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

[bluearmy]

Low res gfs teases and almost clutches defeat from the jaws of victory.

If this is to be the week 2 game, not sure i have the energy for it!

The extended london ens continue to show wide scatter. we really could struggle to shake off the cold.

Edited February 19, 2013 by bluearmy

[fergieweather]

Just a final note to say UKMO will currently cater for 1-3cm accumulations Saturday from more pronounced Thames Estuary convergence zone running SW through central Kent to Sussex. Good agreement in UK4 with UKMO-GM and EC for this. Similar story Sunday albeit with less forcing aloft so less pronounced accumulations in same general area; also eastern areas especially Sat from the first, more pronounced shortwave (currently near Greenland) that'll run around to come SW by Sat... so e.g. Lincs and E Yorks/Humber area prone to 2-3cm too. Cheers.

[Chris W]

GFS has gone a bit loopy in FI, the temperature gradient from Italy to Denmark almost spans the entire scale:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20130219/18/384/h850t850eu.png

[london-snow]

Just a final note to say UKMO will currently cater for 1-3cm accumulations Saturday from more pronounced Thames Estuary convergence zone running SW through central Kent to Sussex. Good agreement in UK4 with UKMO-GM and EC for this. Similar story Sunday albeit with less forcing aloft so less pronounced accumulations in same general area; also eastern areas especially Sat from the first, more pronounced shortwave (currently near Greenland) that'll run around to come SW by Sat... so e.g. Lincs and E Yorks/Humber area prone to 2-3cm too. Cheers.

Sorry Ian is that a thames streamer you are talking about?

Curious as normally a thames streamer affects places like London & SW of that & not kent & into sussex I think that is called a kent clipper?

Could you please clear that up Ian?

[Purga]

So near and yet so far away!

[fergieweather]

Sorry Ian is that a thames streamer you are talking about?

Curious as normally a thames streamer affects places like London & SW of that & not kent & into sussex I think that is called a kent clipper?

Could you please clear that up Ian?

No: we don't use those colloquial terms! This is a Thames Estuary convergence focused around area E of London down through SE suburbs across Kent and SW of there. By Sunday the signal moves E to focus more through tip of Kent.

[Mair Snaw]

So near and yet so far away!

yeah and i bet that we dont get any southward shift on that pattern closer to the time......

[Blizzardof82]

Sorry Ian is that a thames streamer you are talking about?

Curious as normally a thames streamer affects places like London & SW of that & not kent & into sussex I think that is called a kent clipper?

Could you please clear that up Ian?

Oh no not the Thames streamer debate again

[fergieweather]

No: we don't use those colloquial terms! This is a Thames Estuary convergence focused around area E of London down through SE suburbs across Kent and SW of there. By Sunday the signal moves E to focus more through tip of Kent.

I can't show you the entire UK4 output but for sake of geographic explanation attach here a snapshot of SE corner accumulations Sat-Sun to help explain areal focus (have purposefully left scale off as we suspect UK4 overplaying amounts).

[LomondSnowstorm]

So near and yet so far away!

Looks pretty near to me

The 'two troughs go to war' narrative for the 10-15 day period still looks pretty relevant, the one to the southwest probably most likely to edge out with the core of the heights transferring to Canada but with a not insignificant chance of at least a glancing blow of the colder air for Scotland:

[london-snow]

No: we don't use those colloquial terms! This is a Thames Estuary convergence focused around area E of London down through SE suburbs across Kent and SW of there. By Sunday the signal moves E to focus more through tip of Kent.

Okay thanks Ian.

So nothing of note through the london areas forecasted ppn wise.

Oh no not the Thames streamer debate again

No debate Mr Blake just a polite enquiry.

[fergieweather]

Okay thanks Ian.

So nothing of note through the london areas forecasted ppn wise.

Nuances can change. It merely shows potential for this sort of shower alignment focus... not exact placement come the time!

[SMU]

THeres only ever 3 allignments really-

Thames Streamer East North East- around 80 degrees. ( SE london / NW Kent & inwards towards surrey

Kent dangler NorthEast from 50-80 degress ( Central Kent- gravesend- tonbridge etc)

Kent clipper ( right on the eastern tip ) 25-50 degrees -

The UKMO charts look like starting out out Thames streamer favourable conditions but light on convection, then as the atmosphere fills up the winds become ideal for the dangler!!- hence that big spodge over bluebell hill!!!

S

[johnholmes]

atmosphere fills up

what on earth does that mean Steve?

[london-snow]

Nuances can change. It merely shows potential for this sort of shower alignment focus... not exact placement come the time!

It can and i am well aware of that it does seem however like a trend for those areas as it has been quite evident in the past few runs.

Cheers Ian.

[SMU]

atmosphere fills up

what on earth does that mean Steve?

lol it was a quick way of writing the moisture content! rather than bone dry!

S

[johnholmes]

Just been examining a selection of f'cast profiles for later Friday coupled to the UK4-extended snow accumulation prognosis. Bearing in mind the low dewpoints by then, plus the fairly skinny CuSc tops up around -11C, the light snow signal can be assumed to be (a) reasonably prevalent despite the strong capping and likely to settle irrespective of small amounts falling. Effectively anywhere along the E coast prone to a cm or so, stretching inland along favoured topographic strips even across to Cotswolds; S of London down into W Sussex etc., with more widespread likelihood of flurries offering 1cm (in places perhaps 2)across E Yorks, Hull area, Lincs, Norfolk down across Cambs to Beds. Given good set-up for an English Channel shower band before the flow backs, by the end of Friday some snow likely even far away to high ground in the extreme SW, e.g., over Dartmoor.

I am surprised only 32 likes it seems and Ian has offered 167 or a sample from those 167 now viewing what most of you have craved for over the past 7-10 days!

looking at the latest skew-t diagrams for sunny donny and from T+72-120 they are certainly more inclined towards something coming out of the skies than any run I have looked at over those dates than any other outputs. So GFS seems to agree with output from Exeter at the moment. Always a good thing to have model agreement at these time scales. So I may have a slight covering-well well, what a good end to meteorological winter if that does happen.

For those hung up on the term winter please note I sued the definition meteorological of which there has never been any professional argument=end of February!

Edited February 20, 2013 by johnholmes

[SMU]

18z NAE has uppers widespread -12c at 48

http://www.weatheron...M=0&PERIOD==

& a pocket of -13c moving out towards the UK,- considering the 850s have beem watered down this year from the timelines of 144 I have been very impressed at how the cold has been updgraded nearer the time.

In terms of frequency of the -13 line ive only seen it perhaps once or twice in the last 10 years- feb 2005 was one example.

http://modeles.meteo...05-2-28-0-2.png

S

( Kent slapper = Dangler & Thames streamer for essex is ESE at 95 degrees along the estuary- very rare)

Edited February 20, 2013 by Steve Murr

[Timmytour]

So near and yet so far away!

Not sure which way you're looking at it!

From a cold perspective, i think it's a bit of a backtrack from yesterday's 18z

[Timmytour]

THeres only ever 3 allignments really-

Thames Streamer East North East- around 80 degrees. ( SE london / NW Kent & inwards towards surrey

Kent dangler NorthEast from 50-80 degress ( Central Kent- gravesend- tonbridge etc)

Kent clipper ( right on the eastern tip ) 25-50 degrees -

The UKMO charts look like starting out out Thames streamer favourable conditions but light on convection, then as the atmosphere fills up the winds become ideal for the dangler!!- hence that big spodge over bluebell hill!!!

S

Steve, I've always thought the 7 inches of snow we got here in South Herts in Feb 2009 was the result of a Thames streamer...... but in your opinion was it something else?

[Cheshire Freeze]

Here's one for Steve

We'd be measuring snow in feet rather than inches if something like that ever came off!

Edited February 20, 2013 by CreweCold

[SMU]

Feb 2009 was quality- the instability & variation of angle of flow meant that the whole of the SE got plastered at all angled-

The thames was like a gatling gun with the showers.

Some good eye candy in the ENS- it needs some deep easterlies for ice days in March- however the signal is PV lobe will drop into Scandi at day 10- so at least the deep cold will be there-

S

PS another classic chart with instability - sub 532 heights

http://modeles.meteo...48-2-21-0-0.png

http://www.meteociel.fr/modeles/archives/archives.php?day=21&month=2&year=1948&hour=0&map=4&mode=0 -18c !!!!

Edited February 20, 2013 by Steve Murr

[danm]

Steve, I've always thought the 7 inches of snow we got here in South Herts in Feb 2009 was the result of a Thames streamer...... but in your opinion was it something else?

If winds align to a more straight easterly or just a slight ENE'rly then areas further north, I.e all of London, South Essex, South Herts can also come into play. This was the case in Jan 2003. Feb 2009 was also a Thames streamer, the event started as more of an acute ENE, but changed more towards a straight easterly as the night went on meaning all of London, south Herts and south Essex also got the heavy snow, as well as south London and NW Kent - which saw heavy snow from the start.

[TEITS]

Steve, I've always thought the 7 inches of snow we got here in South Herts in Feb 2009 was the result of a Thames streamer...... but in your opinion was it something else?

Thames Streamer is the most over used word on this forum along with members describing a typical UK thunderstorm as a supercell or Mesocyclone in the summer.

Have you noticed how the Wash streamer rarely gets mentioned on this forum. Thats because I don't consider a few showers coming through the Wash a streamer. I have experienced a few Wash streamers in my time but what makes them different to your typical snow showers is how localised the snowfall can be. For example I remember a streamer in the 1990s where Peterborough had nearly a foot of snow and yet to the E,S,W of Peterborough they hardly had any snow. Thats because this streamer was very heavy and yet within a very defined area.

Sorry for the rant but one thing that really annoys me in winter is how members will even refer to a Thames Streamer when a solitary snow showers gets anywhere near the Thames!

Edited February 20, 2013 by THE EYE IN THE SKY

[BLAST FROM THE PAST]

Impressive cold coming for anytime of winter, particularly the south

BFTP