Short range model discussion - into 2018

[The Enforcer]

46 minutes ago, knocker said:

I've been trying to find a forecast sounding to illustrate the possibility of freezing rain later in the week to no avail. Got close with this but it requires a bigger 'nose' of warmer air to be above 0C,

Good - having experienced the 23/24 January 1996 example, that was quite enough.

[icedust]

17 hours ago, johnholmes said:

Current 12z Fax for Wed shows most of the UK within the 510 DM line. Not often seen even in mid winter let alone 2 days before official spring. No worries about what falls from the skies with that upper air.

Hi John, I remember you from my days in the Met Office. at Manchester (Andy Day). Just discovered this site. You are of course correct. 510dm lines are rare these days (Jan 1996 was a good one here in Macclesfield and 1991 (over 20cm)).

Looking at the excellent graphics on weatheronline I see the phenomenal low temperatures at 500mb due for tomorrow. -46!!. and a sub 504 cold pool for Scotland. That has to mean  thunder snow and horrendous conditions for some places, with the eastern side right up the UK getting really bad in many places.

 

[johnholmes]

Well well a voice from the past will pm you.

Yes as you say unusually cold upper air for any month let alone almost into official spring.

The overall pattern seems to me to give the present deep cold into Friday then becoming less marked, see my post (not yet done in the other thread), some areas east, central and southern, even parts of the south west, may well get several inches of snow before the less cold air pushes in.

Not quite the Siberian climate that the models have at times suggested but still pretty notable for late February into early March.

As is usually the case the Exeter Fax chart are going to be the best guides in my view. By all means if any of the other outputs looks similar then fine to use them. For snow watch, the radar should give good guidance, drop the 700mb upper flow on to give an idea of their track. If you understand Skew-T diagrams they are well worth looking at on Extra (if you have it), worth investing if you are a storm or snow fan for the year!

Enjoy for the snow fans and chin up for those wanting warmer weather!

Edited February 27, 2018 by johnholmes

[knocker]

Not close detail but relevant stuff quite clearly defined on this Sat image for 1015 (Dundee Satellite Receiving Station)

Edited February 27, 2018 by knocker

[knocker]

Just to illustrate the continuing uncertainty at the end of the week compare a couple of charts from successive gfs runs for same time on Friday and as John says best wait for Fax updates

[phil nw.]

Looking at the NWxtra short range model and tomorrow does indeed look the coldest day of this spell.

These are for tomorrow 18z

javascript:

Serious windchill in an increasing easterly wind as uppers as low as -17 arrive from the east.This is notable stuff at any time of year let alone going into March.

It may not promise the longevity of famous cold Winter spells gone by but let there be no doubt for a short time anyway this is up there for severity of cold!

[knocker]

And the high res, Modis for 1120 (courtesy Dundee Satellite Receiving Station) shows excellent detail

[johnholmes]

35 minutes ago, phil nw. said:

Looking at the NWxtra short range model and tomorrow does indeed look the coldest day of this spell.

These are for tomorrow 18z

javascript:

Serious windchill in an increasing easterly wind as uppers as low as -17 arrive from the east.This is notable stuff at any time of year let alone going into March.

It may not promise the longevity of famous cold Winter spells gone by but let there be no doubt for a short time anyway this is up there for severity of cold!

Yes phil, I have a shocking memory these days but I honestly cannot remember ever seeing -16C being predicted over Doncaster. It does make we wonder if similar charts had been showing 2 months ago just what the effect across the country would have been. There seems enough travel disruption already and it is almost the end of official winter with the sun way higher than 2 months ago!

[johnholmes]

39 minutes ago, knocker said:

Just to illustrate the continuing uncertainty at the end of the week compare a couple of charts from successive gfs runs for same time on Friday and as John says best wait for Fax updates

It is an unusual direction for a breakdown of deep cold. They are normally seen to come in from the west. This is almost from the south. So it does probably have warmer air at all levels than from the usual area. However, a similar problem remains for the models. Just how quickly does it shift the deep cold air at all levels. As you have illustrated with those charts it is struggling to get a correct fix on the timing.

 

[knocker]

The 1310 high res. MODIS again smashing detail of the wave and convergence further west and south in the Channel

 

Edited February 27, 2018 by knocker

[Biggin]

24 minutes ago, knocker said:

The 1310 high res. MODIS again smashing detail of the wave and convergence further west and south in the Channel

 

That little front near er Swedish lion front feet. Developing or fading ?

[knocker]

2 minutes ago, Biggin said:

That little front near er Swedish lion front feet. Developing or fading ?

It's just a trough and will probably disappear.

[Blessed Weather]

There's lots of focus on the end of the week so I thought I'd take a closer look at what today's ECMWF 0z run is forecasting. It will be interesting to compare this with tonight's 12z for any changes to how this model sees the incoming Low progressing against the very cold air over the UK. Precipitation type is only given as snow or rain, so no clues here regarding the possibility of freezing rain.

I'll start at 06.00 on Thur 1st March when the first precipitation arrives on the south coast. It's all snow with 850hPa temp around -8C and 2m temps comfortably below 0C.

Moving on 6 hours to 12.00 Thurs and it's snowing south of the M4. The 0C 850hPa isotherm still down over France and 2m temps remaining sub zero over southern counties.

By 18.00 Thurs the band of precipitation has made no further progress east, but has intensified over the SW corner including S. Wales. The 0C 850hPa isotherm has arrived at the south coast and 2m temps are lifting above zero along coastal fringes. This looks a particularly disruptive time in the SW and Wales, particularly for higher ground, with heavy snow in strong winds.

By midnight Thurs precipitation starting to turn to wet snow, sleet or rain south of the M4 as both the 0C 850hPa isotherm and +0C 2m temps reach that line. Probably this the highest risk period for freezing rain?

Then by 06.00 on Fri 2nd, as the Low stalls with any progress NE and slowly drifts to the NW, signs that colder air is returning south as both 850hPa and 2m temps move back south.

Jumping to 18.00 on Fri and precipitation has largely fizzled out in the SW corner, but an occluded front, slowly moving north, is giving a period of snow in a band across the UK from NI to the SE corner with favourable 850hPa temps (approx -8C on the front edge and -3C back edge) and 2m temps sub zero.

I'll end there. With model output still very much subject to change it's not worth taking the analysis any further. But ECMWF suggesting a very interesting end to the week. What will the 12z runs bring?

Charts from https://www.tameteo.com/modeles/continente+1-europe-ecmwf-87.htm

[Man With Beard]

Will we get the coldest March day in UK records? Minus 4.6C is the previous lowest mark. Looks possible on Thursday:

[knocker]

I was just about to post this before noticing BW's post above so in answer to the last question a quick look at the GFS without anywhere near as much detail and it is still seems revolve around how quickly and how far north will the warm front travel.

Edited February 27, 2018 by knocker

[knocker]

Just to highlight the very unusual at 1200 tomorrow. Very cold air aloft, steep lapse rate and convective heaven

[icedust]

Who cares about Friday -  yet -   when there is all that potential energy you show above to come out before then.  All snow.  Help!

[knocker]

Updated fax charts 1200 Weds-12-12 Thursday Could well be an increase in showers around the south west associated with the trough and slight veering of the low level winds

 

[marksp]

Blessed Weather, what a great post, many thanks for that, easy to follow,

hope ECM comes off

[The Enforcer]

3 hours ago, Blessed Weather said:

What will the 12z runs bring?

Charts from https://www.tameteo.com/modeles/continente+1-europe-ecmwf-87.htm

Fantastic work. If you are able to post a comparison between the 00z and 12z rain/snow charts I would be very grateful.

[knocker]

Nothing significantly different with tonight’s anomalies. Upstream a continuing realignment of the ridge over NE North America and awakening of the vortex over Banks Island and flat westerly flow across the southern states into the Atlantic.

Whilst downstream the main vortex lobe remains over northern Russia with an associated trough orientated south east across the UK into the NE Atlantic. with the aforementioned westerly flow running south of it into Iberia,

All of this results in the UK being in a negligible north westerly drift that portends a slack surface low pressure area over, or very adjacent, to the UK with the weather being unsettled and temps still below average. Although the detail of both of these facets will require some pinning down by the det runs.

Edited February 27, 2018 by knocker

[Biggin]

Thanks guys, good thread. Really interested in next 3-4 days developments.

[knocker]

This sat. image at 2000 shows the concentration of showers in the north and down through East Anglia and the south east and through the Channel

[egret]

5 hours ago, knocker said:

Just to highlight the very unusual at 1200 tomorrow. Very cold air aloft, steep lapse rate and convective heaven

= thunder snow?

[knocker]

Just now, egret said:

= thunder snow?

Well it certainly cannot be ruled out.