Model output discussion - proper cold spell inbound?

[Singularity]

Who remembers the days when it tended to be GFS making dartboard lows and leaving us shaking our heads while ECM went head-over-heels in for disrupting and sliding lows?

How far we've come shaken things up .

Either way we do look to be headed down the same broad road, it's just that the deeper the trough, the longer the hill to climb (but only by a day or two).

Edited February 7, 2018 by Singularity

[Ice Day]

Obviously GFS precip charts aren't the most reliable, but based on this there could be a few snowy surprises around on Sunday evening.  -8's over pretty much the whole country at 96....one to keep an eye on.  And this is before we get to the main event (hopefully!)

 

[tight isobar]

As the mother pv-lobe will weaken...so the pac- ridge will become the daddy .

Notable flexing run-2 run now.. with russian pen form.. waiting to greet for the split..waving action occuring..and data signals evolving...

Not a wonder as we continue warm and waves.....

@ for note 10 hpa...

#ssw

Edited February 7, 2018 by tight isobar

[Fourty Point Three Degrees]

Cant see any sign of a Scandi block developing on GFS12 or ECM 12 op.

[I remember Atlantic 252]

3 minutes ago, Ice Day said:

Obviously GFS precip charts aren't the most reliable, but based on this there could be a few snowy surprises around on Sunday evening.  -8's over pretty much the whole country at 96....one to keep an eye on.  And this is before we get to the main event (hopefully!)

 

Ay, not often a westerly modelled as chilly as this

[Jemma Croton]

2 hours ago, Steve Murr said:

Evening All 

Ice Cold hope your still with us ....

So the much touted SSW is coming into view & here’s my thoughts + timelines of when / where to expect it...

We have seen lots of posts & comments on it - but whats the reality likely to be -???

The Omni present warming in the GFS charts is usually due to the model & its poorer vertical resolution V the ECM, as a result there is an over reaction / over estimation of how much a warming is going to impact the zonal wind @10MB - so because of this 'bias' when viewing the mid / long term outputs churned out by the GFS we have to be a little on the sceptical side as these are normally moderated & scaled down even wiped out ! 

However we have now seen the evidence in the Berlin site that a downwelling SSW event will make it to the 10MB level & indeed go on to challenge the date record for the time lf year-

( this is NOT the same as the usual deceleration of the zonal wind we see at this time of year as that is more of a gentle reduction all the way to mid april when the vortex breaks its annual westerly influence )

So as highlighted we have passed the point of no return in the stratospheric modelling where a SSW is now just 5 days away for the 12th Feb *** Take note of this date --

The plots below show steep downward curve of a signature warming

Note the main black line being Climo - but the ensemble mean from the GFS running out at mid -20 to -30 M/S...

The clustering is quite close - further backed up by the another illustration of the ensembles from the hannah attard site

 

With the mean bottoming out at -32M/S

*The date record for this time is ~ -17 M/S

& the all time record low ( using Merra data ) is -35 M/S

The ECM berlin forecast below is not as bullish as the GFS coming out around -17 M/S @10MB but none the less still classed as significant event...

So what we have in modelling terms of a SSW due is

* The first one in 9 years ( I dont think last year was classed without checking )

* Possible record breaking reversal of tge zonal wind...

If your thinking whats best in terms of impacting the UK its simple- The lower the negative number the better... - record breaker ? yeah I will take that please... Why?...

The bigger the negative number the stronger the easterly flow is across the mid lattitudes. !! ( think feb 63 / jan 85 & so on )

Whats the models churning out then?

The SSWs are classed as 2 types

- Wave 1 displaced vortex  or

- Wave 2 Split Vortex ..

This is whats expected -

A classic wave 2 Split vortex- with 2 clear areas of poleward flux - over the far East & canada-

Now luckily for me the historic SSWs have already been classified -we are looking for la nina years / W2 / split vortex-

6 years appear as matches

- 28 Jan 1963

- 7   Jan 1968

- 18 Jan 1971

- 1   Jan 1985

- 21 Feb 1989

- 24 Jan  2009

Below are the 10MB increase in temps at the time when the zonal wind hits 0M/S

Obviously they all have 1 thing in common- The huge rise in temps across the pole -

Now the Date of the zonal Mean hitting 0M/S isnt the day of peak blocking -

Looking at the dates above peak blocking appeared 7 - 11 days post Reversal - see below day 11 charts from the above warmings ( 500 MB anomaly )

Whats apparent is HLB is quite prevelent & most are centered ( for us ) around greenland & Western Scandi -

Also all 6 Splits have varying levels of troughing to the south - but all have an anomaly-

So that really leaves with a level of expectation that should at least give us some confidence for Feb over the following dates-

12 Febuary : is 'R' Day- as in the reversal of the 10MB zonal wind where the eastward progessional component is replaced by a westward one

13/14 Febuary : is peak 'R' days where we will know the magnitude of the warming & just how much westward ( reversal ) component there is - Sub -20 M/S is the date records & anything below is the jackpot -

16-18 Febuary - Mid to high lattitude transitioning - This is where depending on how lucky we are for our area we will see MLBs start migrating North to the pole as zonal wind lag filters through the lower layers of the atmosphere & support builds for HLB - look for the 3 key wave patterns ( atlantic / Scandi & pacific (-EPO)

The UK can get very cold in this period if the migrating highs are favourably positioned from the outset....

20-24 Feb - Peak HLB blocking across the NH - peak -AO signature & peak cold overall for the mid lattitudes ...

*** IF the GFS lands with the depth of negativity then Late Feb early march will be on a par with 2013 for AO negativity & possible / probable UK cold / snow....

if the negativity is watered down then the cold signature will be watered down & less dominent in western Europe...

 

Best

S

Bit off topic but... Marry me?

This was like weather porn ?

On a serious note, how refreshing is it to come here after a busy day to find reams of beautiful charts being shared and talked about with excitement rather than the bickering that’s been present the past few days or so.

I’m really amazed by some of what the models have shown tonight and the rather consistent agreement/expectation for a QTR. 

I’m the resident weather nerd among my friends (both online and in real life) and spend winters model watching and then putting posts out with charts and explanations to try and help them people understand what is coming but also wording it in a way that hopefully helps them learn about the factors in play for weather on our (snow depreived) islands. I put rather a lot of time in and yet seems like I’m always the one of us that misses out. So desperate to get my payday. I might even do snow angels in a swimsuit if the weather gods give me reason to.

I can’t really say more than what you guys have already said on things. Brilliant synoptics and some really great posts today on it all.

You guys are awesome. Even the GFS is awesome right now!!

 

[chicken soup]

3 minutes ago, I remember Atlantic 252 said:

Ay, not often a westerly modelled as chilly as this

Will minus 8 be enough  for snow though..it wasn't with the northwesterly the other week.

Edited February 7, 2018 by chicken soup

[bluearmy]

6 minutes ago, - 40*C said:

Cant see any sign of a Scandi block developing on GFS12 or ECM 12 op.

Slp was 1030mb + post T192on the 12z gfs so there was a scandi high throughout. The upper ridge only showing at the very end week 2. it could well take 2 weeks, it may be quicker. WE DONT KNOW YET! 

[I remember Atlantic 252]

1 minute ago, chicken soup said:

Will minus 8 be enough  for snow though..it wasn't with the northwesterly the other week.

Yes, if trough feature as Midlands saw on the evening of 13th Dec, bringing heavy snow off a W'ly, no if convective

 

[Snowy L]

Lows hitting the wall at t135. GFS is getting things done far earlier than ECM. Could it be because its showing a much bigger reversal than ECM?

 

Edited February 7, 2018 by Snowy L

[Stormeh]

4 minutes ago, Ice Day said:

Obviously GFS precip charts aren't the most reliable, but based on this there could be a few snowy surprises around on Sunday evening.  -8's over pretty much the whole country at 96....one to keep an eye on.  And this is before we get to the main event (hopefully!)

Yes Sunday looks very interesting. Looks like western Scotland will be hammered again with heavy snow showers. 

The upcoming SSW is very exciting, lots of potential for deep cold and snow over the next few weeks

[blizzard81]

4 minutes ago, bluearmy said:

Slp was 1030mb + post T192on the 12z gfs so there was a scandi high throughout. The upper ridge only showing at the very end week 2. it could well take 2 weeks, it may be quicker. WE DONT KNOW YET! 

The models certainly don't know yet

[radiohead]

Well that would be interesting...Far too early to look at in detail though.

[blizzard81]

Oh beast from the east, why so shy again? You've just had your nuts warmed up. Time to move west! 

[danm]

Very interesting, the Met Office are now openly discussing the potential upcoming SSW and it’s impact on our weather beyond the 10 day period. Watch the second half of the video for details.

Things are looking very interesting for the second half of the month! 

 

[ITSY]

Watching that monster low south of Greenland actually travel westwards in the later frames of high res is so wierd. Call me a weather nerd but it feels like everything is upside down watching those frames! 

[blizzard81]

The pub run seems to be caught in two minds. A little like it is wondering to have that extra pint or just call it a day

[bluearmy]

Looking through the gefs from the 12z gave me the impression that the model (probably not just this one) was clueless what to do later next week. No surprise to see this op run on a different tack in the mid term.

[blizzard81]

1 minute ago, bluearmy said:

Looking through the gefs from the 12z gave me the impression that the model (probably not just this one) was clueless what to do later next week. No surprise to see this op run on a different tack in the mid term.

It does seem to move closer to the ecm 12z op in the 6 to 8 day range though. 

[tight isobar]

Gfs 18z begins  N-HEMISPHERCALY to look messy and ugly...

Thise are great signs...wouldnt you- if your were about to go through a metamorphisis...but in reverse state!??..

Mjo into phase 8 border..and the noted 10hpa bunsen burners..are throwing data into dissaray...and a clean evolution wouldnt be feasible.....

Ssw of big proportions coming at us!!!!

By week end runs and supports should start the clean up...

[Ice Day]

So the first strat warming peaks around 132 then at 234 the second warming gives us this.  These certainly feel like extremely rare synoptics, is it any wonder the models are all over the place at the moment!

Very cold pool of air to the north east inching its way towards us at 240

 

[blizzard81]

Aaaaaaand! Yes, the pub run went for the extra pint and ended up with brewers droop! 

Edited February 7, 2018 by blizzard81

[ITSY]

2 minutes ago, ANYWEATHER said:

Despite the so called SSW no change in our synoptics in the next two weeks at least  night night

Why are people so passive aggressive on a weather forum? Baffling. The Sudden Stratospheric Warming is not “so called”. It has a 66% historic correlation with significant downturns in UK temperature. If you don’t like those odds, then move country or get a new hobby. 

[Met4Cast]

GFS: I dunno what to do.. so, I'll just move the entire polar vortex lobe slowly Eastwards. That seems likely 

The GFS is utterly clueless here but despite that, it still manages to develop blocking to the North

Whats that, 9/9 runs or something showing blocking now? It wont transpire like that, I don't think I've ever seen the vortex move like that and I've looked through a lot of archive charts, I was a lonely teenager at times.

Bin anything from the models beyond T120, once the SSW has actually taken place, things will start to become clear. Shannon Entropy as we move forward until then.

Edited February 7, 2018 by Daniel Smith

[ITSY]

2 minutes ago, Daniel Smith said:

GFS: I dunno what to do.. so, I'll just move the entire polar vortex lobe slowly Eastwards. That seems likely 

The GFS is utterly clueless here but despite that, it still manages to develop blocking to the North

Whats that, 9/9 runs or something showing blocking now? It wont transpire like that, I don't think I've ever seen the vortex move like that and I've looked through a lot of archive charts, I was a lonely teenager at times.

Bin anything from the models beyond T120, once the SSW has actually taken place, things will start to become clear. Shannon Entropy as we move forward until then.

I’ve missed Shannon.