Model output discussion-mid Autumn and beyond

[The PIT]

Big difference between ECM and GFS. ECM keeps the pesky high for the foreseeable while GFS Finally sinks it and removes for a more mobile south westerly flow. UKMO doesn't go far enough out. At least the ECM injects more cold air into the high.

Until the models agree whats going to happen to the high there is uncertainty of whats going to happens. For cold lovers a bit of frost to cling onto but little else.

[johnholmes]

Keeping out of the incredibly fast moving hunt for cold area. As usual a summation as to what the upper air may look like from about day 6 out to day 14 or so. The usual notes copied from my 500 mb anomaly file for 2018, it is even bigger than the hunt for cold, 49 pages this year!

3 days later 29 December

Ec-gfs bit chalk and cheese to some extent, both have ridges with troughs either side but not much similarity to this really. Overall the sum up for these two would be ridging more than troughing being in charge but with no deep cold showing.

So to noaa the 6-10 is fairly like the one above, (sorry these notes refer to charts I have on file so not on this post) less +ve height values but by 8-14 (click on link to 8-14 days) it has reverted to the atlantic being in charge with quite a strong westerly flow well into Europe, so again no signal for deep cold.

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

Taking a peak at the GFS version of MJO, way out in 5 at the moment and, as you can see from the link below, moving through 6 into 7 as the orbit decreases. 7 would suggest what the coldies might like but who knows?

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml#forecast

Finally the 30 mb temperature chart for the pole. Some days ago I suggested marked temperature spikes have about a 50% probability of bringing cold air into the UK. I've asked in the strat thread for any comments but got none. To me IF we are to get cold from this then it should occur around 7-10 January!

And another addition, what comes of trying to do several things at the same time!

the 30 mb chart link

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/

 

 

Edited December 29, 2018 by johnholmes
adding more info, d usual spelling!

[phil nw.]

Modelling showing much uncertainty beyond day 5-more than usual.

A look at the 3 00z operational runs at T144hrs

 

The high still there but GFS as often the case more aggressive with the Atlantic push against the block compared particularly to the ECM.The cold Scandinavian trough also further east which keeps the cold air associated with it further east.

The London 2m temp.graph highlights these differences

So little can be taken from the means as it does boil down to the strength of the Atlantic jet v the block later next week and where the bulk of the energy will go ie north or south or indeed straight through.

I would put the last option as least likely owing to the ongoing Strat reversal now forecasted to filter down to the lower levels in a few days.This will continue to weaken the zonal(west-east)winds across the Atlantic. 

The latest day 10 ECM forecast

The uncertainty on the upstream flow across the Atlantic very much highlighted on the ECM spreads

 It's a case of waiting for the NWP to settle down both wrt the downwelling zonal wind reduction and the amount of amplification that could be gained from a favourable MJO phase.

[feb1991blizzard]

1 hour ago, johnholmes said:

K

Finally the 30 mb temperature chart for the pole. Some days ago I suggested marked temperature spikes have about a 50% probability of bringing cold air into the UK. I've asked in the strat thread for any comments but got none. To me IF we are to get cold from this then it should occur around 7-10 January!

A

 

I think its because the split isn't wide enough to allow for a strong enough ridge to build in between the vortices to allow a for a downwelling, EP flux charts are not looking poleward either.

[Methuselah]

The GFS T850 ensemble shows the best long-term cooling to date:

Compare with that for Northamptonshire:

Both are clearly headed in the same direction...

[Summer Sun]

Looking at UKMO the colder air later next week won't hang around overly long

[I remember Atlantic 252]

2 hours ago, Summer Sun said:

Looking at UKMO the colder air later next week won't hang around overly long

Upper air SS, but still looks very cold, away from Scotland/Ireland, potential ice days inversion

[phil nw.]

The 00z ens from ECM/GFS and GFSp at day 10

All with similar ideas EPS perhaps with the greater amplification with the Atlantic flow.

Ridging just to the west of the UK by this time with the Atlantic jet quite weak and struggling to get east of the southern tip of Greenland.A Canadian trough upstream with low anomalies also showing over the Alaskan and Siberian regions.

A look at the GEFs days 6-10 mean temperatures at the surface

 

[The PIT]

Models are now in good agreement our boring high to be around for the foreseeable future and after a brief cold snap temperatures soon head back to normal by day but well above by night. Little in the way of rain which is bad news for the dams that need topping up. Overall a quiet boring outlook for a considerable time coming up.

The hunt for cold thread will soon be looking into February for proper cold.

 

[phil nw.]

It looks like a quiet rather cold week under the high but by early next week latest modeling shows it starting to come under pressure from the northern jet. 

The exact timing of course is still to be pinned down from this range but ens means at day 10 do agree on the high sinking a little further south west with Atlantic westerlies infiltrating the north.

Frontal systems becoming more involved in week 2 as they find their way across the top of the high and down across the country although at this stage not a great amount of rain seems likely as they come south.The continuing trend to a Scandinavian trough showing with again the main thrust of Arctic cold going into Europe to our east.

London ens

Again no real change.Temperatures around or just below average after 2/3 colder days this week,little rainfall to speak of and fairly quiet weather overall.

Edited December 31, 2018 by phil nw.

[damianslaw]

2 hours ago, phil nw. said:

It looks like a quiet rather cold week under the high but by early next week latest modeling shows it starting to come under pressure from the northern jet. 

The exact timing of course is still to be pinned down from this range but ens means at day 10 do agree on the high sinking a little further south west with Atlantic westerlies infiltrating the north.

Frontal systems becoming more involved in week 2 as they find their way across the top of the high and down across the country although at this stage not a great amount of rain seems likely as they come south.The continuing trend to a Scandinavian trough showing with again the main thrust of Arctic cold going into Europe to our east.

London ens

Again no real change.Temperatures around or just below average after 2/3 colder days this week,little rainfall to speak of and fairly quiet weather overall.

Yes the trend appears to be the weak northern arm of the jet riding over the ridge by second week of January, forcing core of heights to advance SW, and a trough to dig down through scandi - crucially this will enable much colder surface air to build over scandi, and create an enhanced pressure gradient between heights to our west/south west and to our east, the jet is most likely to take on a more NW-SE axis, with heights advecting further west, and a northerly could then easily surface, a toppler before a more pronounced ridge builds through mid atlantic towards Greenland - if the effects of the SSW play ball, by which stage heights will have built over the Pole, and hence a quick link up would occur, winds then turning to the NE. All a very plausible evolution which would result in the following:

1-7 Jan - Quiet anticyclonic conditions dominate, frost and cold easing gradually, cloud invading heights as time wears on, but temps still around average at best by 6/7th

8-15 Jan - A more mobile 'westerly' flow, becoming north westerly, ending with a short northerly

16-18 Jan - Period of change, northerly collapses, with a deep low moving through the UK from the NW, could be quite a bit of snow of northern flank, it sinks into central europe, heights ridge through mid atlantic to Greeland, heights build to our NE, and the two link with heights to our north

19 Jan onwards - predominantly cold, winds from a north-east direction, significant chance of snow, freezing temps, southerly tracking jet

This is not a forecast - its just one possible scenario.

[johnholmes]

Happy New Year everyone-see you in 2019

[carinthian]

11 minutes ago, johnholmes said:

Happy New Year everyone-see you in 2019

Happy New Year John. You back to Wengen again soon ?

Cheers , Paul

[The PIT]

Well the new year shows our friend the high hanging around with it's exact placement causing conflicting ideas over whether it's mild or cold. Same old story with the weather stuck in a groove it doesn't want to extract itself from.

[johnholmes]

14 hours ago, carinthian said:

Happy New Year John. You back to Wengen again soon ?

Cheers , Paul

Yes 22nd, just walking now but looking forward to it, back 31st, Happy New Year

[phil nw.]

Looking into next week on the GFS12z run and we can see by T144hrs Mon next the influence of the Atlantic meandering it's way over the top of the high and down the north sea.

and this type of setup continues through to day 10 with trend through next week of the high just drifting around near the UK with the occasional weak foray over the north from Atlantic systems as the high gives way before re-positioning.

Next weds and Friday

 

Day 10

 

[phil nw.]

On to the 12z ECM meteociel style

Again by early next week T144hrs similar to the GFS the north seeing some Atlantic energy heading over the top of the high

but after this stage the 2 models differ in the way the jet is modeled.

As can be seen from previous post GFS continues to run the Atlantic jet over the top but this ECM in it's later stages cuts an Atlantic trough se under the high leaving a wedge of heights further north.

Days 8 and 10

this draws in some colder continental air from the east.So this operational run like it's earlier 00z run adds quite a bit of interest for cold fans.
 

Edited January 1, 2019 by phil nw.

[phil nw.]

Gefs days 5 and 10

Pretty much along the lines of the Operational run.The high never far away,maybe the ridge just easing a little further west.The Scuero trough remains in evidence.

Tropical convection(MJO) expected to be in phase 6 within a 2/3 days .The expected pattern

reasonably close to the gefs mean ht.anomalies at day 10 allowing for a few days lag effects of the MJO.

 

 

[phil nw.]

EPS days 5 and 10

Similar to the above gefs maintaining the ridging near the UK and the Scuero trough,no indication of it following the operational from day 8 in sending energy under the high.

[Iceberg]

No charts I am afraid. 

But clear retrogression of the PV daigheter cell after the split. The cell that starts off NE Canada Hudson, by T168-200 has started the unstoppable process of centring around Alaska. 

It should be a clear signal of east or ne cold from t168 onwards. Gfs ens is very much supporting this and ec is strongly hinting at it. 

Obviously strat propergation induced and this kind of retrogression of the daughter cell has been underseen by the pros imho. 

 

[I remember Atlantic 252]

prefer EC to GFS for Monday, very wet on GFS, not bad on EC

[phil nw.]

The 12z models showing fairly good agreement in the general evolution out to T168hrs.

As posted in the short term thread we see that small but quite active low over Scotland whip down the north sea early next week and showing over the low countries by Tuesday .This bringing quite a cold northerly in it's rear.

GFS chart T120hrs

Some snowfall probably over the far north and can't be ruled out over higher levels towards the east as the winds turn on shore mid-week although most will just see an unpleasant spell of chilly rain.

The general idea is the high starts then to topple and recede south west as the jet goes over the top and cuts back into Europe.This turns the quite cold flow to north east  and then east and then the winds drop off as the high settles across the UK again.

Temperatures after recovering a little around this week end fall off again as the polar air moves south early next week and will likely remain just below or around average. 

We are pretty close to a really good northerly early next week but the high is wobbling around just too close and again the coldest plunge goes into Europe.

T168hrs

The ongoing trend of further cold air driving south through the Scandi.trough continues to top up the European cold pool. We are starting to see the cut back of the jet under the block which was not apparent a couple of days ago so these are trends to watch to enable the UK to turn properly cold instead of being on the periphery.

[phil nw.]

Out to a week from now all the models have a similar idea of sending a small wave depression over the high and down the North Sea towards southern Scandinavia pulling in a brief colder flow from the north in it's wake.The high then shown to move back towards the UK.

I shall just post the ECM for this purpose T72hrs and T144hrs

It's soon after that we see ECM and GFS differ with ECM some ridging in mid-Atlantic forcing the jet on a North west to south east angle bringing a colder polar maritime flow.GFS looking much flatter and keeping the high in closer attendance to our south west.

T192hrs shows the differences.

In spite of the variations in the mid-term,modeling in general is continuing to show week 2 heading for a cool zonality type of pattern as the low heights just to our north are squeezed closer.This is because of the mean Pacific ridge pushing into the pole from the SSW.

Reloading incursions of polar air look likely later on as the Azores high get's flattened.

Gefs for C.England and C.Scotland

A steady colder trend from week 2.

[phil nw.]

Decent looking gefs

Day 10/15 and the days 11-15 850 hPa temp.anomalies.

Confirming a cold pattern in week 2 with a nw-se type cold zonal pattern.

[lorenzo]

Strat top down out to 120 on tonight 12z.. downwelling continues from the displacement and split - up above the 10hPa 'nuked' layer looks like this

From the above still tons of transfer happening in the UTLS region which will challenge blocking and ridging - this slowly seems to be lifting out or dissapating from the 'mobile' side of the hemisphere as each run arrives, in a similar fashion to W2 appreciating on Berlin.

Little bit of a trend, but still how much energy is left in the NE Canada Greenland sector is of note, filaments of vortex have proven problematic before and can really throw the anticipated jet pattern awry, no matter what the split flow energy upstream may be.

The 12z is only 120 hrs on GEOS unfortunately so 00z worth the old 00z to 00z check for a change mechanism, damn shame as at present it seems to be a case of what the 12z progresses with the 00z dials back on, from model watching this seems to have always been the case ( regardless of ECM / GFSdebate).. then, when something is truly afoot the 18z GFS follows the pied piper 12z ECM..

Looking at MJO ...

Really useful to see the Cassou analogs today, however... given the vortex segment dialling in to turbo charge the NPAC jet am unsure what we can glean from 'normal' lagged teleconnections here. Wk 2 above will take a mind greater than mine to decipher, the traditional eastward moving block shredded. Perhaps negative MT and relaxation of the pattern to allow meridional Rossby waves to kick in.. too early to tell. Roundy posted a good plot showing the jet extension shove stuff south of the equator, is this a sign of us having surpassed peak zonal injection of oomph into proceedings. If so, can it build into circa 20th, slower moving NH wavelength and be another factor for blockiness..

One thing is for sure, watching an SSW in slow motion vs the dynamical retrospectives provided e.g. http://birner.atmos.colostate.edu/SSW-animations/anim-PV/1979_530K/loop.html is gruelling work... we are gonna be damn unlucky NOT to get something signature out of this event that's for sure...

Edited January 5, 2019 by lorenzo