Spring Model Discussion 18Z 9/3/13 onwards....

[Panayiotis]

Lovely 12z, low tilted to send more cold in from the east...

[AWD]

Is this what we've been chasing all winter?

:p

[mushymanrob]

major changes in the gfs 12z, suggesting a mid/north atlantic high later next week and a slow moving flabby trough over us... reminds me very much of late march/early april 83, heavy slow moving wintry showers.

[Harsh Climate]

Nice chart, but would have prefered synoptics like these in January.

[Thundery wintry showers]

Looks to me like a pretty marginal setup- a mix of rain, sleet and snow on a slow-moving belt of frontal precipitation (mainly rain near the east coast, but snow certainly possible inland, with NW England, W Midlands and inland parts of Wales favoured for snow on this GFS run) and indeed, slow-moving wintry showers to the south of the frontal belt. This morning's ECMWF did show some support for that sort of evolution, and tonight's UKMO is quite similar but with the low centred further north which would take the frontal belt further north, probably into Scotland.

Chances of a grey spell for the northern two-thirds of Britain tomorrow with stratocumulus off the North Sea trapped under an inversion have receded as it appears that the models have overestimated the suppression of convection over the North Sea, but it will be grey in the south due to the proximity of the frontal system in the English Channel. A heavy snowstorm, with lying snow inland and sleety stuff near coastal fringes, is still suggested over the southern Home Counties.

Tuesday looks like being a bright and mainly dry day with just a scattering of wintry showers in the north-east, but Wednesday is forecast to have rather more widespread wintry showers down the eastern side of Britain.

[mushymanrob]

Looks to me like a pretty marginal setup- a mix of rain, sleet and snow on a slow-moving belt of frontal precipitation (mainly rain near the east coast, but snow certainly possible inland, with NW England, W Midlands and inland parts of Wales favoured for snow on this GFS run) and indeed, slow-moving wintry showers to the south of the frontal belt. This morning's ECMWF did show some support for that sort of evolution, and tonight's UKMO is quite similar but with the low centred further north which would take the frontal belt further north, probably into Scotland.

Chances of a grey spell for the northern two-thirds of Britain tomorrow with stratocumulus off the North Sea trapped under an inversion have receded as it appears that the models have overestimated the suppression of convection over the North Sea, but it will be grey in the south due to the proximity of the frontal system in the English Channel. A heavy snowstorm, with lying snow inland and sleety stuff near coastal fringes, is still suggested over the southern Home Counties.

Tuesday looks like being a bright and mainly dry day with just a scattering of wintry showers in the north-east, but Wednesday is forecast to have rather more widespread wintry showers down the eastern side of Britain.

and beyond that an area of low pressure sits over us for some time, like 1983 producing...thundery wintry showers?

just seen the radar, there appears to be quite a large area of precip honing into view and heading towards our southeast... some of you just might get what you want...

Edited March 10, 2013 by mushymanrob

[cooling climate]

The 12z GFS certainly wants to prolong the cold and as I mentioned the other

day this was the form horse to follow. Anyone wishing on milder weather or

spring like weather have a while to wait yet I feel.

It will be very interesting to see the ECM this evening as a return to very cold

uppers in the extended range is definitely a possibility.

Of course if we were to see the possibility of a slider as S. Murr mentions then

the very cold uppers would return much quicker.

As far as the low to the sw is concerned I think what the models are showing is

a classic example perhaps in the way they deal with sliders or southerly tracking

lows in so much as they model them with small increments south but once you

get to within t36-t24 they start to adjust them north.

This does not of course happen everytime but certainly 80 to 90% of the time

from what I have seen over the years.

[-uksnow-]

Seems even at T30 now the 12z GEFS have had a slight shift northwards with by 8pm tomorrow night the majority of them still having a large area or heavy snow over the south coast.

[Thundery wintry showers]

and beyond that an area of low pressure sits over us for some time, like 1983 producing...thundery wintry showers?

I think the key is the positioning of the frontal zone on the northern flank of the low. Looking over the charts during the cold cyclonic spell in early April 1983, the main primary depression was centred further north and this would have kept the frontal zone firmly to the north of the Scottish Lowlands, with an unstable polar maritime airmass to the south- this would explain the widespread thundery wintry showers.

http://www.wetterzen...00119830405.gif

http://www.wetterzen...00119830408.gif

On the latest GFS run the primary depression is sat over southern England and this would keep the frontal zone stuck over the northern half of England and into southern Scotland, with any thundery activity largely restricted to southern England:

http://www.wetterzen...s/Rtavn1801.png

Tonight's UKMO at T+144 bears a very strong resemblance to the early-April 1983 setup though, so it's certainly possible that we could end up with a similar spell of weather. Certainly something to keep an eye on for those interested in the first potentially "active" spell of the season convection-wise.

Edited March 10, 2013 by Thundery wintry showers

[liam300]

Can I ask what models the bbc use when forecasting?

[Met4Cast]

Can I ask what models the bbc use when forecasting?

All of them

[Tom Jarvis]

On phone but ensembles look verry cold

[AWD]

On phone but ensembles look verry cold

Your right there;

Very cold for mid-late March. The mean not going above -4c for the reliable, and pretty good clustering for this too.

Mean not getting above 5c/6c at the surface for London in the reliable either;

Edited March 10, 2013 by AWD

[Tim Bland]

A random question...where in London is the ensembles taken? It has 100% snow risk for te next 48hrs and a high precip spike..I'd presume it's south of the Thames? I very much doubt the precip will get north of the m4 / Thames

[Panayiotis]

A random question...where in London is the ensembles taken? It has 100% snow risk for te next 48hrs and a high precip spike..I'd presume it's south of the Thames? I very much doubt the precip will get north of the m4 / Thames

It may be due to convection either from the Thames(?) or from the North Sea.

[SMU]

http://www.meteociel.fr/modeles/ecmwf/runs/2013031012/ECM1-120.GIF?10-0

An awsome chart if you want snow for central & North/ North western Areas-

S

[BLAST FROM THE PAST]

http://modeles.meteo...fs-0-102.png?12

the models still correcting west....

Can we get a slider like that EPIC CFS carlsberg run the other night-

S

by BLAST FROM THE PAST on 08 March 2013 - 17:16 in Model Forum Archive

So as recently as this morning Carol Kirkwood said 'snowfall not anticipated to be problematic 'anywhere'. Lets see how or if the forecast changes. Many on here have suggested [for days] it would produce more than unproblematic snow. This is dynamically developing situation...however, due to the depth of cold and set up it always looked a possibilty. Great call if the system shunts south and there's no streamers/ almagamted bands of showers, but we are close to this happening now.

I mentioned freeze frame of the day re ECM, well another has popped up and its the UKMO at T144. That LP is diving SSE but to the west side bumping into embedded very cold air. That could be a very interesting 'second' scenario.

and 00z ECM at same timeframe

Indeed Steve, something that caught my eye on Friday and someting that could be just as interesting, if not moreso, than next day or two

BFTP

[Paul]

A random question...where in London is the ensembles taken? It has 100% snow risk for te next 48hrs and a high precip spike..I'd presume it's south of the Thames? I very much doubt the precip will get north of the m4 / Thames

You have to bear in mind that the ensembles are a 1 degree resolution so one grid square will be 100km or so.

[ITSY]

following SM's post, Friday/Saturday could be very interesting for northern central areas on the basis of recent runs. ECM +144

[Ian Brown]

http://www.meteociel...M1-120.GIF?10-0

An awsome chart if you want snow for central & North/ North western Areas-

S

It depends where the frontal zone is on the Northern side of the LP, certainly looks cold enough for snow away from coastal areas and then nowhere really for the Low to go other than sink slowly South, Atlantic shut off.

[Gustywind]

Aren't the upper air temps too high for areas away from far north though, look to be -2 to -4 for most of country on Friday?

[Captain Shortwave]

Aren't the upper air temps too high for areas away from far north though, look to be -2 to -4 for most of country on Friday?

low dew points off the continent will support frontal snow in this instance.

[The Northern Ramper]

following SM's post, Friday/Saturday could be very interesting for northern central areas on the basis of recent runs. ECM +144

However it will correct west and south and miss most of us.

[shotski]

However it will correct west and south and miss most of us.

But if that corrected south & west I would be dancing a happy dance as it would mean snow for most.

[Cloud 10]

A big shift colder for the GFS 12z ensemble mean this evening,and now much more in line with

the ECM 00z for day 10.

ecm 00z.. gfs 12z..

Meanwhile another chilly run from the ECM operational with snow chances galore,especially

for Northern areas.

Whoever writes the weather warning's for the met-office is likely to be very busy

over the next couple of weeks!