Model Output Discussion - 28th November - 4th December

[kold weather]

Roght well here is another thread for another week. At least in the short term it looks like a pattern change to a cooler and more atlantic dominated pattern is about to occur but are the models over-doing the cooler spell, or are they under-doing it??

Whatever is the eventual outcome, I am hoping that this thread can be a little more civilised than the previous thread which at times really did become a farce. So please do stay on topic and respect other people's viewpoints.

[Nick F]

Looks like the Euro trough which sets-up mid-week in place of the vacating Euro high might be a little more stubborn to move on on this evening's runs - particularly evident on the ECM operational. This is good news in that it keeps the jet on NW-SE tilt, keeping the British Isles under Pm air for longer.

Only really in FI does the trough move on allowing the Azores ridge in, so perhaps not particularly mild as we head through early December, though no noteworthy cold either, but some snow events possible for northern areas perhaps as the colder air interacts with some deep depression tracking east/SE under the strong jet

[davehsug]

I do think that as the Countryfile forecast this evening said there was a great deal of uncertainty as close as Friday, that FI is clearly less than t120. Speculating about charts, especially from the pub run, might be fun, but could be as nothing. It might be that snow lovers will squeeze out the best possible outcome from the current pattern, but then again.....

[damianslaw]

Last post from me this eve - models all now agree we will see an invasion of proper polar air by the end of the week with potential for a particularly potent attack as we head into the following week - interesting to see that the trough may become unstuck over us which indeed would withhold the ridging of heights from the azores - but I suspect it would only be a temporary affair, however, interesting all the same and supports the 500MB forecast of a NW flow between the 4 - 9th Dec.

Won't be until tuesday at the earliest that we will no for certain whether a potent polar attack is on the cards and how quickly any ridge from the azores may develop our way.. and in a very volatile set up as we are about to see, no model will be able to get a real grip on shortwave/secondary low developments - I am expecting some very sudden short term developments in the coming days which could hold a surprise or two in terms of surprise snowfall and perhaps less welcoming severe gales.

[Costa Del Fal]

On the 18z ensembles, (Not quite out on NW yet) show next weeks precip as quite an outlier for next Monday so that low is very unlikely. 850hPa Temps look within the rest of the pack though so any cold air is just as likely as other runs.

[weather_it_will]

From T138 to T168 next Saturday/Sunday on 18Z GFS the wind could be very interesting, along with a marginal risk of sleet/snow at lower levels form Friday.

But it's too far out yet, and could change, and we all know the GFS over develops the lows.

[Liam J]

GFS control run takes the storm at the end of the week on a more southerly course which would bring storm force winds into N & W UK. A few charts from the GEM & ECM even at this stage they are showing agreement for an intense depression to track close to or over the UK at the end of the week.

A lot happening this week and as Damianslaw says expect developments to occur at short notice, it's been quite a while since we had such active pattern take hold.

Edited November 28, 2011 by Liam J

[ukpaul]

850 Ensembles 18z - they look a bit Jackson Pollock-esque to me, up down, here, there, everywhere.

London - http://www.wetterzen..._London_ens.png

Aberdeen - http://www.wetterzen...berdeen_ens.png

Manchester - http://www.wetterzen...chester_ens.png

Edited November 28, 2011 by ukpaul

[summer blizzard]

Well ignoring the potential snow event which is highly unlikely to occur, the model outlook can be summed up as cool from the 30th-7th. Snow above about 500 meters, perhaps lowering at times but no snow for the UK cities.

I like the output.

[BLAST FROM THE PAST]

Good runs and an 'improving picture'. Of note is the potential storminess over next week to ten days....worth keeping eye on.

BFTP

Edited November 28, 2011 by Paul

[Cheshire Freeze]

Having looked through the 18z ensembles from the GEFS, and the individual members, it appears that there is a noteworthy risk of a severe wind event around next Sunday/Monday. It's beyond the reliable but around 4/5 runs produce winds of a similar strength with a similar synoptic set up.

[lorenzo]

Won't be until tuesday at the earliest that we will no for certain whether a potent polar attack is on the cards and how quickly any ridge from the azores may develop our way.. and in a very volatile set up as we are about to see, no model will be able to get a real grip on shortwave/secondary low developments - I am expecting some very sudden short term developments in the coming days which could hold a surprise or two in terms of surprise snowfall and perhaps less welcoming severe gales.

Pretty much this - in full agreement. There has been plenty of ' off the charts action' up here - I would like to add that even with modelling as clever as it is have been suprised by some low level sleet and snow here and there with what you would class as 'tropical' uppers, well maybe not equatorial but certainly no where near the usual.

Rapid Cyclogenesis is my phrase of the week from last week and well on the cards again looking ahead,,,

[Kentish Kiwi]

850 Ensembles 18z - they look a bit Jackson Pollock-esque to me, up down, here, there, everywhere.

London - http://www.wetterzen..._London_ens.png

Aberdeen - http://www.wetterzen...berdeen_ens.png

Manchester - http://www.wetterzen...chester_ens.png

Very typical of a zonal pattern. The mean hovers just below average so could be described as cool zonality, but it's more that average will feel 'cool' compared to the mild weather we have experienced throughout autumn and the expectation of mild/warm that has come to be associated with zonality in recent years.

Crucially not many of the ensembles drop much below -5C in terms of 850 hPa's, which would indicate snow will be mostly limited to higher ground in the north, particularly given the early season and Pm airmass associated with any cold.

Edited November 28, 2011 by Kentish Kiwi

[weather_it_will]

The deep low is still there on the 00Z GFS for next weekend, but any low level snow event looks less likely for the south.

Still a long way to go yet, so it can all change one way or the other.

At least it's looking more like winter on the charts now.

[AWD]

GFS 0z brings in a potent cold spell right across the UK around the 5th/6th/7th December with the -5c uppers down in the channel and the -10c uppers not far away from the north of Scotland! Could be some snowfall around the UK then! But it's still out of the reliable, so caution is needed, especially as the ECM as a greatly toned down version of any polar shot around that time!

In the reliable, and with model agreement, both the GFS and ECM still produce some nasty wind storms across the country, with plenty of rain for all, and plenty of snow for the Scottish ski industry, possibly other northern hills! A cool and disturbed couple of weeks to come!

[Cecil Hogmanay Melchett]

GFS 0z offers potential for some of the white stuff as we go through the weekend which is a real unexpected bonus if it comes off.Trouble is im not so sure ecm offers the same.

Over to the experts!!

[Kentish Kiwi]

The mean hovers just below average so could be described as cool zonality

Crucially not many of the ensembles drop much below -5C in terms of 850 hPa's, which would indicate snow will be mostly limited to higher ground in the north

Probably worth noting I hadn't seen the 18z operational at the time of writing that post. The 00z seems like a possible upgrade on last evenings run and would certainly qualify as cool/cold zonality, also the strength of the NW/Nerly winds is a significant factor in what the temperature will actually feel like.

The cold that moves in at around the +141h mark looks to be rather significant as far as early season topplers go. Strong north-westerlies sourced directly from the pole. Would imagine it could bring snowfall to sea level in Scotland and parts of northern England. Exposed northern high ground will certainly be in the firing line with full-blown blizzard conditions a real possibility.

However before the cold air moves in there is a significant wind event for the NW of the UK, which has upgraded slightly on the 00z GFS, from a pretty potent storm system that moves in from the north-west.

[nick sussex]

In terms of some possible snow later next weekend the GFS certainly looks to have more potential, the ECM shunts the cold away too quickly.

I'd be a bit wary of the GFS projections with cold, it does have a tendency to overdo the southwards extent of this. Taking both outputs together for the moment I'd say the highest risk is for the far north.

Further south I think you'd need some elevation but only if the GFS verifies.

You can have a look here at what the ECM ensembles make of this upto 168hrs:

http://www.ecmwf.int/samples/d/inspect/catalog/samplers/banner/mean_sea_level_pressure_and_temperature_at_850hpa!168!pop!od!enfo!enplot!2009112700!!/

After this the ECM holds enough amplificaton to dig some more troughing se, the GFS flattens out and brings the Azores high in, best output by far is the GEM, good for the UK in terms of colder weather, very good for the European ski resorts, however its hardly a model you'd trust at that range.

I think we will eventually see that Azores high ridge ne towards the UK, the GEM makes the best of it with more amplification upstream and some energy under that ridge over southern Europe.

We'll just have to wait and see but its really a choice of three outcomes, high to the south strong jet to the north, milder conditions, high further north a chance of some inversion cold more especially for the se, the current longshot is something like the GEM the ridge will likely topple over the UK with the jet running ne near Iceland, in that case generally dry and cold for most of the UK.

[Nick F]

Yes, a cold looking Pm flow next Monday from 00z GFS op - with -5C T850s/sub 528dam across much of the UK. GFS tends often to be a bit liberal with its cold shots this far off, so I would expect it to be toned down somewhat, especially if shortwaves are picked up on nearer in time which will prevent the coldest air getting far SE.

It certainly looks like the demise of the Euro high for a while with more in the way of troughing over the continent - which will help bring some welcome snow for the ski resorts - so not as bleak as it was looking a few days back, with the jet tending to keep a NW-SE tilt heading into early December - feeding in the cold Pm air. Though still consistent indications (albeit FI) of the Azores high being displaced eastwards across western Europe later on.

[rich1]

http://www.wetterzen...s/Rtavn3841.png

not a cold chart but the capacity is there.

A bit of fun from GEM too, with a cheeky channel low for the 8th with some evidence of some blocking over Greenland

http://www.wzkarten3...cs/Rgem2401.gif

fairly unlikely maybe but do feel that December, while not really a patch on last year, wont be as mind numbing as November was anyway. The 0z op was a coldish run for next week. Some signs of life I reckon, could be worse. seen some variability between zonal, cool zonal, some inversion cold and one or two colder scenarios popping up from time to time in the last day or two

Edited November 28, 2011 by rich1

[Uncle_Barty]

Looking zonal/cool zonal for the foreseeable with some agreement that it may turn more settled in the South in FI.

Standard early winter fayre and still no sign of any sustained cold, and probably no snow for the vast majority.

[johnholmes]

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz6.html

is the link for day 6 computer accuracy statistics.

None of them doing very well in the last 2-3 days.

Remember the stats are for the northern hemisphere not one specific area and are the stats for 500mb.

[Tim Bland]

GEM is pick of the bunch this morning http://www.wzkarten3.de/pics/Rgem2401.gif My bet though; turning milder next week and continuing with high pressure to our south and occasional PM flows into the far north up until Christmas. Into the new year hopefully a warming of the stratosphere should lead to a neggative NAO and more blocking.

[legritter]

morning all ,as i said on last nights post , its those small details which are missing at the moment that could bring us some fun and games come the weekend and next week , so all to play for ,some interesting stuff POSSIBLE ,but not guaranteed .im still researching past winter charts and old diarys ,will post when i find some realistic info . hoping tonights charts start to sing off same sheet . perhaps we can then get stuck into a good constructive model discussion ,regards .

[shedhead]

Certainly better looking prospects for colder conditions on the overnight runs, especially from GFS, but as others have said it is prone to rather overdoing things in the medium range. ECM is somewhat less bullish about the colder prospects, but an interesting period to come nonetheless, even if not for wintry weather.

Edited November 28, 2011 by shedhead