Spring Model Discussion 18Z 6/3/13 onwards....

[Evening thunder]

That's fair enough Ed but I think many on here have witnessed many short term change arounds by the forecasters [particularly upgrades to snow, cold longevity etc] which I find rather odd sometimes as so many people see it happening well beofre the change forecasts are made. Responsibilty also lies in informing people of potential issues. Sometimes the veil of 'responsibilty' is used to cover poor forecasting IMO. Reason I say this is that I have followed different forecasters on the regional news bulletins and some say and speak of the potential way ahead of others. I find the inconsistency very odd at times.

BFTP

Not really, just occasionally the hype/predictions that are usually changing daily in here happen to be correct.

and we can speculate at the various possibilities, one of which is likely to be correct. They can't so much at least to the public, but I'm sure they do behind the scenes.

Edited March 8, 2013 by Stormmad26

[TEITS]

Based on latest NAE and amalgamation with 00z GM, we see dynamic snow accumulations of 5-10cm through Midlands later Sunday. Exeter have re-modelled this, factoring-in diurnal influence and depth temperature. Settling will be intensity-dependent and current prognosis is catering for 5-10cm above 300m; 1-3cm lower levels. It's outside warning criteria (impact-based) for now. However, accumulations in far S / SW overnight into early Monday look a tad more concerning and are being closely watched in output.

Sounds a very reasonable assessment.

Must admit im having difficulty working out potential snow accumulations simply due to the time of year, if this was Dec then the task would be easier. I really cannot think back to many past cold spells in March that have had such significantly cold temps involved.

Speaking of temps something else that interests me is the SSTS especially around E Anglia. These are already below average and considering the output in the short, medium, long range I shall be keen to see how far below normal they will be come April. I certainly won't fancy a swim in Cromer in May or June!

Back to the models and personally I feel parts of N England are more at risk of snow on Saturday than the Midlands. I feel the risk of snow further S will arrive on Sunday including the Midlands as the front travels S.

[Summer Sun]

Now this is scatter lol

Its safe to say the 00z ensemble has gone wrong some where

The full ECM ensemble continues to hint at something milder towards the end of its run

[BLAST FROM THE PAST]

probably because they are, like Ian F, NOT employed by the Met Office but the BBC. That applies to a number of Met trained forecasters, Paul Hudson Look North is just one example.

Cheers John it explains the inconsistency I have noticed, like I say some are worth following as are very good and give a good insight, I don't find my region in that category.

Now freeze frame of the day for me that caught my eye, this could get interesting if it develops and slides down west side of UK

BFTP

Edited March 8, 2013 by BLAST FROM THE PAST

[TEITS]

Now this is scatter lol

Its safe to say the 00z ensemble has gone wrong some where

The full ECM ensemble continues to hint at something milder towards the end of its run

Not surprising though because that is like saying it will turn cooler in summer after experiencing temps of 36C. The low temps being predicted for Sun/Mon just cannot be sustained due to the time of year.

Just add I know you're simply commenting on the ECM ensembles but I wanted to clear this up.

Rather concerned for those in the SW and extreme S because the potential is there for a notable snow event.

Edited March 8, 2013 by THE EYE IN THE SKY

[snowmadchrisuk]

Well current MetOffice thought's are that the low will be to far South and will be dry . Forecast for SW England say's rain dying out Sunday , with Cold, Dry and bright Monday and Tuesday, now all the Models even the UKMO say different , My guess is there placing there bet's on the usual Southward corrections. I have a feeling though this situation will be different with a Northward Correction , with even the Midlands possibly being effected by frontal Snow. I stand to be corrected but If you take Somerset on the Ensembles , it shows it has nearly full ensemble support for precipitation on Monday, Tuesday.

[ukpaul]

After so many M4 North events, could we actually be getting an M4 South event Monday into Tuesday?

The 18z GFS has been interesting recently, it has seemed to be the first to pick out shifts in the pattern, modified slightly later perhaps but putting things onto the final track.

[Weather-history]

The frost on Monday night/Tuesday morning could be very fierce, with very cold uppers, a slight breeze. A pipe freezer even as they use to say in the old days.

[Severe Siberian icy blast]

When looking down on the northern hemisphere we can really see the Atlantic along with the Artic well And truly into deep negative territory , something we haven't had this winter. A very notable wintry march set up by the looks of things , with the Atlantic blocked and a strong high toward Greenland , only leaves one door open . . . The artic express.

A very cold set up by the looks of things. If this were January we would be very happy , but I have the feeling that people underestimate how cold and snowy march can be given the right set up. We are not looking at a short snap , more of a prolonged cold spell .

Edited March 8, 2013 by Severe Siberian icy blast

[snowmadchrisuk]

Well the 6z has gone back to 5c maxes for the whole of next week, that to me would suggest some kind of Snow cover ..

[snowmadchrisuk]

At least the MetOffice now realize there is a risk for Monday , although there suggesting the Far South .

Turning colder over the weekend as cold air spreads south across the country during Saturday. Also during Saturday, a band a rain will move south across England and rain is expected to turn increasingly to sleet or snow down to low levels by the evening. Further snow showers are expected to follow into some eastern parts with a risk of a period of heavier snow affecting the far south on Sunday night. The cold weather will also be exacerbated across all areas for a time by brisk easterly winds bringing a marked wind chill. This spell of cold weather is expected to last across most areas until at least Tuesday and perhaps longer.

Edited March 8, 2013 by snowmadchrisuk

[woldsowl]

With regard to convection and cloud cover, this seems to be a deciding factor for the potential development of showers off the North Sea.

Excuse me for not recalling the date, but one of our heavier falls of snow in January started as convective showers moving in from the SE and when the front moved in from the SW later in the day, the convection appeared to enhance the precipitation as the two merged. Wouldn't this be a possibility rather than the cloud cover just being limiting, or does the band of precipitation moving in need to be closer to the convection? Excuse my lack of technical knowledge.

[That ECM]

At least the MetOffice now realize there is a risk for Monday , although there suggesting the Far South .

Turning colder over the weekend as cold air spreads south across the country during Saturday. Also during Saturday, a band a rain will move south across England and rain is expected to turn increasingly to sleet or snow down to low levels by the evening. Further snow showers are expected to follow into some eastern parts with a risk of a period of heavier snow affecting the far south on Sunday night. The cold weather will also be exacerbated across all areas for a time by brisk easterly winds bringing a marked wind chill. This spell of cold weather is expected to last across most areas until at least Tuesday and perhaps longer.

GFS 06 shows this situation developing. The track of the low will be interesting to see. For once we maybe in a prime spot but I would not rule out a movement north or south.

[Severe Siberian icy blast]

The 06 was one of the most wintry set ups any one will ever see at any given time , very cold conditions , march or not , with lots of opportunities for snow at different times. Brilliant to be staring down the barrel of significant cold in march , something we haven't had for a good few years .

The 06 ends on strong easterlies and -10 850's nationwide

[Roger J Smith]

This map shows the kind of snowfall pattern that might be expected if the GFS forecast is essentially on target with the low, and assuming also that North Sea streamers and Irish Sea streamers set up with some intensity and longevity. I have labelled the colour coded areas but you could re-scale the amounts depending on whether you thought this was too aggressive or not, the pattern itself should verify at some scale. The red line is simply to limit the map areas that I did any forecast within, outside of that I really didn't look at the guidance.

Heaviest snow besides north-central France would be Dartmoor into Somerset, and east Midlands, possibly Tyneside with local max suggested at 20+ cms. Most western coastal regions would just get left-over flurries. This map only applies to Sunday-Monday, by Tuesday you're into a different flow entirely and north Wales, Mayo and Donegal could see heavier amounts in north to northwest winds, as well as Somerset and Devon (again).

One caution on this map, I have shown snowfalls more or less continuously covering large areas, the results in terms of North Sea streamers at least would likely be more hit and miss within those areas but these amounts could fall in the areas shown, some places might get a lot less but I wouldn't be expecting more in other words.

Anyway, it's a theoretical exercise based on the model output and forecasting intuition, if the model is wrong then obviously the forecast will change. I like the GFS recent performance stateside and think it may be leading the pack for this event, also the GEM supports it rather strongly.

Have to conclude before falling asleep, that the record cold uppers for time of year have to be respected, record cold usually means potential for heavy snow somewhere. That somewhere is going to be the northern flank of the approaching low and the best-favoured snow streamer zones. My pick for a snow chase would be Lincoln to Peterborough.

[mcweather]

GFS forecasts earthquake for 16th March shock.

[Man With Beard]

Well just about everything happening winter wise on the 06Z. Snow chances almost randomly scattered about the country. Frontal snow, front-edge snow, back-edge snow, convection, marginal and non-marginal. Deep cold uppers coming and going. Strong biting easterly winds. Potential ice-days. And it just keeps on coming. And starting within T30 not T300. Is it really the spring equinox next week?

[SomeLikeItHot]

Wow the 6z is certainly a very cold run, -10 uppers appearing in some parts of the UK at five different times (including this Monday) out into FI.

[bluearmy]

not sure what to make of it all. i think that a few spots will get disruptive snowfall where the intensity is strong enough. elsewhere, brief accumulations from the heaviest showers. all in all, by the time this is over i have a feeling that most will be dissappointed if they are expecting decent snowcover that hangs around. those of us looking for extremes will be hoping for an ice day. anything else will be a bonus.

looking at the general nwp, i see a west based -NAO as we head into next weekend with the possible snow line retreating north, maybe as far as scotland. i dont see a sustained cold period countrywide as per the 06z gfs op. could end up a n/s split for the third week march which would be very wet for some and white for a few.

Edited March 8, 2013 by bluearmy

[jonboy]

Well just about everything happening winter wise on the 06Z. Snow chances almost randomly scattered about the country. Frontal snow, front-edge snow, back-edge snow, convection, marginal and non-marginal. Deep cold uppers coming and going. Strong biting easterly winds. Potential ice-days. And it just keeps on coming. And starting within T30 not T300. Is it really the spring equinox next week?

No its the 21st two weeks away

[snowmadchrisuk]

Can anyone put up a link to the Icelandic precip ECM charts please? I am at work and don't have the link for them here. It would be useful to see how they compare to the GFS at this point.

http://en.vedur.is/weather/forecasts/atlantic/#type=prec

[chionomaniac]

http://en.vedur.is/w...ntic/#type=prec

Cheers I found at the same time on google. ECM has the main bulk of precip missing the south coast. So far from certain yet.

[shaky]

The 06z nae has moderate snowfall for the northern england the midlands for 18 hours straight startin tomorrow afternoon!whether it settles is a different matter!!

[Captain Shortwave]

With regard to convection and cloud cover, this seems to be a deciding factor for the potential development of showers off the North Sea.

Excuse me for not recalling the date, but one of our heavier falls of snow in January started as convective showers moving in from the SE and when the front moved in from the SW later in the day, the convection appeared to enhance the precipitation as the two merged. Wouldn't this be a possibility rather than the cloud cover just being limiting, or does the band of precipitation moving in need to be closer to the convection? Excuse my lack of technical knowledge.

There were two events with precipitation moving in from the South East. The first was an area of convective showers which developed in the Southern North Sea. This developed into a more organised area of precipitation as it engaged the low pressure system (the one which gave a covering for Wales/Midlands) which basically caused a small low pressure system to form and tracked North West through East Anglia which gave 5-10 centimetres. I believe this was the one you are talking about. It got called "the blob" in the South East forums

[nick sussex]

In terms of how much snow falls but actually settles. It's down to a bit of luck as to when it falls, I would have thought though that in shaded areas if you can maintain a low dew point it could hang around for a few days.

As an example of this we had about 10cms of snow here a week ago last Monday February 25th then temps went 3,7,8 for the next 3 days, it was only by the morning of the 4th day that I said goodbye to the final blob!

I know that's end of February but given the strength of the sun down here I would have thought for the UK around two weeks later given how much further north, you'd manage to hold into some snow, unless we get some bizarre different snow down here!

The key is the dew point staying below freezing. And also getting an air frost overnight to firm up the snow.

Anyway going back to the models it's an interesting set up but could go either way in terms of that possible heavier snow towards the far south, much of this is governed by what low pressure does towards nw Biscay.

Further on if you look at the T84hrs fax chart you can see those fronts developing to the west of Norway, that's likely to head south around 120hrs, theres also the chance of snow off that but this time theres more marginality.

You'll have the triple point, warm front on left and occlusion to the right, areas east of the triple point likely to have a better chance of just snow.

The track of that then is likely to be the next forecasting uncertainty.