Model Output Discussion - The final stretch to Christmas

[Gowon]

The good thing about the latest runs is the depth of cold appears to be better to our SE.. better for any undercuts later.

[Polar Maritime]

Some very nice bitter cold Easterly charts continue to show on the 6z, With such volatile out-put of late i hung off posting. Very nice to see this pattern build.. And can i wish all members a Merry Christmas☺â„⛄

[Tim Bland]

RE flight data ; it will only become an issue in here if the easterly is dropped. If it is upgraded tomorrow it probably won't even get a mention

crazy model output in the last 24hrs. I didn't think we would be looking at an easterly before new year this time 2 days ago! Bare in mind tho NWP as a whole is very volatile at the moment and Entropy is high. This is partially being caused by the start warming IMO. My hat goes off to TEITS who foresaw this easterly long before the models did. He has amazed me for years in this forum with his correct "gut instincts" Merry Christmas everyone !

[J10]

https://forum.netweather.tv/topic/81729-the-alps-snow-thread-season-20142015/page-6

 

Another place set to benefit form this cold weather is the Alps, where some very cold and snowy weather is now projected.

 

It does now look as if much colder and snowy weather is set to hit the Alps. If current models are correct 25-50cm possible for many parts of the Alps. This charts shows the projected snowfall for days 4-6.

 

Source. http://www.snow-forecast.com/maps/dynamic/alps?type=snow.next3to6days&&over=none&&symbols=snow

This is the 850HPa  and the Freezing level line for the next week for the Alps.

 

Today and Christmas Day

 

 

Friday and Saturday

 

Sunday and Monday

 

Tuesday and Wednesday

 

Dropping from over 2000m to sea level by next week.

 

Of course things can and will change especially the detail but the pattern of cold and snowy looks quite likely, as we can be at this far out.

 

The next blog will be  on Saturday, and this will compare to see if the current theme for the weekend and next week still holds true.

 

Edited December 24, 2014 by J10

[bluearmy]

The deep fi para could bring us close to the holy grail

Mind you, even at two weeks range we still get a shortwave east of svaalbardi to scupper the chances of the vortex getting too close!

Edited December 24, 2014 by bluearmy

[karlos1983]

The deep fi para could bring us close to the holy grail

 

few hundred miles further south and I'd be happy

[beng]

Another baby step North with the high on both the 06 opp and P run. Just one more little nudge this evening and things get interesting. Seems slightly less energy going North this morning over the high.

Very cold set up (especially, but not exclusively for the SE) with ice days on the P run but essentially fairly dry. Thames estuary might not be a bad place to be for some cheeky lake effect flurries.

More changes to come for better or worse methinks! Good to see a very measured forum this morning, should be a good few days ahead with a bit more interest.

 

Just to add, Southern North Sea Temps are very warm for the time of year, any 850s <-8 should create a contrast that's enough to trigger significant convection; it seems to me that this might actually help lower heights on the southern side of the developing high and help it nudge that bit further north than currently modelled. None of this apart from the lowering of 850s is currently modelled though - so we'll have to wait and see whether they shift as the low level detail firms up.

Edited December 24, 2014 by beng

[John Snow]

Fascinating model watching. With the development of the Scandi High, it then becomes a race to see whether it can become cut off before the Atlantic attacks.

That would be good for the UK as there would probably be one or more battleground events for the UK as the Atlantic tries to force its way through the block, battleground events with stalling fronts tend to produce copious amounts of snow

Edited December 24, 2014 by John Snow

[Man With Beard]

Haven't much time to analyse the charts this morning, but to be frank, without even looking at the precipitation charts if this chart can't produce heavy snow in the south east, considering the time of year, I don't know what will!

www.meteociel.fr/modeles/gfse_cartes.php?&ech=96&mode=0&runpara=1

if it was the height of summer, you'd know without a doubt there'd be a washout in London from that, so surely there's going to be a lot of precipitation around, if it verifies - which is a fair chance considering the timescale?

[SW Saltire]

Fascinating model watching. With the development of the Scandi High, it then becomes a race to see whether it can become cut off before the Atlantic attacks.

If it is cut off the Atlantic will shear underneath and prolong the cold, the energy goes over the top then its a sinker. Won't be another couple of days before that's resolved I think.

With the serious atmospheric pressure on the vortex, I would favour the former over the latter.

Quite agree MS.

I certainly think we shouldn't be looking at the GFS (old)

- the para is yet to be evaluated re possible bias, which every model has -

in order to assess how the energy will be split. It's shown in the past to be horrendously poor in resolving these situations, with energy thrown over the top always being its preference.

If the GFS does show the undercut (more consistently) then that will be very positive news as the signals it must be picking up on are over-riding its predisposition to fire up the Atlantic and exaggerate the westerly energy.

Anyway, this is still a bit out of reach and we'll have to just wait and see.

John Hammond last night on weatherview didn't seem overly keen for much snow from this low so we shall see what happens...

A much more favourable low - check

Cold surface conditions thereafter - check

A pulse of colder 'uppers' from the east (to varying degrees) - check

The undercut and te chance of a proper serious cold spell thereafter - still to be decided.

Been a great few days and long may it continue.

Merry Christmas all

Edited December 24, 2014 by SW Saltire

[Matty M]

P20 or P5 please

 

 

 

[beng]

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=138&code=5&mode=1&carte=1

 

I'll take ensemble 5.  

[Jason M]

Just to add, Southern North Sea Temps are very warm for the time of year, any 850s <-8 should create a contrast that's enough to trigger significant convection; it seems to me that this might actually help lower heights on the southern side of the developing high and help it nudge that bit further north than currently modelled. None of this apart from the lowering of 850s is currently modelled though - so we'll have to wait and see whether they shift as the low level detail firms up.

I was thinking the same tbh, but air pressure is possibly a bit too high for big showers based on the charts this morning (just my opinion though) although I'm sure that will change for better or worse. Looking through the GEFS running out there are big differences as early as day 4. Compared to the charts yesterday morning things have certainly improved :-)

[492]

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

 

Latest 8-10 day 500mb anomaly charts are very similar to yesterdays although the upper high on ECMWF is positioned slightly further NE and the GFS upper low over the central and eastern Med is more of a feature today. So some consistency over two days with a slight improvement if you like a cold outcome.  

Edited December 24, 2014 by 492

[SMU]

Morning All

Just 1 more day & I will be happy to get back in the mix of posting....

Something to note & to watch out for on the 12s is of course a further little nudge north of the scandi high- however more important is the recurving of the jet underneath & its abilty to create enough lift to form shallow shortwaves

These will help distort the flow more easterly & support cold moving towards the uk rather than into central france.

Also the ECM ensembles are the best in a long time with the caveat that its hard to distinguish between surface cold & surface cold with very cold uppers attached

The ECM control doesnt get above -3 max from day 6-16

Anyway - lots of reasons to be cheerful

Ho ho ho

[Summer Sun]

Haven't much time to analyse the charts this morning, but to be frank, without even looking at the precipitation charts if this chart can't produce heavy snow in the south east, considering the time of year, I don't know what will!

www.meteociel.fr/modeles/gfse_cartes.php?&ech=96&mode=0&runpara=1

if it was the height of summer, you'd know without a doubt there'd be a washout in London from that, so surely there's going to be a lot of precipitation around, if it verifies - which is a fair chance considering the timescale?

 

The GFS P snow depth charts don't show much at all for the SE just a dusting at best further north its a different story. Still time for change of course but the beebs forecast last night only suggested 'a bit of snow' for the SE

 

[Neilsouth]

The GFS P snow depth charts don't show much at all for the SE just a dusting at best further north its a different story. Still time for change of course but the beebs forecast last night only suggested 'a bit of snow' for the SE

 

 

 

Atleast it will be festive, I'd take a covering any day if only light. Last winter we didn't get one frost, that was seriously bad

[fergieweather]

The GFS P snow depth charts don't show much at all for the SE just a dusting at best further north its a different story. Still time for change of course but the beebs forecast last night only suggested 'a bit of snow'

Too early to say. UKMO-GM retains strip of shear vorticity stretching into the SE behind departing low centre, which - coupled with adjacent SST - could offer snow showers for a while. But as stated before, it's the possible outcome in the north that's more compelling re snowfall 'proper'.

[nick sussex]

The models continue to develop different ideas regarding the cold pool to the east.

 

The interaction upstream between shortwaves and the PV are important, if the first attempt at bringing in deep cold fails you might still get another opportunity.

 

Heres the GFS for T168, T192 and T216 hours, note the effect of shortwaves upstream with the PV and the troughing to the west of the UK.

 

Remember here we want that troughing to the west to sharpen up as this then is more likely to eject shortwave energy under the block:

 

 

 

 

Note the PV positioning at the start and how the shortwaves interaction alter its position, in this instance we don't get the favourable trough disruption at T240hrs but bear in mind at this range the amplitude of those shortwaves and how much phasing occurs between north/south jets is liable to change.

Edited December 24, 2014 by nick sussex

[marksiwnc]

Too early to say. UKMO-GM retains strip of shear vorticity stretching into the SE behind departing low centre, which - coupled with adjacent SST - could offer snow showers for a while. But as stated before, it's the possible outcome in the north that's more compelling re snowfall 'proper'.

With regards to the north which areas are likely to see some showers you mean north to north easterly facing coasts and hills??

[stewfox]

RE flight data ; it will only become an issue in here if the easterly is dropped. If it is upgraded tomorrow it probably won't even get a mention

crazy model output in the last 24hrs. I didn't think we would be looking at an easterly before new year this time 2 days ago! Bare in mind tho NWP as a whole is very volatile at the moment and Entropy is high. This is partially being caused by the start warming IMO. My hat goes off to TEITS who foresaw this easterly long before the models did. He has amazed me for years in this forum with his correct "gut instincts" Merry Christmas everyone !

 

 

I do apologies I check with a friend who works at Heathrow who said global flights could be effected by no more then 3/4% on xmas day but some flight routes New York to London etc as much as 30% reduction and some European routes 25/30% reduction as well. So yes you assume it could be a issue re model accuracy particular in tracking a low.

 

Although he said there is increase flight traffic flow 22/23 dec on routes mentioned above which would suggest better model data ? So if they haven’t got as clue now that doesn’t bode well

 

Will make sure I get my fact right next time.

 

~

Edited December 24, 2014 by stewfox

[snowking]

Also the ECM ensembles are the best in a long time with the caveat that its hard to distinguish between surface cold & surface cold with very cold uppers attached

The ECM control doesnt get above -3 max from day 6-16

Anyway - lots of reasons to be cheerful

Ho ho ho

 

As BA posted earlier, I can confirm the Control at least is very much surface cold, with 850's anomalously high from days 10-15.

 

The latter timeframes of the control though play out similarly to the GFS(P) with heights retrogressing and a strong tendency for the Atlantic cyclogenesis to dive SE in to Iberia, whilst ECM EPS mean keener to retain the heights to our ENE instead.

 

SK

[bluearmy]

Steve - the control is surface cold for de bilt, not uppers cold.

I do wonder if we are guilty of rushing a bit on this. need to see some agreement on the Atlantic negatively tilted enough to lift the ridge a bit further north within a T144 timeframe across all the models. That will be stage 1. plenty of pitfalls beyond that. pretty safe to call cold next week but more likely dry than any snowfall. that looks the current long shot but each week 2 run does raise the potential for an approach from the Atlantic getting close enough. at least something to watch over the holidays.

[IDO]

Looking at the GEFS at D9 33%(7) cluster represented by: 

 

About 30% (6) are represented by:   ...best case.

 

The control is an example of the rest, messy that could go either way but the HP appears to slide away: 

 

Still a 40% chance of snow on Sat-Sun for SE and cold next week as HP moves in: 

 

Uncertainty from D7-8. D10 shows the problem, with the PV lobe to our NE looking to move towards us. The control and P give two possible solutions:

 

 

 

The best and worse case scenarios so maybe something in between. The ECM mean at D10 highlights the battle between the (possible) block and the PV lobe:

 

  

 

The ECM mean temp rising steadily after D10 and with most members having little precipitation it suggest a N/S split, settled in the south and the Atlantic running over the north. Nothing really wintry there. By then other drivers may have taken hold so FI just for interest.  In the next week cold and dry for most with maybe some snow over the weekend.

[Neilsouth]

But isn't it the case with the GFS that during many cold spells it's tried to force a high pressure out the way, way to easily I might add?