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Model output discussion - proper cold spell inbound?


Paul

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Posted
  • Location: oldham
  • Location: oldham
11 minutes ago, nick sussex said:

Ok let’s have an internet bet! 

I think they will change. :)

In what time frame? 

Should he models not be picking up the effect of the warming already considering they are modeling the warming?

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Posted
  • Location: Castle Black, the Wall, the North
  • Weather Preferences: Spanish Plumes, Blizzards, Severe Frosts :-)
  • Location: Castle Black, the Wall, the North

The GEFS 00z mean shows predominantly rather cold zonality (broadly westerly flow) for most of the run, coldest further north but towards the end of the run the pressure pattern becomes more flabby in nature. :)

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Posted
  • Location: portsmouth uk
  • Weather Preferences: extremes
  • Location: portsmouth uk

Looking at the GFS this morning is definitely interesting plenty of cold to the east.

And to our northwest and I see a much better chances for blocking to go up into Greenland.

Greenland blocking looks favourite similar to 2009/2010 

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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)
1 hour ago, nick sussex said:

The last February SSW did deliver a quick trop response. We’ve had some minor warmings in recent years but not a major one so this one doesn’t come around that often .

If I remember rightly the reversal there saw the outputs suddenly start correcting west but this wasn’t shown at the longer range.

Until the actual reversal occurs I’d be wary of anything shown. 

 

On this occasion and using the most similar past SSWs it appears corrections south ought to occur within a few days of the SSW date which is looking to be Feb 12th.

Deterministic runs and even most of the ensembles sure are making us wait for much sign of that though.

Something seems amiss here, hopefully the models as opposed to the quick tropospheric response propositions.

 

Not kidding myself when it comes to what we're playing for; it's going to take something very special to overcome increasing day length and sun strength in this day and age with widespread anomalous warmth in the seas N and NE of the UK. With cold air so extensively vacated from over the Arctic Ocean to the continents, it's hard to see a sufficient resource of cold air for a direct northerly to achieve much so it seems to be that the one sequence of events that can do the trick is an advance of a large blocking west from Siberia, through Scandinavia and then on to Iceland or thereabouts. 

From around day 8 onward the 00z GFS showed the desired blocking feature growing ever larger and colder beneath but it just could not manage to either drive the Atlantic lows well SE into Europe or well down into the middle-N. Atlantic; either route opens the door to the sequence described above.

 

p.s. what do people make of this from the GFS 06z holding the Thu-Fri front up a bit and driving cold air into it from the west? Good intensity on the front and it's the time of year that such things are known to occur sometimes.

prectypeuktopo.png ukprec.png

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Posted
  • Location: st albans
  • Location: st albans
10 minutes ago, MR EXTREMES said:

Looking at the GFS this morning is definitely interesting plenty of cold to the east.

And to our northwest and I see a much better chances for blocking to go up into Greenland.

Greenland blocking looks favourite similar to 2009/2010 

Agreed and also likely n of Scandi 

the strat modelling continues to rotate that split Asian vortex chunk towards w Europe around the blocking 

it may well be that the peak response for us would be 23rd/28th Feb although feasible that we could see something more sustained through March. 

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Posted
  • Location: Manchester
  • Weather Preferences: Sunny and warm in the Summer, cold and snowy in the winter, simples!
  • Location: Manchester

Tiny little bumps of warmer air denote embedded shortwave troughs. :hi:

gfs-1-126.png?6

Skirts with the South this time but somewhere might do pretty well with such a cold unstable westerly flow.

Edited by Mucka
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Posted
  • Location: North East
  • Weather Preferences: Thunder , Lightning , Snow , Blizzards
  • Location: North East

Surly this forecast is a GFS over reaction ? 

B60D3A35-CA55-4468-B175-9B092DC91A7C.jpeg

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Posted
  • Location: Tonbridge Kent
  • Location: Tonbridge Kent
35 minutes ago, Tamara said:

Remember reminder:

Its only an island if you look at it from the water:smile:

Feb 2018 :

Massive poleward tropical momentum transport + tidal surge of +AAM tendency  > +MT > fast orbit Phase 5/6 GWO Nino attractor in extra tropics (this weeks easterly 'jab around the edges') 

gwo_fnl.png

>stratospheric pathway dissolution/feedback from dateline convection > -AO/-NAO.   Allowing for some deterministic model variations of forecast, based on the fundamental changes that are underway in the Pacific eastern and central waters, good supporting reason to 'cherry pick' the ECM to illustrate impending ultimate change downstream in terms of the state of Annular Mode

ECMF_phase_51m_small.gif

I don't make forecasts as such, but lets just say the Global Synoptic Dynamical Model (GSDM) timetable is evolving very close to its defined timeline schedule from inception date ~ 22 January when the starting pistol was fired in the tropics c/o the MJO and the poleward momentum process was underway. The extent of the extra tropical +MT propagation sure reflects the huge amplitude of the tropical convection rossby wave trigger

gltaum.90day.gif

Back to a previous posted comparison made in last 2 weeks:

Feb 1978:

Spent most of the month in GWO Phase 5/6 c/o high amplitude MJO and led quickly to a strong -AO/-NAO combination.

Differences? There was no La Nina lag underpinning an entrenched sub tropical ridge +NAO pattern and so the tropospheric/stratospheric pathway was unhindered to a much greater degree.

Well, that and  of course the absence of so much anomalous homogenous warming of tropical oceans which are skewing and rather neutralising the natural effects of strong tropical poleward feedbacks - in addition to the alarming atrophy of sea ice which correspondingly unbalances expected albedo feedback relationships to an increasingly unprecedented state :

Feb 2018 is indeed proving to be a slower burner with, overall, increasingly less cold air relative to 1978 in the NH to share around in terms of cold air advection from the pole and which inevitably therefore favours much less dilution through continental landmasses like Canada, than downstreamacross oceans)

But, all that said:

There is an abundance of pretty cold air to the NW as we watch the next phases of trough disruption. Based on the spatial arrangement of cold vortices which look set to ultimately implode - that doesn't mean (by any means) that the UK and Europe won't yet see their coldest weather of the winter, as the end of official winter gets closer and closer:)

March 2013 provided this on the Costa del Cinq Ports of the SE:

 

post-18450-0-38719400-1391874961_thumb.jpgpost-18450-0-04702200-1363029790_thumb.jpgpost-18450-0-80272600-1391875070_thumb.jpgpost-18450-0-94087500-1386184761_thumb.jpg

It was even worth capturing some:pardon:

 

post-18450-0-18416400-1385128673_thumb.jpg

So, still very much the sort of thing that is more than possible late winter 2018, a few weeks earlier than the fun and games of March 2013 - and so there is no need for anyone to be miserable :smile:

Fantastic and encouraging update Tamara

Many thanks

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Posted
  • Location: Swindon
  • Weather Preferences: Snow. Always Snow.
  • Location: Swindon

Appreciate this isn’t strictly a weather model as it’s the rainfall radar but I’ve been tracking it since 4am with friends all over and is reliably falling as snow with the sleet consistently stopping as it comes inland.

Ironically there seem to be an additional band of snow (over Gloucester ish area on this SS) which from following it seems it’s residual PPN that came in from the SE yesterday, has hit the front from the west and reversed while organising itself into an additional front that wasn’t forecast. It’s ironic because that front is just creeping over me, definitely falling as snow and yet today is the first time it’s changed to say snow won’t happen today.

It’s a perfect example of how snow can pop up anywhere when the conditions are right.

151A4AC8-16AB-4AB2-B0BC-6302E212B35D.png

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Posted
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)
28 minutes ago, Singularity said:

p.s. what do people make of this from the GFS 06z holding the Thu-Fri front up a bit and driving cold air into it from the west? Good intensity on the front and it's the time of year that such things are known to occur sometimes.

prectypeuktopo.png ukprec.png

I'd say unlikely, often I've seen GFS show some back-edge snow on Atlantic fronts but yet to see it happen from a polar maritime northwesterly flow undercutting, the Pm flow is normally too modified at the surface across southern UK (apart from high ground in the west) to have dew points low enough to allow snow to fall to the surface. GFS has this tendency to undercook surface modification in Pm flows. 

Of course in arctic maritime flows direct from the arctic in a long-term fetch northerly - the back edge nationwide snow event more likely as cold dry air with less modification from the north undercuts, but not often we see these, 28th Jan 2004 was a good example with rain turning to thunder snow as an active cold front swept south across all parts.

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Posted
  • Location: Hampstead / Cambridge
  • Location: Hampstead / Cambridge

gfsnh-0-288.png?6

The PV looking a bit confused

EDIT: looking positively drunk 

gfsnh-0-336.png?6

Edited by ITSY
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Posted
  • Location: Drayton, Portsmouth
  • Location: Drayton, Portsmouth

Ah that's better ... three ECM clusters to choose from between D11-D15. A look at how they progress:

D11:

ec-ens_nat_z500scenarios_2018020600_264.

D13:

ec-ens_nat_z500scenarios_2018020600_312.

D15:

ec-ens_nat_z500scenarios_2018020600_360.

A tendency for troughing to decrease and northern heights to increase, I'd say - but nothing sensational at the moment.

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Posted
  • Location: Banbury
  • Location: Banbury
Just now, Seasonality said:

God forgive me for posting a 384h chart from the 06z GFS but this is the sort of outcome we should be aiming for. Poor old vortex well and truly smashed.

 

gfsnh-0-384.png

Beat me to it ..............stunning end BUT at 384, if only eh

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Posted
  • Location: Hertfordshire
  • Weather Preferences: SNOW AND FREEZING TEMPS
  • Location: Hertfordshire

What a stonking chart this is ?. A few more frames on and we would be well and truly in the freezer ?

IMG_1275.PNG

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

Bet the 06Z GEFS throw up a few good'uns as well.....

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Posted
  • Location: Peterborough N.Cambridgeshire
  • Location: Peterborough N.Cambridgeshire
1 minute ago, chionomaniac said:

Bet the 06Z GEFS throw up a few good'uns as well.....

I reckon at least 5 or 6 decent GEFS runs showing a Greenland block and maybe a few showing a Scandi block.

19th Feb continues to be a significant day for me. Wonder can we get a few GEFS runs below -15C?!

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Posted
  • Location: st albans
  • Location: st albans

That, my friends, is a qtr (although it took a few days to get going with the SSW around the 12th!) 

typical hemispheric strong neg AO signature 

would be nice to think that the gfs op has now got the strat evolution  in the right place by day 10 so that the low res portion  becomes consistent from now on ......

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Posted
  • Location: Maidstone ❄kent❄
  • Weather Preferences: Snow,Snow & Snow.
  • Location: Maidstone ❄kent❄
1 hour ago, TEITS said:

For me the key date remains aound 19th Feb when we could see a blocking high develop. I still favour Greenland or slightly E which is even better for us.

Iceland SLP holds at 1015mb but note few runs go above 1030mb.

prmslReyjavic.png

Just a waiting game as I don't expect anything to suddenly change in the model output beforehand.

Hi Teits , hope your ok? Always loved you posts as they are always good to read and easy to understand. ( The Eye in the Sky) i think you used to be called many years ago.

 

Anyway moving on, its looking like the middle to 3/4 of the way now through feb before hopefully we finally see some PROPER SNOW.... My question to you or anyone els  is will it be a struggle to keep snow around long on the ground as its getting closer to the end of winter come 3/4 of the way through Feb.. And this isnt a end of winter post by the way lol.. thats why im asking this question. 

 

As im sitting here now in the sun in my garden sheltered from the breeze its actually feels plesant and dare i say it i can feel some heat in the sunshine down here in Kent. Lovely blue skies.... But give me snow anyday.

 

Thanks ?? 

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Posted
  • Location: Melbourne, Victoria, Australia.
  • Weather Preferences: Snowfall obviously.
  • Location: Melbourne, Victoria, Australia.

Just following on from Tamara's great post above.....

IMG_3845.thumb.GIF.4c13b1420d1183821c03942bee5b26a8.GIF

Frictional Torque is currently going into a negative trend. After a FT peak, then followed the current MT peak, that has sent the AAM to it's current position. Below is my thoughts, based on my observations and forecasts of the key drivers. The FT will continue to decline into the negatives, and bring the AAM into a negative trend, towards a GWO Phase 7 & 8. But the question is will the MT make a full decline as well? Yes, you could try and use NWP to try and work out whether the EAMT will take a dive, or what will the Rockies MT do? These are the questions that need to be asked.

IMG_3846.thumb.GIF.25b172a8e9a9eaca5011be9fe7850d57.GIF

I am referring to the massive +EAMT, and the currently -RMT. Despite the sudden MT dive in the Rockies, the EAMT has been driving the Worldwide MT to levels that are quite literally off the charts. It is this, that has caused this AAM progression, that nobody forecasted and seems to defy the Niña base state. Whether this is an indicator of Niña weakening, or just a minor hiccup, isn't my question to answer, but many experts have been questioning the dominance of a Niña base state.

IMG_3847.thumb.PNG.1f13fdb71de18639ba31c796485f489f.PNG

Anyway, this is my 'forecast'(yellow line), with annotations included. This assumes that the MT has a large negative trend, maybe it doesn't, and acts like a Niño GWO cycle. But I personally doubt this will happen, IMO that shouldn't happen so suddenly. It's one thing to have a +AAM, and another to have a Niño like GWO cycle. Anyway interesting times ahead, let's keep watch for the next steps of the AAM's progression.

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Posted
  • Location: Hull
  • Weather Preferences: Cold Snowy Winters, Hot Thundery Summers
  • Location: Hull

Model output seems to be getting interesting again. One thing to keep an eye on is the cold NW flow set to move over the UK early next week.

Some pretty cold uppers could spread over the whole of the UK. Quite a few ensemble members also develop a southerly tracking low pressure feature which may lead to snow in favoured areas if such a feature forms.

Ensembles in later frames are pretty good with the vortex weakening and cold building to our east with high pressure building. Quite a few have southerly winds heading to the arctic.

Anyhow a good day so far, maybe the SSW will bring some more surprises. The 06z OP goes for some pretty spectacular blocking late on. Hopefully it can occur a bit earlier!

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