Model output discussion - winter proper underway

[nick sussex]

I feel a song coming on! 

Hope at last with a chink of light which might yet Save Christmas .

Some improvements overnight especially from the GFS which tracks the jet further south . For the north especially it’s still possible that snow might fall on the day.

The ECM is not as good though with the low blowing up over the UK. 

It’s really getting the pattern sufficiently se before that happens and getting a separation upstream so low pressure near the UK isn’t attached to low heights over the ne of Canada.

The ECM complicates matters to the west with shortwave energy at T168hrs which stops a better push se.

The improvements though aren’t a case currently of suggesting a winter wonderland as we don’t see the depth of cold but at least there’s a chance for something below average if the pattern can get edged further south and east.

Thats really the key which would be helped by more upstream amplification.

 

[Chris.R]

@Tamara and @Bring Back1962-63  Brilliant posts again. Really appreciate you taking the time as always. :-) 

[bobbydog]

3 minutes ago, karlos1983 said:

And yet I sometimes wonder why the likes of @Tamara go to the efforts of writing such in-depth and informative posts, as one model run can lead to "zonal train for days/weeks to come" type posts, when we have had full warning of this current period of modelling and our possible routes as we head toward the new year.

I appreciate that not everyone will share the views, but so far.......so good imo.

Thanks Tamara, I always enjoy reading your posts!

very true karlos. people seem to pick out the positive details and ignore the caveats and stated possible pitfalls. @Tamara does an excellent job of explaining how favourable background signals COULD lead to our favoured weather type. at no point does she guarantee anything. yet if it falls flat then she must have been 'wrong'....

also, as you say, one bad run can lead to "winters over" type posts. however in this case we are seeing lots of 'bad runs'.... of course, we're not. we are seeing the models showing the forecast return to westerlies during mid december. if anyone cares to read the Netweather forecast, written back in november, Ian (Simpson) forecast a cold blocked start to december, return to westerlies then blocking returning towards the end of the month. (without being able to see into the future or owning a DeLorean,) i would say he's on target so far. no-one promised a white christmas (or anything else for that matter) the major operational models go out to a maximum of 2 weeks (that we have access to) so just because a cold solution isn't showing in that timeframe, doesn't mean it won't happen after. especially if you consider the 'FI factor'. all things considered, there is no reason as yet, to think that the forecast return to blocking won't happen. 

anyway, christmas is coming and so is the rest of winter...

[lassie23]

John Hammond is a cold ramperanyhooos I think the south will be sunny and mild as usual for Christmas, but the north will be pretty unpleasant, maybe a few flakes up there too, but the interest is as others have pointed out, the middle of January, should see some fine cold set ups in those models by then...... can't wait.

[karyo]

The GEFS are still not keen on progressing the MJO into phase 8.

It stays on phase 7 for a few days before dying a death.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foregfs.shtml

[Seasonality]

At the five day mark a cooler run from the 6z to the 12z, incremental changes as we get closer to Xmas could yet make a difference for some.

[Laurence Hill]

2 hours ago, Quicksilver1989 said:

Hello

Haven’t posted in a while given the model output had been fairly repetitive. However the 06z offers a route to colder weather. An interesting run that could have a lot of potential with a few tweaks.

So the thing that has been notable with recent output is the development of a very strong area of high pressure around western Canada. Some recent output has seen some quite remarkable SLP values, with yesterdays 06z seeing SLP values of ~1070mb across NW Canada!

I don’t think the high will get that strong but it does look like being quite a powerful anticyclone.

We see its development quite early on after T+96. Here is the view at T+114:


Again situated over NW Canada with a cold plunge over Central and eastern North America looking likely. This may fire up the jet, though a split in the Polar Vortex is still possible if the Russian/Arctic high links up with it.

This is shown quite clearly at T144, so the North America high increases even further in its influence.

Interestingly the ECM and UKMO offer some support for this. This high starts to have a knock on effect around Greenland.

At T174 high pressure starts building around Greenland. Given the cold polar air isn’t shifted this becomes a very intense cold based high. The ECM and UKMO are not as bullish on Greenland height rises but in recent weeks I’ve noticed the GFS has done quite well with it. Transient northerlies have been a persistent theme of this winter so far. So the GFS may be onto something.



The development of this high helps split the polar vortex. It is now shunted away from the south of Greenland somewhat and is split to our North and over NE North America. This shunts low pressure systems further south.

Cold air starts building to the North but the Greenland high isn’t strong enough to keep the cold air moving south over the UK persistently.



Though this may change. It could be very easy for the warm air being pumped up into the arctic by the North American high to reach Greenland and therefore helping develop a more stable block. Also the GFS after T240 tends to flatten a pattern anyway.

In the end our potential to avoid a euroslug high would be increased if the link up between the arctic high and American high occur with ridging over Greenland.

It may not happen but its worth watching. Also some stormy weather on boxing day seems to be a recurring theme…

Really appreciate the way you have taken the time to annotate those charts, it does make it so much easier to follow.

[bluearmy]

Whilst it’s always tricky to second guess a run early on, the 12z is less likely to get the Alaskan upper ridge as far into the pole as the 06z did- hence week 2 should progress with less upstream amplification and less dog south of the jet. More akin to the 00z than the 06z

 

[offerman]

2 minutes ago, Sharpedge said:

Really appreciate the way you have taken the time to annotate those charts, it does make it so much easier to follow.

The problem is that Azores high is elongated it needs to be I next a more vertical position to ridge up link up to the Greenland high forcing down and prolonging the cold 

until that Azores either retreats further westward of north northwestward then our chances are very slim at this conjuncture .

[Weathizard]

Pacific ridging to the pole much less prominent on this run compared to the 6z. 

[karyo]

15 minutes ago, bluearmy said:

Whilst it’s always tricky to second guess a run early on, the 12z is less likely to get the Alaskan upper ridge as far into the pole as the 06z did- hence week 2 should progress with less upstream amplification and less dog south of the jet. More akin to the 00z than the 06z

 

I have to say that 'dog south' sounds quite worrying!

But yes, the 6z often comes up with amplified solutions that are not followed by the 12z.

The ICON also looks unfavourable for cold.

[Derecho]

6 minutes ago, Weathizard said:

Pacific ridging to the pole much less prominent on this run compared to the 6z. 

Yup it doesn't quite work out on this run unfortunately, maybe the 18z can throw up something better.

Saying that the UKMO 12Z is far better

Edited December 18, 2017 by Quicksilver1989

[Weathizard]

Pretty large difference at day 6 to our west, UKMO could deliver something to Scotland/normal favoured areas from the NW, difficult to tell at this range.

[bobbydog]

boxing day looks like a day indoors watching the wizard of oz....

[Had Worse]

3 minutes ago, bobbydog said:

boxing day looks like a day indoors watching the wizard of oz....

I hope thats mild on her bike so we can see something more festive.

[johnholmes]

For the past 3 days I have been doing what I suggest to other folk.

Checking T+240 at 00Z and 12Z counting down so we are now at T+192. Initially not much similarity 00 to 00 or 12 to 12. Slowly evolving over the 3 days is the pattern on both 00 and 12, take a look for some kind of pretty deep low west of the UK with most of the country in a very strong Polar Maritime airmass from a SW'ly direction. Take a look, and like I suggested the continuity is getting there both on the 00 and 12 z outputs. No idea what the 06 and 18 show as I never both looking at them until below the T+120h mark.

[Seasonality]

Interesting hemispherical profile to usher in 2018. Heights linking across the pole. 

[bluearmy]

Gfs op takes a gefs 06z from the top shelf later on!

certainly an evolution that’s been advertised off and on across gefs suites recently 

[nick sussex]

A new phrase to the add to many we've seen!

PVLT!

PV Lobe Transfer, the issue with the GFS is the early transfer of a lobe from the Pacific to the Canadian segment.

That happens between T96 and T120hrs which lowers heights over Greenland.

The UKMO doesn't do that and you can see the differences that means at T144hrs.

Edited December 18, 2017 by nick sussex

[ArHu3]

9 minutes ago, Seasonality said:

Interesting hemispherical profile to usher in 2018. Heights linking across the pole. 

Bitter cold all the way into California and even Mexico, quite impressive really but scorching hot in Europe 

[johnholmes]

5 minutes ago, ArHu3 said:

Bitter cold all the way into California and even Mexico, quite impressive really but scorching hot in Europe 

I assume you are taking the mick?

[Seasonality]

4 minutes ago, ArHu3 said:

Bitter cold all the way into California and even Mexico, quite impressive really but scorching hot in Europe 

Well, not bitter cold in Europe I'll grant, but not scorching hot either.

 

[Swave Snow]

1 minute ago, johnholmes said:

I assume you are taking the mick?

he must be

[Daniel*]

A Boxing Day gale keeps coming up, certainly the rear end of December is looking disturbed and cyclonic possibly extending into the first week of January nonetheless things could turn more interesting .

....and rather cool far from mild as such there could be a few surprises.

[knocker]

After a relatively quiet week the gfs this evening also displaces the Canadian vortex around the Xmas period with the cold trough dropping along way south and with height rises in the western Atlantic the jet is fired up as low pressure dominates the Atlantic. This portends some unsettled weather for the UK, very windy at times with temps around average.