Model output discussion - Winter has arrived

[NewEra21]

2 hours ago, West is Best said:

You do need cold uppers for snow. What was 'produced' yesterday was mostly rain and sleet, especially at low levels. Many of us on here remember the days when snow would fall consistently out of the sky and pile up sufficient snow to wade through and sledge in, even in early December. That's snowfall and you roughly require -5C 850hpA for it to occur in the UK at low altitudes. 

The majority of Essex, Suffolk and Norfolk had falling and settling snow yesterday. Even near to the coasts. And EA is as low level as you can get, and that's with the still relatively warm North Sea SSTs. 

So yes it is favourable to have -5 and much, much colder 850s for the nice dry powdery snow etc that we all crave. But yesterday just showed that snow is still very possible in the most marginal of situations.

Edited December 5, 2020 by NewEra21

[Drifter]

1 hour ago, West is Best said:

I was referring to England. Scotland is sufficiently far north for the same rules to be a little less rigid.

Sounds like nonsense - what does Scotland being further north have to do with it?
It has more ‘high ground’ which is why parts of Scotland can get away with higher 850’s. 

[SMU]

1 hour ago, swfc said:

Indeed Steve just lookedanythoughts on it building going forward. Tia

Morn - 

Hum not sure yet - The lack of deep coldnin Europe is being maintained by the Ural block thats acting as a barrier - we need to get some sort of retrogression west & troughing into Scandi for the floodgates to open.

We can suffice with what we have however it will also be marginal air ...

The best run of the day ironically coming from the UKMO that was the worst yesterday. > At 144 its detached High pressure to the North allowing a trough to sink into Scandi whilst still deflecting the atlantic > thats what I would be hoping for.

The GFS / ECM send the jet ( split ) south & a small portion over the top which doesnt allow any troughing to sink south...

[damianslaw]

1 hour ago, snowlessayr said:

you do not need -5 at 850hPa, here just off the west coast of Scotland we got couple of inches yesterday. I haven't had lying snow here since 2018, this was from -2 or -3 upper air temperatures. The vast majority of big snowfalls come from slider scenarios which most don't have -5 upper air temperatures, you just need the flow off the right wind direction. if we always need -5 at 850hPa, then we would get nowhere near as much snow as we receive during winter which granted usually isn't much anyway

Agree with above, correct me if wrong but a number of places below 100m daw some snow at least falling from the sky, areas if N Canbridgeshire for instance,even s coast and a but if cover, reason being simply the intensity of precipitation, heavy stuff lowers the temps, this is the crucial factor.

[Penrith Snow]

To  my eyes the key development this morning has been the models forecasting a slow movement north of the Russian block. This cuts off the supply of warm uppers into Eastern Europe on its Western flank.

This will allow Europe to steadily cool down and if the pattern remains the UK will eventually become very cold.

I remember the February 1986 Easterly started off very disappointing despite great synoptics with a  chilly drizzle from a mild Europe, this was following the introduction of very mild uppers into Europe from a poorly aligned deep low over Biscay, eventually much colder uppers arrived from the East after the formation of a Scandinavia High.

And that was early February rather than early December! 

Andy

[jules216]

7 minutes ago, Penrith Snow said:

To  my eyes the key development this morning has been the models forecasting a slow movement north of the Russian block. This cuts off the supply of warm uppers into Eastern Europe on its Western flank.

This will allow Europe to steadily cool down and if the pattern remains the UK will eventually become very cold.

I remember the February 1986 Easterly started off very disappointing despite great synoptics with a  chilly drizzle from a mild Europe, this was following the introduction of very mild uppers into Europe from a poorly aligned deep low over Biscay, eventually much colder uppers arrived from the East after the formation of a Scandinavia High.

And that was early February rather than early December! 

Andy

Unfortunately this is incorrect according to EPS this morning.It May be a step away from cool Down in central part of Europe after day 10. Most clusters have me still Up to 5C after day 10 with no probability of winds other then SW or S. And that is at altitude od over 650m asl.

[sunnijim]

24 minutes ago, damianslaw said:

Agree with above, correct me if wrong but a number of places below 100m daw some snow at least falling from the sky, areas if N Canbridgeshire for instance,even s coast and a but if cover, reason being simply the intensity of precipitation, heavy stuff lowers the temps, this is the crucial factor.

You are not wrong, amazed and heartened to see significant snowfall at low levels in the Battle area of East Sussex yesterday ( still melting slowly at 2pm)

Higher ground on the Sussex coast near Hastings had  snowfall too.

[Updated_Weather]

26 minutes ago, damianslaw said:

Agree with above, correct me if wrong but a number of places below 100m daw some snow at least falling from the sky, areas if N Canbridgeshire for instance,even s coast and a but if cover, reason being simply the intensity of precipitation, heavy stuff lowers the temps, this is the crucial factor.

I’m 67m in Essex and we had a few CM yesterday.

[Methuselah]

It's a 'developing situation' peeps... It may come to nothing, but at least there are signs of a significant build-up of cold air, away to our NE?

    

Apologies, guys -- I keep being 'redirected' to that sheety Volkswagen site. So cannae post the T850 chart!

[BlueHedgehog074]

Good point by Steve about the UKMO. Yesterday, it was showing this at 144 hours on its 12Z run:

Low Pressure more blown up in the Atlantic. Less of a negative tilt to it. 
 

And today, it’s become a bit more GFS-sy (at least from what some of its runs were showing yesterday) with some notable height rises between Eastern Greenland and Scandinavia. No Low Pressure leaking away North-Eastwards between that Greenland and Scandinavian gap that the 12Z run had above.

UKMO 00Z

Consequently, that Low to our West on this morning’s run is less big, more negatively tilted and more squashed. Looks like if the run went out further it would quite likely slide under the Scandinavian and Russian blocking. Perhaps then drawing in more of an Easterly flow over the UK. Heights a touch less lower over Spain, especially the Northern part, which I think helps too. (But to be fair, Steve did cover some of these aspects above )

The NOAA 8 to 14 day 500mb chart continues to show a stretchy North-West to South-East aligned upper trough the UK and extending East a bit into parts of Central Europe. Blocking over Scandinavia maintained with both an upper ridge and higher than average heights in those parts. Despite the upper flow curving West to South-West through the UK, it is pretty slack. And remaining pretty chilly I would imagine with us likely to stay on the Northern side of the Jetstream still. 

No deep cold likely yet I would have thought, but no mild, full, Atlantic, Westerly onslaught either.

Edited December 5, 2020 by DiagonalRedLine
Re-read post and got both runs mixed up

[jules216]

The clusters at days 8-10 reflect the problem here.Despite blocking the cold pool will be at a premium.Elevation needed.

[blizzard81]

Great runs this morning apart from the gfs op. Ukmo has improved dramatically and the ecm op is heaps better than yesterday mornings run. 

[damianslaw]

As others have said, shifts in UKMO, sliding trough incoming against heights which have advected further west. All eyes currently on those Russian heights, will they stay in situ or begin to extend west.. 

UKMO showing a developing arctic high as well.

I can see an evolution to a much colder outlook more so than a milder one, not often been able to say that in most of our recent winters.

In the meantime colder than average temps for early December for the foreseeable, more cold rain than snow, but distinctly winter weather with frost and fog, maxes held in 3-6 degree range, and remember at this time of year, maxes often only last a small number of hours on the 12pm to 3pm window.

Edited December 5, 2020 by damianslaw

[Griff]

15 minutes ago, damianslaw said:

As others have said, shifts in UKMO, sliding trough incoming against heights which have advected further west. All eyes currently on those Russian heights, will they stay in situ or begin to extend west.. 

UKMO showing a developing arctic high as well.

I can see an evolution to a much colder outlook more so than a milder one, not often been able to say that in most of our recent winters.

 

Just catching up on a lot of excellent posts here after a manic few days at work... 

It seems the mood has improved along with the outlook since midweek. 

After a few discouraging runs against the overall pattern, nice to see some cause for optimism this morning. The online chatter amongst the 'professionals' suggest -nao rather than the usual Atlantic mild wet. 

FYI it seems to be we're stuck in a loop every couple of days about the importance of cold 850s.... Probably less frustrating than the usual GFS bashing for being a terrible model. Makes a nice change. Seemingly the bias for SSW has gone after the last upgrade... Does that mean the current modelling might be more accurate? Definitely something to watch out for from mid December! 

Edited December 5, 2020 by Griff

[claret047]

3 hours ago, West is Best said:

You do need cold uppers for snow. What was 'produced' yesterday was mostly rain and sleet, especially at low levels. Many of us on here remember the days when snow would fall consistently out of the sky and pile up sufficient snow to wade through and sledge in, even in early December. That's snowfall and you roughly require -5C 850hpA for it to occur in the UK at low altitudes. 

Here in parts of Essex we had quite a bit of snow which settled in the early hours.

Next week does not look great apart from high ground for snow and even then it will be in fairly short supply as we seem to be apart from the periphery of the country between areas of low pressure, with fog under lighter winds, especially in the south being a problem and with it being slow to clear suppressing temperatures. Faux cold as some on here gleefully call it. Temperatures will generally remain below average with some night time frosts and with a tendency for the weather to become more unsettled later in the week. Beyond that, although I am far from an expert I do believe it will all be very much on a knife edge and by mid month the colder air will start to make inroads across the North Sea.

Kind Regards

Dave

[jules216]

Nice Scandi High on Icon6z.How badly we need some trigger low around east of Ukraine.We would be close to a great cold spell.

[Bristawl Si]

The Russian High doing its Winter Worst, as the trough just sits right here at mo, giving cold rain. A sign of things to come this Winter for the UK? Oh, for a December 2015 right now.

 

[Tim Bland]

GEM is the pick of the bunch for me this morning. It throws up an Atlantic ridge at day 9 and the cold starts to build to our north east ready to pounce...

[johnholmes]

Sat 5 December from the 500 mb perspective?

Ec-gfs and both show a ridge from n’ern Europe/Russia west into Greenland, something they have not been too consistent with; a small but deepish low just w of this which is the n’ern end of the main trough extending into eastern n America, another trough then over Alaska with a ridge far east of Russia. Beneath the main ridge a large area of _ve heights and troughing, stretching from well w in the atlantic over the uk and into Europe and the med. The flow is very slack in the uk area.

Noaa is not dissimilar with the only area showing significant +ve heights is associated with a similar ridging from n Europe/Russia west into Greenland/pole and almost linking with small +ve’s into the far eastern Russian ridge. Troughing from the main ne Canada trough  into the uk and Europe with most –ve heights shown almost into w Ireland. Contour heights are about what to expect this time of year over the uk (N-S).

So what about the weather to expect?

Well the often mentioned Scandinavian/Russian high is, in my view, in its current position, doing the cold lovers no favours. So for the 6-10 day outlook. Too far away and the flow into the UK is s of east, never the best of winter directions for any deep cold. I think the atlantic will make some headway into the country at times, then a pulse of ridging from the main ridge returning us to more settled conditions. In this fog and frost, dependent on cloud cover and mostly dry. During the more unsettled spells fairly windy away from the eastern fringes and with rain at times, possibly fairly heavy. Any snow almost entirely on higher ground and more northern areas. It is possible, no more than that, for some wet snow further south if the bottom few thousand feet cools off enough in a ridge set up. Just what will happen to the main +ve heights and ridging (Scandinavia/Russian) is unclear to me. The 8-14 NOAA keeps the +ve heights and ridging in much the same place but the flow way west is not, at least on the 8-14 chart, suggesting any change to a meridional flow nor to any deep cold advecting west from this ridge. What happens beyond 2 weeks down the line I have little idea, not my area.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.ncep.noaa.gov//favicon.ico Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Edited December 5, 2020 by Polar Maritime

[mountain shadow]

15 minutes ago, jules216 said:

Nice Scandi High on Icon6z.How badly we need some trigger low around east of Ukraine.We would be close to a great cold spell.

If that fledgling Scandi High could cut itself off from the Ural High with Low Pressure bringing Arctic air on its Eastern flank we could get some proper cold into Central Europe to affect West.

[danm]

11 hours ago, damianslaw said:

Last night and today proof once again if needed you don't need very cold uppers to produce snow, indeed most of our snow comes in very marginal situations, fine margins. 

Indeed. One of our best snowfalls in London in the post 2008/09-2012/13 era had uppers of around -1/-2c, 10th December 2017:

[bluearmy]

Some of the sypnotics on show this morning would absolutely be banked for December at first glance by the coldies but a few of the variables not quite right and pattern perhaps a couple hundred miles too far north given the lack of continental cold and high sst’s 

the models seem to be drifting around trying to settle on the way forward ......perhaps by the beginning of the week we will have a better idea. Good to see all the ens dropping euro heights again at the end of their current runs 

there are some potentially v wintry scenarios on the table this side of Xmas and by contrast, not that many mild ones .....of course the middle ground doesn’t cut it for most on here. 

[sheikhy]

Pretty big turnaround on the gfs!!flat as early as 96 hours!you just knew once ecm comes on board and the ukmo the gfs would go the other way!!

[bluearmy]

5 minutes ago, danm said:

Indeed. One of our best snowfalls in London in the post 2008/09-2012/13 era had uppers of around -1/-2c, 10th December 2017:

I’m not sure what WIB is thinking but he’s just wrong. It may well be more correct to say that you generally need to have had -5c uppers in place for a period prior to the snowfall arriving 

[Kentspur]

9 minutes ago, danm said:

Indeed. One of our best snowfalls in London in the post 2008/09-2012/13 era had uppers of around -1/-2c, 10th December 2017:

Very interesting you say this- here on the cusp of SE London and Kent we had rain and sleet mainly with nothing settling I remember seeing the models forecasting the cut off point of the snow line to be the Thames Estuary to my dismay