Model Output Discussion 29th December - Into mid-Winter.

[knocker]

The anomalies this evening are not without interest although they are in pretty good agreement. Upstream it looks like some changes are under way.

At the moment a rather stretched vortex Alaska to Greenland  with a quite intense trough Alaska (note the strong WAA into North N. America) and another trough running a long way south in the western Atlantic. Although all three seem to be handling this Atlantic amplification the same it is not quite true on closer inspection as the ecm has a sharper ridge and for a brief time extends it a little further NE. This could easily also put the surface, again briefly, further to the NE and combined with the trough taking up a tighter position to the SSE introduce an easterly component in the south. As this option is quite quickly out of the frame post day ten the percentage play taking all three models into account is an Atlantic trough with the surface high positioned to the SW/S of the UK and a pretty slack W/SW upper flow. To note NOAA has high confidence

In the 10-15 period the WAA seems to have done for the Canadian vortex and is now more aligned from Alaska across the Pole or even N. Russia with the EPS. Downstream a slackening of the amplification with the weak trough slowly moving east in conjunction with the ridge. Ergo this indicates perhaps a continuing N/S split  with the HP still being influential in the south. Temps about average. But there is no unanimity on this so for the moment best left in the pending file.

 

 

Edited January 9, 2017 by knocker

[snowking]

5 minutes ago, beng said:

 

The wave that Ian Ferguson was referring to is I suspect, the system in the channel on the latest 72h fax

A near triple-point (not entirely sure what the correct term would be there) across the 528dam boundary from an Atlantic flow with an uncertain trajectory...for a forecaster, what could possibly go wrong

[beng]

Just now, snowking said:

A near triple-point (not entirely sure what the correct term would be there) across the 528dam boundary from an Atlantic flow with an uncertain trajectory...for a forecaster, what could possibly go wrong

Yes the MO must love that - ha ha. 

[Shunter]

Interesting PM Update from CPC this afternoon...seems the EC Ensembles today are providing greater weighting across the CONUS !   

So maybe some support upstream for the EC solution

6-10 DAY OUTLOOK FOR JAN 15 - 19 2017

TODAY'S NUMERICAL MODEL SOLUTIONS ARE IN GOOD AGREEMENT ON THE 500-HPA FLOW 
PATTERN PREDICTED OVER THE FORECAST DOMAIN. TROUGHS ARE FORECAST OVER 
ALASKA/EASTERN PACIFIC AND THE CENTRAL CONUS, WHILE A RIDGE IS ANTICIPATED 
ACROSS THE SOUTHEAST CONUS. TODAY'S 500-HPA BLEND CHART DEPICTS ABOVE NORMAL 
HEIGHTS ACROSS MOST OF THE CONUS, WHILE BELOW NORMAL HEIGHTS ARE FORECAST OVER 
ALASKA. THE ENSEMBLE SPAGHETTI DIAGRAMS INDICATE LOW TO MODERATE SPREAD ACROSS 
THE MAJORITY OF THE FORECAST DOMAIN. THE GREATEST WEIGHT FOR THE BLENDED HEIGHT 
FORECAST WAS GIVEN TO THE 0Z ECMWF ENSEMBLE MEAN SOLUTION BASED ON 
CONSIDERATIONS OF RECENT SKILL AND ANALOG CORRELATIONS, WHICH MEASURE HOW 
CLOSELY THE FORECAST PATTERN MATCHES CASES THAT HAVE OCCURRED IN THE PAST.

ABOVE NORMAL HEIGHTS AND STRONG WESTERLY FLOW ACROSS CANADA ENHANCE 
PROBABILITIES FOR ABOVE NORMAL TEMPERATURES FOR THE EASTERN HALF OF THE CONUS, 
AND PARTS OF THE NORTHERN AND SOUTHERN PLAINS. BELOW NORMAL HEIGHTS TILT THE 
ODDS TO BELOW NORMAL TEMPERATURES FOR ALASKA. BELOW NORMAL TEMPERATURES ARE 
FAVORED FOR PARTS OF THE NORTHERN AND CENTRAL GREAT BASIN DUE TO SURFACE HIGH 
PRESSURE PROMOTING LOW-LEVEL TEMPERATURE INVERSIONS OVER A DEEP SNOWPACK. THIS 
IS CONSISTENT WITH CALIBRATED REFORECAST TEMPERATURE TOOLS FROM ECMWF ENSEMBLE 
FORECASTS. 

THE TROUGH FORECAST OVER ALASKA AND PACIFIC OCEAN AS WELL AS AN ASSOCIATED 
FRONTAL SYSTEM FAVOR ABOVE MEDIAN PRECIPITATION FOR EASTERN ALASKA AND THE 
WESTERN CONUS. THE PREDICTED BROAD TROUGH OVER THE CENTRAL CONUS TILTS THE ODDS 
TO ABOVE MEDIAN PRECIPITATION FOR MOST OF THE EASTERN AND SOUTHEASTERN CONUS. 
BELOW MEDIAN PRECIPITATION IS FAVORED FOR PARTS OF THE NORTHERN AND CENTRAL 
PLAINS, THE CENTRAL ROCKIES, THE CENTRAL GREAT BASIN, THE SOUTHWEST, AND 
WESTERN ALASKA CONSISTENT WITH PRECIPITATION ESTIMATES FROM THE GEFS AND ECMWF 
ENSEMBLE MEMBERS.

TODAY'S OFFICIAL 500-HPA BLEND CONSISTS OF 10% OF TODAY'S 0Z GFS ENSEMBLE MEAN 
CENTERED ON DAY 8, 10% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED ON DAY 8, 10% 
OF TODAY'S GFS SUPERENSEMBLE MEAN CENTERED ON DAY 8, 40% OF TODAY'S 0Z EUROPEAN 
ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF YESTERDAY'S 0Z EUROPEAN ENSEMBLE MEAN 
CENTERED ON DAY 7, 5% OF YESTERDAY'S 12Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 
7, AND 20% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY 8 
 

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO 
GOOD AGREEMENT AMONG THE MODEL SOLUTIONS AND THE VARIOUS SURFACE TOOLS.

8-14 DAY OUTLOOK FOR JAN 17 - 23 2017 

TODAY'S ENSEMBLE MEAN DYNAMICAL MODEL FORECASTS ARE IN GOOD AGREEMENT ON THE
PREDICTED 500-HPA CIRCULATION PATTERN OVER NORTH AMERICA FOR THE WEEK-2 PERIOD. 
TROUGHS ARE ANTICIPATED OVER ALASKA, THE EAST-CENTRAL PACIFIC, AND MUCH OF THE 
CONUS. TODAY'S 500-HPA BLEND CHART DEPICTS ABOVE NORMAL HEIGHTS ACROSS MOST OF 
THE EASTERN AND CENTRAL CONUS, WHILE BELOW NORMAL HEIGHTS ARE FORECAST OVER 
ALASKA AND PARTS OF THE WESTERN CONUS. THE GREATEST WEIGHT FOR THE BLENDED 
HEIGHT FORECAST WAS GIVEN TO THE 0Z ECMWF ENSEMBLE MEAN SOLUTION BASED ON 
CONSIDERATIONS OF RECENT SKILL AND ANALOG CORRELATIONS, WHICH MEASURE HOW 
CLOSELY THE FORECAST PATTERN MATCHES CASES THAT HAVE OCCURRED IN THE PAST.  

 

[Pembroke Dangler]

14 minutes ago, beng said:

 

The wave that Ian Ferguson was referring to is I suspect, the system in the channel on the latest 72h fax

No I think it's the one to the west of the outer Hebrides see the kink in the isobars if it flows south could develope into a small low (not the polar kind) could be mixed rain/sleet/snow due to warm sectors etc

Edited January 9, 2017 by Pembroke Dangler

[beng]

13 minutes ago, bluearmy said:

 Very interesting control brings the easterly and then retrogresses the ridge to mid Atlantic/griceland - euro upper trough expands nw.  Then broad scandi trough (not deep) expands sw. cold to frigid throughout 

jet drops split flow to our sw days 10/12.

southern arm stays strong throughout into the med. 

not completely out of sync with the mean/anomoly 

https://mobile.twitter.com/BigJoeBastardi/status/818438598835970048

 

Maybe some support for that from the forecast strat at 30 hPa?

[beng]

4 minutes ago, Pembroke Dangler said:

No I think it's the one to the west of the outer Hebrides see the kink in th me isobars if at flows south could develope into a small low (not the polar) kind could be mixed rain/sleet/snow due to warm sectors etc

Don't think so as he's referring to Thursday and says Northern extent not certain. :-)

[Frosty.]

The Ecm 12z ensemble mean shows the arctic blast later this week before high pressure builds in and it becomes settled with widespread frosts and some freezing fog would be likely too..but first we have a cold shot from the nw / n with snow showers, ice and widespread frosts..at last some snow! :- )

[SMU]

Evening All - 

So just my second post today -my observations This morning & again this evening is that the models have edged closer to the solution - by this even though theres a huge difference between the 'BIG 3' they are actually on the same wavelength with energy & locations at 96- the clear seperating factor is the amplitude of the wave -

Have we been here before ? Well yes, @120/144 many times in the last 10 years & most of the time ~ 75% the euro combination was correct - & of that 25% ( ish ) the Scandi High & anything related to split energy the GFS was nearly always wrong- leaving its successes with Greenland highs & some Northerlies ( most of these calling failure when the ECM was to amplified around greenland at day 8-10 )

Today the very rare occasion we stand at 96 ( even possibly 84 ) where the model consensus is poor over the NE states-

Ironically this disparity is further enhanced by the seemingly tight ensemble clusters for each run favouring their own OPs progession with the GFS mean 850 plots showing a rapid rise for london opposing the ECM mean that improves very slowly - This manifests in 4c difference @ 850 on the 17th for London & then considerably more day 9/10 OP V OP ( mean V mean is smoother as you would expect )

So as indicated they all have the same pattern @96- A Small closed low close to the southern tip of Greenland & the track of this related to the inflection point is where the divergence begins- This is 100% correlated to the angle of the jet coming up from the SE states of the US from 72-96. The rule of thumb being that returning arm of the jet will follow the original jet - so the gradient coming up NE from the states will go SE perpendicular at the same angle & the system over greenland is the inflection point.

The ECM/GEM/NAVGEM & to a slightly flatter extent the JMA/UKMO have a well defined & acute inflection point -

EG -

The GFS + GFS mean has a poor angled jet with low inflection

EG

Remember the GFS has an easterly fast bias.

Based on history & all things considered these are my probabilities tonight -

T96- the inflection point being sharp enough for the T96 low to slide into Scotland & the UK at 120 = 80% with the GFS 'miss' tracking it towards Scandi 20% - the assumption post this of course that 80% generates some form of Scandi ridging behind the low...

Post that 144-onward ( assuming ridge varifies )

Probability of a scandi High + Dry cold continental surface feed -65% 

Probability of the above plus bitter Easterlies 35% ( up from yesterdays 25% thoughts )

I think we should put the Easterly excitement on ice for 24hours to see how much amplification we do get assuming that the GFS finally falls into line 18z + 00z as ive only seen the ECM 72 wrong once or twice - its stats are 97%...

lots of detail before this, The models today have started homing in on the 72-96 shortwave pattern & within that the development of troughs & kinks within the Northerly flow hitting us Thurs -

If you live in the North/North west / NI & parts of Wales you could have high expectations to see some white stuff this week- other locations hope we go full ECM mode as the rest will get some if that lands...

have a good one

S

 

Edited January 9, 2017 by Steve Murr

[ghoneym]

28 minutes ago, Pembroke Dangler said:

No I think it's the one to the west of the outer Hebrides see the kink in the isobars if it flows south could develope into a small low (not the polar kind) could be mixed rain/sleet/snow due to warm sectors etc

The tweeter mentions Exeter, and Ian Ferguson mentions the centre of the low which is almost over Exeter, I think he is talking about the low down there rather than the "wave" West of the Hebrides

.

 

Edited January 9, 2017 by ghoneym
spelling

[SMU]

GFS has fallen...

18z v 12z inflection

[SMU]

15 minutes ago, ghoneym said:

The tweeter mentions Exeter, and Ian Ferguson mentions the centre of the low which is almost over Exeter, I think he is talking about the low down there rather than the "wave" West of the Hebrides

.

 

What he is saying is the UKMO raw is 'over' developing the low ( to the wave ) almost making it a closed low-

Expectation is it will be a wave based on MOGREPS ENS - northern extent unsure & the fact that the column of air isnt cold enough for snow at that time- rather a wintry mix..

[feb1991blizzard]

3 minutes ago, ghoneym said:

The tweeter mentions Exeter, and Ian Ferguson mentions the centre of the low which is almost over Exeter, I think he is talking about the low down there rather than the one West of the Hebrides

.

 

Yes he is, but the tweeter is talking about the Met Office, which is based in Exeter - and the discussion inside the building, not the Low pressure.

[radiohead]

Isn't it great to have a chart like this at 66 hours?

[Ali1977]

4 minutes ago, ghoneym said:

The tweeter mentions Exeter, and Ian Ferguson mentions the centre of the low which is almost over Exeter, I think he is talking about the low down there rather than the one West of the Hebrides

.

 

That low is further North with snow now showing upto the M4 corridor, proper snow as it hits the cold and not showers. Pinch of salt with the GFS precious charts but it's obvious with the tweet that it could happen

[Met4Cast]

Less shortwave issues at T66 over the high, GFS on it's way towards UKMO/ECM it seems! At long last, we might have all 3 following the same sheet

[The Enforcer]

12z GFS remains obsessed with 'rain day' Saturday, but now 12z UKMO is trying to introduce 'rain day' Thursday and most annoyingly 12z ECM is toying with 'rain day' Friday, with 850s above -5C popping up almost out of nowhere.

Oh for a clean Arctic flow.

Edited January 9, 2017 by The Enforcer

[Iceberg]

Quite strong support for the wave to skirt along the channel 850s show the movement nicely with 5-8cm of snow for s.england m4 to 10 miles from the south coast in Thursday 

[Ali1977]

7 minutes ago, Steve Murr said:

GFS has fallen...

18z v 12z inflection

Doesn't look any better at 72 steve, not sure it has fallen unfortunately , in fact the 18z looks flatter

Edited January 9, 2017 by Ali1977

[khodds]

4 minutes ago, Ali1977 said:

That low is further North with snow now showing upto the M4 corridor, proper snow as it hits the cold and not showers. Pinch of salt with the GFS precious charts but it's obvious with the tweet that it could happen

Am I right in thinking though that (if it follows history) the low will correct North on each run and be no where near southern England by T0? 

EDIT: sorry - it's not a low but a wave my bad..

Edited January 9, 2017 by khodds

[WillinGlossop]

1 minute ago, Ali1977 said:

Doesn't look any better at 72 steve, not sure it has fallen unfortunately 

Jet less strong and further south......

[SMU]

12 minutes ago, Ali1977 said:

Doesn't look any better at 72 steve, not sure it has fallen unfortunately 

Just wait

Azores low not breaking through at 72 its slower inline with ECM so you dont get any phasing

look at angle of UK flow 78 v 84 - better angle...

[radiohead]

That wave is more pronounced on the 18Z GFS. Becomes a closed low crossing the channel. Hi res models should handle it better than the global GFS.

[JBMWeatherForever]

So if GFS has fallen then the chances of a bitter easterly must have risen - Lots of excitement ahead me thinks!

[samadamsuk]

From what I can tell, the low Thursday shows marginal snow, but no accumulations (although it's an experimental chart) - knife edge though - I'm not sure if the intensity will allow for some evaporative cooling - I suspect very localy in slack winds if so