Model output discussion - winter proper underway

[phil nw.]

6z GFS Op run would be a nice Christmas present for coldies.

Comparing that run to the ens though we see a big divergence to cold against the majority around day 10 onwards.

The Op run finds the extra amplification of the Azores high which diverts the path of the northern jet out of Canada and within a short time we see the split with more energy forced south

leaving us with a cut off high cell and the easterly underneath.A classic evolution to an easterly coming off the amplified Azores high-it's not always a pain you see.

Unfortunately it is a minority solution at the  moment with in the gefs and the extended eps showing no interest yet either.

All that can be said though is that it is a possible outcome given we achieve that amount of ridging as even a strong looking vortex segment to our nw can be tamed in such circumstances.

   

[nick sussex]

Signs of life once again from the GFS which at least is playing with some different solutions towards day 10 as opposed to the ECM.

I'd be less willing to believe in the Christmas Miracle of 2017 if the MJO wasn't on the move and expected to enter some favourable phases.

 

[northwestsnow]

6 minutes ago, nick sussex said:

Signs of life once again from the GFS which at least is playing with some different solutions towards day 10 as opposed to the ECM.

I'd be less willing to believe in the Christmas Miracle of 2017 if the MJO wasn't on the move and expected to enter some favourable phases.

 

Yes the mjo forecasts sound OK nick... wonder if something else is going to over ride that signal?

Perhaps nina is a little too strong.

 

[johnholmes]

1 hour ago, Daniel* said:

It does seem to happen a lot 06z is more amplified than 00z I can't stick my finger why, this is probably coincidental nothing changes merely the time the run comes out. 

different basic data goes in might be part of the reason, somewhere in the Net Wx learner area is information about this. But not sure how up to date it is.

[SMU]

Afternoon All

A couple of days off from the MOD thread feels like having a nice shower ! It’s a pity someone didn’t drown the models over the last 48-72 hours..

Anyway we are edging along to Christmas with 12 days ( 288 hrs ) to the big day - & things have taken a turn for the worst in terms of NH profiles - however will it last?

This end of November & the start of winter has all been about the disconnect of the troposphere from the stratosphere- & whether that relationship can stay intact long enough that we can continue to see blocking in favourable places to promote cold over the UK-

This has worked so far however we will shortly be putting this to the test as we see a burst of faster winds at the 10MB level in the stratosphere - the image from the Hannah attard site shows this very clear-

The problem with just looking at this level though doesn’t show you whether that wind speed is filtering down through the layers-

The height where the Trop / strat coupling occurs at about so we should not only look at the windspeed @10MB but also below between around 30MB

The image below shows the wind anomalies across the height profile - where the burst of energy is being detected -

As we can see the lower layers have been running below average for a while oscillating down to well below average - 

if you look close you can see that the burst of winds struggles to penetrate down to past 10MB indicating that any strengthening of the vortex may be short lived V it’s pre disposed base state this year which is weak -

As an aside from this some Historic data in EQBO years generally suggest a contraction of the vortex into a more concentric circle is often a signal of vortex implosion in the lead up to a SSW ( one to watch )

I think we see a strong vortex develop in the next 5-8 days possibly a bit longer before the pattern breaks again back to the preferential state of a more broken & sporadic vortex leading to chunks being spread around-

The -EPO ridge ( prominent in LA Nina years ) will be a semi permanent feature this year & I will be looking for this to support Atlantic ridge get going forward -

Christmas ( being cold ) is still in the picture although because of the timescales we may be looking for cold later in the Xmas period as opposed to sooner...

lets get the next 72 - 96 hours under our belt & start to watch for repetitive signals for further blocking again...

best

S

[comet]

Lets hope we see more charts like this from 06z run this morning.

This would probably lead to a very long and protracted bitterly cold and wintry spell for Europe and the UK. Now that is what I would call the start of a big freeze. Here's hoping.

 

Edited December 13, 2017 by comet

[Tamara]

I think that's a perceptive post from Steve M from a "top down" perspective

Its also created some interest in my own mind in terms of the timings of the peaks of energy higher up in the stratosphere shown on the Hannah Attard plot back in November and now suggested very soon again in December, and as advertised in terms of NWP over the polar field.

There is very much a symmetrical cyclical look to them

I think that the EQBO is making it hard for positive zonal winds to downwell, but also the timing of the spikes leads to thinking that its the lulls in the tropical cycle that are (very briefly) allowing the more traditional La Nina pattern to try to organise the vortex and the tropospheric pattern.

Albeit with AAM still higher relative to the Nina base state - hence the Phase 8 GWO transitional phase representing the floor limit of any drop.

This "natural lull" drop back in angular momentum is enough to promote the re-appearance of the Alaskan ridge.  But then, as allowed by the very east based nature of the La Nina pattern, the tropical pattern in the Pacific re-boots with the next convection cycle and as a consequence angular momentum is also increased once more. This leads to a further step back up of amplification flux c/o rossby wave activity from the tropics>extra tropics (+ve mountain torque)>stratosphere - and means the EPO ridging becomes a poleward feature before becoming absorbed as part of another (conceivably even bigger than the last ) vortex destabilisation and general -AO phase

Assuming, with such plausible reasoning, the above proceeds accordingly:

Taking into the account the additional factor to come of the seasonal wavelength change into January,  as much discussed, and the implications of it in terms of re-arrangement of the synoptic pattern and height rises to the NE, the prospects ahead beyond the Christmas/New Year period are ever more interesting and increases the chances of Annular Mode coupling of the AO and NAO...

[frosty ground]

could lead to a rather could Northerly this.(note a further correction west)

[northwestsnow]

GFS bringing a cold north wester again from around 21st onwards...

[Man With Beard]

Thank you very much @Tamara and @Steve Murr - if you and our other experts get together and write a book named "Teleconnections made simple" I will be your first customer, as I really need to get my head round all this stuff!!

Until then I'm stuck with interpreting model output data - and it looks like the GFS 12Z is repeating its trick from the 06Z of a fresh WAA burst towards the southern tip of Greenland

and actually even better!!

What a tease this model is. Still, as I explained earlier, this is the very pattern I have been watching and hoping might emerge for the past few days. Let's see if any other models will follow in the next 48 hours!!

 

[Paul_1978]

4 minutes ago, frosty ground said:

could lead to a rather could Northerly this.(note a further correction west)

Indeed. The Atlantic height rises are getting more pronounced as each run goes by. A good trend.

[northwestsnow]

what an amazing christmas present from 12z!!

Snow showers moving south through the British Isles on friday 22nd December!!

[feb1991blizzard]

Never mind the Northerly bit, this is going to turn into a ridiculous Easterly as the high topples, exept this time via  more plausable and less convoluted route.

[Glacier Point]

Mild spell looks in a bit of bother on the 12z GFS. That date around the 22nd again. Much more amplification across the Pacific and Atlantic sides.

Edited December 13, 2017 by Glacier Point

[Snowman.]

GFS shows a wave 3 attack at D10

[frosty ground]

1 minute ago, feb1991blizzard said:

Never mind the Northerly bit, this is going to turn into a ridiculous Easterly as the high topples, exept this time via  more plausable and less convoluted route.

Was thinking the same, the correction west and North will lead to a better Easterly assuming the same outcome of collapsing high.

[Methuselah]

Ought to bring snow to Scotland, NI and the east coast of England, at least? Typical Friday!

[Summer Sun]

UKMO has the milder air in place from Monday

[feb1991blizzard]

Here comes the slider.

[terrier]

well the mild spell does'nt look like lasting long at all on tonights gfs12z. are we starting to see signs that GP tamara steve murr have been alluding to this evening.Think the model watching could become fun again in the days ahead,

[Johnp]

Xmas Day snow......north of the M4 ??

Edited December 13, 2017 by Johnp

[northwestsnow]

6 minutes ago, Glacier Point said:

Mild spell looks in a bit of bother on the 12z GFS. That date around the 22nd again. Much more amplification across the Pacific and Atlantic sides.

The million dollar question stewart...is it plausable one wonders!!

[comet]

Without a doubt the strong MJO and subsequent warming early November in the strat has pre-conditioned the atmosphere making it much more susceptible to MJO forcings etc. Great run this from the 12z gfs.

[Man With Beard]

And here comes your December 25th slider - and the Daily Star's prediction of a White Christmas comes off - what could possibly go wrong?!

    

 

[bluearmy]

 Can’t even say that op evolution has been spotted in recent ens runs! 

Gets to the eps mean/anomoly for day 14 but via a very different route !!