General Model Output Discussion

[weather eater]

Another great run coming out from the GFS, snow potential for many areas of the country. I pretty much agree with TWS, I'm certainly not writing of the easterly and if we get it in a reliable range I will be happy to ramp, even if it doesn't look like delivering in my neck of the woods. But we do need to keep things in perspective, if only because the model thread becomes a dreadful place when major ramps turn to dust.

[PB22]

Good or bad in your opinion?

Those are a couple of cracking charts for cold and snow lovers, but it could be viewed in a number of different ways. It would perhaps suggest though that the Met Office are tending to go with their own model in that the Greenland block may not go anywhere fast as the UKMO run kept the block more stable rather than the ECM and GFS which want to move it further south and east with time. In return, this could mean that the easterly progged by the ECM is not necessarily viewed as a likely outcome for next weekend. Regardless, its a very cold outlook!

[Bristawl Si]

For those wanting a shorter term look at model progged snow for the weekend, Ian Fergusson has just posted in the south west thread a latest NAE chart for Sunday - snow potential for S.E. and central southern england, and just into the West Country.

[J10]

Indeed, the GFS has toned up the warmer air in recent runs (a consequence of the shortwave being placed further west with each run- shortwaves tend to have warm cores) and it seems the other models have done the same. As a result this event is pushing warm side of marginal for many western areas, and temporarily in the south. I also suggest that near east coasts of Scotland and NE England, the precipitation may start off sleety before turning to snow during the afternoon. For the south a rain to snow event is likely.

Which event is this relating to, as it now looks mainly dry over the weekend, over western areas anyway.

[PB22]

Not quite as good from the 18z with regards to the easterly as the upper high is a little further to the SE so the high pressure builds over the UK instead...however as I said before it still is very cold because of the broad evolution...and of course its a much snowier run overall then the 12z, esp for the Midlands region...

So broad evolution not quite as good as the 12z, but still stunning and very cold indeed!

Would give some exceptionally cold nights under that high Darren, and by T+192 there is an easterly across the south again in any case!

http://91.121.94.83/modeles/gfs/run/gfs-0-192.png?18

http://91.121.94.83/modeles/gfs/run/gfs-1-192.png?18

[kold weather]

Mind you by 180hrs it gets to the easterly still, just a much slower evolution...

Upper high looks nice and solid as well at that point, building close to Iceland...the broad evolution looks pretty well nailed on now at least with regards to the broad upper pattern, the models all agree with the broad upper pattern but the surface pressure is something the models are still uncertain about, however the great thing is the very cold set-up does look pretty likely, regardless of the synoptics!

[Altostratus]

A good run from the GFS in the reliable time frame. I wouldn’t worry too much about what happens with the positioning of the high. The details of this will be firmed up over the next few days. Those fax charts look excellent. With the occluded front and embedded troughs circulating around the low, it looks like there is potential for a lot of snow almost countrywide.

[snowking]

Well the 18z actually fairly similar looking to the UKMO Fax this evening (and therefore the 12z UKMO too)

Very much an upgrade in prospects for the midlands along with SW england and S wales as precipitation looks to feed in bands through these areas from the NE of england....

Not quite a snowy as the 12z ECMWF further SE, though obviously areas favoured in the SE from a NEly flow still look good

I should imagine these runs would leave our central and western members a little happier and more hopeful whilst maybe leaving SEern members a little less impressed

Either way though cracking synoptics!

SK

[Thundery wintry showers]

Which event is this relating to, as it now looks mainly dry over the weekend, over western areas anyway.

GFS precipitation suggests a fair number of showers coming into western parts of England on the southern flank of the system tomorrow, with the chance of some of the precipitation on its northern flank making it across to parts of the west for a time.

[kold weather]

The evolution in FI no-where near as cold as the 12z GFS becuase the high drags in slightly less cold air from around the upper high rather then from frozen Europe...however that is rather splitting hairs as it would still be very cold indeed...but the 12z is better for the overall synoptic evolution...

[nick sussex]

Another great run coming out from the GFS, snow potential for many areas of the country. I pretty much agree with TWS, I'm certainly not writing of the easterly and if we get it in a reliable range I will be happy to ramp, even if it doesn't look like delivering in my neck of the woods. But we do need to keep things in perspective, if only because the model thread becomes a dreadful place when major ramps turn to dust.

Agreed the gfs is another very good run with broadly the same pattern, the important thing is the consistency. Regarding the ukmo the fax charts look very good, different from the ecm but still very wintry. People can look at it two ways the ukmo keeps the block stronger and further north there is very little chance of a sinker there, but whether that turns into an easterly is a bit more open to question. It's really not good or bad but just different depending on what you're looking for, of course certain areas would prefer certain synoptics, for me the gfs and ecm would be brilliant the ukmo not as good for me at this elevation but what will be will be, i'm not getting frustrated, hysterical etc theres nothing any of us can do but sit and wait to see how things evolve.

To be honest they all give lots of snow to the Pyrenees and so i'm really quite happy either way.

[J10]

GFS precipitation suggests a fair number of showers coming into western parts of England on the southern flank of the system tomorrow, with the chance of some of the precipitation on its northern flank making it across to parts of the west for a time.

I wouldn't mind a few more showers tonight, but not so much tomorrow as it does turn milder, as it has taken long enough to get some snow on the ground.

Hopefully the band of precipitation associated with the short wave for tomorrow evening, will continue to fragment before it gets here.

Looking longer term for the models, looking very good for a long period of very cold weather, and probably snowy for many as well.

[Gerry]

Thanks Kold.

ECM indicating sub -35c air over us between 120 and 168h or so then.

Here you go Jim -40 uppers at 500hpa covering CET zone on 12z ecm from 120-168 accompanied by 850's of -10 to -14 accompanying precip charts are seriously underplaying the convective potential.

[karyo]

Tonight's T+96 and T+120 FAX charts:

http://www.meteociel.fr/ukmo/fax/fax96s.gif

http://www.meteociel.fr/ukmo/fax/fax120s.gif

Looks more akin to the UKMO output at this stage.

It looks good to me! Plenty of front and trough action affecting a good part of the UK, not just the east!

Karyo

[Snowaddict]

GFS 18Z Control Run follows the ECMWF 12Z Operational Guidance very nicely indeed...

In fact, it's an absolute stunner!

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=0&code=0&mode=1&runpara=0

SA

[PB22]

Here's the ECM 12Z ensembles for London:

http://www.meteogroup.co.uk/uk/home/weather/services/ensemble_forecast.html

Again, the operational run was towards the top end, and the mean is never far from 0C!

[bluearmy]

18z ens mean keeps the high further north than the op run giving a better easterly flow. cold, cold, cold

[keithlucky]

In many years of watching radar activity i have never seen so much activity from the polar region front after front moving south,I dont think i see this in my lifetime again.

[PB22]

Not a bad mean ensemble from the GFS for T+204!

http://91.121.94.83/modeles/gens/run/gens-21-1-204.png?18

[Guest North Sea Snow Convection]

I think the fax charts siding with the UKMO puts (perhaps?) quite a different complexion on the outlook period and the evolution to the easterly suggested by the ECM. It effectively retains the pattern seen since before xmas and sustains a moderately cold pattern rather than leading to a much less marginal very cold one. It also means that, paradoxically northern, north eastern and western areas look more favoured to see snow than south eastern areas - despite all the excitement generated by the ECM.

In terms of the longer term pattern it might also mean that the cold gets 'lifted out' from the south west again - but that is conjecture atm. From an IMBY perspective it is (only potentially atm) disappointing but it does kind of prove the point that one shouldn't get excited by bitterly cold charts showing Siberian easterlies too prematurely.

The reason i say it retains the pattern seen, is that with the trough to the north, if it gets stuck over the UK as it sinks south, it cuts off the cold air advection from the north east that the ECM suggests coming over the top of the northern flank of the low. This trough, as Steve M suggested earlier, needs to clear the south coast to let the very cold air in. The fax suggests that this might not happen subsequently, or at least it will be delayed - and the ramifications of this are (potentially) that the coldest air might take a different trajectory, or simply as before, be kept to out east and north east. As long as the high is kept further north west then the status quo will remain.

Edited January 1, 2010 by North Sea Snow Convection

[kold weather]

It gets there in the end though Tamara, the solution from the UKMO is probably the snowiest for the country as a whole, note its a carbon copy of the UKMO which ends up here:

http://www.wetterzentrale.de/pics/Rukm1441.gif

However it is a synoptic outlier with regards to how it handles the Greenland high, the other big models all topple the high then send it towards Scandinavia.

Still all solutions are bitterly cold!

[johnholmes]

latest lrf ideas for well into January out-link below

http://forum.netweather.tv/topic/47443-lrf-or-attempting-them/page__st__221__gopid__1688646&

[nick sussex]

I think the fax charts siding with the UKMO puts (perhaps?) quite a different complexion on the outlook period and the evolution to the easterly suggested by the ECM. It effectively retains the pattern seen since before xmas and sustains a moderately cold pattern rather than leading to a much less marginal very cold one. It also means that, paradoxically northern, north eastern and western areas look more favoured to see snow than south eastern areas - despite all the excitement generated by the ECM.

In terms of the longer term pattern it might also mean that the cold gets 'lifted out' from the south west again - but that is conjecture atm. From an IMBY perspective it is (only potentially atm) disappointing but it does kind of prove the point that one shouldn't get excited by bitterly cold charts showing Siberian easterlies too prematurely.

Evening Tamara well theres very little support in the GEFS ensembles for the UKMO raw output and i'm very surprised they didn't modify the fax charts towards the ecm operational run, the ukmo raw output isn't bad at all it just looks rather messy and the upstream pattern would still likely edge this south and east with time. Personally i think its wrong from as early as 96hrs and in a straight fight between it and the ecm at that timeframe IMO theres only one winner. I really wouldn't worry about it, i've gone with an easterly a few days back and one operational run from the ukmo is not going to change my mind about this.

[Guest North Sea Snow Convection]

It gets there in the end though Tamara, the solution from the UKMO is probably the snowiest for the country as a whole, note its a carbon copy of the UKMO which ends up here:

http://www.wetterzen...cs/Rukm1441.gif

However it is a synoptic outlier with regards to how it handles the Greenland high, the other big models all topple the high then send it towards Scandinavia.

Still all solutions are bitterly cold!

Are there any 850 temps available for the UKMO beyond t72 anywhere. The trouble with the fax chart and the UKMO to my eye is that it might well have less cold air wrapped up in it. Troughs sitting over the UK, or a sluggish airstream pattern and slow evoution south don't look as cold as the ECM to me. More ppn for the country as a whole (which dont get me wrong is good ) I'm just concerned that the downside is that it is more marginal

Happy to be wrong, hung drawn and quartered though!

Edited January 1, 2010 by North Sea Snow Convection

[bluearmy]

Are there any 850 temps available for the UKMO beyond t72 anywhere. The trouble with the fax chart and the UKMO to my eye is that it might well have less cold air wrapped up in it. Troughs sitting over the UK, or a sluggish airstream pattern and slow evoution south don't look as cold as the ECM to me. More ppn for the country as a whole (which dont get me wrong is good ) I'm just concerned that the downside is that it is more marginal

Happy to be wrong, hung drawn and quartered though!

wouldnt worry too much tamara - thicknesses below 520dam