General Model Output Discussion

[Paul Sherman]

Please carry on here in Readiness for the GFS 18z and please try to stay on Topic as all off topic Posts will be moved to the Cold Spell Discussion

Regards

Paul S

[Uncle_Barty]

Quick question... I have read about the 'Atlantic trough being negatively tilted' recently - can someone explain what that means? Is it a reference to the axis of the trough not being north/south, but more north-west/south-east? or is it north-east/south-west?!

[SMU]

2 possibly 3 steps to the Easterly.....

Its a rare beast the siberian high, its recent departure from NW europe ( last 20 years) has largly been due to lower snow cover over Eurasia & the perpetual + AO pattern.

The Siberian high needs a southerly bifercated jet to allow a ridge to continue to be 'thrown' & Migrate West...-

Because of its location,IE a long way from here its almost impossible to see a ridge achieve an uninterupted uniform Journey west-

Its a case of move ridge West, gets blocked- then a shortwave drops in south across its western flank & it retrogresses west again, we then see it get blocked by the jet again,until we see another shortwave digs SE across its southern flank allowing the pathway westwards again-

looking at the outputs & the way the jet is carving out the ridge it will take a good 2 or 3 shouts of the Siberian express before the UK sees conditions condusive to snow,although at the second bite we could see cold enough air at the surface for snow *IF* a shortwave is digging in the exact right location across us-

To see this happening you need to look at the NH plots NOT the NW europe ones-

I think the JMA run tonight looks the best-

Retrogression 1-3...........

take T 24- ( stage 1)

Jet

note the shortwave dropping through scandi, that will change the way the high is tilted on its axis- IE alligned NE SW- When its that shape the CAA is moving west under the high-

Over 24 Hours from 24-48 the upper air cold pool is now shifted Westwards -into Eastern Europe-

REMEMBER THE SIBERIAN HIGH WILL NEVER MAKE IT TO WHERE WE WANT IT UNLESS THE ATLANTIC JET AMPLIFIES IN x2 STREAMS ( BIFERCATES)

Look at T72 over central / Northern Europe, the HOOK shape of the jet, its gone from 24 - 48 - 72

Its pulled the shortwave South then WEST -

Also note how its CUT OFF- so theres no contiuned trailing arm of the jet-

As soon as that jet clears through Northern scandi & the shortwave drops south- because there is know no jet then the high can ridge west-

Note the 72 to Chart to the 96 chart ( 500 mb)

look where the cold has got to for 96-

approaching central euope- only to be stopped again waiting for the cut off jet to come through....

Also observe whats happening in the atlantic at 96 ( the last 96 Jet chart on JMA)

THe second 'hook' developing-

Guess whats going to happen now-

T96- T120-T144

http://www.meteociel.com/modeles/jma/run/JN144-21.GIF?12-12

we have the second shortwave diving South through - & a ridge being carved out to the NW, as the shortwave gets through to the south- that jet has been cut off from the flow just like the first 'hook'so as a result at 144 theres nothing stopping the newly formed ridge thats to the WNW of the UK ridging East & joining the big high to the East-

see what happens 168 to 192-

http://www.meteociel.com/modeles/jma/run/JN168-21.GIF?12-12

http://www.meteociel.com/modeles/jma/run/JN192-21.GIF?12-12

Ridging complete & the upper cold pool is continued to be ushered west-

http://www.meteociel.com/modeles/jma/run/JN120-7.GIF?12-12

http://www.meteociel.com/modeles/jma/run/JN144-7.GIF?12-12

http://www.meteociel.com/modeles/jma/run/JN168-7.GIF?12-12

& finally on our doorstep-

http://www.meteociel.com/modeles/jma/run/JN192-7.GIF?12-12

Note the 192 chart again-

http://www.meteociel.com/modeles/jma/run/JN192-21.GIF?12-12

see the third hook of the jet to the SW of the UK-

1/2 days later would be a stunning chart-

At this point is worth saying this is just the JMA, however ECM is identical on the 2 stages, apart from the ridge is not quite as far west as JMA at 192- infact its here-

http://www.meteociel.com/modeles/ecmwf/run/ECH1-192.GIF?12-0

& here we go 216 + 240-

http://www.meteociel.com/modeles/ecmwf/run/ECH1-216.GIF?12-0

http://www.meteociel.com/modeles/ecmwf/run/ECH1-240.GIF?12-0

Poor end result...???

Lines up with this-

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560129.gif

+24

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560130.gif

+48

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560131.gif

+96

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560201.gif

Im not saying that this exacly how is will pan out but the summary would be-

days 4/5- mildish with southerlies ( temps just above the Seasonal ave)

days 6/7-- Orientation of flow more South Easterly POSS easterly- temps around 5c

days 8/9-- more direction of Easterly in the flow + possiblysignificant colder

Day 10 & beyond.... An attack from the East best case sceario-worst case slightly less cold SE'winds with the train not quite making it

CIAO

Steve

Edited January 12, 2010 by Steve Murr

[bluearmy]

Quick question... I have read about the 'Atlantic trough being negatively tilted' recently - can someone explain what that means? Is it a reference to the axis of the trough not being north/south, but more north-west/south-east? or is it north-east/south-west?!

North west/south east jim. will encourage the lows to head into the continent and undercut which drags the block west rather than heading ne over the top of the block which will surpress it.

anyway, encouraging dutch ens

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

probably no more than 20% of the runs breaking zero by the latter part of the tun

[Uncle_Barty]

Thanks, bluearmy, thats what I thought.

[SMU]

& just to add, because debilt is that be farther east- on the continent stage 2 of retrogression is enouth to get those surface temps below freezing again....

S

[Glacier Point]

2 possibly 3 steps to the Easterly.....

Im not saying that this exacly how is will pan out but the summary would be-

days 4/5- mildish with southerlies ( temps just above the Seasonal ave)

days 6/7-- Orientation of flow more South Easterly POSS easterly- temps around 5c

days 8/9-- more direction of Easterly in the flow + possiblysignificant colder

Day 10 & beyond.... An attack from the East best case scearion- slightly less cold SE'winds with the train not quite making it

CIAO

Steve

I'm seeing the Global Wind Oscillation undergo a switching between phases 0 and 4 over the next 20 days which might be useful in generating that discontinuous restrogression.

http://www.esrl.noaa...gcm/gwo_40d.gif

Falling torques will drive towards phase 0 in the next few days (shutting off northern flow).

The average life cycle of torques is 10 days, so back to phase 4 (northern arm flow increases) around 23rd.

Falling torques again, 25th onwards. Interesting timeline given the Madden Julien Oscillation may well be entering phase 7/8 around that time.

CPC 8-14 day mean height anomaly shows the Atlantic locked out:

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

Edited January 12, 2010 by Glacier Point

[sandstorm2]

2 possibly 3 steps to the Easterly.....

CIAO

Steve

That is a most brilliant summary of what you think might happen and thank you for taking the time and effort to post it.

SS2

[SMU]

I'm seeing the Global Wind Oscillation undergo a switching between phases 0 and 4 over the next 20 days which might be useful in generating that discontinuous restrogression.

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

Falling torques will drive towards phase 0 in the next few days (shutting off northern flow).

The average life cycle of torques is 10 days, so back to phase 4 (northern arm flow increases) around 23rd.

Falling torques again, 25th onwards. Interesting timeline given the Madden Julien Oscillation may well be entering phase 7/8 around that time.

Indeed you need that rollercoaster shape in terms of peaks & troughs to influence the westerly retrogression...

feb 1956 redux..........

S

[bluearmy]

just to add that for the second day running, NOAA cpc have 100% confidence in their anomoly output which GP posted. if we are to head down that slow route back to frigid, cant see much chance for the jan cet to recover, given the mainly continental flow in the interim.

[Tom Montalbano]

Thats quite an example of a severe polar continental outbreak Steve posts there, in 1956.

Courtesy of Robin Stirlings "The Weather Of Britain".

The temp. fell from 7c at 8.00 a.m to -2c at noon, heavy rain to fine powder snow, 31st Jan.

Max. temps on the 1st Feb at Ipswich and Felixstowe were just -6c, with -5c recorded at Kew and Ross-On-Wye.

As Steve suggests, we need a few dice to roll our way to get the very cold air to back west again but who knows this winter has bucked the trend of recent winters, so far!

Regards,

Tom.

[January Snowstorm]

I must admit GP & Steve Murr you bring a wealth of knowledge to the forum.

You guys are excellent at what ye do here, take a bow!

[Nick F]

Poor end result...???

Lines up with this-

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560129.gif

+24

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560130.gif

+48

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560131.gif

+96

http://www.wetterzentrale.de/archive/ra/1956/Rrea00119560201.gif

Im not saying that this exacly how is will pan out but the summary would be-

days 4/5- mildish with southerlies ( temps just above the Seasonal ave)

days 6/7-- Orientation of flow more South Easterly POSS easterly- temps around 5c

days 8/9-- more direction of Easterly in the flow + possiblysignificant colder

Day 10 & beyond.... An attack from the East best case sceario-worst case slightly less cold SE'winds with the train not quite making it

CIAO

Steve

Only difference with the 1956 analogue to what is being progged by the models this evening is the lack of a deep cold vortex dropping down across NW Russia and then drifting SW and W like the 1956 charts you show. I believe these cold pools give greater inertia for lows to undercut the block and of course bring deep cold air west.

Otherwise, there's certainly cause for hope that we'll get winds sourced from the east at some point over the next few weeks, and the source certainly won't be warm.

18z bit slow coming out this evening?!

[damianslaw]

Great post by Steve Murr showing the potential evolution to a blast of Siberian air, but as ever there is some way to go before we are in near reach of such an evolution and very much appears to hang on the strength of energy being exerted into the northern arm of the jet. In recent weeks most energy has been in the southern arm, helping to aid strong heights to the north, now, however, those heights are dissapearing and our best shot at very cold conditions will now come courtesy of deep heights far to our east advecting westwards.

Interesting watching how the shortwaves crashing through the russian high look like fairly weak affairs which as Steve says would help those heights to ridge further west.

Will be interesting to see what happens this weekend with regard to the atlantic, those fronts look like stalling to the east of us and we will maintain a southerly flow, it is suggestive that the atlantic is still fairly weak and it won't take much for those heights to the east to advect our way.

My tentative guess is that we are more likely to be dominated by continental air next week than atlantic, however, the big question I can't answer is whether the continental air will be associated with deep cold uppers i.e. siberian origin or a less cold flow just off the near continent on a S/SE flow.

[snowingtequila]

looks like the 18 is going to bring an easterly in next week

http://91.121.94.83/modeles/gfs/run/gfs-0-174.png?18

http://91.121.94.83/modeles/gfs/run/gfs-0-192.png?18

[SMU]

Cheers PPL-

18z now on board with 3 stage retrogression-

2 hooks ( 2 stages ) at 132- meaning cold air will be very close to the east by 150

http://91.121.94.83/modeles/gfs/run/gfsnh-5-132.png?18

third hook + undercut developing here-

http://91.121.94.83/modeles/gfs/run/gfsnh-5-168.png?18

cold for UK 180/192-

day 8/9 what I was estimating earlier...... error at this range in terms of timings is + 1 or -1 day...

S

[igloo]

looks like the 18 is going to bring an easterly in next week

http://91.121.94.83/...fs-0-174.png?18

http://91.121.94.83/...fs-0-192.png?18

yes it looks like it wants to bring the block further west on this run lets hope this is the start of further inprovements

[rich1]

Colder evolution than the 12z, seems to be following one of the colder runs on that last ensemble suite

trend has been there on a few runs, more particularly some of the ECM ones over the last day or so

[Tom Montalbano]

As well as 1956, the path back to a decent easterly would have a similar route that Feb 91 took.

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910131.gif

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910201.gif

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910202.gif

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910204.gif

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910205.gif

http://www.wetterzentrale.de/pics/archive/ra/1991/Rrea00119910207.gif

Regards,

Tom.

[bluearmy]

IF we head down the evolution offered by the 18z, will be interesting to see if we do indeed pick up the residual cold pool shown on the earlier ens and now on the 18z op around the 20th. the deeper large cold pool shown a little later on the 18z would be more difficult to rely on as it has rarely shown up on the output thus far.

looking to see if the ecm 00z picks up the baton. up till now, the 12's have seemed more interested in the straight easterly than the 00z run.

[January Snowstorm]

A guy on the radio this morning asked if the end of the world was nigh after all the wierd weather of late

If the 18z came off, I think I would wonder, a truly bitter bitter flow

[Cloud 10]

ecm gfs18z

Good agreement at +168 between ecm 12z and gfs 18z.

Maybe TEITS's tea leaves speak the truth.

[NorthNorfolkWeather]

Is this interesting or what??

First things first, ensembles for Norfolk ( MBY) are close and consistant out to T168, then they go haywire.

So what does the ECM say for SLP from T168 to T216

T168 looks good, beginning of an Easterly pulling in colder air

T192 and T216 we find ourselves in a boring, nondescript col, followed by the beginnings of an Atlantic attack.

But, going back to comments by people with much more knowledge than myself (GP, SM, JH for example ) cold air is difficult to move, looking finally at the 850 at 216, the overall wind direction is Easterly keeping the Atlantic at bay. Final point, that LP in the Med, 100 miles further South OR 10 Mb lower and we will not be in a col, we'll be in an Easterly

[kold weather]

Looks to me like at the moment we are treading very close to both a southerly flow and another easterly flow. However I've always though the most logical solution as long as the PV doesn't become a total beast is for there to be enough of a cut-off low heading SE to allow the upper high to be propped up near the UK and given the power of the high pressure to our NE its going to merge and send us into a HP spell with SE/E winds.

This would probably result in fairly cool conditions, and limit milder days to just 2-3 and with the possiblity of something much more interesting down the line.

The ultimate evolution of that pattern would be as Steve shows either Feb 1956 or Feb 1991, but they can be very long winded affairs to get the bitter stuff in, took about 20 days for all the pieces to finally get into place for Jan-Feb 91.

[weather eater]

One thing that's being missed in this jamboree conversation about returning easterly flows, is the gale that's heading our way this weekend, from a very unusual direction.