Model output discussion - cold spell approaching?

[Battleground Snow]

The control shows how it can be perfect even in a slightly west based NAO. As the Pacific / Arctic high forces the Asian vortex further south along with the colder uppers.

Huge signal for the Pacific ridge at this range on the mean. 

Also attached graph which is showing a decent cluster of cold members. Screams snowy more than deep cold.

[That ECM]

3 minutes ago, Frosty Winter said:

GEFS 06z look very good beyond the 21st with a clear trend for colder weather now. Average goes down to around -5C but many runs also go colder than this well.

The 1st chart really demonstrates the direction of travel.

[chris55]

58 minutes ago, ICE COLD said:

Look at that

I can see why talk of the Pacific Ridge has been about, this is a good visualisation of how helps, it moves over the pole and re-enforces the negative flow and supports the Greenland ridge!

Lovely charts!

[Griff]

1 minute ago, That ECM said:

The 1st chart really demonstrates the direction of travel.

Absolutely, a satisfying evolution

[East_England_Stormchaser91]

Crucial runs coming up and these next 96hrs will be very tense watching. Expecting a few Wobblies here and there in dealing with the mix of shortwaves. As long as we keep seeing the coldest uppers currently on the planet keep moving towards us, and decent amplification up the US East coast then it’s all good! 

[Griff]

Late to the party, with home school commitments... 

Para is in a rush compared to gfs

 

 FYI nice gem this morning... 

And compared to ecm.. 

 

So... These aren't at day 10  

Not used to this, what happens next?

[Frosty.]

Looking at the GEFS 6z mean / average...the trend is coldies friend..god I love saying that!!!

️ 

Edited January 12, 2021 by Jon Snow

[Tim Bland]

Best set yet!!!

[johnholmes]

1 hour ago, Timmytour said:

I love the boom charts and all that kind of stuff, just because there is a thrill in the chase alone.  But in terms of hopes for a reality of cold, this is one of the best posts I've seen in a long time. Suddenly transports a cold spell from being "that'll be nice if it happens" to "there's a real chance we could actually get a cold spell here!".  Over the years I've seen JH's cautions consistently bear fruit, so this definitely makes me sit up!

Very kind-thank you

Another source of what 'might happen' is this link, from ECMWF

http://www2.wetter3.de/Fax/00_ECMWF_ENS_p0_500hPa+144_240.gif

[That ECM]

6 minutes ago, Tim Bland said:

Best set yet!!!

Indeed and we are getting to the point where the mean is being skewed by a few. If you take the main cluster and put the mean in the middle of that lot then it’s superb imo. From about the 21st to the 25th there is very little between zero and minus5. It’s below or way above.

Edited January 12, 2021 by That ECM

[NewEra21]

3 minutes ago, Tim Bland said:

Best set yet!!!

Without a doubt the best yet, just goes to show once again that no matter the obstacles ahead the end result seems to always be leading to cold!

[MATTWOLVES 3]

I was just having my weetabix when I nearly choked on em...ensemble fever is coming guys..

Ohh and the 2nd warming as already started,let's put the boot into that Vortex again. Courtesy of Marco P.

[Ali1977]

This is a really really strong signal, the mean is actually dragged less cold up by a few really mild outlying ENS, and this is the south of the U.K.!!!!

 it would be interesting to see some spaghetti from up North

 

Edited January 12, 2021 by Ali1977

[Cloud 10]

15 minutes ago, Griff said:

 

 

 

So... These aren't at day 10  

Not used to this, what happens next?

 

Forum procedure demands you look for the end of the possible cold spell before its begun.

[Rayth]

3 minutes ago, Ali1977 said:

 

 it would be interesting to see some spaghetti from up North

 

As per request 

 

 

[AmatuerMet1963]

Well, as you know I'm not very knowledgeable maths wise and the advanced nature of some of the data, which is out of my understanding, But I do watch Windy com every day, and look at various models and projected forecast for about 12 days . According the ECM sunday 17th looks interesting,  and a very long finger of purple has got as far as Moscow, showing -26C, about the lowest its been through December.   

But in only 4-5 days later, the ECM places the purple finger  all but to back to Siberia. I believe we need a Scandinavia high to allow any beast to flow.??? Of course the Newspapers, media outlets are having a field day with dire warnings which cant at this stage be substantiated - just click bait!

A lot of shifting going on, and even my windy charts are all over the place up to the 21st. If there's any smell of snow, it seems to be contained to Up North, and i mean NORTH. There is no projection for snow to reach North West England like Lancashire at this stage.

[snowking]

Still a lot of trials and tribulations to go through yet during the next 8 days or so, but I set a target date a few days ago of the 15th for ensemble suites to start to resolve the situation into the final third of the month with a little more clarity (following the early leads hinted at by operational modelling). We're now starting to edge towards this clarity I hope at least, with the 6z ensembles posted above advertising the expected sharp decline in 850mb temperatures as we head into the final third of the month and, increasingly it seems, into the opening period of February. The ECMWF ensembles demonstrate this nicely too closer to the surface:

We should still remain cautious - as is visible there, there's stiil a few stragglers in the suite advertising something much more mundane. For this reason, ensemble means will continue to be watered down somewhat, and of course being in the UK we cannot completely rule out the milder option, given the propensity for the atmosphere above our heads to lean towards a habit of clutching defeat from the jaws of victory. But the forecast is very much suggestive of the stratosphere driving things, rather than the troposphere as has been the case up until now, into the medium term. Stratospheric forecast still divergent between GFS and ECM operational runs at least but both continue to advertise further displacement of and disruption to the polar vortex for at least the next 10-15 days.

Whilst none of this guarantees epic cold for the UK we do look, in the extended range, to be in the vicinity of a broad NW European trough right through into February - high risk, high reward at times as a result. But as time goes on, and we start to see an 850mb temperature profile like the one below to our North and East, any sort of marginality should become less...well, marginal, as time goes on. Spot the difference between the two profiles below:

I'm not ruling out deeper cold reaching our shores towards the end of January (in fact I'm still fairly confident this will be the case), but even if the very coldest air doesn't quite make it to us, for as long as we're locked into a cold trough with the near continent freezing up and plenty of movement within the trough, there will be snow opportunities aplenty, just as, in fairness, there have been already this month unless you happen to live in the South-Eastern quadrant of the country (this should not be forgotten, pre 2009-2013 the spell we have already experienced would have been notable for many)

I appreciate part of the fun in here is the ride, checking over the details of every operational run, for some finding that historic snow event at T+300, for others trying to find how the cold spell is going to end before it is even forecast to establish, never mind actually even being established in the first place. But if you appreciate your own sanity, the theme and the dates have not changed and at the moment look unlikely to change - final third of January, broad trough vaguely to our East, height rises to our North-West and the cold slowly creeping around the Arctic high from Asia into Europe. Even with some unfortunate phasing of lows, something would have to go really drastically wrong for that broad theme not to come to fruition. Here it is via both ensemble suites:

Let's give it a few days and check in again, but I'm fairly confident it will be the same. Are we guaranteed a historic cold spell? Absolutely not. Does it look likely we will be using the S word fairly frequently for the final third of this month and beyond? I would say so.

Edited January 12, 2021 by snowking

[Nick F]

On the subject of the ensembles, looking at the 00z EPS, the T2m for London shows quite a tight cluster colder than the mean compared to the spread of milder than the mean, which suggests to me a cold outlook persisting.

But uncertainty how deep the cold we get lingers, the 00z EPS at T+300 shows the UK on the periphery of very cold air over Scandinavia in the means, close enough I think, that we could easily tap into that, but with low pressure systems signalled to move in from the NW/W/SW. rather then staying to the E or SE with high pressure to west, may hamper the deep cold reaching us. But, given some luck with synoptics, we may tap into the Scandi deep cold.

[Methuselah]

9 minutes ago, Cloud 10 said:

 

Forum procedure demands you look for the end of the possible cold spell before its begun.

I'm already looking for the eventual breakdown of 2021's first summer heatwave! It's always best to think ahead!

Edited January 12, 2021 by General Cluster

[winterof79]

1 hour ago, Froze were the Days said:

Now that HAS west based NAO all over it...we don't want to see that!

Western based NAO run to the end.... Jubbly

Edited January 12, 2021 by winterof79

[Met4Cast]

The "will they wont they" love affair between those two lows seems to have been resolved this morning, it turns out they are getting a divorce and wont be phasing after all. This leads to one of the best ENS means we've seen so far.

This is also the best set of GEFS ensembles we've seen for a while too with a marked trend downards in the extended. If you looked at the few stragglers that go warm I'd expect you'd find that they're still phasing the two low pressure systems, they need to get it go!

Marked cooling trend clear on the EPS too. So the direction of travel has clearly shifted towards a colder one. Temperatures will fall back below average & it seems we are indeed heading towards a Greenland high. We've overcome one hurdle, what's next?

There is some evidence to suggest that we could see a more west based Greenland high, this would prevent sufficient forcing on the low dropping south to our east & could mean the low drops over the UK, not necessarily a disaster but generally we'd see some mixing out of colder air in this scenario. 

In any case, a much better set of models and we should hopefully begin to see more consistency now those pesky lows are resolved. 

[Purga]

Stunning set of ENS for the 06z!

[Troubleatmill]

all important for snow chances and so often the difference between rain and snow for low levels, from the 21st the dew points are looking good too!  

[NewEra21]

1 minute ago, Purga said:

Stunning set of ENS for the 06z!

Indeed. Hopefully this is the turning point and we can see some consistency now.... 

[warrenb]

4 minutes ago, Purga said:

Stunning set of ENS for the 06z!

So going by the mean we have 3 days of -5 before the high drifts west and the Atlantic comes up from underneath. For a good cold spell you want solid -8 to -10. Note the control and the Op both go warmer toward the end as the pattern backs west.