moving south into our region friday night..Could be an interesting NMM 06z update coming shortly!

[SMU]

http://www2.wetter3.de/Animation_06_UTC/78_35.gif

Updated GFS 06z now up to 41cm - thats 4cm up on the 00z....

S

[Jason M]

I must admit that I just cant see massive accum snow away from high ground. I may be proved wrong (hopefully will be), but whilst heavy falling snow looks very likely in many areas this doesnt always equal deep laying snow. With ground temps above zero in many areas and the lateness of this snow, I cant help feeling that many areas will just get a couple of CM's of slush.

I can see 24 hours of snow here, but only very modest accum on the ground. Gut feel is that rainfall in the SW will be the main story.

We will soon find out though :-)

Jason

[Mark Neal.]

hope springs eternal for parts of the SW/Central southern England from an IMBY perspective, as Steve M alluded to, GFS & NAE models suggest snowline moving south into our region friday night..Could be an interesting NMM 06z update coming shortly!

Oh I do hope so AJ. Each model run keeps showing a southward correction on the 2nd front snowline, through Fri night the snow-line heads down into Warwickshire,Beds,Worcestershire. Then later in the night- for first thing Sat Am- Down through Cotswolds- Oxon-Bucks-Chilterns into Home Counties. Wonder if it will settle? Well it did last Sunday morning after Heavy Rain, so we could get lucky!

Midlands,NW England- Enjoy! As you look to be Ye sweet spots through tonight into tomorrow :-)

[Beast of Plympton]

I must admit that I just cant see massive accum snow away from high ground. I may be proved wrong (hopefully will be), but whilst heavy falling snow looks very likely in many areas this doesnt always equal deep laying snow. With ground temps above zero in many areas and the lateness of this snow, I cant help feeling that many areas will just get a couple of CM's of slush.

I can see 24 hours of snow here, but only very modest accum on the ground. Gut feel is that rainfall in the SW will be the main story.

We will soon find out though :-)

Jason

I fear you may be right. GFS has 74mm of rain IMBY for the rest of today and tomorrow. Had some snow this morning but that backed off as the upper air temps have retreated northwards. Luckily I live on a very big hill so flooding isn't really an issue up here, however I do really feel for the people lower down today and tomorrow.

Edited March 21, 2013 by Beast of Dartmoor

[johnholmes]

Now we have the fine scale models available be it NMM from Net Wx or NAE UK Met it might be a good idea for someone, not me, to look at the parameters for snow, aka the Net Wx Guide for your locality and see just what your chances are assuming of course the model shows precipitation over you?

It does work quite well for lowland areas, remember to factor in your height, if you have height it will give you a better result if it is snow you want and also how close to any windward coast you are, in that case look VERY closely at parameters like Td and 850mb temperatuures and scan the skew-t for your area for temperatures from 850mb down to the surface.

Good luck everyone if you are wanting snow.

spare a thought for anyone in the SW on low ground though, and do remember IF the models are correct for the large snowfall totals being predicted for higher ground that it will have implications for anyone near the major rivers that flow away from those areas when the thaw arrives. It is not just the immediate effect for low areas in the SW but a much wider threat once the cold eases.

Edited March 21, 2013 by johnholmes