The hunt for cold - Model discussion (late November)

[Mike Poole]

Knockout.  Done and dusted.  

Surely.  same as 12z.  You can say these sometimes show up in FI and don't happen, the corollary is that if they are going to happen, they always show this far out!

[feb1991blizzard]

Getting towards the kind of temperature values at the top of the strat that we need in order to reverse the zonal winds.

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018120618&var=TMP&lev=1mb&hour=384

[booferking]

2 minutes ago, feb1991blizzard said:

I do - yes please!!

One example. 

[StormyWeather28]

Does SSW ever lead to a Northerly? If it does deliver cold weather is it always from an Easterly? 

[Nick F]

Now that the models have well and truly given up on any shred of half decent cold sent via the Scandinavian High, as it's too far east, it's well and truly a hunt for cold on here I see this evening! Looking for any shred of evidence that the stratospheric Polar Vortex is going to implode later this month or in the early New Year.

So will the compromised SPV be our silver bullet to the cold and wintry promised land? Remember, even if there is a SSW, no guarantees that it will work in our favour, even a lesser displacement of the PV into Eurasia is no guarantee.

Having said that, we are closer and closer to a SSW, probably a technical one in January, so at least an increased chance for long-lasting  high latitude blocking.

Before then, we may just be offered an olive branch from the constantly changing patterns in the troposphere as waves of energy (westerly bursts) wax and wane off the Pacific thanks to El Nino, plus the MJO wave may head back to colder phases later in the month, all to offer another stab at high latitude ridges which may work in our favour.

A waiting game for now I'm afraid ...

[booferking]

Jma going along with the nw/se exis along with height rises out west towards Greenland..

[Duane S.]

12 minutes ago, feb1991blizzard said:

Getting towards the kind of temperature values at the top of the strat that we need in order to reverse the zonal winds.

https://www.instantweathermaps.com/GFS-php/strat.php?run=2018120618&var=TMP&lev=1mb&hour=384

Yep, that’s gotta be close. I fancy a late December SSW is quite feasible.

 

[feb1991blizzard]

4 minutes ago, booferking said:

Jma going along with the nw/se exis along with

height rises out west towards Greenland..

 

With those charts at the end, we could get some snow due to evaporative cooling.

[Mike Poole]

11 minutes ago, StormyWeather28 said:

Does SSW ever lead to a Northerly? If it does deliver cold weather is it always from an Easterly? 

Yes, quite possible.  The SSW means the winds reverse in the stratosphere and become easterly on average (at 10 hpa and 60 degrees north, to be precise).  What happens then as I understand it is this downwells to affect our weather down here over a period of weeks.  What happens also depends on whether it splits the vortex in two or merely displaces it.

The split SSW in Feb was so strong it flipped the winds right round the planet from westerly to easterly, but that I think is quite rare.  Usually it means a significantly more meridional jet stream, which could leave us in a northerly, easterly, equally a southerly depending on position, hope that helps.  

[feb1991blizzard]

17 minutes ago, StormyWeather28 said:

Does SSW ever lead to a Northerly? If it does deliver cold weather is it always from an Easterly? 

It could lead to a Northerly if its a displacement SSW and displaces the Vortex to our East, it depends on how it propgates and where the high pressure sets up in the troposphere, although it does most of the time seem to be an Easterly, you might want to ask that question in the strat thread though with the level of expertise over there, someone will probably go back through the archives and give you some stats and a much longer detailed post.

[damianslaw]

9 minutes ago, feb1991blizzard said:

With those charts at the end, we could get some snow due to evaporative cooling.

Indeed you don't need deep cold uppers at this time of year to produce snowfall, heavy precipitation in 528 dam air, can do the business - thanks to evaporative cooling. Yes such synoptics tend to produce the wet snow stuff, an often temporary affairs, but significant amounts can fall with very modest height. 

[feb1991blizzard]

1 minute ago, damianslaw said:

Indeed you don't need deep cold uppers at this time of year to produce snowfall, heavy precipitation in 528 dam air, can do the business - thanks to evaporative cooling. Yes such synoptics tend to produce the wet snow stuff, an often temporary affairs, but significant amounts can fall with very modest height. 

Yes - the reason i said that is because the winds are very light but there are upper troughs and surface kinks in the isobars denoting pressure gradient and thus likely PPN.

Edited December 6, 2018 by feb1991blizzard

[Duane S.]

As I posted, my fear was always that the undercut was going to occur too far North, albeit I did think the Scandi ridge extension would get a lot further west than it is currently looking like doing so initially.

Watch this space though. I think the jet axis on the NW/SE path is very much one to be watched. It wouldn’t take much here to turn the Atlantic from foe to friend. And if it does, watch the block fight back...

[Nick F]

1 hour ago, feb1991blizzard said:

Not often one sees such a marked positive height anomaly over Greenland and Iceland at week 5 but more strikingly at week 6 in EC weeklies, normally the anomalies are muted at that range. EC longer range smelling the SSW coffee?

[feb1991blizzard]

Just now, Nick F said:

Not often one sees such a marked positive height anomaly over Greenland and Iceland at week 5 but more strikingly at week 6 in EC weeklies, normally the anomalies are muted at that range. EC longer range smelling the SSW coffee?

It must be Nick - and it must be a majority cluster at that, like you say, for the pattern to stay similar but the anomaly actually grow the further into the run is a big signal.

[Duane S.]

Gfs Para worth raising an eyebrow or two to. Very much along  my thoughts..

[Rocheydub]

5 minutes ago, Nick F said:

Not often one sees such a marked positive height anomaly over Greenland and Iceland at week 5 but more strikingly at week 6 in EC weeklies, normally the anomalies are muted at that range. EC longer range smelling the SSW coffee?

Ahhh! The "smelling the coffee" quote. Guaranteed to fail!!! 

[northwestsnow]

3 minutes ago, s4lancia said:

Gfs Para worth raising an eyebrow or two to. Very much along  my thoughts..

That looks better

[Duane S.]

8 minutes ago, northwestsnow said:

That looks better

It would be nice to think this was the start of a trend back the other way

We will know soon enough.

[feb1991blizzard]

17 minutes ago, s4lancia said:

It would be nice to think this was the start of a trend back the other way

We will know soon enough.

This doesn't fill one with much optimism in the medium range.

 

on the other hand, this does.

Edited December 7, 2018 by feb1991blizzard

[ALL ABOARD]

First time the GFS para has gone for it like this so far 

Toasty. 

[Cheshire Freeze]

Have I ever said how much I love and rate the EC46?!

I'd imagine we'll be getting a pretty wintry long range update from the Metoffice pretty soon if that sticks.

Edited December 7, 2018 by CreweCold

[Smiler1709]

Evening all

just a quick question, during the winters of 47/63/87 etc is there any evidence that these big winter events started after a SSW? Can you get a prolonged wintry spell without a SSW? 

[BlackburnChris]

To be fair , these toastie ssw strat charts have been at +384 for the last 3 weeks, (just scroll back through this thread) might be a trend ok, but goes to show you can't take a +384 chart literally as it should be at T+0 by now. For me I think mid Jan onwards will be interesting , especially if you have been following the Sunspot activity , lowest I've seen in years . 

Edited December 7, 2018 by BlackburnChris

[Trom]

Hmm, I'm not so sure I get sucked into this SSW in January theory just yet.   Obviously, the Strat is easier to model as it has less volatility than the troposphere but we are talking a month's time.  I'm not so sure that I've seen anything particularly accurate at that range.  If true then with a 2-3 week down welling you are looking at late Jan/early Feb period of cold potentially.

What is encouraging is that all the main models have pointed to wave one events.  I always think of wave one as a nudge to the vortex, compared to the scattering effect of a wave 2.  For some reason, I always think of snooker players breaking off.

My main point was that it looks interesting in the long term and to remind people that December snow at low level is an anomaly (2010 skewed peoples expectations). 

 

Edited December 7, 2018 by Trom
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