Model Output Discussion

[Methuselah]

Here goes. Another one...

[TEITS]

Here is an interesting chart.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslReyjavic.png

When it comes to N blocking I always look at the Iceland SLP mean.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslReyjavic.png

The mean for 12th Dec is now 6mb higher than a few days ago. This suggests HP over Iceland is gaining support.

The mean around Scandi stands at 1030mb.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslOslo.png

Obviously this doesn't mean N blocking will occur but its worth keeping an eye out for the SLP mean and if it rises over the next few days.

[Stu_London]

Looking at the models on 24 hours comparison (00z yesterday, to 00z today), the operational run is an upgrade from yesterday. Ensemble wise, there is perhaps 1 more colder run on todays, so a slight upgrade.

The cold runs on GFS occur from around the 240hr mark so I wouldn't expect a huge amount from the ECM yet. Someone has commented it is not a million miles away from GFS at 240 which would be a positive.

To put things in perspective, although the GFS is a slight upgrade this morning, the uncertainty with the other models and the general way modelling works would still lead me to believe that a cold spell is a less than 10% possibility in the model range up to +384

[Pennine Ten Foot Drifts]

Copied from closed thread:

All I will ask is, have we really not seen these types of charts in deep FI in the last ten years ? Or is it a bit of a case of selective memory ??? When the outcome is so desirable it is all too easy to see the evolution as appearing very plausible. At this stage I remain very much with IB, the reliable looks absolutely typical (if perhaps slightly wetter) December weather, and unfortunately I expect to see a regular appearance of phrases like 'if only the jet would play ball.......', 'the trough is just too far west...........', 'pressure just too low around the GIN corridor......', 'stubborn Euro heights..........' etc, (or to paraphrase, 'if only........' !!!), over the next two weeks.

[TEITS]

Copied from closed thread:

All I will ask is, have we really not seen these types of charts in deep FI in the last ten years ?

The answer is NO.

We might of seen these F.I charts in the past during Jan/Feb but I can't remember seeing such N blocking this early in the season in F.I.

[nick sussex]

The ecm de bilt ensembles show two clusters in the latter part of the output.

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

It looks like a cooling trend with one clustering and an easterly with the other, however again the real interest is so far out that at the moment its impossible to say what will happen.

I'm firmly sitting on the fence here because no matter how many factors you have signalling northern blocking alot of things need to go right for this to be able to deliver cold and wintry weather to the UK and western europe.

[chionomaniac]

I am inclined to sway more towards the TEITS rather than the mild option but it may take some time to get there.

What we are essentially seeing is the polar vortex splitting at around T+200. This is no transient feature and has been modeled for some time. The split extends right up into the middle stratosphere. This is significant suggesting that once the split forms, it will not disappear overnight. The split leaves two main sections of daughter vortices - one over Canada the other over Siberia. Current modeling suggests that the Canadian daughter vortex will be the stronger. Now this is where it gets interesting. The position and strength of these vortices, alongside any reducing residual vortex left elsewhere, will be critical in determining whether or not an Easterly will occur. The models are throwing up differing solutions to height rises between the two vortices. One thing that has been consistent is the suggestion of height rises over Alaska and the Pacific region. What we have to hope for is that we can see similar height rises to out north allowing the jet to undercut and bring us our easterly. With this type of set up we have a good a chance as any.

Look at the negative zonal wind anomalies for 60-90ºN and how far they extend into the stratosphere due to the split at T+192.

c

Edited December 2, 2009 by chionomaniac

[karyo]

I am inclined to sway more towards the TEITS rather than the mild option but it may take some time to get there.

What we are essentially seeing is the polar vortex splitting at around T+200. This is no transient feature and has been modeled for some time. The split extends right up into the middle stratosphere. This is significant suggesting that once the split forms, it will not disappear overnight. The split leaves two main sections of daughter vortices - one over Canada the other over Siberia. Current modeling suggests that the Canadian daughter vortex will be the stronger. Now this is where it gets interesting. The position and strength of these vortices, alongside any reducing residual vortex left elsewhere, will be critical in determining whether or not an Easterly will occur. The models are throwing up differing solutions to height rises between the two vortices. One thing that has been consistent is the suggestion of height rises over Alaska and the Pacific region. What we have to hope for is that we can see similar height rises to out north allowing the jet to undercut and bring us our easterly. With this type of set up we have a good a chance as any.

Look at the negative zonal wind anomalies for 60-90ºN and how far they extend into the stratosphere due to the split at T+192.

c

Thanks for that chiono. Is this the result of the recent stratospheric warming? I am asking because the stratospheric temperatures have recently returned to below average and the forecasts don't look promising for the foreseable! http://strat-www.met.fu-berlin.de/cgi-bin/times?plot=temps&alert=1

Karyo

[Frosty.]

Here is an interesting chart.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslReyjavic.png

When it comes to N blocking I always look at the Iceland SLP mean.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslReyjavic.png

The mean for 12th Dec is now 6mb higher than a few days ago. This suggests HP over Iceland is gaining support.

The mean around Scandi stands at 1030mb.

http://charts.netweather.tv/ensimages/ens.20091202/00/prmslOslo.png

Obviously this doesn't mean N blocking will occur but its worth keeping an eye out for the SLP mean and if it rises over the next few days.

Despite the FI eye candy we still havent had a cold snap of note so far and this time last year we had already seen 3 cold spells so it's taking a lot longer this time. The gfs 00z in FI was probably the most wintry sequence of charts i've seen in a long while but the chances of it occuring are probably no higher than 0.1%

Remaining unsettled with temps veering from slightly below to slightly above the seasonal average during the next 7 to 10 days IMO.

[chionomaniac]

Thanks for that chiono. Is this the result of the recent stratospheric warming? I am asking because the stratospheric temperatures have recently returned to below average and the forecasts don't look promising for the foreseable! http://strat-www.met.fu-berlin.de/cgi-bin/times?plot=temps&alert=1

Karyo

See strat thread Karyo.

Oh and I will point out the worse case scenario is that after the split a segment of residual vortex resides near southern Greenland allow us to be caught up in southerlies that eventually manage to cross the NP! A similar thing happened in Feb.

Edited December 2, 2009 by chionomaniac

[Iceberg]

The charts have always shown some northern blocking so those ensembles arn't really a surprise.

It's whether the LP's go south enough and or stop in the atlantic to allow us to benefit from this.

Atm there is no realistic sign of this happenening.

We've always had some FI Candy even in November and December but hopefully we largely ignore it or treat it as a nice to have, (just like winning the lottery).

Re the split vortex, we've not really had any stable vortex yet this year, so I am tempted to be pessimistic about the split vortex, it might lead to cold, but it equally might not, I think it's a fairly neutral development.

Depending on where the split occurs we *might* get more amplification of the jet, but again it's not a certainty.

[Cal]

Synoptic Porn , Lol

http://www.wetterzentrale.de/pics/Rtavn3841.png

[Methuselah]

GFS is being very persistent (so far) with its idea of a cold blast in FI...But (somehow?) I really don't think we'll be seeing sub-12C 850s into the SE??? That's bloody cold!

[Shunter]

the 06z brings the initial belt from the east at T312 so moving forward

http://www.wzkarten.de/pics/Rtavn3123.png

[TEITS]

Im probably jumping the gun here but if an E,ly does arrive i.e 06Z then this would deliver far more convective snowfall than if it occured in Feb.

The simple reason is due to the SSTS in the N sea. This is another reason why im so excited with the current F.I charts because -15C upper temps screaming across the N Sea would bring huge amounts of snow.

The same happens around the Great lakes of the US. You will often find lake effect snow fades into the latter half of the winter due to the great lakes freezing up. This is why in some respects I don't like frequent cold N,ly outbreaks during Nov, Dec.

[Harsh Climate]

http://www.wetterzentrale.de/pics/Rtavn3602.png

This is the greatest chart I have ever seen! Shame the chances of it coming off are probably below 1%....

[londonsnow]

http://www.wetterzentrale.de/pics/Rtavn3602.png

This is the greatest chart I have ever seen! Shame the chances of it coming off are probably below 1%....

FI etc but yes an astonishing chart that

[DAVID SNOW]

Synoptic Porn , Lol

http://www.wetterzentrale.de/pics/Rtavn3841.png

LoL ...What a run...Maybe, just maybe

[Shunter]

http://www.wetterzentrale.de/pics/Rtavn3602.png

This is the greatest chart I have ever seen! Shame the chances of it coming off are probably below 1%....

Its a developing synopsis, lets see if the consistency remians as we head through the next 48 hours or so.

The 06z op brings -14 850's into Kent on 15th December.

NOAA are still highlighting great uncertainty in their early morning discussions....

http://www.hpc.ncep.noaa.gov/preepd/preepd.html

Although the timeline hasn't reached the ECM longer forecast reaches yet, there is still some other support for this blast from the East here..

http://www.wxmaps.org/pix/temp4.html

[Harsh Climate]

This is why I like the GFS running out that far, because it shows you what could happen if everything went our way for once and what the results would be. But only a fool would get excited about it lol..

[nick sussex]

Im probably jumping the gun here but if an E,ly does arrive i.e 06Z then this would deliver far more convective snowfall than if it occured in Feb.

The simple reason is due to the SSTS in the N sea. This is another reason why im so excited with the current F.I charts because -15C upper temps screaming across the N Sea would bring huge amounts of snow.

The same happens around the Great lakes of the US. You will often find lake effect snow fades into the latter half of the winter due to the great lakes freezing up. This is why in some respects I don't like frequent cold N,ly outbreaks during Nov, Dec.

You do make me laugh Dave! I think most people on here would take frequent northerly outbreaks, rather than waiting for a possible easterly with very cold uppers running over a warmer than average north sea! i admire your optimism, if the PV does split then its just hoping the pieces go in the right place, perhaps i'm just a bitter old cynic now after so many easterly let downs, i would agree there are differences at this stage of winter compared to some previous PV limpeted to southern Greenland scenarios, for the moment I'm remaining lukewarm over any output and will just sit back and see how things pan out.

[TEITS]

If the 06Z went out even further you would have a belting N,ly as pressure begins to rise over Greenland.

The alternating N,lys/E,lys is what happened in 1947 as HP alternated between Greenland/Scandi and at times stretched across both areas.

Im going to resist getting too excited but the potential for mid Dec is huge.

[Methuselah]

Im probably jumping the gun here but if an E,ly does arrive i.e 06Z then this would deliver far more convective snowfall than if it occured in Feb.

The simple reason is due to the SSTS in the N sea. This is another reason why im so excited with the current F.I charts because -15C upper temps screaming across the N Sea would bring huge amounts of snow.

The same happens around the Great lakes of the US. You will often find lake effect snow fades into the latter half of the winter due to the great lakes freezing up. This is why in some respects I don't like frequent cold N,ly outbreaks during Nov, Dec.

Yes, as you say, it would be something special (if it ever happens! )...You're not suggesting that the North Sea's going to freeze over, are you Dave??

[Nick L]

If the 06Z went out even further you would have a belting N,ly as pressure begins to rise over Greenland.

The alternating N,lys/E,lys is what happened in 1947 as HP alternated between Greenland/Scandi and at times stretched across both areas.

Im going to resist getting too excited but the potential for mid Dec is huge.

Are you still going to abstain from looking at every model run as they come out if this continues?

[Stu_London]

Another interesting operational run - is that 3 on the spin.

Definate upgrade from the 06z yesterday.

Ensembles will be interesting from around the 11th. There were about 3 or 4 that went cold on yesterdays 06z and about 5 or 6 on the 00z today.

Whilst FI should be treated with extreme caution and there is virtually no chance of any given scenario beyond +300 playing out exactly, it has been useful for spotting trends in the past, particularly with pressure rises to our north and north east.

Interestingly, the solution that the 06z playes out would give a shot of some pretty sustained cold and wintry weather rather than our normal 1-2 day affairs.