Model Output Discussion - cold spell to end Autumn

[Singularity]

  

Shallow low Thu-Fri, N. American trough actually retrograding slightly, and clean, quite intense cold flow across the UK by day 8. 

A good effort from JMA and shows how wide the spread of outcomes remains  

[Frosty.]

Just now, blizzard81 said:

The ecm is far more promising than the jma in the latter stages for long term cold. 

Indeed it looks like a locked in cold pattern towards the end..very good output for coldies  today, better than yesterday..trends! 

[Scandinavian High.]

6 minutes ago, Steel City Skies said:

I wouldn't worry about the uppers at that range, tbh. What is encouraging is the regular return to cold in the longer term

Folks where saying this to current cold snap uppers to warm for snow and look what happened london saw its first snow yesterday:.

[nick sussex]

Interesting.

Whats expected upstream is possibly a brief break in the high amplitude pattern before this re-loads.

So some energy gets thrown east as that happens before the PV pulls back nw again.

Turning colder late week into the following weekend, slightly below
seasonable. A pile-up across the N Atlantic early week the upstream
pattern buckles and becomes amplified by late week. A H5 ridge-trof
pattern across N America both energy and Arctic air become displaced
S across E Canada/CONUS within the mean H5 trof with no where else
to go. Two things worth noting.

Some indications that the H5 ridge-trof pattern breaks briefly allowing energy to
escape before H5 ridge-trof pattern reloads, there is less certainty
in specifics further out in time as there are a lot of moving parts.

[blizzard81]

1 minute ago, Frosty. said:

Indeed it looks like a locked in cold pattern towards the end..very good output for coldies  today, better than yesterday..trends! 

Let's hope it stays that way this time. Had enough of this constant roller-coaster. I feel sick. 

[phil nw.]

ECM just falling short in this run when looking for better chances of snowfall lower down.We do need the better Atlantic ridging that JMA,GFS and UKMO are suggesting so that we achieve that sharper transit of cold south.

ECM if that verified would be less cold overall and although remaining on the cold side not the deeper cold uppers. 

Overall though a decent set for coldies this evening just again the ECM a little less tasty but time yet for it hopefully to find a bit more amplification.

Edited December 1, 2017 by phil nw.

[swebby]

16 minutes ago, Singularity said:

......"Important caveat that if tropical convection doesn't behave as ECM and GFS are predicting over the coming week, the balance of power will shift again - though the observed AAM kick today is an encouraging sign that it just might. ".......

Hmmm, in that case a house of cards springs to mind, my confidence in how those models handle tropical convection is not great.  

[Methuselah]

6 minutes ago, abbie123 said:

Folks where saying this to current cold snap uppers to warm for snow and look what happened london saw its first snow yesterday:.

True. But yesterday's 850hpa's were around -6 or -7C...If the ECM is right (let's hope it's not!) and -4 is anything like representative of reality, cold rain is all low-lying areas can expect...How horrible!

[I remember Atlantic 252]

GFS just seems to be holding low close to us for too long, no other model does, expect on 18Z for the low to clear quicker, cleaner northerly, but not as snowy for the west

[Met4Cast]

I think people are putting far too much emphasis on the 850hPa temperatures the ECM is showing for a date that's over a week away. It's utterly pointless looking at those details so far out when very small changes could easily turn things more favourable. 

ECM still out of kilter with the rest of the models but it's a vast improvement on the runs we've been seeing over the past couple of days.

[Singularity]

14 minutes ago, nick sussex said:

Interesting.

Whats expected upstream is possibly a brief break in the high amplitude pattern before this re-loads.

So some energy gets thrown east as that happens before the PV pulls back nw again.

Turning colder late week into the following weekend, slightly below
seasonable. A pile-up across the N Atlantic early week the upstream
pattern buckles and becomes amplified by late week. A H5 ridge-trof
pattern across N America both energy and Arctic air become displaced
S across E Canada/CONUS within the mean H5 trof with no where else
to go. Two things worth noting.

Some indications that the H5 ridge-trof pattern breaks briefly allowing energy to
escape before H5 ridge-trof pattern reloads, there is less certainty
in specifics further out in time as there are a lot of moving parts.

Cheers as usual for updating us - this is where the segment splitting away idea comes from although I will concede that a larger-scale evacuation with the dregs left behind rebuilding ECM-style does have some credence when looking at it from this angle. Both options offer interest, but ECM at a later timeframe and with dependency on the sliding low moving in a nice way (so not as per the 12z det.). 

Oh and this is the H-W phase space finally updated. Gives a loose overview of what's at stake. Interesting how GEFS powers straight on while ECMF weakens for a time before waking back up in a very useful position but after rather a long period of time. GEFS seems much better from this perspective for knocking down the La Nina, but these lines can hide some important aspects of the MJO. Would like to see a bit more enthusiasm from ECMF on this diagram nonetheless.

Okay, I think that's enough from me for a Friday evening  

Edited December 1, 2017 by Singularity

[Sky Full]

Now then, when I am shown a precipitation chart this is what I want to see....

.    or  

Only seven days away - surely it can't be that far off what's going to happen...??  

[Methuselah]

3 minutes ago, Danny* said:

I think people are putting far too much emphasis on the 850hPa temperatures the ECM is showing for a date that's over a week away. It's utterly pointless looking at those details so far out when very small changes could easily turn things more favourable. 

ECM still out of kilter with the rest of the models but it's a vast improvement on the runs we've been seeing over the past couple of days.

No-one's putting emphasis on anything, Danny, I'm merely reporting what the model says...I suppose I could have just assumed that -4 really means -8 and gone on from there...But what would have been the point of that?

[nick sussex]

If we take a blended solution with the outputs meeting halfway then that's a decent starting point.

And we're not looking at two solutions with one offering mild mush and the other cold.

It's not like the ECM later doesn't have scope for improvement and those NOAA discussions are optimistic because it might be a brief attack from the PV which then heads back nw.

The Azores high is stuck to the west and that's good news. At this point I just want to get the earlier timeframe locked in so the low clearing east and getting the ridge to the nw.

The inference from NOAA and looking at the US forecasters fax chart for T168hrs is they prefer the more amplified solution.

I'll have more news when the State Forecasts update.

[comet]

I see other posters are now jumping aboard the cold train for December and perhaps onwards although with different reasoning my own and others although if all roads lead to winter nirvana then who gives a jot how we get there. Ecm this evening does seem to fast but can not be completely discounted. Love to see the gfs somewhere near correct (not quite as deep a low) giving a countrywide major snow event. Massive difference with the gfs extended output between the 06z and 12z the 06z throwing a strong Alaskan ridge into the Arctic but completely missing on the 12z thus not as amplified until FI near the end.

 

 

 

 

 

0

[ACCOUNT DELETED]

4 hours ago, nick sussex said:

Well yes but the reason I’ve referred to it as displaced is because we often see the Azores high ridging east into southern Europe in response to the more common winter jet stream pattern.

Its not allowed to do that here because the jet is curving se into the Continent.

So you’re right it’s over the Azores but has been blocked from extending eastwards and displaced from where it’s normally located especially during recent winters.

 

Ah I get what you're saying now.

Many thanks for the informative reply, much appreciated  

[Frosty.]

In terms of longevity and eventual potency, this Ecm 12z day 10 chart absolutely oozes wintry potential, it reminds me of the charts we had in Nov / Dec 7 years ago.  We already have other output showing wintry weather even sooner (ukmo 12z day 6)..hopefully all roads lead to cold from later next week!!

I'm really hoping the next cold shot will be more substantial (longer / potent) compared to this week's cold snap.

[Catacol]

Tamara got there first... but the anticipated WDT update today is above expectations. Injection of atmospheric momentum will, without doubt, serve to extend the period of amplification and counter any sense of a flat Nina pattern. For me this means my December best guess is bust already, because I neither expected such an early surge of renewed poleward energy nor to such a level. However the possibility of this was always made clear - timing out.

So it’s time to modify that best guess. Fergie’s tweet is significant - it suggests the jet will break out to the south with amplification allowing maintenance of heights to the NW. Trop led pattern continues to suggest the vortex will not lead the dance yet (another surprise if I’m honest) and chances of a below average December are increasing. Damianslaw’s earler post was an excellent illustration of possible pattern shape.

Going forward this all sets up for a rather interesting January... earlier than hoped for when posting a couple of weeks back. MJO into 7-8-1 orbit by months end may indeed now be a possibility on the back of the AAM spike and weak Nina pattern. End product? Do not rule out easterlies in early January with bumper lows running into the block. As GP has said - if we can get enough cold pooling over Russia, and extended forecasts are seeing pooling in central Russia 6-8 degrees below average by mid December, then a severe spell of weather in mid winter is not beyond the bounds of possibility now.

Vortex recovery or a deepening Nina could still, of course, override this. Ill be checking ENSO conditions carefully later...

[feb1991blizzard]

Extended eps are flatter across the atlantic with less defined Atlantic / Greeny ridge, still decent with flow from slightly n of west but not as greater N'ly component as the 0z suite.

[Chesil View]

Can't help it but with Tamara's GP's and Catacols educated musings. Could it just be that Steve Murr's 1962 analog from a few days back might actually come close to the mark? Just wondering to myself that's all.

[comet]

32 minutes ago, Catacol said:

Tamara got there first... but the anticipated WDT update today is above expectations. Injection of atmospheric momentum will, without doubt, serve to extend the period of amplification and counter any sense of a flat Nina pattern. For me this means my December best guess is bust already, because I neither expected such an early surge of renewed poleward energy nor to such a level. However the possibility of this was always made clear - timing out.

So it’s time to modify that best guess. Fergie’s tweet is significant - it suggests the jet will break out to the south with amplification allowing maintenance of heights to the NW. Trop led pattern continues to suggest the vortex will not lead the dance yet (another surprise if I’m honest) and chances of a below average December are increasing. Damianslaw’s earler post was an excellent illustration of possible pattern shape.

Going forward this all sets up for a rather interesting January... earlier than hoped for when posting a couple of weeks back. MJO into 7-8-1 orbit by months end may indeed now be a possibility on the back of the AAM spike and weak Nina pattern. End product? Do not rule out easterlies in early January with bumper lows running into the block. As GP has said - if we can get enough cold pooling over Russia, and extended forecasts are seeing pooling in central Russia 6-8 degrees below average by mid December, then a severe spell of weather in mid winter is not beyond the bounds of possibility now.

Vortex recovery or a deepening Nina could still, of course, override this. Ill be checking ENSO conditions carefully later...

Seems to me they are playing catch up. Signs were there long before now. Lol  we could still all be wrong.

Edited December 1, 2017 by comet

[feb1991blizzard]

Just for fun EPS number 38 gives a right dumping for Wales and parts of the Usually snow starved SW.

[phil nw.]

Day 7 GFS mean-850's and the 2mtr temperature graph-Warks.

 

One word-cold.

[bluearmy]

16 minutes ago, feb1991blizzard said:

Extended eps are flatter across the atlantic with less defined Atlantic / Greeny ridge, still decent with flow from slightly n of west but not as greater N'ly component as the 0z suite.

An interesting one Feb - if the Atlantic ridge is ebbing too far north then the system coming around the top may be forced to run se to our east. A flatter pattern to our west allows the low to head se into the base of the troughing or drop far enough to the west which could mean warm sectors are avoided. the spread on the ecm days 8/10 reveals that we could see the Atlantic low coming in further west. The extended eps continuity good with nw European low anomoly and sceuro upper trough manitained. 

[Man With Beard]

Quite surprisingly it seems the big 3 are now roughly in the same direction for the next 7 days. GFS has picked this pattern several times in the past few days so well done there!

As an aside, worth taking note that the ECM op was a complete outlier next to its ensembles last night by D8 - and has now joined them today. I think I'll pull this example out every time someone says the ensembles are a waste of time