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Model output discussion - proper cold spell inbound?


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9 minutes ago, Captain Shortwave said:

I think Lorenzo's post in the strat thread is worth a read, as to me it certainly offers an explanation on why we saw the strong signal for the UK to turn cold from around the 19th/20th and why this signal has somewhat vanished from the model output.

It seems that a few days ago we were getting a clean separation between the two lobes of the polar vortex throughout the layers of the stratosphere which pretty much gave a clean route for heights to build in the Atlantic and allow a flow from the east to develop as a result. The reality is that the two lobes don't stay separated for a long enough time with the Siberian lobe transferring to the stronger Canadian lobe which prevents the strong ridging in the Atlantic which allowed the quick route to cold. Someone may correct me on this though as I probably have misinterpreted something here.

I have linked the post below.

 

So what does this leave us with, well surely all imperical evidence would suggest that whilst heights remain low towards Greenland and Canada, surely the strength of the jet coming off the eastern seaboard should weaken and potentially pull back west in time which should allow heights to build northwards over Europe. Could this develop into a proper cold easterly over time remains uncertain but the extended outlook still favoured a continental feel to our weather though it looks more likely to be cold and frosty rather than snowy.

Good post, people really should take a look at the link. Explains why models may be struggling here. 

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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 p

Well it's probably fair to say that I've been rather quiet on these forums for the last few years really, especially since 2013. After 15 years of internet weather watching, and more importantly,

Well - ho hum - let's have a sit rep. My eyes are hanging out on stalks.  The pacific first - engine of the climate system. How is our AAM looking in the face of the current high amplitude MJO?

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Another thing that puzzles me is that i was of the understanding that given timings the mjo forcing and ssw effects were not going to happen in tandem (the ssw would have to have been around a week or so earlier) so i would have expected to have seen the effects of the mjo forcing in outputs before ssw. Therefore is it at all possible given as at the same time the Ecm flipped it also killed the mjo to the circle that we are seeing the effects of another mjo fail and not the ssw.

I couldn't imagine given the amazing amplitude of the mjo that even if there was no ssw it would have shown itself in outputs even if it did fail. It seems to be the consensus that what we were seeing in the outputs was the ssw.

Please excuse me if i sound stupid this is my first year at trying to understand the teleconnections and mjo and add them to my model knowledge:)TIA 

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24 minutes ago, Captain Shortwave said:

I think Lorenzo's post in the strat thread is worth a read, as to me it certainly offers an explanation on why we saw the strong signal for the UK to turn cold from around the 19th/20th and why this signal has somewhat vanished from the model output.

It seems that a few days ago we were getting a clean separation between the two lobes of the polar vortex throughout the layers of the stratosphere which pretty much gave a clean route for heights to build in the Atlantic and allow a flow from the east to develop as a result. The reality is that the two lobes don't stay separated for a long enough time with the Siberian lobe transferring to the stronger Canadian lobe which prevents the strong ridging in the Atlantic which allowed the quick route to cold. Someone may correct me on this though as I probably have misinterpreted something here.

I have linked the post below.

 

 

I made this point yesterday morning to @Singularity

 

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2 minutes ago, mountain shadow said:

The reality is the models have backed up a quick tropospheric response to provide decent favourable high latitude blocking for us, we therefore need to wait until early March.

You wont get much cold out of any blocking in March as the sun will be too strong  .

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6 minutes ago, - 40*C said:

You wont get much cold out of any blocking in March as the sun will be too strong  .

Tell that to March 2013..

11 minutes ago, mountain shadow said:

The reality is the models have backed up a quick tropospheric response to provide decent favourable high latitude blocking for us, we therefore need to wait until early March.

Do we? I still think 19th-24th will be the transition to blocked, whether the cold reaches the UK is a different story. I see no reason why it'd take until early March.

Edited by Daniel Smith
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14 minutes ago, Chris101 said:

Another thing that puzzles me is that i was of the understanding that given timings the mjo forcing and ssw effects were not going to happen in tandem (the ssw would have to have been around a week or so earlier) so i would have expected to have seen the effects of the mjo forcing in outputs before ssw. Therefore is it at all possible given as at the same time the Ecm flipped it also killed the mjo to the circle that we are seeing the effects of another mjo fail and not the ssw.

I couldn't imagine given the amazing amplitude of the mjo that even if there was no ssw it would have shown itself in outputs even if it did fail. It seems to be the consensus that what we were seeing in the outputs was the ssw.

Please excuse me if i sound stupid this is my first year at trying to understand the teleconnections and mjo and add them to my model knowledge:)TIA 

Good post .  There’s a time lag with the MJO so it’s unlikely the blocking failure would be in relation to that.

It could be more to do with the post by Lorenzo which explains things re the strat.

I would be shocked if there’s no impact on the NH pattern.  The impact is effected by the base state of the AO at the onset , so the size of the reversal added with the positive AO at the time should lead to a stronger downwelling into the trop .

KS also touches on the issue of blocking , it’s not like the blocking is in the wrong place there is no blocking shown at higher latitudes which suggests a longer wait .

I think we’ll know over the next few days, now that the SSW has occurred hopefully the way forward might become a bit clearer.

 

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34 minutes ago, bluearmy said:

I made this point yesterday morning to @Singularity

 

Indeed you did and well done for doing so :good:

It seeded my growing suspicion that the charts for later next week have been influenced more by the MJO projections than stratospheric developments.

This has now increased even further as I have compared the behaviour of the weaker vortex across the past 8 GFS runs with the tropospheric patterns and found that since the idea of a sustained split lasting for many days was lost, there's been little pattern in the pace of the rejoin with respect to how soon and strongly HLB establishes N/NE of the UK in the troposphere.

In other words, I'm led to conclude that a quick tropospheric response aligned to a split vortex pattern propagating down was lost from the output several days ago and so when looking at the period Thu-Sun next week, we've been chasing MJO-driven Scandinavian highs ever since.

 

This would allow for some more confident expectations for that period if it wasn't for the fact that the balance of power between that and the Canadian vortex segment is extremely uncertain given the combination of model disagreements on MJO behaviour and inherent difficulties handling tropospheric vortex strength when there is steady weakening taking place above it. 

It's not even certain that the weak vortex traversing NW. Eurasia will perform the merger soon enough to prevent the quick response to the SSW after all, though I am starting to see that as a long shot.

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The flatter trop pattern is even more noticeable on the 00z strat ecm charts 

approaching the point where those who feel the models will begin to react to the reality of the reversal will see if they are to be proven right - interesting times indeed !

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Love the passion of this thread in the search of snow and cold.GFS Friday night was the single most best winter run you could ever see but that seems an eternity away now.Models will only get to grips with SSW during the week and there will be back and forth swings from winter nirvana and pleasant spring warmth over next few days.I think this week will be a continuation of what this winter has been all about with some cold days with some snow about in NW britain and accumulating snow above 500ft asl and some wet days Midlands southwards.Temps 3-5 for Northern Britain and 5-9 for Midlands Southwards.After that from next weekends nobody can say with any great confidence but for cold and snow lovers(myself included) we still have a ticket for the raffle although i appreciate we are slowly running out of time.I will just sit back and enjoy this forum and what will be will be but Keep the faith snow lovers:good:

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12 minutes ago, karlos1983 said:

It’s so cryptic in here sometimes, I’m not sure if it’s because people just like to talk in riddles because it makes one sound clever, or so they can sit on the fence if they don’t spell it out! Odd! 

Short term, the GFS ups the anti on Tuesday’s possible snow event! 

FC09242A-F65B-47D1-9AD2-7E18159C7087.thumb.png.e5bc6e5b9d646fbb8b4ca60169409655.png

Ah the club within a club. Sometimes start a sentence with the words "surprised know ones mentioned" blah blah.

 

anyway, a step in the right direction by the gfs I would suggest. Ukmo at t144 is not without interest also.

IMG_0538.PNG

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1 minute ago, Steve Murr said:

GFS much more in tune with what we would expect to see in any transitional phase around Day 7

874074FF-AFFB-4B55-9073-7EC6ABE00E2F.thumb.png.c5d22ebf3947f7a40fa6f7fcd8427cb4.png

What I've noticed is slowly the Block to the East has started to back further West after a few runs in decline. Interesting 

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•back in the madhouse●

Iv'e used my noggle and refrained posting- due to model miss-management, and the daggers in here!!!?..

12z gfs offering up better variation of heights...and also some gain from the mother canadian lobe being syphoned across the eastern qud [email protected] output seems to be sniffing out the ssw...

Ecm 'should gain in evolvement on its 12z...more to this angle.

Lets see how we play out!!??

gfsnh-0-162 (1).png

Edited by tight isobar
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