Winter Model Discussion 18Z 3/2/13 onwards.

[Gibby]

Good evening folks. Here is the latest report on the 12z output from GFS, UKMO and ECM for today Tuesday February 5th 2013.

All models show a cold Northerly flow developing over the UK in the next 12 hours. Sleet and snow in parts of the East and rain and sleet elsewhere will clear away South late in the night. Following on behind will be cold and strong north winds with snow showers developing near Eastern coasts by morning while many other areas become dry and clear with an inland frost given shelter. Tomorrow will see a dry and sunny day following any remaining sleet from Southern areas first thing in a cold North wind but Eastern Coastal areas will continue to see snow showers, settling in places. Tomorrow night will become dry and clear for many with winds decreasing steadily with a sharp frost likely in places. On Thursday all models show the Northerly flow weakening as a weak front moves in from the West bringing some rain and sleet and hill snow through the day. This then is shown to die out in over time leaving the UK in a rather cold and quiet end to the week and start to the weekend with some brighter intervals and much lighter winds.

GFS then shows Low pressure sliding South down the Western side of the UK and down into Europe over Sunday and Monday bringing a messy mixture of rain and snow across the UK before receding it back South later in continuing cold conditions. High pressure clings on to the East over Tuesday before milder Atlantic weather spreads across the UK from the middle of the week with rain at times. Through FI tonight the weather remains unsettled and windy with rain in somewhat less cold conditions for a time. Some of the rain could be heavy and fall as snow especially later in the run.

The GFS Ensembles show 850 averages below the seasonal normal for the entire run with the operational on the mild side of the pack from midway. This is more notable due to the fact that the mean for southern Britain is at its lowest annual point of around -3C next week before the seasonal change begins to take it slowly upwards. There is plenty of precipitation through the run and no doubt some of this would fall as snow almost anywhere.

The Jet Stream shows the flow continuing to tumble South over the UK over the coming days before the flow backs West and SW somewhat late in the reliable timeframe to a position moving South over Ireland and the SW approaches for a time leter in the weekend and start to next week.

UKMO for midday on Monday shows Low pressure over France with a cold and wintry Easterly flow over the UK. Residual sleet and snow left from Sunday and Sunday night will move steadily away from Southern Britain through the day as pressure rises to the North.

ECM follows UKMO with the pattern shown slightly further West than UKMO bringing a greater snow threat for all on Sunday/Monday prior to a ridge from a Scandinavian High moving SE on Tuesday bringing a dry and settled day for all albeit very cold. then as we move further through the week this run shows further attempts of the Atlantic moving in from the West with trough disruption around the vicinity of the UK continuing the messy mix of a rain and snow risk through the week. the run ends at Day 10 with the Scandinavian High doing a good job of holding up the milder Atlantic air with further trough disruption likely shortly after day 10 with further snow risk likely then.

In Summary we look to be sliding into a rather cold or cold spell. As the January spell conditions do not look like becoming record breakingly cold and bears some resemblance to the January spell tonight with disrupting troughs and Low pressures sliding SE across the UK though if this setup evolves as shown we will at least have a strong Scandinavian High to support a greater longevity to the cold, a point that ECM illustrates with the block holding firm at Day 10. GFS does show a milder setup tonight but it is on the warmer side of the pack within its ensembles of which many support colder evolutions. UKMO at 144hrs is also worthy of note tonight showing a raw Easterly flow following a snowy spell the day previous. There looks no quick way back to mild from that.

[Tamara]

Ecm, shows the cold increasing by t+144 on its 12z run, compared to the 06z. Ecm is really not budging and I think it really is on the money, it would have changed its output by now if there was no certainty in its output and to be honest I would have thought by now it would have downgraded the cold output, but conversley the reverse!! Here is the two ecms 06z and 12z today....

I guess you mean the 00z I agree with you and made a similar point earlier about how well the model has handled this scenario

[ChartViewer]

Yes - I know, but we were stuffed by the tertiary warming that upset the apple cart somewhat. I wonder how many on here know how close we came without that!

Hi Chio, prob not many not many of us but it would be appreciated if at some stage post Winter...someone of knowledge could demonstrate those December, Jan stumbling blocks that caused the breakdowns or upsetting of the apple carts....would help us a) maybe understand more on what causes breakdowns beyond normal signals eg jet, shortwave etc and b. why a tertiary warming did upset the apple cart

Edited February 5, 2013 by ChartViewer

[london-snow]

My punt posted on the 27th January 2013 -

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Okay so based on my previous thoughts here is my punt on the way forward :

28th - 2nd : A much milder week ahead however with showers or longer spells of rain during this period. As we move into the weekend i am looking at the atlantic to become cut off and introduce a more settled period of weather where frosty weather will take hold through much of the uk and temps to take a drop to just below average.

3rd - 7th : After a dry start i am looking at a much more colder & wintry pattern to take control from the north.

Beyond this period or just a tad before i am looking at the northerly to tranfer to north east ~ east and become locked in for some time.

That's my view & punt so don't take for gospel. Good times ahead i feel.

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Not to far off the mark maybe...

[ANYWEATHER]

I guess you mean the 00z I agree with you and made a similar point earlier about how well the model has handled this scenario

Sorry,yes 00z! Yep, confusing my gfs and ecm zzzssss! Anyway many thanks ..Ian. Ok, made the changes to my previous post!

Edited February 5, 2013 by ANYWEATHER

[chionomaniac]

Hi Chio, prob not many not many of us but it would be appreciated if at some stage post Winter...someone of knowledge could demonstrate those December, Jan stumbling blocks that caused the breakdowns or upsetting of the apple carts....would help us a) maybe understand more on what causes breakdowns beyond normal signals eg jet, shortwave etc and b. why a tertiary warming did upset the apple cart

I will probably give a debrief on the strat thead at the end of the season. Certainly the SSW displacement and split and now wain has dictated the pattern since January. And the pattern in December was a precursor to this. Whereas the blocking hasn't occurred with the strength as anticipated, there has been a certain predictability to the tropospheric/stratospheric large scale interactions this winter so far.

Edited February 5, 2013 by chionomaniac

[Snowman.]

Evening Steve ,

The orientation of the high on the last two charts look perfect for a severe cold spell from the east .However would the uppers we can see to our east keep there depth as they migrated there way toward to the uk?

I suppose with a very cold land mass as it moves toward Europe and as its such a vast area of land they can maintain there severity , depends on the angle they come at the uk , over the North Sea then they will weaken somewhat but if they come in a more southeast direction they may well be maintained .

Prehaps may lose a couple as it makes its journey over the seas but -8 -10 over most of the country.

[Brad lough]

Hi just to help me learn to understand the charts etc I've just checked the nae chart page under the ecmwf it's saying -6 -7 temp at 850 for mon I know there's more to it but would this help in regards snowfall etc

[Grimsby Snow Lover]

Hi just to help me learn to understand the charts etc I've just checked the nae chart page under the ecmwf it's saying -6 -7 temp at 850 for mon I know there's more to it but would this help in regards snowfall etc

Might be a little marginal to lower levels/around coasts but should be fine for the bulk of the UK. But as you said there are many other factors that need to be correct for snowfall too.

Edited February 5, 2013 by Grimsby Snow Lover

[Ian Brown]

Alot of snow showers moving into the E/SE at +144.

http://www.wetterzen...cs/Recm1441.gif

No, the front has cleared and you would be left with residual cloud. It is the opposite to the set-up needed for convective snow showers !

[Brad lough]

Thanks

[Ian Brown]

Something in evidence tonight is the rare phenomenom of cold pool growth as it crosses from eastern Europe. This doesn't happen that often but in the right conditions the uppers increase in cold over the continent as they head in our direction.

So looking at the 850's on the ECM at T+192 over Europe they don't look too great:

A bit better by T+216

But building nicely by T+240 and this is both a cold continental cold pool growth as well as an Arctic feed.

I wonder what the ECM ensembles will be like tonight. We still have a good few weeks left before the mean zonal winds increase at the top of the strat filters down to the trop. For once we could have classic delayed indirect effects from the SSW as well as the direct effects seen earlier - it was always a matter of time, waiting until the Pacific block dissipated, which allowed the tropospheric vortex to take residence over there.

Its T240 so no need to over analyse it but with the jet profile, the Scandi High can come no further West.

[chionomaniac]

Hi just to help me learn to understand the charts etc I've just checked the nae chart page under the ecmwf it's saying -6 -7 temp at 850 for mon I know there's more to it but would this help in regards snowfall etc

I think that it is pretty safe to suggest that the majority of the precipitation from Sunday onwards across the majority of the country will be snow according to the ECM.

850's sub -5ºC with a continental flow hopefully with low dewpoints:

Precipitation making some inroads by end of day Sunday

By Monday I can't see any marginality if the ECM is correct

But still far too early to be looking at this really, other than for fun!

[Ian Brown]

So guys going by sundays charts where is the rain/snow borderline likely to be? Going by the comments it looks as though the midlands/south east look like being in the fireing line, whilst south wales and the west country missing out with yet more rain......any clarification will be much appreciated!!

It's hard to say at this stage where the PPN will be or where the boundary between rain and snow will be. Too far West and it's rain, too far East and you could be dry. But I'd be confident of rain for Ireland and SW England.

[SMU]

Ian you make it up as you go along-

240 if it arrived as modelled would see the scandi high being tugged West from the pulse of WAA coming NW across Ireland-

144 chart is very showery especially for the SE with heavy snow developing as the cloud deck moves into the continent.

S

[chionomaniac]

Its T240 so no need to over analyse it but with the jet profile, the Scandi High can come no further West.

Likewise- it's T+240 and the jet profile may be further west / east / south /north.

The point of the post Ian was too demonstrate how cold pools can grow over the continent in the right conditions - not to suggest that it will verify or not.

[bluearmy]

the ecm op has snow for the eastern extent of the precip but oxford is snow whereas winchester and reading have sleet and then snow. much too early to be looking at this in detail. the 12z ecm ens mean has backed the atlantic back at day 10 and the russian ridge/scandi high looks very strong to our east. much indication of slider opportunities on that chart

[UV-RAY]

Likewise- it's T+240 and the jet profile may be further west / east / south /north.

The point of the post Ian was too demonstrate how cold pools can grow over the continent in the right conditions - not to suggest that it will verify or not.

Two good points Chion, but at +240 there is plenty of time for corrections either way. Very interesting model viewing again.

[Mair Snaw]

Had to take a break for a couple of days as have the OUTLAWS staying, living in a remote village up in the peak district would it be advisable for me to get shot of them before the weekend as i would wanna be snowed in with them here!!!!! was really thinking that i would come on here tonight and it would have all gone wrong but its not so advice please?? should they stay or should they go??

Just to add very happy with the output today and some stunning charts and looking forward to some serious lamp post watching in my area soon, after the snow showers of today left 1-2 cm briefly.

[Man With Beard]

Enough agreement at T120 to imagine that the "slider" is highly likely to happen. ECM in particular pretty much perfect at T120

Here the cold all stays on the right side of the low pressure. However, it is still T120 and a few things could happen - it could go too far west meaning most may not get much snow (though those in Devon and Cornwall won't be complaining). It could move through very quickly and not snow for a particularly long time. And could become a much weaker feature as per GFS (many an approaching low has been weakened nearer the time recently, I've noticed). The ideal scenario really is for the low to keep the same track as the ECM is showing and then get stuck over northern France for a while - this would lead to serious snowfalls and cold rushing in from the east. So lots still to be established. And not impossible that the low could head a bit further east leaving central/western areas with marginal snow/rain.

Further out, not really much point getting too hung up on T192+, except that unless there is a decisive breakthrough from the Atlantic, any snow that falls at T120 is likely to stick around for several days away from the coasts. But it is interesting that the models are already struggling to get the Atlantic back in (even GFS at times) - considering the massive back down from forecasts of zonality last week to what we have right now, you couldn't rule out a further strengthening of the Scandi High and yes, as Steve Murr points out, ECM T240 definitely one to keep an eye on with that cold pool tracking down through Eastern Europe - if that made it here, expect max temps of -4/-5 daytime - probably only a 10% / 20% shot at the moment but one year it's going to happen again, no reason why it can't be now.

Edited February 5, 2013 by rjbw

[bryan629]

Hi All, just been flicking through tonights ECM and noticed something i cant explain, probably because im still learning .

on the image at 120 hrs there is a deep low at the tip of greenland and the slider low to the west of uk, then at 144 ( second image) the low has slipped down south, so wheres the low at the tip of greenland gone... no trace of it ... surely it cant just disappear in 24 hrs can it

http://images.meteociel.fr/im/3193/ECM1-120_esr3.GIF

http://images.meteociel.fr/im/4321/ECM1-144_emr7.GIF

[Long haul to mild]

No it's not, it's a term for when the wind has temporarily gone in one direction after a frontal clearance, which is all what we are looking at here. There is no reason for shower activity. People are looking at blue on the chart and a continental source and jumping to the wrong conclusion.

Considering that a deep area of low pressure has passed through, I would expect the Easterly flow on the Northern flank of it to be unstable and would be very surprised if troughs did not form in it.

Will be interesting to see what the T120 FAX charts show tomorrow night in respect of this.

[snowice]

Well Looking at the ECM T+120 might get across the Irish SEA ,We cant miss it again?

[Guest bjaykent]

Considering that a deep area of low pressure has passed through, I would expect the Easterly flow on the Northern flank of it to be unstable and would be very surprised if troughs did not form in it.

Will be interesting to see what the T120 FAX charts show tomorrow night in respect of this.

Surely the warmer temperature of the north sea would still be producing shower activity along the east coast?

[Blackjack10]

First post in here, and a bit of a beginner's question, but here goes. Have been looking at all these cold charts and reading everybody's posts re. snow and easterly winds etc, yet daytime temperatures are set to remain 3 or 4 degrees above freezing quite widely across the UK throughout? Now I know that these forecasts are based on GFS output (I think), but should the ECM be the model that verifies what kind of daytime temperatures would we be looking to experience across the country? My model reading skills aren't high enough to interpret the ECM showings and equate this to ground temps

Thanks in advance to anybody who answers, and apologies if it is a stupid question....