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reef

Winter Model Discussion - Cold Hunting 08/01/13 00z Onwards

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Pity GEFS only fly in the ointment. It does not get any better.

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Mods. Any chance of a new thread please I would love to bookmark this before 18zs come out

Yes.

New thread before 18Z.

Please start finishing off. Thanks.

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Wow - so many pages to catch up on. Brilliant enthusiastic posts and slamming 12z runs across the models. ECM serves up what we all thought it had hidden in it's ensembles and thankfully that monster charge up of LP at 168 last night is gone!

Tremendous charts and even better considering the background of the 20th December through to now where we were enduring a period of zonal action to test the faith of many. Ian B - Hats off for the post, had a good chuckle there. Seemingly stuck in a zonal rut, like clockwork the Stratosphere breaks the pattern and delivers. MJO Harmony, Unquestioned impact, and more to come.

The Greenland shredder of lows returns and the model seemingly wants to drive head first into moving that cold pooling to the E and NE in our direction. Fantastic stuff the much maligned / appreciated* delete as applicable EC32 supports some cold temp profiles way out into later January, perhaps with MJO stalling there is a slightly better lead here than previous?

Lots of charts from the ECM12z, so here is a slight variance 850 temps/streamlines. Lovely flow leaving the continent.

post-7292-0-05924900-1357676550_thumb.pn

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A very difficult time for those within professional forecasting. For example, the Irish Met's outlook at 18.50 this evening is entirely erroneous IF the latest ECMWF guidance is proven to be correct.

Despite the obvious cross model agreement at T+96 - I would advise exceptional caution. We have been here before and given that we are SO close this time, I can't imagine the carnage on here if everything goes wrong.

SA

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Limited snow from north of the midlands though? (Genuine question)

IF these charts verify, we in the North East will likely get hammered, lots of 'lake effect' snow.

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Probably as they change to the 12z at 10.30, so now they are still using the 06z which didnt show the cold and snow for Saturday.

We won't have time at 1030 on regional to discuss. With 45-50 seconds can only do next 24hrs. But yes, will be in receipt of updated full UKMO analysis for weekend by then.

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Good evening. Here is the report of tonight's 12zs from GFS, UKMO and ECM for today Tuesday January 8th 2013.

All models show a more changeable pattern to the weather for the remainder of the week as well as lowering temperatures. A front is shown over Southern Britain currently moving slowly SE and clearing the far SE tomorrow. A slack ridge of High pressure follows with fog and patchy frost over the North. the ridge is pushed slowly away East on Thursday with a new trough slowly pushing in from the West through the day bringing rain into the West and SW through the day. Things are more complex late in the week and into the weekend with some dry, bright and increasingly colder conditions occurring for many. Low pressure though will be moving down from the NW affecting many Western and Southern areas as things stand with rain, possibly turning to snow later in the weekend as colder air digs into the UK.

GFS then shows further cold and shallow Low pressure areas maintained near the UK as we move into next week with High pressure strengthening to the North. There would no doubt be further outbreaks of rain, sleet and snow early next week with frost at night. Through FI tonight the pressure continues to build to the North with Low pressure developing over Iberia and later the Meditteranean keeping winds from the East and delivering deeper and deeper cold air across from Europe. Where the interaction of these cold and strong east winds meet warmer air coming up from Iberia unsettled conditions are shown to prevail with periods of disruptive snowfall, especially in the South should thi run verify. Frosts would become severe overnight, especially in the drier NW.

The GFS Ensembles tonight show a cold spell on the way. there is as always a lot of spread between the members in the second half of the run with the overall mean being below the long term average. Precipitation is also widely shown through the run and no doubt with low uppers and ground temperatures low some of it would undoubtedly fall as snow.

The Jet Stream shows a disorganized flow currently with an arm well to the North of the UK and a weaker one to the South. later in the week and weekend and next week the Southern arm becomes stronger with it's entry into Europe well south of the UK ensuring the UK comes under the risk of cold air on the North side of depressions.

UKMO at midday on Monday shows a ridge of High pressure sinking South over the UK with a cold and bright day likely following frost. As the ridge slips South over the 24 hours after midday on Monday the synoptic pattern is conducive to bring a cold Arctic blast in the days that follow.

ECM shows a totally different chart to UKMO at 144hrs with Low pressure down near the SW with cold air wrapped around its Northern flank with rain, turning to snowfall as it runs East away into Europe. Following on behind will be very cold and frosty North or NE flow with high pressure out to the NW and slacker lower pressure over the South and East where snowfall would be quite likely at times.

In Summary a cold spell is well and truly on the way. The charts are becoming increasingly cold and synoptically very wintry with some good cross model support on the fundamental pattern albeit the specifics between models day to day being very different. The change is underway as from now with some more traditional problems of fog and frost mixed in with a few bands of rain to see us through the working week. the main interest comes as from the weekend when the risk of snowfall over the UK (not just the North or higher ground) becomes much more probable. It does look like if it sets in as shown early next week the cold spell could last some considerable time.

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MattHugo81

12Z EC ENS now on board. EC clusters definitely more grouped around the blocking pattern. Hence EC ENS support the UKMO, GFS, ECM Det models

08/01/2013 20:28

bomb.gif

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We won't have time at 1030 on regional to discuss. With 45-50 seconds can only do next 24hrs. But yes, will be in receipt of updated full UKMO analysis for weekend by then.

I will switch sky from BBC South to West this evening then :)

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Ha - who needs a sledge when all you need to do is read this forum when a cold run appears! Some thoughts:

1. Has this run thrown the MetO a curve ball, because their forecast showed little suggestion of widespread snow and low temps.

2. If so then I have a wonderful image in my head of lots of people in Exeter running around in different directions, with the chief forecaster scratching his head and wondering whether to substantially change the short/medium term text in the next update.

3. If not then let's all be realistic and wait for the inevitable downgrade on the next run.

HOWEVER I agree with the direction of SteveM tonight: these charts have swung around at short range: normally this is the sort of thing we see with a cold outlook at 192 that suddenly goes up the spout at 120. Now we have a weekend that looked pretty average at 192 that suddenly upgrades. My experience, such as it is, suggests that when models suddenly swing and latch on at about 120 in a new direction then that evolution is very likely. Normally I would say that 3. above is what will happen. Tonight I'm wondering if it is 2. instead, and we will see a big shift in the MetO text forecast soon.

GFS 18z will be important - normally a bit of a joke in model terms I find, but even the 18z is pretty decent at 120 and below. If it picks up the same signal from 72 - 120 tonight then I think it is game on.

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From Matt Hugo, who probably thinks bugger they keep typing for me.

@MattHugo81: 12Z EC ENS now on board. EC clusters definitely more grouped around the blocking pattern. Hence EC ENS support the UKMO, GFS, ECM Det models

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Slightly better pressure anomalies at 192:

Yesterday

EDH101-216.GIF?08-0

Today:

EDH101-192.GIF?08-0

Overall ensemble mean very diluted, but certainly better than yesterdays 12z:

EDH1-192.GIF?08-0

SK

This from Matt:

12Z EC ENS now on board. EC clusters definitely more grouped around the blocking pattern. Hence EC ENS support the UKMO, GFS, ECM Det models

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Quick..someone call the Metoffice and let them know it's soon going to be very cold with snow. help.gifclapping.gif

'Apparently a Netweather member phoned the Met Office earlier today to say there is an Easterly on the way. Don't worry there isn't'....'

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Against some other opinions I think the model output confidence is as high as you can get it out to 130 tonight-

Post this time there is only 2 solutions on offer- the ECM & GFS big guns- & the others that take the greenland evergy along the northern flank of the scandi high as opposed to sliding south down the western flank-

The timing of this cold is perfectly alligned to a downward propergating warming- as posted in the strat thread the best analogue from my findings was 1985- I think this came up a few times-

As for the greenland high we have cause to be very optimistic, the GFS operationals are now at least 6 runs on the trott for a GH & the ECM has now jumped on board-

As for the Warming not having any effect on this first bout I do slightly disagree- the zonal wind has decreased as an imeadiate response so the jet will respond by decelerating- it is no coincidence that the first high appeared as the fiurst effects were felt & now as we get full propergation so the greenland high can show its hand.....

snow in the forecast as early as day 3 18z- so theres not much more we could ask for-

What can we want-

just a slightly deeper low to the east at 96-120 like the gem just to force the upper level cold pool into effecting more of the UK- also that would bring snow showers further inland over the weekend.

Post that the slider low if it varifies could hit the same areas that the northern edge of the band effects friday night- so a possible double whammy-

Expect more of the same from the pub run- remember if the split flow is there at 96 then 100% varification of the GH & wham bam for the UK

S

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Don't start posting in this thread from now......

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