Winter Model Discussion 18Z 19/2/13 onwards.

[Methuselah]

And, while there's not too much going-on, here's a chart from April 1978...-10C uppers impossible?

http://www.wetterzentrale.de/archive/ra/1978/Rrea00219780411.gif

[cooling climate]

by the time the -10c uppers clear away tonight, that will have been 84 hours of sub -10c in the se third of the uk. anyone care to have a look and see when we last managed that? i checked dec 10 and winter 09/10. neither managed it anywhere in the uk. could be one for kev ?

given that this maybe a rare occurrence, so many of us seem to have dismissed it as we havent seen widespread snowfall. does that make us 'shallow' as weather nuts ?

Good post and very much agree. three days here with daytime temps around 1.5c and could have

been colder had we had snow cover. Picture in the paper yesterday of icicles in travalgar square

middle of London quite impressive. So yes even though we had little snow it has as you say been

a note worthy cold spell and had the blocking high been just three or four hundred miles further to

the north then it could have been even more memorable.

Onto the models and I would not right off pressure building to our north ushering in a potent

east/northeasterly airflow into the second week of March.

[Frosty.]

The Gfs 06z puts the uk in a rather cold no mans land before we get repeated pushes of mild air up from the southwest in FI, there are some pleasantly mild days on the 6z towards mid march, will they survive on the 12z..it's anyones guess when it's the gfs.

Just seen countryfile, the chart for friday didn't look like it's anywhere close to producing a Nly, maybe the northerly is now off the agenda sadly, it does look like slowly becoming brighter during the week from the north but then a weak front becomes draped across the far northwest and north around midweek with some drizzle or light rain on it, slowly fizzling out as pressure rises more strongly either side of it.

One thing's for sure, the ukmo 00z op run looks nothing like the chart behind darren bett on friday, sorry no pic of it but it looked rather bland.

Edited February 24, 2013 by Frosty039

[mushymanrob]

No, cold weather is pointless without snow.

exactly, i can understand the liking for snow, but this raw dull nothingness?

True.But why didn't we get any heavy snow showers in this set-up?

Similar set-ups in the past have delivered so why hasn't this one.

actually i disagree with this (bib), because historically i cannot remember the heavy snow/showers (as some predicted) off this type of set up. this dull raw cold weather though is typical off these synoptics for this time of the year... again i cite march 69 and feb 83 as two prime examples.

For convection though the problem has always been the proximity of the upper ridge and surface high. This has effectively put a lid on any convection above that -10C at 850mb. This was well predicted by the upper air charts from 4 or 5 days away if not longer and shows well again this morning if you go into skew-t ascents on Net Wx, free or Extra versions.

Looking at 1 December 2010 when this area received 35cm in15 hours the relevant temperatures were

850mb=-13C; 700mb=-21C; 600mb -24C.

The slight lid at 600mb and drier air above still allowed some tops to reach 18-20000ft.

The tops limited to 5-6000ft most of the time is almost certainly why few places had anything other than slight snow showers and the very reason that UK Met never ever went for much snow.

Obviously there have been exceptions but the overall situation did not favour snow in anything other than small amounts.

Some folk yet again let their hopes and beliefs in one or two OTT posters get the better of them-fact, sad but true I'm afraid.

and if people had listened to you then there wouldnt have been wild predictions of 'heavy snow showers for everyone' .

im not au fait at all with the technical side of meterology, i do have 40 years + of simple records. i know similar synoptics dont always mean similar conditions, but they arent that far off.

[fergieweather]

and if people had listened to you then there wouldnt have been wild predictions of 'heavy snow showers for everyone' .

im not au fait at all with the technical side of meterology, i do have 40 years + of simple records. i know similar synoptics dont always mean similar conditions, but they arent that far off.

With such a subsided, well-capped flow and CUSC tops struggling even to 6000ft - well-handled by forecast ascents even some days prior - it never had the promise of anything more than moderate showers at most, with any accumulations over 1-2cm very much dependent on convergence/shower stream alignment. I recall one post fortelling of "20-30cm of snow", which was self-evidently a journey into the realms of Maddenology based on even cursory perusal of the ascents freely available.

[Frosty.]

and if people had listened to you then there wouldnt have been wild predictions of 'heavy snow showers for everyone' .

Nobody on here ever made a wild prediction of heavy snow showers for everyone did they mushy?

And yesterday there were some moderate to heavy snow showers across northern england which caused travel disruption and that was never really part of the overall expected outcome in the days before it, from my understanding, it was always likely to be further southeast where the bulk of the snow flurries were expected.

[chionomaniac]

With such a subsided, well-capped flow and CUSC tops struggling even to 6000ft - well-handled by forecast ascents even some days prior - it never had the promise of anything more than moderate showers at most, with any accumulations over 1-2cm very much dependent on convergence/shower stream alignment. I recall one post fortelling of "20-30cm of snow", which was self-evidently a journey into the realms of Maddenology based on even cursory perusal of the ascents freely available.

Yes, the majority of posts in the last week were very level headed with the realistic expectation of a dry easterly. There were the odd predictations of snowmaggedon type scenarios - sadly, these do seem to get more attention than the others! The GFS predicted last week around 2mm of precip when looking at the meteograms for London and even this could have been an overestimate!

[phil nw.]

by the time the -10c uppers clear away tonight, that will have been 84 hours of sub -10c in the se third of the uk. anyone care to have a look and see when we last managed that? i checked dec 10 and winter 09/10. neither managed it anywhere in the uk. could be one for kev ?

given that this maybe a rare occurrence, so many of us seem to have dismissed it as we havent seen widespread snowfall. does that make us 'shallow' as weather nuts ?

You make a good point Nick.

I would think quite a few of us would have been aware of this as the 850`s are usually looked at on each run and a walk outside confirms how bitterly cold it feels- let alone reads on the thermometer.

I agree though the thread has been less frantic,shall i say,since it became apparent that there was little if any snowfall on offer in this current spell.

Edited February 24, 2013 by phil nw.

[Purga]

Yes but it's the thrill of the chase for cold which makes the model output forum the best place to be during winter, aswell as the disappointments there are also nice surprises and the swingomenter could change again any time since the outlook beyond 5 days is nowhere near set in stone yet so expect even small synoptical changes to have a bigger overall impact, no sign of mild weather returning in the next 10 days and for this time of year, that is impressive in itself.

I agree and having lived for a while in a cold continental climate where snow and sometimes severe cold were pretty much guaranteed throughout the winter months, there is nothing quite like the UK for winter drama!

Although very frustrating most of the time, the rare times when some bit of real winter shows up albeit brief, is quite special, because of it's rarity. I must say that there are many occasions when I sorely miss 'proper' winter and try not to be too dismissive of what poor old GB offers!

[Tristrame]

With such a subsided, well-capped flow and CUSC tops struggling even to 6000ft - well-handled by forecast ascents even some days prior - it never had the promise of anything more than moderate showers at most, with any accumulations over 1-2cm very much dependent on convergence/shower stream alignment. I recall one post fortelling of "20-30cm of snow", which was self-evidently a journey into the realms of Maddenology based on even cursory perusal of the ascents freely available.

Ian what was going on in the irish sea last night from about 6pm?

If you look at the radar for the 6hrs to midnight,a big streamer developed and grew between Anglesea and south wicklow on the Irish coast.

I got about 5cm's at the coast and theres a good 10cms on the hills here.It was falling very heavy,those cloud tops must have been more than 6k feet?

Worth noting for the record I think when analyising the current set up.

[LomondSnowstorm]

I agree broadly regarding the modelling of the 'dry easterly' for the southeast, since the coldest uppers never really delivered the kind of convection you would 'typically' expect, and the models and the MO in particular did a good job of picking that up.

It's untrue to say there was no convection though, since a streamer did develop into the Lothians early this morning and gave 1-2 inches quite widely, albeit most of it's gone now. The MO did put the main risk of snowfall further north than others and certainly totals fitted with the amounts suggested from convergence bands, so I wouldn't say it was completely unforecast, but the specific convection line itself did seem to be missed by pretty much everyone as a major feature. Anyway, it just goes to show that 'the dry zone' is a moveable feast and proximity to the high or upper air temperatures are not the sole drivers of what weather you end up with on the ground.

[Frosty.]

The latest met office update in my terminology says next weekend and into the following week it will turn cold or very cold in the far north & n'east with wintry showers/snow for a while, that would be very much as the gfs 00z showed with a glancing blow of the northerly during next weekend but then weakening as it pushes further south, it will be interesting to see if the ecm 12z looks more like that later since the 00z didn't, however, it also sounded like the ukmo 00z at T+144 (chart shown on previous pages) so there is still hope.

Edited February 24, 2013 by Frosty039

[nick sussex]

I agree broadly regarding the modelling of the 'dry easterly' for the southeast, since the coldest uppers never really delivered the kind of convection you would 'typically' expect, and the models and the MO in particular did a good job of picking that up.

It's untrue to say there was no convection though, since a streamer did develop into the Lothians early this morning and gave 1-2 inches quite widely, albeit most of it's gone now. The MO did put the main risk of snowfall further north than others and certainly totals fitted with the amounts suggested from convergence bands, so I wouldn't say it was completely unforecast, but the specific convection line itself did seem to be missed by pretty much everyone as a major feature. Anyway, it just goes to show that 'the dry zone' is a moveable feast and proximity to the high or upper air temperatures are not the sole drivers of what weather you end up with on the ground.

That's a really good point LS.

When you look at areas that saw at least some more convective snowfall it was those which initially looked like doing poorly from the set up.

Especially last nights events on the east coast of Ireland which was totally unexpected, I know we've seen these Irish Sea situations before but the flow there was quite slack and I didn't see any trough on the fax charts.I'm not sure however what the sea temps are for the Irish Sea, perhaps that was a factor.

[fergieweather]

Ian what was going on in the irish sea last night from about 6pm?

If you look at the radar for the 6hrs to midnight,a big streamer developed and grew between Anglesea and south wicklow on the Irish coast.

I got about 5cm's at the coast and theres a good 10cms on the hills here.It was falling very heavy,those cloud tops must have been more than 6k feet?

Worth noting for the record I think when analyising the current set up.

Yes, it was well-signalled by UKMO in both MOGREPS (see attached run from Fri) and UK4 (Fri output also attached) but being outside UK borders wouldn't have been mentioned in UKMO forecasts domestically.

[mcweather]

Yet again the models(UKMO excluded ) things have promised big only to water things down to next to nothing.

As ever the mantra trust nothing past 144 ( even the ECM) holds true.

Whether the models go out beyond 144 in high res is immaterial, the fact is beyond 120/144 even moderate detail. positioning and track of systems etc is affected by far too many variables to be anywhere near as precise as needed to make claims of blizzards deep cold or anything else for that matter.

Do what I do. admire the pretty pictures for what they are and then forget them until they appear with T120 and at that point give them a 50% chance happening and then wait until T48 before even beginning to get excited.

That way much heart ache, nerve shredding, gnashing of teeth and toy throwing can be avoided.

Believe me 40 years of serious weather watching have taught me this. I almost wish for the days when the only outlook was the Farming Today programme look at the week ahead. Much less stressfull and far fewer disappointments and more in the way of the odd nice unforecast surprise.

[Frosty_wsm]

Nobody on here ever made a wild prediction of heavy snow showers for everyone did they mushy?

Well said, the charts during the build up to this current cold spell never showed that and nobody in this thread ramped up saying there would be either.

[fergieweather]

That's a really good point LS.

When you look at areas that saw at least some more convective snowfall it was those which initially looked like doing poorly from the set up.

Especially last nights events on the east coast of Ireland which was totally unexpected, I know we've seen these Irish Sea situations before but the flow there was quite slack and I didn't see any trough on the fax charts.I'm not sure however what the sea temps are for the Irish Sea, perhaps that was a factor.

Hmmm....I'm assuming the Irish Met folk forecast it, though? Here's how the UKMO modelled the sharp shortwave passage aloft across into Ireland last night with very pronounced PVA... it had been a feature in Exeter models since Thursday's runs, hence presumably also quite apparent to the Irish forecasters too....

[Thundery wintry showers]

Indeed, as John has explained very well, a pronounced "dry lid" starting at around the 850h-900Pa level has strongly inhibited convection and resulted in cloud spreading out into a sheet of stratocumulus. The "lid" has eroded a bit over SE Scotland and NE England during yesterday and today, and now starts at around 750-800hPa over east Lothian:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20130224/06/00/sound-EastLothian-00.png

This is probably the reason why today's weather has been relatively bright and showery over SE Scotland and NE England today, though still restricted to mainly light showers.

As the colder 850hPa temperatures become mixed out from the SE over the coming 24 hours, we can expect the "dry lid" to strengthen again which will result in a return to extensive stratocumulus and the odd bit of drizzle. The skew-t forecast for East Lothian for 36 hours' time shows the convective inhibition extending right down to the 900hPa level:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20130224/06/36/sound-EastLothian-36.png

On the other hand, after midweek the high pressure is forecast to relocate to the north-west of the British Isles and this should allow sunnier conditions to extend down from northern Scotland, into southern Scotland and most of the northern half of England. It may stay cloudy in the south for quite a while though.

High pressure then looks set to control the weather for the foreseeable future, with below-average temperatures, though sunshine amounts beyond the end of next week are hard to determine at this stage.

[Frosty.]

High pressure then looks set to control the weather for the foreseeable future, with below-average temperatures, though sunshine amounts beyond the end of next week are hard to determine at this stage.

Latest met office update does sound like it's going to turn more unsettled and wintry further northeast next weekend into the following week (locally very cold for a time) Tws

[nick sussex]

Hmmm....I'm assuming the Irish Met folk forecast it, though? Here's how the UKMO modelled the sharp shortwave passage aloft across into Ireland last night with very pronounced PVA... it had been a feature in Exeter models since Thursday's runs, hence presumably also quite apparent to the Irish forecasters too....

Thanks for the info. Certainly though when one looks at easterlies its certainly a surprise though to see areas of eastern Ireland doing better than many areas of the east and se.

I know you can get shower activity building in the Irish Sea but given the lack of convection across the majority of the east and UK in general it was still a surprise to see those radar returns in the Irish Sea.

[bluearmy]

Yet again the models(UKMO excluded ) things have promised big only to water things down to next to nothing.

As ever the mantra trust nothing past 144 ( even the ECM) holds true.

either you have most of us on 'ignore' or you haven't read the thread properly mc. 84 hours of sub -10 c uppers cannot be dismissed as 'watered down next to nothing'. there has to be to this than just looking for deep snow. from my point of view, this sustained period of very cold uppers is more of an event than a 6" snowfall. i can look back on several of those this past few years. i cannot recall an 84 hour period of those low uppers. i await the answer as to the last time it occurred.

[cooling climate]

Ian apologies if I missed it but did you do a tutorial on skew-t diagrams as I would like to be

fully conversent in reading them rather than rather limited knowledge I have at the present

time.

[Thundery wintry showers]

It was John who wrote it, here:

[cooling climate]

It was John who wrote it, here:

http://forum.netweat...kew-t-diagrams/

Excellent, cheers.

[Panayiotis]

I can tell you that the 12z wont go the same way as the 06z, energy over Greenland completely different, this will stop any retrogression. Northerly(if any) being postponed ...

Edited February 24, 2013 by Panayiotis