[SE and East Anglia generalweather discussion 08/11/2017 onwards]

Was moderate snow here near Heathrow (work) for 45 minutes from around 1pm, about 2 cms accumulated in that time, stopped now.

Video.MOV

Was nothing but rain/sleet at home in Croydon and most the way until Heathrow area on the way to work late morning.

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

Anyone know if it’s snowing around Heathrow? Only I’m headed there for work from home soon, here in south London we had some settling snow earlier, but since 8.30 it’s been sleet/rain turning the dusting we had to slush.

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

3 minutes ago, alexisj9 said:

If they really think it will over lap may be a higher warning should be given for the area. Blizzrds are not something people should be driving in.

I guess it depends how heavy it looks on models, heaviest snow probably NW of London over Midlands and east Wales, but for sure, won't be pleasant 50-60mph gusts driving snowfall even it isn't heavy.

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

1 minute ago, Paul Sherman said:

Lol

Hows your luck, no weather done here then nothing to see - 

Miss out on the Yellow Wind and Yellow Snow and in the Void!

Snow chase round the M25 and up the M40? 

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

12 minutes ago, ReindeerMarmalade said:

Yellow snow warning just updated to include London, Berks etc

 

Overlap of the high winds and snow for my locale in London, could be interesting! Blizzards on the Berkshire Downs and Chilterns too?

[Model output discussion - winter proper underway]

Very quiet in here considering what's on offer from the 18z GFS, guess everyone's either out or in the regionals talking about tomorrow!

Anyway, continued theme where the 12Zs left off with a blocked pattern of high building over Scandi linking with Azores high ridging NE with a cold pool developing over eastern Europe, which would invite a cold continental flow over the UK.

12z EPS control indicated exactly this scenario unfolding on days 10-14.

[Model output discussion - winter proper underway]

19 minutes ago, The Enforcer said:

Do you know the resolution of the ECM?

0.125 or around 9km grid spaces: https://www.ecmwf.int/en/forecasts/documentation-and-support

Looks like UKMO global has now gone from 17km to 10km grid spacing, so should see improvements with this model: https://www.metoffice.gov.uk/research/news/2017/increased-resolution-of-global-forecast-models

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

Good luck everyone tomorrow, in what looks like a risk of snow shifting south to cover more of our area. I'll be at work at Heathrow tomorrow, so be interesting if there is some snow or whether it stays further north.

Anyone noticed the frontal wave feature running along the south early Thursday gets undercut by cold air from NW to bring a snow risk for our area according to GFS:

[Model output discussion - winter proper underway]

30 minutes ago, shaky said:

That still looks brillaint for the midlands as a whole!!much further north compared to the ecm!!

UKMET-G, their global model, is not run to such a high resolution as the ECM as far as I'm aware, so may not verify aswell as EC det. - but we'll find out tomorrow.

Monday's low over France and its precipitation looking at tad further north in track on 18z GFS op, bringing rain, sleet and northern edge snow across SE England on Monday after overnight sleet and snow from Sunday has cleared first thing. Wintry showers returning to northern and western coasts elsewhere on Monday.

Pretty chilly in the week ahead, temps on Monday and into Tuesday indicated by GFS to struggle to get above freezing over the snowfields of central areas

though temps perhaps recovering to average across the far south on Wednesday briefly, as some cloud and rain with mild sector moves through, but colder Pm air returns from NW for Thursday, 18z GFS shows the cold Pm air perhaps undercutting a frontal wave across the south bringing northern edge snow even, though I suspect this may not verify as such, sleet/snow showers in the north and west.

Then a cold northerly Friday and Saturday, further wintry showers for windward coasts.

So-all-in all, a cold week ahead, with further snow chances for some.

[Model output discussion - winter proper underway]

1 hour ago, Joshua said:

Unfortunately, due to a data transmission issue we're currently not receiving the data for the Met-Office global model. We're hoping the data will be available again soon.

It seems they are currently offline. Never mind - they only show 72, 96 and 120 hours ahead as far as I can see.

UKMET-G charts for tomorrow:

ECMWF:

 

[Model Output Discussion - cold spell to end Autumn]

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.

[Model Output Discussion - cold spell to end Autumn]

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.

[Model Output Discussion - cold spell to end Autumn]

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.

[Model Output Discussion - cold spell to end Autumn]

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.

[Model Output Discussion - cold spell to end Autumn]

39 minutes ago, Weather Boy said:

John, for the years on this forum I've been puzzled about the difference between 'surface' And, erm, 'real' high for want of a better word and I still don't know. 

 

Furthermore,  how do you tell the difference from a chart like that? 

 

Assistance gratefully received from a bit so newbie....!

A surface high is usually always present over Greenland, as much of the interior landmass is an ice sheet which creates cold dense air on the surface (resulting in high pressure) while above the surface in the mid-upper levels the airmass is often cold shown by the low heights/ upper low (blues on 500mb charts) - this cold air circulation aloft over Greenland, often part of the tropospheric Polar Vortex, usually drives a strong westerly jet further south over the Atlantic, even if there is a surface high present over Greenland.

However, when there is warm air advection aloft from the south over Greenland, it causes geopotential heights to rise in the mid-upper levels (greens and yellows on 500mb charts), which combined with a surface high, creates a vertically-stacked high or ridge that contains very stable air with descending air aloft so cause blocking, which diverts low pressure systems around it. These blocking highs of course can happen anywhere, so long as there is high pressure at the surface and warm air aloft, Azores high is a semi-permanent version of this.

[Model Output Discussion - cold spell to end Autumn]

1 minute ago, Quicksilver1989 said:

Yup it doesn't quite work out later on with the Atlantic looking like it may wake up again



Though it's all fine margins and it could easily change for the better. I hope that deep low hangs back over NE Canada so we don't have energy spilled into the North Atlantic.

It wouldn't surprise me if we got another northerly reload... they seem to occur every week at some point now 

Yep, problem is with 18z is that the Euro trough to our east doesn't collapse, rather retains cold core over NE Europe which inevitably merges with trop PV low heights edging east form Canada.

[Model Output Discussion - cold spell to end Autumn]

6 minutes ago, norfolksnow said:

Hi well as a senior forcaster, what would be your opinion? instead of commenting on a run!

Thanks Jason

For Sunday I would go for the general consensus of snowline north of the M4 and north of Greater London, where it settles more of gamble, but parts of Wales and Midlands and southern parts of N England esp. The Peaks look to stay all snow. I don't think there will be anymore nudges north in track more likely south if there is anymore changes. As for Monday's low, more difficult as the centre and the precipitation circulating around it may end up missing SE UK altogether!

[Model Output Discussion - cold spell to end Autumn]

8 minutes ago, Quicksilver1989 said:

Good 18z so far, shame about that mild sector on Wednesday but it quickly turns cold again on Thursday, maybe an easier path to Scandi later?



If we get a slack flow developing with an incoming ridge this run could turn very cold.

Been earmarked by the models for a while for some amplification in the H500 flow tail end of next week, with a NLy reload, it's whether or not subsequently the trop PV over NE Canada can hold back and not drift east to flatten the flow out again and allow a block to form over the GIN corridor - which is being highlighted by the 12z runs. Very deep low modeled by 12z and 18z heading towards Davis Strait straight may help reinforce ridging downstream to the east of Greenland.

[Model Output Discussion - cold spell to end Autumn]

GFS edging a little further south with Sunday's low with each subsequent run today.

ECM 00z & 12z fairly similar in track with Sunday's low, though Monday's deep low affecting S England a little further north, while 18z GFS has trended further south with Monday's low compared to 12z. Be interesting to see if GFS trends further south still with Sunday's low on 00z.

 

 

[Model Output Discussion - cold spell to end Autumn]

Extended EPS mean does paint an increasingly mobile / zonal picture out to day 15, as the Euro trough de-amplifies and heights rise toward SW Europe as the trop PV over eastern N America expands east over NW Atlantic. The signal for height rises to the NE rather faint too. As I mentioned earlier this afternoon, the flattening of the +PNA ridge is creating deamplification of the H500 flow downstream and allowing low heights to spread east out of Canada and more jet energy to flow and de-amplify the flow across the N Atlantic.

This from the CPC prognostic discussion today:

Quote

THE 500-HPA FLOW PATTERN DURING THE 8-14 DAY PERIOD IS PREDICTED TO BE SIMILAR  
TO THAT OF THE 6-10 DAY PERIOD, THOUGH WITH CONSIDERABLE DEAMPLIFICATION. THIS  
SIGNALS AT LEAST A TEMPORARY BREAK IN THE HIGHLY AMPLIFIED FLOW PATTERN ACROSS  
NORTH AMERICA, BUT ONLY TIME WILL TELL IF THE HIGHLY AMPLIFIED FLOW PATTERN  
WILL BE RE-ESTABLISHED SHORTLY THEREAFTER. INSPECTION OF THE WEEK-2 SPAGHETTI  
CHARTS CONTINUES TO REVEAL MODERATE TO LARGE SPREAD OVER THE EASTERN PACIFIC  
AND WESTERN CONUS, AND LOW SPREAD OVER THE CENTRAL AND EASTERN CONUS. 

http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html

However, the extend ens means are prone to change and the 12z GEFS mean indicates H500 mean ridging over Norwegian Sea and Svalbard, so there is still chance yet of this height rises to the NE scenario unfolding in the run up to Xmas.

Anyway, lets enjoy the cold and snow prospects on offer the next 4 days and hopefully, in the meantime, the medium-longer term outlook will improve from EC/EPS over next few days.

[Model Output Discussion - cold spell to end Autumn]

41 minutes ago, phil nw. said:

Just looking beyond the next few days and to the medium term there looks to be some readjustment of the pattern going on.

Both suites show a weakening of the Alaskan/W.NA ridging around days 10/12-GEFs a llitle later.This releases the hold on the Canadian vortex which is currently being drawn back by the upstream amplified pattern,We can see the signs of the change upstream on the day 10 patterns.

                                      

More east to west pressure on the Atlantic heights with signs of the northern jet breaking through so this may just explain the uptick in the later temp.graph for London

No suggestions of full on zonal by any means but there may be a period of just below average(temp wise) westerlies rather than the current cold Arctic outbreaks from further north.

 

Afternoon Phil, entirely agree with your analysis.

In the medium range the 00z EC and EPS mean this morning seem to be pointing to a deamplification of the 500mb flow pattern over the NE Pacific with a dampening of the PNA ridge … this leads to a slight relaxation of the eastern N American trough allowing the trop PV cold to shear off NE towards Greenland and far NW Atlantic and flattening the 500mb flow over the Atlantic and the more zonal look to the flow into NW Europe. However, this is quite a marked change from yesterday’s 12z EC, that tended to keep the flow more amplified over the Atlantic which allowed height rises to the N and NE of the UK as the Euro trough begins to fill southwards.

Part of me thinks that the more zonal look from the EC this morning could be the lagged response (10 days) of the current ‘warm’ phases of the MJO working through on the northern hemispheric flow pattern, but a pattern that is inherently very amplified and will take a lot to deamplify. But this could be a temporary transition to a more mobile rather than blocked pattern over the Atlantic around mid-month. ENS, certainly GEFS anyway, less so EPS for now, definitely pointing to height rises to our N and NE after mid-month towards Xmas period - with the trop PV over E Canada and Davis Strait perhaps less likely to favour mid-Atlantic ridging as upper flow energy extends over the N Atlantic towards western Europe but increasingly on a southerly track. Would like to see the EC and EPS come back on board though with this idea. So until they do, would not pin too much hope on the height rises to the NE just yet …

But, thank goodness we are fortunately not chasing cold spells in FI, as we have one unfolding over the next few days, with many areas in for a shout of seeing some snow falling, even if it doesn’t settle. Northern and western Scotland, N. Ireland + Nern Rep. of Ireland, NW England, Wales and Midlands look to be sweet spots for accumulating snow atm, so looking forward to seeing the pictures and reports flooding in here. Friday and Sunday look most prime periods for significant accumulations.

[Model Output Discussion - cold spell to end Autumn]

Wales, Midlands and parts of N England getting a good pasting according to ARPEGE, such a fine line to shift the risk further north or south, which is possible at this range

[Model Output Discussion - cold spell to end Autumn]

The slider further south on 00z EC det. Looking at the 6hr frames on weatherbell snow in a swathe just N of the M4 from South Wales to Thames Estuary and south of a line from southern Cumbria to the Humber also across the N of Rep. of Ireland and N. Ireland. Slider trough weirdly has 3 circulations. Also shows a good 12-18 hours of snowfall for parts of Midlands and N England before it peters out early Monday.

Nasty low following further south into France too like yesterday’s 12z.

[Model Output Discussion - cold spell to end Autumn]

4 minutes ago, Nick L said:

Hi-res models such as UKV and Euro4 have plenty of snow showers piling in through the Midlands overnight on Thursday and into Friday. UKV even has snow showers getting towards London. Could be some decent accumulations through Shropshire and Staffordshire.

Nick Miller after the news showing as such too + GFS showing decent penetration inland of showers on the strong NWly across England on Friday:

Anyway, on another note, London 12z EC ens in and shows the det close to the mean - which itself stays below 5C right through to the 21st - which is good to see.

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

3 minutes ago, lassie23 said:

bbc don't paint a very wintry picture here, 5c by day and rain with southerly winds on sunday with 7c temps

Still too much uncertainty to rule out snow for Sunday, as the low may still track further south then advertised. There is always a chance of snow in the northerly flow as the low clears Monday morning too.