Model Output Discussion - 05/01/2016 18z onwards

[tight isobar]

As chionomaniac' flags up the kara high...im quite surprised of its non mention of late when it's really the main driver of the polar disorientation! !!

[Geordiesnow]

2 minutes ago, nick sussex said:

I think given the timeframes involved if the UKMO has actually picked up on the right trend then we should see this in the GFS 06hrs run.

Even allowing for the GFS 06hrs run not being viewed as the best the extra 6 hours of newer data and the fact its what happens before T120hrs should mean that if theres anything to the UKMO it would edge towards it.

I'll be surprised if it does Nick, if anything that trigger low/trough is keep on projecting to be further westwards, if the ECM/UKMO predictions for Monday was accurate with this feature(when the ECM initially backed the UKMO of having it further East and out of the way/), we would be in a cold NW'ly flow by Monday yet this morning runs(barring the UKMO) still has the UK in a SW'ly flow thanks to the trough. Can't underestimate how the change in prediction of this trough has affected the output in terms of how quickly the floodgates open, forget about any west based NAO being the spoiler, its the trough that could be ruining things here. The west based NAO would only ruin how long such cold would last but its not a spoiler in how cold it could of become in the shorter term. 

It would kind of sum this winter up though sadly that the UK would remain wet in the short term until that trough does eventually clear and the air following on behind is not as cold as it could of been as it has been modified. Still you never know, miracles do happen but I just think its unlikely now. 

[Duane S.]

5 minutes ago, nick sussex said:

I think given the timeframes involved if the UKMO has actually picked up on the right trend then we should see this in the GFS 06hrs run.

Even allowing for the GFS 06hrs run not being viewed as the best the extra 6 hours of newer data and the fact its what happens before T120hrs should mean that if theres anything to the UKMO it would edge towards it.

I'd agree with that Nick. If even a partial move to a more amplified solution isn't shown on the 06z we should probably expect a watered down UKMO this afternoon. Either way, I do feel this evolution to cold has got a lot of twists and turns left in its locker yet. 

[Nick F]

It is a danger, with the omega block building too far west over western Greenland/Labrador Bay and a strong jet cutting underneath, that the door is open for lows to slip through to the UK from the SW. It would have been far less traumatic if an Atlantic ridge to Greenland build further east.

What is unusual, is how far south the low(s) are coming up from, quite unusual to see a deep sub-tropical low in January south of the Azores move NE to the UK. So as John Holmes said, it may not be modelled well. The movement of this troublesome low will depend on how it phases with a shortwave upper trough in the strong westerly flow beneath the Greenland block which is modeled to move east past the Azores later next week. If the shortwave picks up the low and deepens it, it will naturally swing NE towards the UK. If the low doesn't phase properly with the shortwave ... then the low will just languish near the Azores and we are more likely to have un-impeded northerly flow.

So, a lot of uncertainty past t+144 with regards to developemnts to the SW. It's still getting colder next week, though some uncertainty how long the cold will last across southern areas, the cold likely hanging on across the north though, even if lows attack us from the SW.

Edited January 8, 2016 by Nick F

[feb1991blizzard]

8 minutes ago, chionomaniac said:

Even if the west based -ve NAO and Azores low does come and scupper any possible cold spell - and that is certainly not assurred, the NH profile is still very disturbed from the Kara high episode so I wouldn't rule out another favourable block. 

The west based NAO was always going to be the tripwire this winter and has appeared in numerous wENSO analogues.

Any chance of a top down SSW occurring to re-inforce the Arctic blocking in Feb, i cant see many more cold snaps with just trop induced episodes, eventually surely the zonal pattern will re-establish if the mid-upper strat vortex doesn't start getting disrupted soon.

[Singularity]

In many ways the Azores low is not the main catalyst for the undoing of sustained cold prospects; it's behaviour is a consequence of earlier changes.

What looks to me to be the main issue with the 00z ECM det. is the fact that the U.S. trough is able to push further east than was the consensus 48 hours ago, triggering a rearrangement of the Arctic profile as the Arctic High links with the western U.S. rather than the mid-Atlantic ridge. This may be related to the extent to which that shortwave gets west of the UK at +120 hours - the ridge is under attack from both sides at once.

The Azores low is then free to make a run at the UK - though not with the full on height rises over Europe that GFS keeps coming out with. 

Speaking of which, that is also a consequence of the U.S. trough getting further east, but in this case (the GFS 00z det.) there are residual low heights over the western U.S. to prevent the Arctic High running away to that location. So the Azores low can't come east so easily - but by phasing with the U.S. trough (achievable because it's moved so close), it finds the energy needed to power NE anyway.

 

I will put my hands up and admit that I did not expect to see ECM re-arrange the Arctic profile so dramatically on its 00z det. run. A trend toward a west-based neg. NAO is fair enough but the removal of the Arctic High contradicts what I've gathered from the MJO/GLAAM signals. Looking at the ensemble mean, it looks like all manner of blocking positions are being explored:

Which leaves me wondering if it's the model or myself misreading the signals.

 

Considering all of the above, I suppose if the subtropical low manages to stay further south(west) then we'd just about get away with the GFS pattern over the U.S.

I still believe that GFS/GEFS are seriously undermined when it comes to their longer range guidance capabilities at the mo, but after the morning shift by ECM and its ensembles, I can't see much reason to disagree with the modelled U.S. pattern out to a week's range, though that trough could still revert to a position a bit further west. Too early to place much faith in it either course - uncertainty reigns supreme.

[mountain shadow]

And if this moisture laden sub tropical low does push In against colder air it opens up a tantalising prospect of a monumental dumping of snow somewhere. 

[tight isobar]

think after current modeling in regards ro the messy walk in' to the incoming cooling trend.

Eyes should be turned to the yugorsky peninsula @kara sea...I think that's where hope may reign for a more pronounced cold going down the line...

[radiohead]

If anything the 06Z GFS seems to be a step even further away from the 0Z UKMO. Will be interesting to see how it handles the Azores low in the later stages, I still feel that aspect is very likely to change as we go forward.

[IDO]

The disruption to the mid latitude by the LP system even more dramatic on the 6z with the WAA cut off from Greenland over 3 days earlier than the 0z:

current run   0z 3 days later with cut off:

Totally new development so no idea what happens from here!

Edited January 8, 2016 by IDO

[warrenb]

The problem is the sub tropical low has formed right where the northward push of the high is supposed to come from. So a giant shortwave to the south scuppers the cold rather than a small shortwave to the north.

[PolarWarsaw]

Morning, 

Well the charts did what I feared they may overnight, but they actually went too far the other way and allowed the Azores low to virtually ruin every run in the mid-latter time period. I've gone from fearing it may get in the way to thinking that the models don't know how to handle it yet and think they are probably over-playing it slightly. The fact that forecasters on Twitter are gung-ho for a DECENT Cold SPELL, not just a 2-3 day snap suggests that we may see a few upgrades yet. This pattern shouldn't be sniffed at still, it's going to bring us at least 3-4 days of jacket weather and the potential for a few flurries in select places. 

If anything, this MIGHT work out better in the long run with a few harsh frosts cooling soil and the earth down for a potential Torpedic assault later in January.

Edited January 8, 2016 by Polar Maritime
To move discussion on..

[rory o gorman]

We now have the room to develop a shortwave on wednesday .... Continues to trend west . 

[tight isobar]

6z 

And pinpoint Greenland begins to close her doors. ..

Seen enough of this run already! 

[shaky]

Looks better and slightly further east at 144 hours!!

[karlos1983]

3 minutes ago, tight isobar said:

6z 

And pinpoint Greenland begins to close her doors. ..

Seen enough of this run already! 

Not convinced, we shall see

fl starts way back as far as I'm concerned, jury still well and truly out on this, and that is currently the ONLY thing that is assured right now.

[booferking]

Second bite of the cherry the GFS is going for @168.

[Southender]

Better to my eye. Azores LP further South and a renewed blast of energy trying to ridge back up to join the Greenie HP

[Singularity]

Just now, tight isobar said:

think after current modeling in regards ro the messy walk in' to the incoming cooling trend.

Eyes should be turned to the yugorsky peninsula @kara sea...I think that's where hope may reign for a more pronounced cold going down the line...

I agree with the overall concept there - the potential for Feb is by far the greatest of the winter.

The hope has been for some entertainment in the meantime, which remains possible for many, though it looks very difficult for southerners to get much out of it unless things change again. I must say the difference between the raw UKMO and the other models with respect to that shortwave on the western flank of the trough, at just +96 hours, is astounding. 

The +84 FAX does show the shortwave feature, though with the ridge to the west appearing more of a wall against movement west. 

This is mainly due to a more coherent link between the mid-Atlantic and Greenland though. We need the UK to keep hold of that shortwave and ideally absorb it as per the 00z UKMO but it does look to be the outside chance unfortunately.

 

Meanwhile... GFS 06z out to +156, and that Azores low isn't reaching north like it did on the 00z which is helpful as that ridge in the mid-Atlantic ridge stays stronger. This positive is rather counteracted by the high heights over Greenland fleeing west, however. 

On the other hand, high heights are migrating toward Greenland from Siberia. This could be an amusing run if nothing else. Also worth watching in case the Azores and U.S. troughs merge but with a negative tilt (angled SE to NW with eastward progression limited), as this is how an omega block could be achieved. You never know!

[radiohead]

Azores low is more blocked on this run.

Edited January 8, 2016 by radiohead

[Man With Beard]

Well this is mind-boggling. On the GFS 06Z, the loop around Greenland attempts to close faster. But the "Bermuda low" gets less involved, meaning less forcing from the south. Meaning by T168, the chart is somehow colder than on the 00Z! What a mess.

High pressure from the Atlantic making another dash through the gap towards Greenland at T180?

Edited January 8, 2016 by Man With Beard

[london and south east kent]

Hi all its still good for cold next week the gfs is slowly going with the ukmeto my take on  early next week we all will be in the cold air Monday from the north with some snow  A round later on..

[Iceberg]

The sub tropical air does not come through on this run and instead in the Day 7-9 timeframe the Tm is pushed northwards as WAA. Far too many judging a very complicated set up too early, but it goes to show the total uncertainty still in the models.

[That ECM]

So the gfs shows what a tricky situation this is and how difficult it is to have much confidence past T96!!!!

[bradymk]

GFS 6Z showing us to keep the faith in the mid range due to the continued inconsistency. We still have some disagreements in the 3/4 day range let alone 8 days time when we have an Azores low that needs to be modelled correctly. History tells us that will probably play a big problem with inter run consistency, so for now, we keep waiting...