Model Output Discussion - cold spell to end Autumn

[sunnijim]

6 minutes ago, Man With Beard said:

Yes but nothing substantial

Given the whole set up at the moment ( never really likely to produce the goods for the extreme South) and never really expecting snow on the South coast,an 'upgrade to a potential hour long 'back edge blizzard' that doesn't stick is somthing akin to winning the Euromillions after finding enough loose change for one ticket.

I await the 06z to see if it backs the overnight ECM!

[damianslaw]

Sticking to the reliable - next 48 hours, a case of nowcasting, all very messy and unpredictable, where will the slider position itself, where will the low pressure on Monday anchor itself to the south, where will frontal features fall, trough features, shower bands... all too difficult to call.

Looking ahead towards next weekend, all models agree on a generally cold outlook for the time of year under an amplified flow still, a bout of westerlies mid-week, these are not warm westerlies either, they have a cold source, so temps average at best in the north, but something milder in the south, then another northerly feed by the end of the week, not as potent as the one just gone, but enough to bring frost and wintry showers again.

ECM and GFS are hinting on a more pronounced atlantic charge as we enter the last week before christmas, but also signs of heights building to the north east and the azores high looks like it wants to surge NE as well and join hands.. but at this range not worth focusing on too much.

 

[Faronstream]

Still looks pretty mild when we are entering the days  before christmas on GFS, seems to be a new trend

[stratty]

Just now, Faronstream said:

Still looks pretty mild when we are entering the days  before christmas on GFS, seems to be a new trend

.........although I'm hoping this will be the new trend!

 

[Chesil View]

Just now, stratty said:

.........although I'm hoping this will be the new trend!

 

That will definitely be the trend. lol

[bluearmy]

Eps extended build the pos PNA again and begin to drop the Canadian trough into eastern USA. Downstream, the Azores heights into w Europe is the left over gift from the earlier easterly push of the Canadian vortex. Hopefully the clusters will reveal if there are binary routes forward on this as we approach Xmas week. 

[Summer Sun]

Arpege looks the best call for Monday with the rain restricted to the south and SE if any snow does fall it is likely to be very transient

GFS looks a little Isolated again the thoughts of the experts

Edited December 9, 2017 by Summer Sun

[SLEETY]

Rinse and repeat from the models at moment

mild blip mid week then another cold blast again towards next weekend

[Frosty.]

5 minutes ago, SLEETY said:

then another cold blast again towards next weekend

I wouldn't call it another cold blast later next week, nothing like what we have now for example, colder yes but not a blast.

[shaky]

Gfs further north again!!!wow this is crazy!!!meto v gfs now lol!!

[blizzard81]

5 minutes ago, shaky said:

Gfs further north again!!!wow this is crazy!!!meto v gfs now lol!!

Latest meto forecasts on TV agree with the gfs 06z. I am happy with that from a selfish point of view. I have often found the gfs to be very accurate with location of precipitation at short range so I think midlands and southern half of northern England will be the sweet spot tomorrow. 

[bobbydog]

right now in the mid-strat, we are seeing this-

this continues right through to the end of the run (i.e. 2 weeks).

at that point, we then also see this-

i really can't see this stratospheric profile translating into the 'zonal' type winters we have seen in recent years.

the fat lady has a sore throat and is on a diet this year....

 

 

 

(cant seem to remove this extra chart^^)

Edited December 9, 2017 by bobbydog

[Nick F]

31 minutes ago, Summer Sun said:

Arpege looks the best call for Monday with the rain restricted to the south and SE if any snow does fall it is likely to be very transient

I think the rain and snow 00z GFS was showing across S England on Monday is related to an old occlusion left over from Sunday's low(s) moving through bringing the snow across Wales and Midlands - rather than from the deep low moving NE across France. 06z GFS seems to have got rid quickly south in the morning any rain/snow from the occlusion, the precipitation from low over France only clipping Kent really. 

UKMET-G and ECMF do confine precipitation to the far SE of England from the low over France, like ARPEGE, could be cold enough in the northern edge of the precipitation for some snow, most likely North Downs, maybe a bit of wet snow lower down.

UKMET-G:

12z Monday

00z Tuesday

ECMWF

GFS seems to be a lot faster with Monday's low moving through northern France, if it ends up deeper it will be further north, so will bring precipitation and risk of snow on its northern edge further N and NW.

Edited December 9, 2017 by Nick F

[bluearmy]

20 minutes ago, shaky said:

Gfs further north again!!!wow this is crazy!!!meto v gfs now lol!!

Hardly - maybe 20 miles which is a reasonable fluctuation, run to run. S half Norfolk/ n half Suffolk the favoured exit point for the low. I can see this possible drifting a tad further south to s half Suffolk but that about it. the key remains how far north the less cold surface and zero degree isotherm get. Monday is still uncertain as the models are unlikely to have the cycle right on this system yet and how much it deepens will affect how far north it gets - of course it may not develop as currently modelled anyway.  

later in the run we need to be looking for how the Atlantic evolves. I suspect the operationals will get an inkling of direction of travel ahead of the ens on this. Certainly the mean will be skewed to climatology away from mean features such as the North Pacific ridge/Canadian vortex 

[blizzard81]

I wonder why, and this is especially true with the ecm, the 12z op runs are more amplified than the 00z op runs? Just something I have noticed over the years. 

[Nick F]

yes, I think the models should generally settle now on the track of tomorrow's low, maybe 20-40 miles drift north or south, but in the great scheme of things very little, though may make the difference for rain or snow in 20-40 mile zone north of M4 corridor and Greater London. The low enters mid-Wales and exits somewhere over East Anglia .. so general idea of snow north of M4/London and generally south of rough line between Liverpool and Scarborough seems to be a good bet.

[gottolovethisweather]

11 minutes ago, Nick F said:

I think the rain and snow 00z GFS was showing across S England on Monday is related to an old occlusion left over from Sunday's low(s) moving through bringing the snow across Wales and Midlands - rather than from the deep low moving NE across France. 06z GFS seems to have got rid quickly south in the morning any rain/snow from the occlusion, the precipitation from low over France only clipping Kent really. 

UKMET-G and ECMF do confine precipitation to the far SE of England from the low over France, like ARPEGE, could be cold enough in the northern edge of the precipitation for some snow, most likely North Downs, maybe a bit of wet snow lower down.

GFS seems to be a lot faster with Monday's low moving through northern France, if it ends up deeper it will be further north, so will bring precipitation and risk of snow on its northern edge further N and NW.

 

Thanks, @Nick F, I believe you are correct re: the developing low, although as they're very tricky to accurately forecast when coming up from said region, I firmly believe it might pack a last-minute wintry surprise for some. In fact, you suggest just that with your final sentence. Fascinating times ahead and all set to happen within the next 48 hours, lol.

Edited December 9, 2017 by gottolovethisweather

[Nick F]

Yes, enough of analysing tomorrow's and Monday's lows with a fine toothed comb. We will just have to see on the day, nowcasting style, how it pans out in reality for where snow stops.

This morning's model guidance continues to suggests the highly amplified wave patterns over the northern hemisphere relaxing in the medium term, with current 5 wave pattern reducing to a number 4 or 3 wave pattern as the tropospheric PV lobes / vortices retreat polewards over N America and Europe. IMO maybe a response the warmer 5 and 6 phases of the MJO working through on the NH upper flow pattern. But we may still hold on to cold air if we can keep the tropospheric PV at bay to the NW and have some pressure rises nearby to the N and NE as per yesterday's GFS and EC operational runs, though this morning's ops have moved away from this idea ... for now. 00z EPS mean showing the +PNA ridge over western N America / far NE Pacific returning though in the extended period, so this may amplify the flow again downstream.

Plus, as Chino hinted at yesterday, model MJO forecasts now trend with more amplitude away from COD and into phase 7 - which may encourage HLB and colder a patterns in the second half of December and/or into early early Jan - given the lag time.

As we enter a three year solar minimum period and have an easterly QBO on our side (think 09/10 and 10/11 period of winters) certainly plenty to be optimistic about longer term, despite the short-term possibility, after next weekend, of a spell of more mobile, unsettled and less cold weather. Even most of the coldest of winter months in the past don't have have wall-to-wall cold, with milder periods inevitable and so it is likely we will have re-occurring cold snaps or hopefully longer spells of cold given this background state leading into this winter.

[karlos1983]

So by next Friday certainly not Zonal

cold air digging in again and plenty of time for that to improve/extend. Happy days 

[Nick F]

5 minutes ago, karlos1983 said:

So by next Friday certainly not Zonal

cold air digging in again and plenty of time for that to improve/extend. Happy days 

Tail end of next week has been earmarked for a northerly reload for a while, its after the brief Nly that is in question over whether a more mobile/zonal and unsettled westerly regime off the Atlantic transpires or whether the trop PV can hold back to the NW and allow pressure to rise over NW Europe ... certainly 06z edging away from the former i.e. zonal outlook next weekend and early following week.

Edited December 9, 2017 by Nick F

[Polar Maritime]

If your post it missing or goes missing it's because it doesn't belong in here. Please use the regional threads for snow chasing, And the meto thread for musings around weather warnings. Also there is the banter thread for general chit chat. The threads will be busy today so please think before posting in here.

Thanks 

[tight isobar]

8 minutes ago, karlos1983 said:

So by next Friday certainly not Zonal

cold air digging in again and plenty of time for that to improve/extend. Happy days 

6z cold more-or less throughout.

and cant help but notice more snow chances coming into the mix as pop up scenarios.

The partial block stedfast, with an almost iron grip.

850s wavering but overal cold @surface and overheads.

Edited December 9, 2017 by tight isobar

[Ice Day]

So next Saturday and the cold air is still holding on, although it's looking pretty dry (nothing wrong with that!). As Karlos said above, certainly nothing zonal in the reliable

[karlos1983]

4 minutes ago, Nick F said:

Tail end of next week has been earmarked for a northerly reload for a while, its after the brief Nly that is in question over whether a more mobile/zonal and unsettled westerly regime off the Atlantic transpires or whether the trop PV can hold back to the NW and allow pressure to rise over NW Europe ... certainly 06z edging away from the former i.e. zonal outlook next weekend and early following week.

Ah sorry, I’ve found it hard to find anything relating to beyond tomorrow in here for a while 

But even so at D6 things can still change, so I’m thinking as you say, the former looking less likely. More runs needed 

[Ice Day]

Now into FI, but a slack easterly flow setting up for the southern half of the country.  Mind you, the PV is looking the most organised so far this autumn/winter.  Transient only hopefully!