Model Output Discussion - The Start Of Winter

[knocker]

Tonight's anomalies.

 

NOAA has the trough north of the UK aligned south, slack area of low pressure Pole to low in the pacific. Some amplification of the HP north America. The Azores HP lying west/east south of the low pressure area.

 

The ECM has the trough and Azores similar But has a trough Siberia and a ridge mid Pacific. The GEFS not having much to do  with the ridge and generally keeps the Pacific low, Also tending to push the Azores HP a bit further north. Both have the HP north east Europe. So the main area of difference is Siberia and the Pacific

 

In the extended time frame not a huge difference  but perhaps a slackening of the weak trough over the UK.

 

The upshot regarding the surface analysis. is not much change with low pressure to the north and north east and HP to the SW. Temps generally below average but a tad variable with  passage of active systems.

 

Charts courtesy weatherbell.

Edited December 4, 2014 by knocker

[shaky]

More amplified 18z!! Better and stronger heights across the atlantic into western greenland! !

[Cloud 10]

Look at this 12z GEFS member!

 

 

900mb...

 

The 18z op run looks fairly benign compared to that..

 

[Northern Sky]

thanks but what is the term expected evacuation of low heights mean, not being awkward I just do not understand that phrase?

Surely it just means he expects the low pressure to move - evacuation removal, clearance, shifting, expulsion, eviction

[Polar Maritime]

A few post have been deleted, Being one liners and adding nothing to discussion, Please stay on topic.

 

Thanks, PM

Edited December 4, 2014 by Polar Maritime

[Snowy L]

Not too much difference between the 12z and 18z, one thing is that in the 7+ day range the vortex area over Greenland looks smaller compared to the 12z.

[Gibby]

If it's cold your after the 18z operational is as boring as it can get as far as I'm concerned as there seems nothing to even raise an eyebrow at if its cold your after. The progressive Westerly bias continues with nothing more than fleeting glances of a cold feeling day between milder and cloudy weather with some rain at other times. I put my own odds of a 10/1 chance against a white Chrismas using the GFS 18z data tonight.

[knocker]

The situation at T132 GFS 18z and the evolution

 

Charts courtesy weatherbell

Edited December 4, 2014 by knocker

[Smiler1709]

It's lucky christmas is three weeks away and the models don't have a clue what's going on in 5 days let alone 2 or 3 weeks, the gfs 6z will look nothing like the 18z come the morning then it will change again by that evening. We still won't have an accurate forecast for Xmas on the 20th so I'm gonna take any predictions or guesses tonight with a huge pinch of salt when regarding a white or green christmas.

In the mean time, wintry weather to the north west, cold and possible frost elsewhere. That's already a huge improvement on last winter.

[Mucka]

GFS still not smelling the coffee and ensembles look pretty flat too.

Day 10 ECM not far off its ensemble mean with trough to the E/NE and maintaining a generally NW flow while GFS has the Azores high ridging across the UK and a W/SW flow. The ensembles are differing in much the same way overall. Quite different actually and GFS would have temps above average while ECM below. GFS has actually thrown out a few horror shows of late so it was nice to see the ensembles look like they were moving more toward ECM this morning but that trend hasn't continued. Let's see what tomorrow brings.

[Tamara]

A lot written about the MJO in the last day or so (can't think why though    )....

 

Its obviously not the be all and end all of course in terms of how the hemispheric jiigsaw comes together, but as it is one element that has been raised in well laid out detail amongst the authors themselves as pertinent to upstream patterns in the remainder of December then it shouldn't be a surprise to see it discussed on here  - as it does play one important role, within the current evolving pattern, at this time

 

The atlantic sector amplification tease is playing out by very very slowly for adjusting future amplification prospects upwards in the modelling. ECM forecasts in this respect maybe being too cautious of progression eastwards through the Pacific and a little nod at least towards the more bullish GEFS.

 

Greater and longer emphasis now on Phase 7 towards 8 and the 'circle of death' further postponed. This keeps up the interest from after mid month for extra pain to be dealt out to the polar vortex and make progression towards an SSW.

 

Away from tropical convective forcings and trapped Equatorial Rossby wave trains - there is something of a pincer movement set to happen on the vortex (and thus restriction on eastward energy transport across the pole) as the Greenland/Canadian vortex sector eases backwards a little along with the Aleutian Low adjusting back home from its Alaska vacation and thus turning the EPO back positive. Bit more re-cycling going on there...Oct > Nov > and now again in December

 

The net effect upsteam > downstream is once more a southward displacement of the jet stream and tilt NW/SE, as advertised in the models. It isn't a surprise therefore to see the regenerated gradient infused modelling within the 10 day period as cold and winter returns stateside

 

On the Siberian side of the pole, we look to see usual service resumed as the annoyingly displaced Asian Low is dissipated and the Siberian High starts to re-assert once more. Cue return to SIA wave activity feedback watch soon enough I would think ....courtesy of the stratosphere thread.

 

With the Siberian squeeze from the NE re-asserted and the upstream Pacific pattern adjusting then it makes sense that, accordingly, we see AO profiles staring at future descent from the + spike. Models have been re-adjusting overtstaed predicted flatness of the pattern in the last day or so and therefore too much angst over the Azores High as a spoiler is misplaced.

 

As suggested in my update summary post the other day, the recent pause in wave activity and less temporarily favourable Siberian and upsteam Pacific pattern has only cost us the possibility of a fast(er) track to an earlier winter SSW during December. This 'low risk probability' was based on the massively accelerated October snow cover and the swiftly imprinted Siberian -AO  feedbacks as a consequence - but no-one at all would have been able to foresee such temporary hitches and delays

 

Such is the life of those who try to read between the lines with longer term pattern predictions    

 

So, back to the safety and assurity of T0...Today has been just a degree or so above freezing here - a massive drop from daily mid teen digits seen so often right through late autumn and up till this time. With the upcoming pattern set to deliver a chilly mobile unsettled phase, with the 'S' word nicely coming into the forecasts for some northern parts, there is very little discernibly tropically maritime based in the fortcoming outlook. Little to complain about especially within the context of much else to consider as we head towards the close of the year and into the next one.

 

Ciao - bueno notte

 

 

[knocker]

My query regarding negative tilting trough was answered, many thanks, but this may add a little meteorological meat to the bone.

 

In forecast discussions you will come across the terms positive, neutrally and negatively tilted trough. When a trough is positive or neutrally tilted it is usually not referenced at such. However, when it becomes negatively tilted it will be referenced as such. The tilt of a trough is the angle the trough axis makes with lines of longitude. A negatively tilted trough tilts horizontally (parallel to surface) from the northwest to the southeast. What is the big deal about having a negative tilt?

(1) indicates a low pressure has reached maturity,
(2) indicates strong differential advection (middle and upper level cool air advecting over low level warm air advection). This increases thermodynamic instability.
(3) Indicates good vertical wind shear.

 

http://www.theweatherprediction.com/habyhints/127/

Edited December 5, 2014 by knocker

[Mucka]

Nice to see you going for a raging Easterly last 10 days of December Tamara.

What? I read between the lines 

 

Great read and along with Matt Hugo's tweet I feel I can dismiss the guff GFS has been churning out of late.

[SMU]

Perhaps the winds of change starting to blow tonight in terms of the model suites - Deep bomb lows have lead to rapid increase in pressure over Scandi before-

 

Look at this historic chart

http://modeles.meteociel.fr/modeles/reana/1991/archivesnh-1991-2-2-0-0.png

 

people say its curtains for the UK with deep lows moving East off the states - well they don't come deeper than that- 

 

just 5 days later

http://modeles.meteociel.fr/modeles/reana/1991/archivesnh-1991-2-5-12-0.png

 

lets see what tomorrow brings- but the models are definitely moving to a more amplified solution....

 

also a significant increase in snowcover over Europe in the next 8 days

 

http://www2.wetter3.de/Animation_18_UTC/00_35.gif  to

http://www2.wetter3.de/Animation_18_UTC/192_35.gif

S

Edited December 5, 2014 by Steve Murr

[bluearmy]

Adding to Tamara and Steve's insight, I would be astonished if there weren't any wintry clusters amongst the ECM 32 dayer post the 21st.

the mean by that stage is tricky with the overall message still Atlantic high waxing and waning with troughs dropping in as the Russian ridge holds firm. The Canadian vortex is also probably not going to disappear but also not growing intense enough nor dropping far enough south or east to scupper our chances for cold.

[Mucka]

Mornin' Blue,

Well UKMO is quite interesting this morning. Nice deep trough at 144, Azores high forced West and closed low just off the Eastern seaboard, hmmm.

 

 

I wonder if that would disrupt like JMA last night or better?

 

GFS just wants to eject it East still instead of disrupt it SE

 

GFS

 

GFS 00z ensembles suggest a couple of potent Northwesterlies will set up next week. I would be surprised if snow didn't fall to low levels in the North of England in some showers.

 

 

They don't look much like last December do they?

Edited December 5, 2014 by Mucka

[knocker]

Adding to Tamara and Steve's insight, I would be astonished if there weren't any wintry clusters amongst the ECM 32 dayer post the 21st.

the mean by that stage is tricky with the overall message still Atlantic high waxing and waning with troughs dropping in as the Russian ridge holds firm. The Canadian vortex is also probably not going to disappear but also not growing intense enough nor dropping far enough south or east to scupper our chances for cold.

 

As far as I can see on the 21st there is HP NE Canada,  weak trough north of the UK, HP Russia and trough Alaska-Siberia. On that evidence not any major changes with the Canadian vortex non existent. After that the Russian HP has moved east with more emphasis on the mid Atlantic HP.. Temps around average.

Edited December 5, 2014 by knocker

[bluearmy]

As far as I can see up to the 21st there is HP NE Canada, weak trough north of the UK, HP Russia and trough Alaska-Siberia. On that evidence not any major changes with the Canadian vortex non existent. After that the Russian HP has moved east with more emphasis on the mid Atlantic HP.. Temps around average.

As we discussed before, drawing conclusions from the mean beyond week 2 is fraught with danger. I'm just looking at the general movement of the anomolys , heights and uppers and deciding that there must be some cold clusters. When Ian is awake, I'm sure he can fill us in - the tone of the new meto 30 day will confirm either way.

Note that Ukmo and ECM both develop a shortwave feature in the base of the upper Atlantic trough day 6. ECM scoots this across the uk and I expect would deliver a snowfall across the n of England/ borders, more so higher up day 7/8.

Edited December 5, 2014 by bluearmy

[knocker]

The GFS still looking at some nasty weather for the north next week at T144 and sticking to the westerly pattern with lows to the north by  T240.

 

The GEFs anomaly is roughly the same story as the EC32. There are no major changes in the pipeline to my uneducated eye,

 

Charts courtesy weatherbell

Edited December 5, 2014 by knocker

[knocker]

As we discussed before, drawing conclusions from the mean beyond week 2 is fraught with danger. I'm just looking at the general movement of the anomolys , heights and uppers and deciding that there must be some cold clusters. When Ian is awake, I'm sure he can fill us in - the tone of the new meto 30 day will confirm either way.

Note that Ukmo and ECM both develop a shortwave feature in the base of the upper Atlantic trough day 6. ECM scoots this across the uk and I expect would deliver a snowfall across the n of England/ borders, more so higher up day 7.

 

I wasn't actually attempting to draw conclusions blue, just taking a broad view without quantifying near time variations in the analysis. I seem to remember some getting quite excited about some indications in week three yesterday but I may be wrong.

 

The GEFS seems to be taking a similar route. As a matter of interest do you see major changes in the pipeline and if so where from?

That is a genuine enquiry.

Edited December 5, 2014 by knocker

[Captain Shortwave]

Whilst the Canadian high isn't the smoking gun we need for real cold, the ECM shows that with just a weaker lobe over Greenland, we pretty much end up in a almost polar maritime dominated pattern with any milder periods being very brief. From now onwards there could be widespread frost any night where skies are clear and showers will frequently turn wintry, even to lower levels at times.

High latitude block seems elusive though, still it's not a particularly bad pattern, rainfall will probably be around average and temperatures a little below par.

The GFS and GEM on the other hand show milder solutions with  old air not really getting a foothold apart from brief bursts in the reliable timeframe.

Edited December 5, 2014 by Captain shortwave

[knocker]

I don't know whether this was posted yesterday but it is of interest.

 

El Nino Update: It is here now and is impacting circulation… but don’t cancel off Winter just yet!

[winterof79]

Whilst the Canadian high isn't the smoking gun we need for real cold, the ECM shows that with just a weaker lobe over Greenland, we pretty much end up in a almost polar maritime dominated pattern with any milder periods being very brief. From now onwards there could be widespread frost any night where skies are clear and showers will frequently turn wintry, even to lower levels at times.

High latitude block seems elusive though, still it's not a particularly bad pattern, rainfall will probably be around average and temperatures a little below par.

The GFS and GEM on the other hand show milder solutions with  old air not really getting a foothold apart from brief bursts in the reliable timeframe.

Morning Captain,it will be interesting to see the GFSP when it returns.I am with SM on this and a few others.I see a sudden rise in heights from one of these explosive lows before long.

http://www.meteociel.fr/modeles/ecmwf/runs/2014120500/ECM1-240.GIF?05-12  

Of course its all speculation at this jucture.I will settle for this at present  http://modeles.meteociel.fr/modeles/gens/runs/2014120500/graphe3_1000_269_30___.gif

[IDO]

A change this morning on the ECM FI charts with an Arctic high blocking the transference of the Canadian (et al) PV towards Siberia. So it just circulates back to Canada:

 

 

That should keep us in a revolving door of LP systems sending pulses of PM air from the NW. Whether that could develop into any type of blocking in the medium term is doubtful.

 

GEM has the PV scattered into several lobes and the upshot is a much flatter pattern and a reverse of ECM, with a milder upper flow:

 

 

 

GFS op and control have no Arctic high and maintain their recent trend of draining the Canadian (et al) PV:

 

 

 

So respectively at D16:

 

 

 

The upshot of that at D16 is that the mean indicates a slacker flow compared to the coming period: 

 

So little change from the GEFS in FI.

Edited December 5, 2014 by i'm dreaming of...

[bluearmy]

IDO, I think we were due one more round of the Canadian vortex before its due to weaken. So another pulse of the northern arm days 12/13 before we wonder what comes next...........

(And I say weaken rather than disappear - I don't expect to see it gone though who knows what might happen as the month draws to a close)

Edited December 5, 2014 by bluearmy