Model Output Discussion - 28th November - 4th December

[Duane S.]

We are indeed 'lucky' (not sure if that is the right word though) to have things of interest (cold wise) to look at with the state of things at the moment.

Pretty standard fare looking ahead from the start of the first week of winter. I really do struggle to see how any sustained blocking over Greenland can occur for AT LEAST a month so any WAA that heads up that way following amplification will be welcome but highly likely only very temporary and will, at best, result in a spell of PM airmass for most of us in the form of a toppler. I still favour the PV shifting westwards towards Canada but due to other factors I just can't see this opening up a window for blocking, yet...

Charts not really showing it but I think any hope of a decent cold spell for southerners at least (Northern climes can still get decent and even severe snowfalls with the current synoptics) will be building pressure to the NE. But I still think we will see a Euro high re-forming before any chance of that.

[phil nw.]

Yes, your always going to default back to a flat jet with +ve NAO with sort of set-up. I think as per the winter forecasts any sustaied cold is going to be near on impossible without a big warming event in the stratosphere...plenty of time for that!

I would generally agree with that Kold but the big unknown is how much amplification we continue to see through the next few weeks.

If the jet keeps buckling south and interupts the tendency for Euro. Hts. we could keep getting regular shots of Pm air as modelled for next week.

http://hw.nwstatic.co.uk/gfsimages/gfs.20111202/06/96/hgt300.png

It really depends on the movement of the vortex and where it decideds to spill southwards into mid-latitudes--it doesn`t have to remain tightly locked in a neat circle around the Arctic such as we had for much of 88/89 Winter for example.

The other factor is if,as has been suggested,the core of the vortex tends towards Canada then the possibility of Hts to our North East become a bigger possibility.

[Thundery wintry showers]

The problem with that scenario is that unless the vortex shifts a long way west, and preferably weakens a touch, any pressure rises to the NE are likely to be confined to Scandinavia and thus we'll end up relying on a continued NW-SE tilt to the jet (undercutting the Scandinavian high) if we are to avoid some kind of cloudy damp stalemate. Anyone remember those repeated near-misses during January 2006 when the state of the atmosphere looked rather more favourable than now for a full-on easterly blast? In all honesty I don't see a Scandinavian high becoming a significant feature anyway this side of the 15th December.

[chionomaniac]

Not much comment on the GFS 6Z run. It still shows some great cold barreling into the North Atlantic. I wonder how much SST's will be modified by this. However, on balance, I think that I will call this run the teleconnective run, because generally it follows in line with the teleconnective offerings.

Cold Zonality > milder Zonality > Ridge over south / Eastern areas > ridge extending to Scandi.

[MP-R]

Lots of interesting scenarios still on the table dispite a raging PV +NAO and cool stratosphere! Just goes to show we can moinitor the atmosphere and make educated "Forecasts" But even the experts can be caught out by mother nature!

I Especialy like this option from the GEM this morning http://www.wetterzen...cs/Rgem2041.gif

As you say, a number of things can change even in this set up. I remember this shortwave, similar to the one shown on the GEM for Saturday 10th, brought a surprise snowfall:

http://www.wetterzentrale.de/archive/ra/2004/Rrea00120041219.gif

Other than that, a very active Atlantic for the entire run with high pressure flirting with the south rather than the north. The GFS shows how there isn't much southward movement of lows either so the most likely route for cold is going to be from the north or even more likely northwest, favouring north and western areas should anything wintry arrive.

[kumquat]

Aren't the upstream amplifications that we're starting to see (albeit not particularly large at this stage) potentially partially responsible for what may become the basis for deceleration of the zonal mean - increasing the likelihod of a SSW?

Perhaps we're seeing the initial stages of SSW right now?

[snowmadchrisuk]

Chart of the day so far for me is from the Gem . Not much hope of it coming off given how strong the Vortex currently is , but if the Vortex does tend to setup to the West of Greenland there maybe a chance of a small window allowing a 2 day shot of something from the North.

[legritter]

just spent a while on charts ,i dont usually put my kneck on the line but i think the 144 168 timeframe could be one to watch .im pretty confident that some cold shot is on its way .its been teasing for a while . whilst the stratosphere is a key ,other keys can open the door ,just my outlook , just need pressure too fall by about 10 mb to our far sw ,in the outlook ,cheers

[Guest Kent-Weather]

As tantalizing as the second bite of the cherry on Friday 9th December looks (as included by the 500-1000 thickness)..

We should also note 2 things. Its T+168 which I wouldn't get too excited over, a lot can change.Plus more importantly, we have the infamous wishbone effect in terms of precip.

Edited December 2, 2011 by Kent-Weather

[Jeremy Shockey]

Despite many posters predicting a flat progressive pattern from mid Dec to New Year , the wording of the MetO 16-30 day outlook ( starting 17 Dec ) suggests a bit more of wintery interest for the North , even to low levels during this period.

'' It is also likely that there will be some colder spells, chiefly across northern parts of the UK, with these bringing snow to lower levels here.''

[Zakos]

Interesting that the majority GFS ensembles show the northerly at the end of next week to be a 72 hour event, whereas the GFS operational hints at a ~48 hour event. The southern extent, longevity, and potently of this cold spell are still unknown. At this stage, it seems very likely to occur IMO. it looks likely to be more potent and prolonged than the initial blast, with a countrywide snow risk. This, however, could be downgraded, even with the current upgrade trend. If the northerly is still there on the 18z and 12z GFS, and the ECM backs it up again, with no significant downgrades, I would say its set in stone. Remember the models picked up on the soon to occur pm blast at ~168 hours...

[snowmadchrisuk]

Just to add to my previous post another good chart this morning comes from the No Gaps .. Cannon Model I know but you never know ..

The 528 dam line would cover most of the country if that came about.

[nick sussex]

Interesting that the majority GFS ensembles show the northerly at the end of next week to be a 72 hour event, whereas the GFS operational hints at a ~48 hour event. The southern extent, longevity, and potently of this cold spell are still unknown. At this stage, it seems very likely to occur IMO. it looks likely to be more potent and prolonged than the initial blast, with a countrywide snow risk. This, however, could be downgraded, even with the current upgrade trend. If the northerly is still there on the 18z and 12z GFS, and the ECM backs it up again, with no significant downgrades, I would say its set in stone. Remember the models picked up on the soon to occur pm blast at ~168 hours...

Generally northerlies with mutton dressed as lamb height rises over Greenland last no longer than a maximum 48hrs, and that is doing well, i've seen countless northerlies from the GFS which get watered down to a 36hrs event before the jet pushes the cold into Europe, in this instance the GFS isn't even progging a decent temporary pressure rise over Greenland.

Remember it takes time for polar air to head south, often by the time the real cold reaches the UK the pattern is already pushing the cold into the North Sea. The best after the northerly is a more favourable topple of the high to keep some cold over the UK before the jet flattens that.

I'm not trying to be negative here but what we're seeing isn't even the normal GFS northerly, I fear people maybe getting their hopes up.

But given the dismal state of the stratosphere all this is a bonus anyway so we should just be grateful for that temporary upstream amplification.

[Frosty.]

I'm loving the way the models look for the next week, despite the awful teleconnections and a very cold stratosphere, the models have thrown up a fairly wintry week for the uk, a very wintry week for the far north with a snow shower blitz and frosty nights, even a chance of more persistent snow at times but for most of the uk it will be swinging between cold and less cold but still a good chance of wintry ppn at times even to southern england. the 6z has shortened the cold snap by a few hours later next week but even FI looks mixed with mild and cold interludes.

Edited December 2, 2011 by reef
Stick to the models

[nick sussex]

GFS operational runs have been discounted by NOAA this morning, they're only using a small portion of the GEFS ensemble mean.

Full discussions here:

http://www.hpc.ncep.noaa.gov/preepd/preepd.html

[TEITS]

Have to be honest im not finding the model output to be particularly exciting. Any snowfall looks mainly for higher ground with the exception of Scotland who could see snowfall at lower levels. Rather more concerning is the potential for mid month to become dry across the areas that really need an abundance of rainfall. For my location even a winter with average rainfall may not be enough to prevent a continuation of drought conditions. So any settled, dry spells via HP is most unwelcome for me.

[Frosty.]

GFS operational runs have been discounted by NOAA this morning, they're only using a small portion of the GEFS ensemble mean. Full discussions here: http://www.hpc.ncep.noaa.gov/preepd/preepd.html

Lingering uncertainty.. :smilz38:

Anyway, the first cold snap for northern britain is nailed, anything beyond that is a bonus.

[Robbie Garrett]

Edited December 2, 2011 by Robbie Garrett

[Frosty.]

Lingering uncertainty.. :smilz38: Anyway, the first cold snap for northern britain is nailed, anything beyond that is a bonus.

Latest meto update still sounds wintry for northern uk but not so much for the south sadly.

[Bottesford]

Enough about the drought now - got a wonderful little thread going on about that right here:

Now those models...

[J10]

This is the latest snow blog with the usual Synoptic charts for Europe for the next 7 days.

[Andy_]

-10 850hpa air makes it to Central and North Eastern Scotland on latest GFS run

[nick sussex]

Some very big differences upstream between the UKMO and GFS, if those shortwaves aren't a problem past 144 hrs then the UKMO is miles better in terms of the pattern.

The Canadian trough engages the eastern USA low much further west, this could help build better WAA into Greenland.

If the ECM follows the UKMO and doesn't make a big issue of those weak Atlantic shortwaves then expect some interesting developments!

UKMO 144hrs:

http://www.meteociel...=144&carte=1021

Also NOAA discounted this mornings GFS 00hrs and 06hrs operational runs for being too quick and too far east with the pattern, lets hope they're right!

Edited December 2, 2011 by nick sussex

[Cheshire Freeze]

Some very big differences upstream between the UKMO and GFS, if those shortwaves aren't a problem past 144 hrs then the UKMO is miles better in terms of the pattern.

The Canadian trough engages the eastern USA low much further west, this could help build better WAA into Greenland.

If the ECM follows the UKMO and doesn't make a big issue of those weak Atlantic shortwaves then expect some interesting developments!

UKMO 144hrs:

http://www.meteociel...=144&carte=1021

Also NOAA discounted this mornings GFS 00hrs and 06hrs operational runs for being too quick and too far east with the pattern, lets hope they're right!

Yes Nick, the UKMO is very good run in it's progression. The 168 chart, I think, would have been a very cold looking one.

[Zakos]

Some very big differences upstream between the UKMO and GFS, if those shortwaves aren't a problem past 144 hrs then the UKMO is miles better in terms of the pattern.

The Canadian trough engages the eastern USA low much further west, this could help build better WAA into Greenland.

If the ECM follows the UKMO and doesn't make a big issue of those weak Atlantic shortwaves then expect some interesting developments!

UKMO 144hrs:

http://www.meteociel...=144&carte=1021

Also NOAA discounted this mornings GFS 00hrs and 06hrs operational runs for being too quick and too far east with the pattern, lets hope they're right!

Hi Nick. Briefly, What effect on the UK's weather do you expect is likely to occur if the UKMO is right?