Model Output Discussion - Colder spell ending, what's to follow?

[legritter]

Evening Gang ,a very encouraging Ecm tonight ,Rain and more rain and to be honest i can see some flooding issues over the coming week .The encouraging bit is Low pressure gradually gets shunted further south and we have Much lower 850s waiting to flood south .Pressure rises to our far north , lets hope we can progress from tonights ecm with some arctic hights ,keep the faith gang its early days ,we can still be curtain twitching come Christmas time ,i shall be watching tomorrow's charts from behind the sofa ,with my dog wagging his tail twice for a good chart and one wag for a bad chart .Great posts on this wonderful forum ,is the Advance guard of Winter waiting with its troops to deliver us coldies a fantastic chart viewing experience over the coming months ,cheers gang STEllas all round .take care all .

 

[Uncertainty]

Good evening all

Now that the dust has settled on our latest disappointment, it’s now a question of whether our long hoped for December cold spell has been dashed or delayed. I am going to present some evidence for the latter, with the firm caveat that anything interesting to those of a cold persuasion remains at least 10 days away, and given recent history remains hard to put any ‘real’ faith in. Nevertheless, with the AO and NAO set negative for the next few weeks at least, we only need one burst of Atlantic amplification to tap into the cold air waiting to the North (it sounds so simple doesn’t it).

The first factor to consider is the movement of the MJO. After meandering weakly between phases 4 and 5 for what seems like an eternity, the GFS suite today finally takes the signal towards phase 6 at reasonable amplitude. No surprise then to see this manifesting in more colder solutions appearing at day 11+.

The CFS too with a push across the West Pacific

The ECM, unfortunately is much less keen and kills the signal off.

So, supposing the American models have got this sussed, where does that leave us with our North Atlantic amplification push?

GEM and GFS on Christmas morning:

 

Notably good agreement at 300 hours out, a nice pattern then with good heights to the North West and lower, but not especially low heights over the Low Countries.

Still no firm evidence of a big block in the Atlantic and associated WAA, so no Omega style Greenland block on the menu at present, but higher, stronger heights than usual seems likely.

 This is evident by viewing the pressure and heights at 500mb, rather than using anomalies. This paints a somewhat less exciting picture.

Still a mean westerly flow but weak. There are some good members in there though, the control being a prime example.

But if the above MJO argument holds, then the ECM should be flattest, right?

Well the ECM was the pick of the day 10 op for me and has been discussed above. It wouldn’t take much for it to turn cold if that low to the south west stayed elongated and rolled under the the developing high to the NW. If we are to get a memorable cold spell, this is one of the ways it might manifest itself. But Was the op a flash in the pan? An ECM op day 10 garden path special that we’ve been conned by so many times in the past? Not according to the EPS, I’ve delved through those individual EPS again for the big day and wow, still genuine signs for high pressure to the Northwest, low pressure to the East. Dan and Nick have generously posted the day 15 temperature and height anomalies above but they mask some phenomenal members roughly one sixth of which produce a stonking Greenland high with associated euro trough and thus a white Christmas for many parts of the UK. Another 15 or so members have high pressure to the west and a cool, seasonal NNW flow. It remains the case as I’ve said before that the traditional flat zonal Xmas pattern is not well supported at present.

The cause of the ECM’s amplification signal in spite of its weak MJO signal could be more +EAMT or perhaps the effects of the stronger signal for a weaker vortex but it’s not clear to me. I’d love to hear anyone’s thoughts on that as my personal view here is that getting the MJO into phase 6 with good amplitude is the crucial variable here.

The future of the strat is highly uncertain, but for our period of interest it doesn’t seem to be strengthening in time to kill a potential cold spell, it’s still reeling from the moderate wave 2 hit it’s presently receiving.

Those bias corrected CFS member which do go strong do so in January. We may well see VI in early January, the seasonals seem to be seeing it too but that’s for another day.

In summary like it or lump it there’s another chase/opportunity/pipe dream on and it might be our last/best chance for the winter. 
 

[bluearmy]

@Uncertainy  not sure the eps show that much snowfall for Xmas day across the uk

 

[BLAST FROM THE PAST]

48 minutes ago, Jason M said:

That's just riding the polar front. It is likely headed NE to give us a splash of cold rain (if you run the ECM chart sequence it shows this). 

No it doesn’t?

 

BFTP

[tight isobar]

1 minute ago, BLAST FROM THE PAST said:

No it doesn’t?

 

BFTP

Certainly doesn’t.. the dice is loaded.. for the Xmas period... and that isn’t a ramp -or massive overview...@intresting is an- understatement!!!

[Jason M]

18 minutes ago, BLAST FROM THE PAST said:

No it doesn’t?

 

BFTP

Is that a statement or a question? Assuming the former I respectfully disagree as its clear from the two preceding ECM charts that its headed NE. It sure isn't going SE through the Iberian high. Even if it went through the channel it wouldn't change anything as its not a trigger low. That said, we will never know for certain as the next ECM charts will be completely different anyway. 

 

Edit: Don't be sad Cackerjack. Knowing ECM it will have a 1987 redux at day 10 tomorrow!

Edited December 12, 2020 by Jason M

[Uncertainty]

1 minute ago, bluearmy said:

@Uncertainy  not sure the eps show that much snowfall for Xmas day across the uk

 

Yes clearly not BA but I’d still rather have the pattern they broadly suggest and be in with a chance. Perhaps I should have suggested said White Xmas for ‘a few’ not ‘many’!

[Ventnor Viking]

Everything slightly further north on this run so far. Needed it to go south really. 

12z

18z

Edited December 12, 2020 by Ventnor Viking

[johnholmes]

17 minutes ago, BLAST FROM THE PAST said:

No it doesn’t?

 

BFTP

Yes it does no it does'nt; are you two starting a pantomime show?

Showing actual charts would help those who may not understand, then they can make their own mind up.

I'll put a link in from Net Wx so folk can do just that. Please correct it if I put the wrong link in.

Thanks

ECMWF Weather Charts - Netweather.tv

WWW.NETWEATHER.TV

 

[bluearmy]

The gfsp from this morning has finally updated and seems BFTP has been fiddling with the controls .... 

[Ventnor Viking]

On the plus side the GFS is further east so could produce some eye candy in FI

12z

18z

Edited December 12, 2020 by Ventnor Viking

[Griff]

7 minutes ago, bluearmy said:

The gfsp from this morning has finally updated and seems BFTP has been fiddling with the controls .... 

Wowzers some signal for blocking in never never land, oh well, never mind... 

Edited December 12, 2020 by Griff

[Matt H]

7 minutes ago, bluearmy said:

The gfsp from this morning has finally updated and seems BFTP has been fiddling with the controls .... 

Looks pretty good to me!

[northwestsnow]

43 minutes ago, bluearmy said:

@Uncertainy  not sure the eps show that much snowfall for Xmas day across the uk

 

Looks WNW flow maybe?

[fellmike]

Whats happened to that high over russia ? Thought we were in for easterly this weekend

[TSNWK]

Pincer move to the north of low at 222.. seems to more heights over the Atlantic and scandi.. even a wedge?

be interesting how this goes in the run to Christmas.

 

[Mucka]

6 minutes ago, TSNWK said:

Pincer move to the north of low at 222.. seems to more heights over the Atlantic and scandi.. even a wedge?

be interesting how this goes in the run to Christmas.

 

Yes the continuing trend to re-strengthen the Scandi ridge very much in evidence again this run.

Seems to be helping slow the trough which in turn could help any amplification upstream.

 

18z V 12z

 

Edited December 12, 2020 by Mucka

[Tim Bland]

There’s some amplification but it would prob be a transient ridge. Nicely timed for Xmas though 

[blizzard81]

1 hour ago, Man With Beard said:

I can only think it's because their supercomputer can't see any distinct groupings. Bit surprised tonight though, as when I scrolled through the 51 members individually, there seemed a big grouping going for a mid Atlantic high

That is strange. Maybe because good news is banned this year huh! Thank you for your thoughts. I must admit, I always sit up when I see your posts. Always very informative

[feb1991blizzard]

1 hour ago, BLAST FROM THE PAST said:

No it doesn’t?

 

BFTP

It does i am afraid, these ridges just are not gaining traction, just transient ridges within the overall zonal flow, a classic sign that the atmosphere just isn't primed, suggests the global teleconnections are weighted towards mid latitude ridges only, its a classic tell tale sign.

[Mucka]

6 minutes ago, feb1991blizzard said:

It does i am afraid, these ridges just are not gaining traction, just transient ridges within the overall zonal flow, a classic sign that the atmosphere just isn't primed, suggests the global teleconnections are weighted towards mid latitude ridges only, its a classic tell tale sign.

Could turn out that way certainly but worth remembering this is deep FI and GFS is prone to be over progressive the further out it gets.

We will need to see any Atlantic ridge being modelled consistently soon if there is any hope of some cold weather for Xmas though.

[Mike Poole]

27 minutes ago, fellmike said:

Whats happened to that high over russia ? Thought we were in for easterly this weekend

The high over Russia has gone now, it was only ever going to deliver an easterly via promoting a SSW event and a lucky fall of the dice over the northern hemisphere.  That is off the table now.  

GFS pub run T270 shows what might be on the table if the Atlantic amplification coming from MJO forcing happens.  It might not though.  The table might look like this:

Edited December 12, 2020 by Mike Poole

[BelgianBlizzard]

       All a bit transient I'm afraid... Low after low

[blizzard81]

12 minutes ago, feb1991blizzard said:

It does i am afraid, these ridges just are not gaining traction, just transient ridges within the overall zonal flow, a classic sign that the atmosphere just isn't primed, suggests the global teleconnections are weighted towards mid latitude ridges only, its a classic tell tale sign.

I would understand your point if there was more of a up and down snake like pattern to the gfs and ecm ext ens. However, there isn't. They just go one way. This could change of course but today the trend is clear as we approach Christmas. I think 'cold' is the watchword

[Mucka]

Some interesting example of the resurgence of the Scandi ridge in GFS ensembles with this being one of the more dramatic.

If it happens then we need the undercut and WAA to head toward Greenland like this.