General Model Output Discussion:

[yamkin]

Yes, but isn't this deep cold and possible snow continually being pushed back in time? It's only a couple of days ago that the models were showing a major snow event for New Years Eve/Day. That seems to have been played down somewhat during today by forecasters. FI to me is about T48 at the mo!

Keep an eye on the model runs leading up to Thurs/Fri. UKMO & GFS models at the moment have got snow for the S/SW/SE this Thurs/Fri. BBC MetO forecasts are now showing snow on Thurs/Fri.

Edited December 29, 2009 by yamkin

[Paul]

To highlight the uncertainty at the moment, the precipitation ensembles tell their own tale.

At 24 hours there's reasonable agreement of where the main rain/sleet/snow band will be, albeit with some discrepancy in terms of the intensity but this is pretty normal:

By 48 hours though there's a wide range of options, varying from the front not actually moving very far at all from the 24 hour charts, too the front having virtually cleared the south coast by this point.

At 72 hours, some members still have the front in play in the south, then we also have the variety of options in terms of convective showers moving through off the north sea. It's worth bearing in mind that the ensembles at 1 degree resolution are not going to be able to pick out convective cells etc, so any precipitation will be painted on with a broad brush!

At 96 hours the big uncertainty is the prec moving into the east and south of the country, again very low confidence in any particular outcome

By 120 hours it's all eyes southwest - how far northeast will the potential band of rain,sleet and snow reach

So with so much uncertainty as early as 48 hours, it's reasonable to say that anything beyond that is extremely low confidence with a range of scenarios being shown and probably a range of other scenarios possible which aren't being shown..

[mcweather]

Although Ian mentioned the GFS the next part of the sentence is a reference to all models "and other rampimg of distant, speculative and often known cold/snowy-bias modelling that sits poorly with statistical certainty"

Yes but the ECM isn't a col/ snowy bias model. Its what the Met office us for the longer term forecasting.

By the way on a more general note Just seen tonights ecm ensembles and the ecm12z was NOT a cold outlier there were plenty of colder runs.

[john mac]

We Shall see yamkin wouldnt like to call it yet, SM didnt seem that confident of seeing anything significant from thurs/fri

[SMU]

That is pretty impressive, but south of Scotland, where has the really cold weather been? ( i know that -AO is one of many things that is required for really cold weather...)

Hi-

Just a couple of bits on this-

The AO started in a negative state for Decemeber,however over the period has become progressive in terms of the decline towards the very low numbers we are now experiencing-

The AO expression as we should know forces cold into the mid lattitudes,but not ALL the mid lattitudes, China has seen the full force, as well as parts of the midwest-

Now the NAO is rapidly declining the couplet is complete -

Even though the NAO wasnt that negative - with a background record breaking -AO the second half December CET for 2009 is looking to be circa 1.5C & whilst that isnt recordbreaking I doubt you will be able to find many Decembers with that statistic - maybe a handful-

to go on from that the tanked -AO looks to developing an even lower trough around the third & combine that with the NAO then the first half of Jan could & should return a CET below -1c-

Again this isnt nailed, But I would say we are firming up at least a first 7 days close to Zero-

with this in mind a full 4 weeks return around ~1c cant be sniffed at & hasnt been prevelent around these parts for many many years-

So whilst your locale hasnt been 'that' cold YET, the statistics certainly back up my thoughts-

My CET thinking is also TOP end as well, If things pan out EXACTLY as planned then the first 7-10 days CET will be WELL below freezing-

thanks

Steve

Edited December 29, 2009 by Steve Murr

[Ian Fergusson]

Yes but the ECM isn't a col/ snowy bias model. Its what the Met office us for the longer term forecasting.

By the way on a more general note Just seen tonights ecm ensembles and the ecm12z was NOT a cold outlier there were plenty of colder runs.

Hi - noticed part of my note from another thread has been reproduced here.

Indeed - my comments were related solely to the GFS focus (i.e., as often overly-evident as the 'bible', as many of you on this side of the forum would probably agree). It was not aimed at ECM or other modelling and interestingly, I'=d add that the recent UKMO GM run wants to paint a more drastic solution for New Year's Eve, while this is considered in a minority solution even by the UKMO (incidentally, the earlier data assimilation issues with the GM have now been resolved).

Hope this clarifies - not in any way intended as a snipe at any of the very informed and learned posts on this thread!

Best

Ian

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Hi-

Just a couple of bits on this-

The AO started in a negative state for Decemeber,however over the period has become progressive in terms of the decline towards the very low numbers we are now experiencing-

The AO expression as we should know forces cold into the mid lattitudes,but not ALL the mid lattitudes, China has seen the full force, as well as parts of the midwest-

Now the NAO is rapidly declining the couplet is complete -

Even though the NAO wasnt that negative - with a background record breaking -AO the second half December CET for 2009 is looking to be circa 1.5C & whilst that isnt recordbreaking I doubt you will be able to find many Decembers with that statistic - maybe a handful-

to go on from that the tanked -AO looks to developing an even lower trough around the third & combine that with the NAO then the first half of Jan could & should return a CET below -1c-

Again this isnt nailed, But I would say we are firming up at least a first 7 days close to Zero-

with this in mind a full 4 weeks return around ~1c cant be sniffed at & hasnt been prevelent around these parts for many many years-

So whilst your locale hasnt been 'that' cold YET, the statistics certainly back up my thoughts-

My CET thinking is also TOP end as well, If things pan out EXACTLY as planned then the first 7-10 days CET will be WELL below freezing-

thanks

Steve

Thanks for that, i shall look forward to the first week of Jan with interest!

[MAF]

.........

So with so much uncertainty as early as 48 hours, it's reasonable to say that anything beyond that is extremely low confidence with a range of scenarios being shown and probably a range of other scenarios possible which aren't being shown..

FI around 36-60 hours then Paul. just about where i usually put it anyway

[yamkin]

We Shall see yamkin wouldnt like to call it yet, SM didnt seem that confident of seeing anything significant from thurs/fri

Here are the ppn charts for Thurs/Fri. Nothing significant snow wise, but worth keeping an eye on, hence why BBC forecasts are now showing snow for S/SW/SE.

[Matt12]

I doubt anything too extreme (i.e. cold/snow of record-breaking proportions) will verify, as there is far too much uncertainty at the moment. You only have to see how the South-east was supposed to get significant snow during thursday/friday earlier today, but now this looks increasingly unlikely according to all the latest weather forecasts (we probably won't see much/just the odd light shower). This just illustrates how we can't even forecast a day/2 days ahead at the moment.

I seriously doubt that we will have anything more than a sustained cold period of weather with some snow. Still, interesting weather ahead, even if it won't be in the record books.

Edited December 29, 2009 by Matt12

[nick sussex]

The good news keeps on coming this evening. NOAA sing the praises of the ECM model and slate the GFS, upstream signals and extended outlook back the ECM output as being plausible. Here are the main quotes most pertinent to downstrean in western Europe.

RECENT ENSEMBLE MEAN FORECASTS ARE IN GOOD AGREEMENT ON THE EXPECTED 500-HPA

HEIGHT PATTERN FOR THE 6-10 DAY PERIOD OVER NORTH AMERICA. THIS PATTERN

FEATURES UPPER-LEVEL TROUGHING NEAR THE ALEUTINAS, UPPER-LEVEL RIDGING

EXTENDING NORTHWARD ALONG THE WEST COAST OF NORTH AMERICA FROM CALIFORNIA TO

EASTERN ALASKA, AND A STRONG BLOCKING RIDGE NEAR SOUTHERN GREENLAND

THE 500-HPA HEIGHT ANOMALY PATTERNS FROM THE EUROPEAN ENSEMBLE MEAN AND THE

CANDIAN ENSEMBLE MEAN INDICATE A RIDGE JUST OFF THE WEST COAST, WHILE THE GFS

INDICATES A BROADER, LESS AMPLIFIED RIDGE CENTERED ALONG THE ROCKIES. THE

DOWNSTREAM TROUGHS IN EACH OF THE SOLUTIONS ARE ALSO SHIFTED EASTWARD

ACCORDINGLY. PREFENCE WAS GIVEN TO THE 00Z EUROPEAN ENSEMBLE MEAN SOLUTION DUE

TO IT'S VERY RECENT HIGH ANOMALY CORRELATION SCORES, WHICH ARE APPROACHING

0.90.

AMONG THE OPERATIONAL MODEL SOLUTIONS, THE 00Z AND 06Z GFS LACKED RUN-TO-RUN

CONSISTENCY, WITH THE 00Z SOLUTION DIFFERING GREATLY FROM YESTERDAYS 18Z

OPERATIONAL GFS SOLUTION

DURING THE WEEK TWO PERIOD THE ENSEMBLE MEAN SOLUTIONS GENERALLY SHOW A SLIGHT

AMPLIFICATION OF THE EXPECTED CIRCULATION PATTERN BUT OTHERWISE VERY LITTLE

CHANGE FROM THE FORECAST FOR THE 6-10 DAY PERIOD. THE STRENGTHENING RIDGE ALONG

THE WEST COAST OF NORTH AMERICA IS CONSISTENT WITH AN INCREASINGLY POSITIVE PNA

AND A CONTINUED NEGATIVE AO.

In a nutshell the Greenland block remains strong, they like the ecm ensemble mean solution which is fine, basically we want them to keep backing this model, the troughs they talk about being edged eastwards is whats needed to edge the pattern east and stop a western based negative NAO from setting up, the slight amplification of the current pattern should mean the scandi trough aligning well but its crucial the block remains far enough east. So overall their discussions give weight to the ecm operational run but theres still alot of weather to get through and alot of model drama to come. The best chance however for the UK to see synoptics that many thought not possible again. Fingers and everything crossed that the ecm can stick to this trend.

[azores92]

just a couple of points to make, as we look for more sustained cold. it is not worth looking for snow events more than 24-48 hours notice. it is a very rare occasion when a snow event comes off as shown more than 48 hours out. marginal is mainly the rule with snow, regardless on how the models show it. dont get excited until it falling outside your bedroom window, things can change rapidly with tracking systems, warm sectors etc.

in summation, this has been a fairly chilly december all in all, there have been 3 times when snow has fallen, 2cm settled, and now its been washed away. enjoy the cold while it lasts folks, things can rapidly change in the models, but if the ecm came off(unlikely to be like that imo), it would be a memorable spell of weather.

[snowlover2009]

that is a a stonking ecm run and not even the coldest at all

what would daytime highs be like?

lows would be record breaking in many parts.

[phil nw.]

The good news keeps on coming this evening. NOAA sing the praises of the ECM model and slate the GFS, upstream signals and extended outlook back the ECM output as being plausible. Here are the main quotes most pertinent to downstrean in western Europe.

Thanks Nick.

That`s positive news to extending the-nao a little further east in time then,which i think is what GP mentioned in one of his recent posts.

Maybe you will get some snow down there soon,based on 12z ECM.

Edited December 29, 2009 by grab my graupel
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[john mac]

Great news nick, it just goes to show how well the ECM is perfoming ATM, yet another feather in its cap, good agreement starting to apear for next week, the building blocks are set IMO.

[nick sussex]

To celebrate the remarkable ECM run i've dug up another link to it's ensembles, this goes out to 15 days and in much bigger format.

http://www.weerplaza.nl/15daagseverwachting/default_pluim.asp?r=midden

Just a quick note before the gfs 18hrs run, given the pattern might amplify further in the outlook it's absolutely crucial that the block can edge east enough to ensure that western Europe remains in the coldest air, keep an eye on the eastern seaboard of the USA you want that trough to edge ne'wards reducing the westward movement of the Greenland block and locking it in far enough east, if it does that then get the shovels out and make sure you're heating is up to scratch

Edited December 29, 2009 by nick sussex

[KTtom]

Glad its not just me who has a bitter taste in their mouth today. I'm not going down the 'even larger teapot' road, but with the current sypnotics you would expect a little more than 10 hrs heavy rain! Despite my location I'm certainly not alone. As you say, ECM sypnotically looks great but until you look out you're window don't take anything for granted.

[snowlover2009]

I doubt anything too extreme (i.e. cold/snow of record-breaking proportions) will verify, as there is far too much uncertainty at the moment. You only have to see how the South-east was supposed to get significant snow during thursday/friday earlier today, but now this looks increasingly unlikely according to all the latest weather forecasts (we probably won't see much/just the odd light shower). This just illustrates how we can't even forecast a day/2 days ahead at the moment.

I seriously doubt that we will have anything more than a sustained cold period of weather with some snow. Still, interesting weather ahead, even if it won't be in the record books.

can we not just enjoy the charts though? what charts do you want to see for the uk to have record minimums? a few parts of the coutnry would get them.

[john mac]

To celebrate the remarkable ECM run i've dug up another link to it's ensembles, this goes out to 15 days and in much bigger format.

http://www.weerplaza.nl/15daagseverwachting/default_pluim.asp?r=midden

[/qu

Nice to see your having a little ramp there Nick, Confidence is definately growing for next week, i thought it would be i bit busier on here tonight considering what the ECM has shown us

[bluearmy]

UNCERTAINTY ABOUT THE STRENGTH OF THE BLOCKING RIDGE NEAR GREENLAND AND POSSIBLE SHORTWAVES MOVING THROUGH THE SOUTHERN STREAM

ARE REFLECTED IN THE LARGER SPREADS SEEN FOR THOSE AREAS

you omitted this sentence nick.

mind you, the shape and size of the block means that even though it looks to retrogress to eastern canada, we will hopefully avoid the unpleasant side effects of a west based -NAO which ended the last cold spell down here.

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

[Yeti]

Not sure if they have been posted already but the ECM ensembles are very good:

http://www.knmi.nl/exp/pluim/vijftiendaagse/Data/15DAAGSE_06260_NWT.png

Lots of support for the op - and with the NOAA report that Nick has quoted it looks like things may get very interesting indeed.

EDIT: I see they have already been posted!

Edited December 29, 2009 by Yeti

[nick sussex]

To celebrate the remarkable ECM run i've dug up another link to it's ensembles, this goes out to 15 days and in much bigger format.

http://www.weerplaza.nl/15daagseverwachting/default_pluim.asp?r=midden

[/qu

Nice to see your having a little ramp there Nick, Confidence is definately growing for next week, i thought it would be i bit busier on here tonight considering what the ECM has shown us

Well if you can't ramp at that run then you're not a model anorak! It really was superb and even i might see a snowflake or two but just happy to get rid of this warm rain. If we look at the trend of the last week the ecm has been the one to follow, let's hope the gfs and ukmo come on board.

UNCERTAINTY ABOUT THE STRENGTH OF THE BLOCKING RIDGE NEAR GREENLAND AND POSSIBLE SHORTWAVES MOVING THROUGH THE SOUTHERN STREAM

ARE REFLECTED IN THE LARGER SPREADS SEEN FOR THOSE AREAS

you omitted this sentence nick.

mind you, the shape and size of the block means that even though it looks to retrogress to eastern canada, we will hopefully avoid the unpleasant side effects of a west based -NAO which ended the last cold spell down here.

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

I didn't even see that but its not as important as where the block goes, regardless of its strength if it goes too far west that would be a problem, i'm happy that its the main uncertainty and not the location of the block.

[john mac]

ame='john mac' date='29 December 2009 - 21:32 ' timestamp='1262122371' post='1681468']

Well if you can't ramp at that run then you're not a model anorak! It really was superb and even i might see a snowflake or two but just happy to get rid of this warm rain. If we look at the trend of the last week the ecm has been the one to follow, let's hope the gfs and ukmo come on board.

I completely agree with you nick, the GFS and theUKMO need to come on board especially the GFS to save its credibility, But your right we should enjoy these charts that the ECM have shown us as we dont get charts like that hardly especially in the medium range

[meerkat63]

The good news keeps on coming this evening. NOAA sing the praises of the ECM model and slate the GFS, upstream signals and extended outlook back the ECM output as being plausible. Here are the main quotes most pertinent to downstrean in western Europe.

Good post as always Nick and it does appear to my rather untrained eye that the GEM model (not to forget the superb output by ECM tonight) has hinted for some time that all is not lost with our Greenland HP by any means. The threat is indeed there of a western based negative NAO and in that regard I thought I would post (or pilfer!) something GP penned in the technical thread for any others who may not have noticed it.

"Composite reanalysis for phases 5-6 indicate that the GWO will trend the mean blocking ridge to work its way back east towards days 11-15, towards Iceland with lows being forced underneath the block. The GFS ensemble mean height anomaly for this period (500hPa) tends to support this notion:

http://raleighwx.eas...htAnomalyNH.gif

Temperatures across this period are likely to remain depressed, particularly so during days 6-10 and not returning to above average during this time. Obviously, at this time of year, beow average conditions are likely to present potential for snowfall, especially given a pronounced trough just to the south west of the UK allowing surface depressions to attempt to work up into the cold reservoir of air lodged over NW Europe.

we are in essence seeing the impacts of the changing wavelengths and climatological effects which should ensure a much larger and deeper cold pool across the NW parts iof Europe and the NE Atlantic.

For what it's worth, the GEM ensemble mean t300 onwards shows the block to become more orientated towards Iceland in line with the analysis above. It's also worth noting that this set up does lend itself to a potential channel-low type event sometime days 6-12." GP

Edited December 29, 2009 by grab my graupel
Reduced quote size

[john mac]

Has the pub runs started coming out yet?