Rob K

Re Ian F's talk of Met O thoughts basically turning to rain south of the M4... the raw five-dayers with very latest data (updated 0000 Jan 16) don't seem to back that up, e.g. my area shows no rain symbols at all, just light or heavy snow from Fri evening right through to Saturday. But no doubt will all change several times before D-day!

mm of rain is approx cm of snow...

Cold enough for snow from direct westerlies in Ireland http://www.wetterzentrale.de/pics/Rtavn1202.png The world has gone mad!

NAE is on a different page from the rest of the models. http://expert-images...011718_1518.gif Some head scratching going on at Exeter now I reckon However looking at GFS, that is about as far as mild air gets in before being pushed back... then the main front arrives http://www.wetterzentrale.de/pics/Rmgfs482.gif to http://www.wetterzentrale.de/pics/Rmgfs722.gif

NAE still pushing the 0C isotherm in by T42.... has to be a concern! It might all push back if there is an undercut but already rain into the SW again

To be fair colder air did move in during the event giving it a boost:http://www.wetterzentrale.de/pics/archive/ra/1996/Rrea00219960207.gif

18Z run hasn't come out yet. Should be rolling out shortly...

Question about the UKMO model - is it somehow lower resolution than GFS/ECM? I ask because the UKMO charts always seem to have very "clean", smooth isobars, compared to outher models. E.g. see this link comparing ECM, UKMO and GFS side by side at 144hrs: http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&VAR=model_pslv&CONT=ukuk&MODELL=modens&BASE=-&MODELLTYP=1&VAR=model_pslv&WMO=&ZOOM=0&PANEL=0&ARCHIV=0&HH=144&modeladd=gfs&modeladd=ukmo&modeladd=ecmwf&modeladd=nae&submit=go GFS in particular has shortwaves and troughs all over the place. ECM has little kinks here and there. UKMO just has a big round dartboard!

Kev's pic was a 2m temp ensemble rather than 850s. Only thing I can think is higher resolution vs the ensembles?? BTW a question for anyone who knows - does ECM model run at finer time intervals than the 24hrs we see?

I don't claim to be an expert but yes this from Feb 1996 does have a lot of similarities if you compare to current output! http://www.wetterzen...00119960206.gif

II take your point but the NAE is much more progressive with the mild sector than JMA. NAE has 0C into mid Wales at 48hrs; JMA keeps it out in Ireland

Maybe not as good but not mild by any stretch. 526dam in London, 523dam in Birmingham even as the low rolls in at 144hrs.

Ian how is the NAE regarded? I was given to understand it is a high-res model just for Europe but how does it compare with the "secret" Met Office models?

Of course, Ian, but does the data the Met Office is working with also support a disruptive spell for much of the country on Friday and Saturday, as we are seeing in GFS, GME and raw UKMO output? Edit: sorry just saw your previous post. Thanks.

On GFS the -5C isotherm is actually heading WEST from Wales northwards as the front pivots! Lovely.

Bloody hell that's a blinder! FWIW the 850s are 4C lower over Wales on GME at T+48 than on the NAE. Major major model disagreement.

Chilly maybe but NAE has the 0C isotherm well into wales by T+48! http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/01/15/basis12/ukuk/t850/13011712_1512.gif That is well ahead of even the supposedly progressive GFS 06Z!

Ian you tease...

Looking at the archive charts it looks more marginal back then, with the 0C isotherm into the SW http://www.wetterzentrale.de/pics/archive/ra/1978/Rrea00219780218.gif

Not sure what you mean? The fax chart at 96hr as drawn is about as classic a "SW frontal snow" chart as you could get. If it happens like that of course, which is highly unlikely! Why do you think it isn't? SE winds, an occluded front heading into cold air and the trough disrupting and sliding under the block up the Channel! However that chart has since been replaced by the 84hr chart (look at the forecast time, it is the same), which to my eye is much less favourable - it shows more of a straight-on attack rather than an undercut, although the trough is doing its best to disrupt. Also the cold air makes less inroads west, looking at the 528dam line. Bear in mind that in this set-up, the 528dam line is not too critical.

Just as well then that there are still three days before the front moves in to get the cold in from the east then! Much of central Britain will stay below freezing day and night from tonight until Friday at least, based on current output.

Yes I am surprised GFS performed best - must be an artifact of the time chosen. As I recall, GFS was totally out on its own with not sending the weekend shortwave SE over the UK, and instead wanted to send it NE to Svalbard. It was consistent for several runs in a row before caving in.

The charts for next week are looking very similar to January 1984. Compare: with That month was very snowy in the north, especially Scotland with 2ft of level snow in places, but only 1 day of lying snow in London. Read about it here: http://www.personal.dundee.ac.uk/~taharley/1984_weather.htm

GFS Ensemble mean at 144 looks rather like UKMO too. http://www.meteociel.fr/modeles/gefs_cartes.php?code=21&ech=144&mode=0&carte=0 Undercutting looks the new favourite!

If the block holds firm to the north then the UK is on the northern side of the incoming low, forcing cold easterlies or south easterlies across us. If the lows go over the top of a sinking high, we are in the southern side of the low and get milder westerlies. Undercutting Atlantic lows are as rare as hen's teeth but are responsible for many of the biggest UK blizzards of the past.