Spring Model Discussion 17/3/13 6PM onwards....

[Thundery wintry showers]

A rather complex synoptic situation at the moment with various fronts circulating around the low pressure. Into tomorrow and Tuesday the synoptic picture looks like simplifying with a frontal system stuck over northern England, which looks set to give a wintry mix of precipitation at low levels and snow on high ground. Into Tuesday as colder air pushes down from the north-east the precipitation is likely to turn increasingly to snow for all.

http://www.wetterzentrale.de/pics/brack0a.gif

This is the FAX chart for 00Z Tuesday showing that persistent frontal system.

Sunshine and showers can be expected both to the north and south of the frontal system. To the south the showers will mostly fall as rain, hail and sleet, while to the north it will be a case of snow and graupel showers firing in off the North Sea.

There is strong cross-model agreement that into Wednesday we will get sunshine and snow showers over eastern Scotland and north-east England, with a few well-scattered flurries perhaps over Lincolnshire and East Anglia, with cloudy weather and some light sleet or snow for the south of England, and dry sunny weather elsewhere. Again I think the FAX chart is probably the best illustration:

http://www.wetterzentrale.de/pics/brack2.gif

After that, the setup continues to look reminiscent of the 21st March 2001 and there are serious question marks over how long the cold air will hang on for.

The GFS, although it brings milder air quickly into the southern half of England, looks quite a snowy run for southern Scotland and northern England as the fronts are projected to become slow-moving on Friday/Saturday with temperatures close to freezing over those areas. During next Sunday and Monday (a long way off of course!) the GFS shows the fronts buckling back southwards again with brighter weather and snow showers following into the northern half of Britain with maxima close to freezing.

The GFS is essentially the halfway house solution tonight because the ECMWF run would push the milder air up as far as northern Scotland by Saturday whereas the UKMO, with its "slider" to the south, would most likely see the frontal boundary kept further south, therefore with increased chance of snowfalls in the southern half of Britain with brighter conditions further north and snow showers for the north-east.

[bluearmy]

the 00z ecm op failed to make much progress ne with the first frontal band. the 12z makes it hundreds of miles further north. that pretty well sums it up. whereas this morning we appeared to be trending to a cross model consensus on the back end of the week, the 12z's drift us apart. i thought we may have an answer from tonights 00z runs. i rather doubt that now.

[mushymanrob]

The ECM seems to have been out for a night on the tiles and has found itself waking up in bed with the GFS.

Something it will surely regret in the morning

on the other hand the ukmo might be wrong and the ecm/gfs might be right.lol

[Purga]

on the other hand the ukmo might be wrong and the ecm/gfs might be right.lol

Impossible - why? Because UKMO is the colder solution of course!

[legritter]

A bit of a setback tonight especially for more southern posters but ,a week is a long time in meteorology and tomorrow morning charts could very easily flip back .reading todays MET office outlook i do have my doubt on the atlantic low so perhaps over the coming days it will get modelled further south .as always if you take many charts at 168hrs there is a big swing from one run to the next ,and many a time you could easily see a difference of 20mb or sometimes more .tonights late Fax charts will give us more clues as it will show expected synoptic situation for mid day friday .what ever this weeks outcome ,expect some interesting weather as the Boundary between two very different air masses will be close to our shores or Right on top of us .any new posters or beginners please pop into NET WEATHER learning area as this is a good source of learning ,and remember we have another good season coming if the cold wintry weather moves away , spring storms and summer heat with hopefully some good Spanish plumes .its never boring here on Net Weather and always someone there to help .cheers

[-uksnow-]

Clearly a fair number of options from the ECM ens tonight

120 mean:

144 mean:

168 mean:

The synoptics on the mean even at only 120hrs away become quite 'muted'.

[-uksnow-]

Yep - EPS members at 168 have everything but the kitchen sink thrown in

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2013021412!!/

[johnholmes]

In the difficult pattern for the models to try and give detail I believe most of you will benefit from not trying to put ANY detail on any run at anything beyond about T+48-72 at the moment. For this time in March it is a fairly rare looking set up so little wonder the models are struggling going from a cold option to a mild one or vice verca.

Even the anomaly charts are not at all straight forward. A fairly westerly flow over the past couple of days (I've been away for the previous 5 days so not seen anything in that period) and the 00z output from ECMWF-GFS was still not out prior to leaving this morning.

It looks a pattern of fairly cold unsettled westerlies at 500mb with the possibility of both northward extension of milder Atlantic air and colder air from somewhere north of 55N to the west of the UK.

Certainly not much sign away from the far SW of any real mild air and about a 60% risk of a fairly notable snowfall from about the Peak north to the Southern Uplands before this weekend, with a smaller risk for hills south of this. Just how far north this band gets is for the models at probably T+24 to give better guidance. How low the snow gets is another largely unknown factor.

Good model watching and however much some castigate UK Met I suspect watching their changing Fax charts will be as good a guide as any along with their text forecasts on the web. Some will disagree I know but I would suggest to new folk this may well be the best guide (as it of course should be) to this very interesting complex and difficult forecast spell this week, let alone further ahead?

also copied into the other thread

added 2057

NOAA 8-14 outlook and see other thread for comment on what may be a significant feature

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

Edited March 17, 2013 by johnholmes

[damianslaw]

Its not surprise to see the three main models showing subtle differences in the position of the low pressure projected to influence the country by Friday. There is alot of time to go between now and Friday.

I think back to the 18th January when most models were projecting the snowy frontal attack to make sufficient inroads into northern england even at the short 24 hour timeframe, but they had to make a major backtrack when it became apparent the front was going to struggle against the block to the NE. Heights to the NE have a habit of catching the models out, often they underestimate their strength particularly in the latter part of winter and during spring- for this reason, I won't be surprised to see the ECM shift everything on a more southerly course again.

Longer term - GFS still painting a very cold pattern especially for the north, notable as it is the one model which tends to be very progressive at the first sign of any atlantic onslaught. The jet shows not sign of tracking north anytime soon.

One strong possibility for the end of next week - is a very slow disruption of the trough and possible shortwave energy being ejected SE off the main core of central heights - a very messy set up would be the result with two areas of low heights over the south of the country and a bitter NE/E feed to the north of the frontal boundary.

[shotski]

Yep - EPS members at 168 have everything but the kitchen sink thrown in

http://www.ecmwf.int...t!2013021412!!/

The only problem is, looking at that spread at t-168 only 4 or 5 members show some form of

undercutting for the uk.

[Snowman.]

thats just what march has been , so cold and gloomy ,that one cant even go for a walk without a winter coat , I for one want a to feel a warm breeze and see a few convective spring setups soon and then a proper summer come may/june

I enjoyed 2 ft snow drifts.

At least I got something that didn't rhyme pain.

[-uksnow-]

The only problem is, looking at that spread at t-168 only 4 or 5 members show some form of

undercutting for the uk.

Thats funny - because i count 27.

[bluearmy]

The ecm ens have been trending away from a decent slow breakdown for a few runs now. Fewer and fewer runs prolong the cold. The spread on a renewed easterly still showing but more muted on the latest run.

[shotski]

Thats funny - because i count 27.

God I hope your right, but I can only see 4 or 5 scenarios that would produce a true undercut.

Edited March 17, 2013 by shotski

[SP1986]

Looking at it, I can only really foresee a southeasterly 'undercutting' taking place, this may well serve to prolong the cold conditions, perhaps into April. I'm not sure I buy the 'round low' scenario that would push milder air in more quickly.. time will tell though.

[Summer Sun]

Anyone got the ECM ensembles through yet? Still stuck on today's here

[shotski]

Anyone got the ECM ensembles through yet? Still stuck on today's here

Yeh, they show the 12z operational to be a MASSIVE mild outlier but I'm not going to show you it

[-uksnow-]

The fax says yes to channel low part 2

updated 120hr fax

Sticks with raw output!

[Summer Sun]

Yeh, they show the 12z operational to be a MASSIVE mild outlier but I'm not going to show you it

Thought it would be too good to be true lol

[Bradowl]

Yeh, they show the 12z operational to be a MASSIVE mild outlier but I'm not going to show you it

Who'd have thought that it would be showing temps of 21c+ in 10 days time.

[SMU]

Suddenly at 78 the GFS starts going for the undercut- backtracking towards the UKMO-

lets see how far North the 0c isotherm gets this time....

S

[-uksnow-]

Suddenly at 78 the GFS starts going for the undercut- backtracking towards the UKMO-

lets see how far North the 0c isotherm gets this time....

S

Unfortuantely..even further north

[Argyle1980]

The fax says yes to channel low part 2

updated 120hr fax

Sticks with raw output!

think its to late in the year for us people of the far south west..... We need some cold from some where, help!

[bluearmy]

The faxes were quite early tonight. Rushed? Perhaps - the T 96 has the thickness lines omitted!

[mushymanrob]

i see the latest fax supports the notion i presented earlier that the uppers just are not low enough for a frontal snowfall of any significance away from high ground at least. i cant see it, although i take on board what those with superior knowlege are saying.