Winter Model Discussion - The Hunt For Cold - 12th Dec

[Ian Brown]

There's a twitter comment from Joe laminate floori that it's showing negative NAO for next 30 days (believe it when I see it!) - hopefully Matt will be along at some point with an update.

I'm still waiting for its strongly -ve NAO December pattern that it forecasted all November....

[nick sussex]

Indeed, and if the Russian high was not there but instead we had a euro high further south then there would be almost no chance of a cold outbreak. I remember in the bad winters some people calling for a reset (as if we could just push a button!) and, on a couple of occasions we got just that: a Bartlett high (or as close to one as makes no difference) and a raging jet pushing from SW to NE. Cloudy and mild in the south and east with occasional (but not much) rain and mild, wet and windy in the north and west.

If we're looking for cold then we stand a higher chance with the Russian high in place than a euro high...

I do take your point re the Russian high, even though its centred a long way east it does enough in terms of throwing a ridge nw towards Scandi to help if the upstream pattern plays ball, better still would be if we could see a separate lobe cut away from the main part.

And yes my snow potential ratings and optimism rating will be back! I decided not to post the optimism one yesterday for fear of jinxing things but it obviously made no difference given the trend from the early outputs! lets hope for a better trend in the GFS 06hrs run.

[WhiteFox]

Yes the weather will do whatever it wants, it has no feelings for our feelings and the models likewise.

And it shocks me how sometimes this is forgotten! People even seem to take it personally when an easterly forecast from 7 days out fails to materialize. In general, the only truly nailed on forecast, by which I mean temperature and precipitation is right now. I can look at the excellent NW radar and tell that we're in for a wet morning in Reading.

In the 1-12 hour period, we are almost sure of temperature and rainfall (I say almost because in some situations we still have unexpected snowfall or heavier rain as demonstrated by Ian ferguson updating the forecast for kent this afternoon).

Up to 24 hours we have a very good idea of temperature and a pretty good idea of PPN as we can see the observations and satellite images.

The problems start when we look at forecasts based on systems which have not yet formed, or are in the process of forming. In some scenarios, a slightly deeper than expected depression can have big consequences for the picture further down the line. The work of GP, Steve Murray, chino, John Holmes and others is excellent because it helps us to understand the larger scale setup which will affect the probability of certain weather types prevailing over a given period. All the forecasters mentioned have truly impressed me over the years with their ability to spot a pattern change from impossible time frames and I for one am immensely grateful that they spend the time and energy doing this for us.

Of course, what no-one can do is give us an exact forecast for temperature and PPN at a point in time at a particular location with any accuracy more than a few days (at most) ahead. This is why it despairs me a little to see people stating that medium to longer range forecasters are clueless. The Met O is aware of the limitations which is why they choose not to mention specifics (even last week there where some questions as to why the Met O wasn't issuing early warnings) more than a few days in advance. All the medium to long range forecasters I respect on this forum also only mention general trends, but still seem to be unfairly criticised when we don't see raging blizzards and months of cold when they have mentioned a change to a colder pattern.

As for the computer models, they are a tool, and no professional forecaster that I know of would rely only on one model to make a forecast for more than five days in the future. There are and always will be too many variables at the surface in localized areas to do this.

[chris55]

Ecm great this morning and the 2nd run to have high pressure ridging out of Norway towards the UK with the small Low in the Barents sea trying to send energy towards the eastern side slicing between it and the (now) far off Russian high.

Can we get a little bit of Christmas magic, lets hope so.

[TEITS]

I'm still waiting for its strongly -ve NAO December pattern that it forecasted all November....

Must admit im not a massive fan of any model that goes beyond +240.

My simple reason being is if the chaos theory has an impact on the models within the +384 period i.e GFS then what chance has a model that goes to 30 days.

[chris55]

I do take your point re the Russian high, even though its centred a long way east it does enough in terms of throwing a ridge nw towards Scandi to help if the upstream pattern plays ball, better still would be if we could see a separate lobe cut away from the main part.

And yes my snow potential ratings and optimism rating will be back! I decided not to post the optimism one yesterday for fear of jinxing things but it obviously made no difference given the trend from the early outputs! lets hope for a better trend in the GFS 06hrs run.

Yep thats my thinking Nick, getting a bit of energy inbetween, as the ECM is hinting at is what we need!

[beng]

I'm still waiting for its strongly -ve NAO December pattern that it forecasted all November....

LOL - yes me too.

[snow drift]

Subtle changes upto here. Its trying to get there.

[nick sussex]

Still no agreement within 120hrs regarding the shortwave into Holland, this is quite important , we need to see this ejected cleanly to allow some ridging to the ne to exert more forcing in the trough.

At least we need to see the shortwave develop off the eastern USA, come on GFS get to it!

[TEITS]

Quiet a significant difference in the positioning of the LP at +120 compared to the ECM as I mentioned earlier.

http://modeles.meteo...gfs-0-120.png?6

As Nick mentioned ideally it would be better if a SW developed underneath this LP.

Still no agreement within 120hrs regarding the shortwave into Holland, this is quite important , we need to see this ejected cleanly to allow some ridging to the ne to exert more forcing in the trough.

At least we need to see the shortwave develop off the eastern USA, come on GFS get to it!

Yep a kind of domino effect really with regards to the SW into Holland.

Edited December 14, 2012 by THE EYE IN THE SKY

[Cheshire Freeze]

I'm still waiting for its strongly -ve NAO December pattern that it forecasted all November....

Every time I raise this point I get told that the forecast has come true but I'm yet to witness a strong -NAO so far this December.

ECM looking better than GFS this morning. I would like to believe the scenario as it's very rarely less reliable than the GFS at 120 hrs IMO, but obviously there are exceptions......like when any cold is forecast blah blah blah etc etc

Edited December 14, 2012 by CreweCold

[WhiteFox]

Still no agreement within 120hrs regarding the shortwave into Holland, this is quite important , we need to see this ejected cleanly to allow some ridging to the ne to exert more forcing in the trough.

At least we need to see the shortwave develop off the eastern USA, come on GFS get to it!

I happened to be driving past the ECM HQ in Reading this morning at around 7am. The car in front of me had the number plate EC12 GFS and turned into the ECM's entrance. I suspect collusion! (Note that this post may be slightly fictionalised for literary purposes)

Edited December 14, 2012 by WhiteFox

[chris55]

Similar to ECM at 138 (144) only difference is the tilt of the Low to the West

[TEITS]

This potentially could be a better run.

http://modeles.meteo...gfs-0-156.png?6

At +144 the GFS is much more towards the ECM than the UKMO.

Beat me to it Chris.

Edited December 14, 2012 by THE EYE IN THE SKY

[Southender]

It's so frustrating to watch. The PV is battered, big old HP on the continent, with bone chilling air. Yet we cannot seem to take advantage.

Still. There is hope with an undercut at the mid-range. Here's hoping.

Edited December 14, 2012 by Shrimper

[TEITS]

At least if an E,ly does occur we won't have to watch it develop in F.I and have the agony of following it into the reliable. This COULD be one of those situations where the E,ly develops at a much earlier timeframe i.e +144 at short notice over the next few days.

If I think back to the output a several days ago and compare to what its showing on the 21st Dec then it really is chalk and cheese.

[snow drift]

This demonstrates what a complicated situation this is.

[nick sussex]

A better GFS run so far and interestingly it does tie in more with the upstream pattern expected by NOAA:

From this mornings update:

HPC OVERNIGHT MEDIUM RANGE GUIDANCE HAS BEEN PRIMARILY DERIVED

FROM YESTERDAYS 12 UTC ECMWF ENSEMBLE MEAN. THIS SOLUTION

MAINTAINS GOOD CONTINUITY WITH PRIOR HPC DAYSHIFT GUIDANCE. THE

ECMWF ENSEMBLE MEAN BY NATURE SEEMS TO MITIGATE TO SOME DEGREE

LESS PREDICTABLE EMBEDDED SYSTEM SPECIFICS/INTERACTION VARIANCE

AND BECOMES INCREASINGLY WITH TIME ON THE MORE AMPLIFIED SIDE OF

THE FULL ENVELOPE OF MODEL AND ENSEMBLE SOLUTIONS NEXT WEEK. THAT

SOLUTION SEEMS REASONABLE CONSIDERING WATER VAPOR IMAGERY WAY

UPSTREAM OUT THROUGH THE WRN PACIFIC THAT SHOWS QUITE A BIT OF

ENERGY FEEDING AND QUICKLY LEADING TO AMPLIFYING DOWNSTREAM FLOW

IN A MANNER CONSISTENT WITH A ROSSBY WAVE PACKET. WHILE FLOW

AMPLIFICATION IS EXPECTED IN THIS SCENARIO...FORECAST SPREAD WITH

SYSTEMS STILL SUGGESTS GREATER THAN NORMAL UNCERTAINTY.

Bearing in mind here that if the flow amplifies off the eastern USA this will help sharpen any troughing to the west, if we can hold onto enough forcing to the ne the natural progression is an undercut as the energy will then be forced se.

More encouragingly here we see a separate lobe of high pressure set up, this is far better than some huge high.

Edited December 14, 2012 by nick sussex

[chris55]

Slowly slowy things are getting more interesting.......and at least no one can say theres no cold pool to tap into! Although we have struggled to tap into that cold pool on the last two attempts maybe it could be third time lucky!

We need the cut off high to the east to develop IMO to stop the pattern being forced east as we have seen recently. Lots of things need to fall into place (as ever) but at least theres a chance, and something to chat about.

Edited December 14, 2012 by chris55

[Troubleatmill]

Think we need this little ridge of the azores high to flatten out to allow the low pressure to head in a more easterly south easterly direction, dont think we want to see any link up as it would only progress into a euro high

[snowmadchrisuk]

P/V has gone back to wanting to displace East where recent days have wanted to bring it back West , so that can only be a good sign IMO

[WhiteFox]

It's so frustrating to watch. The PV is battered, big old HP on the continent, with bone chilling air.

The lack of a strong PV is what makes the ECM charts of more interest for their forecast. We have seen many occasions over the years where the Russian high displaces to the west and threatens our shores. In most cases, however, this is accompanied by a fairly strong PV over or near Greenland which significantly reduces the likelihood of the cold air reaching our shores.

The difference between the GFS and ECM is that the GFS system is deeper and therefore pulls in a SW flow whereas the ECM's shallower system has S to SE flow with the system elongating towards Greenland. A classic battleground situation and without a strong PV a greater (although still small) chance of verifying than in some previous winters I've seen.

Whenever we are on the extreme western edge of a Russian high there is always a high risk of nothing materializing.

[chris55]

Losing the battle on this run in high res, but we are still in the war!

http://www.wetterzentrale.de/pics/Rtavn1861.png

[Paul]

Definitely something potentially interesting afoot - glimmers of hope for cold to return for Xmas even in the GFS output, more than that in the ECM output, and the ECM32 brings the cold back to our shores on around Xmas eve and keeps it there until the new year....

[Methuselah]

Whilst not paying much, if any, attention to shortwaves, I'm closely watching the (possible) development of the cold block, out to the Northeast...as that does look interesting!

Edited December 14, 2012 by Rybris Ponce