Model output discussion 13th Feb onwards

[Frosty.]

Well..it's only taken 16 weeks ..cough..16 weeks of hope turning to despair time and again but it now looks like the first proper cold snap is only a few days away according to the Ecm 12z op run, thursday is the day of transition and from friday it becomes colder and colder and more unsettled and for the first time, low pressure will get to the north east of the uk and finally unlock winds from the Arctic with the highest risk of snow since last march...I know it sounds like a bad joke but winter is coming to a backyard near you by the end of this week  ENJOY IT MY FELLOW LONG SUFFERING COLDIES..we deserve it BOOM

[Summer Sun]

ECM ensemble shows high pressure building early next week

 

 

By t240 it moves back out into the Atlantic

 

[Cloud 10]

Looks to be quite a potent cold front crossing the UK on Thursday,with a large temperature

contrast between north and south in the afternoon.

 

[knocker]

Before many start hyperventilating and put defibrillators on standby the unsettled cooler spell looks to be quite short lived. The Thursday rainfall from the cold front is still on track with some unstable convective outbreaks behind that could be quite wintry,  especially up north. But at the moment that's it with NCEP- GFS building the AZ high much more next week to the extent in dominates. The ECMWF is not quite so agressive with the AZ high build up but by Weds has it in control.

Edited March 18, 2014 by knocker

[The PIT]

Downgrades gradually increasing and following the pattern set in winter. Once again a steady loss in the cold uppers if this keeps on we'll back at average temperatures. At the moment it's looking cool and wet away from Scottish hills.

[Polar Maritime]

No real change this morning, the GFS has a slacker Northerly shot but still cold enough to give snow over the Midlands North even to low levels. With -4/-8 850 uppers covering most of the UK.

 

 

While the ECMWF is pushing the colder uppers further South today, with -8 850 uppers covering all of Northern UK.

 

 

Im sure the the cold uppers will wobble a little more over the coming few days which is to be expected.. but a cold shot with Wintry potential is still on the cards for the weekend. 

Edited March 18, 2014 by Polar Maritime

[Captain Shortwave]

Hmm one issue is the GEM, which has consistently gone for no cold snap this weekend, and also no return to drier conditions next week.

The model drops a low towards Iberia which prevents a northerly establishing and also forcing the Azores high away from the UK.

The models does bring in a cyclonic easterly, but it's not particularly cold.

 

I have to admit only the ECM looks to be bringing cold enough conditions for low lying snow. GFS looks toned down and the UKMO only is around -6C 850s.

Still time to improve/or vanish. But the GEM is the sticking point as it's been pretty blunt in saying no to this for several runs now.

[Frosty.]

No DOWNGRADE this morning, we are going to see a change to windier, colder, brighter and showery weather once an active cold front bringing a band of heavy rain across the uk clears away southeastwards during thursday which heralds an increasingly cold polar maritime airmass digging in for at least a few days with showers, some heavy and thundery which will be gradually turning wintry, cold enough for hail, sleet and snow, the snow mainly in the heavier showers and over hills, and more generally for scotland, perhaps leaving a covering overnight on low ground and significant falls for northern hills / mountains. The GEFS 00z mean shows how the isobars veer to a colder direction by the end of this working week and throughout the weekend. Into next week, high pressure builds in from the azores but with a cold airmass in situ, we can expect overnight frosts following fine, pleasant and sunny days. The mean eventually shows unsettled and chillier, showery type cyclonic conditions returning towards the end of the month.

[johnholmes]

A cold snap for sure looking at all the various outputs over the past few days, say Friday into Sunday/Monday then a settled period developing for at least a few days as surface high pressure starts to dominate under the developing upper ridge shown on all 3 main anomaly charts, see links below

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

 

this has been a consistent trend over a few days as the colder burst, also indicated several days ago, changes to the upper ridge suggestion.

[Gibby]

Hi folks. Just a few minutes to spare before I endulge in another day of Canaries heat to give you a snapshot of how I see the models this morning as printed over on my website.

 

This morning's analysis tells a story of changeable conditions typical of the time of year with a mix of low pressure from the Atlantic delivering spells of rain alternating with some drier, colder and brighter phases when some wintry showers could fall, especially over the North and East. Some models show High pressure becoming dominant again after the coming weekend's showery theme which if verified would mean more warm and dry weather by day but frosts and fogs at night.  However, this improvement is by no means set in stone with other output suggesting Low pressure sliding down across the UK meaning rather cold and unsettled weather prevailing with rain or sleet at times, and no doubt some snow over the hills, especially in the North Whichever is right as indicated earlier will be just typical early Spring weather when it is almost possible to have four seasons in one day.

[Summer Sun]

Certainly signs of another pressure rise from the 24th on the GFS ensembles we then have a fall in pressure from the 29th

 

 

Edited March 18, 2014 by Summer Sun

[draztik]

 

Canadian Ensembles less bullish about the pressure rises shown by GEFS.

[knocker]

Hmm one issue is the GEM, which has consistently gone for no cold snap this weekend, and also no return to drier conditions next week.

The model drops a low towards Iberia which prevents a northerly establishing and also forcing the Azores high away from the UK.

The models does bring in a cyclonic easterly, but it's not particularly cold.

 

I have to admit only the ECM looks to be bringing cold enough conditions for low lying snow. GFS looks toned down and the UKMO only is around -6C 850s.

Still time to improve/or vanish. But the GEM is the sticking point as it's been pretty blunt in saying no to this for several runs now.

 

Sorry not sure I'm following that. The comparison Sat 00 although Weds 00 well.......

 

Edited March 18, 2014 by knocker

[draztik]

The recent mild conditions seen by many over the last week or so will be replaced by much cooler air if GEFS is correct. Days 3-8, 6-11 & 11-15 temp anomaly below.

the ec32 shows this too, with below average/average conditions lingering well into April, with cfs ensembles trending cooler into next month too.

just a snapshot(usual caveats apply) but for mid April, ec32 trends cooler.

Edited March 18, 2014 by draztik

[roys]

BBCweather forcast say blue air mass from Thursday on wards looks cold 

[Thundery wintry showers]

I am not expecting much in the way of widespread snow at low levels this weekend, but I continue to see some interest from a convective point of view- there could be widespread hail from this setup and some impressive cloud formations associated with cumulus congestus and cumulonimbus cells.

 

The GFS snow risk charts for Saturday highlight the relatively low likelihood of widespread snow at low levels:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20140318/06/108/uksnowrisk.png

And so do the 850hPa temperatures.  In frontal situations, sometimes 850hPa temperatures between -1 and -5 can be sufficient for widespread lowland snowfalls, but in showery setups they ideally need to be below -5C, while projections show values mostly between -2 and -4:

http://cdn.nwstatic.co.uk/ecmimages/20140318/00/ecmt850.120.png

 

Convective available potential energy is projected to be quite low (not surprising given that we're only in March) so thundery activity is likely to be isolated, but I do think that some sharp showers with hail and perhaps the odd rumble of thunder are possible, mostly in the west on Friday and in the east on Saturday.  Sunday will probably see fewer showers as the ridge of high pressure moves in from the west.

Edited March 18, 2014 by Thundery wintry showers

[Weather Boy]

I am not expecting much in the way of widespread snow at low levels this weekend, but I continue to see some interest from a convective point of view- there could be widespread hail from this setup and some impressive cloud formations associated with cumulus congestus and cumulonimbus cells.

 

The GFS snow risk charts for Saturday highlight the relatively low likelihood of widespread snow at low levels:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20140318/06/108/uksnowrisk.png

And so do the 850hPa temperatures.  In frontal situations, sometimes 850hPa temperatures between -1 and -5 can be sufficient for widespread lowland snowfalls, but in showery setups they ideally need to be below -5C, while projections show values mostly between -2 and -4:

http://cdn.nwstatic.co.uk/ecmimages/20140318/00/ecmt850.120.png

 

Convective available potential energy is projected to be quite low (not surprising given that we're only in March) so thundery activity is likely to be isolated, but I do think that some sharp showers with hail and perhaps the odd rumble of thunder are possible, mostly in the west on Friday and in the east on Saturday.  Sunday will probably see fewer showers as the ridge of high pressure moves in from the west.

 

I know that those snow risk charts are quite experimental, even at short range, but does anybody know if they take into account elevation or not?

[vladthemert]

OK people can anybody explain what black pressure means for the risks to uk.  Although 2nd april long way off this predicted above scotland

 

[Polar Maritime]

OK people can anybody explain what black pressure means for the risks to uk.  Although 2nd april long way off this predicted above scotland

 

 

Could be Blizzards for the North.

[vladthemert]

Could be Blizzards for the North.

 

Thanks polar Maritime comes off winter here with a bang.

 

I convinced surely its an error seen this before crazy long forecasts.  Looks like would be cold here outside the worst.  

[Summer Sun]

-4 850's covering all of the UK at t144 with -6 850s over many parts away from the far south and west

 

t120 850's now available

 

 

Weak ridge of high pressure moving in on Monday

 

Edited March 18, 2014 by Summer Sun

[Summer Sun]

GFS once again shows high pressure slowly building next week

 

 

Beyond this it turns unsettled once again

Edited March 18, 2014 by Summer Sun

[Captain Shortwave]

GEM has finally joined the northerly party

 

GFS

 

UKMO

 

So a chillier weekend up ahead, though 850s looks very marginal south of the Scottish border.Nice longer northerly shot would be better here to get a more direct and prolonged hit. 

[Barry12]

OK people can anybody explain what black pressure means for the risks to uk.  Although 2nd april long way off this predicted above scotland

 

 

One ensemble member predicts that at T+384, I certainly wouldn't worry about it, unless of course you worry about getting struck by lightning.

[Polar Maritime]

No real change for the cold shot this weekend, the slight fluctuation of fine details regarding 850s is to be expected at this range as usual..

 

The last few frames from the GFS look very disturbed. We could be heading for a prolonged spell of cool/cold and unsettled weather, with at least the 0c 850's over the UK throughout much of the run.

 

Edited March 18, 2014 by Polar Maritime