Model Output Discussion - 26th December - 1st January

[IDO]

That is not true, there is plenty of potential for cold in the form of PM incursions, albeit transitional.

The GFS has a PM excursion hitting south of the Midlands on the 3rd Jan and that is it to the end of the run, the 14th. Of course if you are in Aberdeenshire you may get another 48-72 hours of PM. For the height of the winter to say this is "cold" is very annoying, as it clearly isn't. Of course GFS may be barking up the wrong tree but I am commenting on the output, not what could be. Basically from the 4th Jan HP takes over for the south.

There are no frosts forecast; we are basically in an average to mild regime.

A lot like November.

No snow , two frosts, three hours of wet snow; that is my story, so I don't want to here that it hasn't been a bad winter, because that sounds as crass as it is.

[Robbie Garrett]

That ECM chart is from 00z Robbie, not 12z.

I thought it had updated, but it's still updating now. 168hrs is 12z!! Sorry!

[nick sussex]

Well at least the ECM at 168hrs keeps the Azores high further to the west compared to the GFS 12hrs at the same timeframe.

We await the delights or not as maybe the case of its 192-240hrs output.

It really can't be any worse than this mornings satanic offering so really the only way is up!

[Tom Montalbano]

GFS 12z Ensembles.

http://hw.nwstatic.co.uk/ensimages/ens.20111229/12/t850London.png

Regards,

Tom

[nick sussex]

Looks pretty cold in the eastern USA at 120hrs!

http://www.meteociel.fr/modeles/ecmwf.php?ech=120&mode=0&map=1&archive=0

Overall good agreement across the models for a typical mixed bag of weather, a few swipes of colder air more especially for the north, interspersed with milder interludes.

The GFS makes more of the Azores high, the ECM looks to keep this mainly displaced a bit further to the west and south.

The ECM 240hrs is an improvement in terms of cold or should I say less horrifying for cold and snow lovers in here with a slightly better NH pattern, overall I'd sum up the output as pretty typical winter weather for the UK.

If I win the Euromillions I'll hire a couple of jets and take us all over to Canada in time for that deep cold plunge shown at 120hrs!

[Frosty.]

Another gfs run to instantly forget for cold prospects, every gfs run is more or less the same with tropical maritime air dominant at least for the southern half of the uk and any cold incursions in the north are so brief as to be hardly worth mentioning, as it is, the gfs 12z shows a brief cold shot for next monday and then another on tuesday but then milder for the rest of the week but colder again at the end of next week in the north then milder again, for southern uk there is hardly any cold air to be found on the whole run..but at least i'm remaining positive

Edited December 29, 2011 by Polar_ Low

[Shunter]

Can anyone explain how time after time GFS op is a mild outlier or at least a milder member? It seems to have been like that for most of the festive period. In my relatively brief model watching experience I've never seen such consistency in it compared to its ensembles.

I'd also like someone to comment on its reliability as opposed to the other members. I appreciate that the other members are lower res, and therefore supposedly less accurate (so I repeat my question on another thread - what is therefore the point in low res?).

In situations like this where the GEFS members seem to defy the op and vice versa, which usually rings true?

Yes and if ( like some on here believe ) the GFS operational run is the form horse this year, it renders the other 19 perbutations a waste of time. Or it could be that the Operational run is not calibrated correctly in which case it distorts the ensemble mean considerably every 6 hours.

[Frosty.]

Theres nothing in the models to suggest any cold from our east or north east. So far there is no pattern emerging on the GFS ensembles other than current zonal. So what I would really appreciate is when members harp on about cold coming mid/late Jan they back it up with some sort of evidence.

If you read steve murr's amazing post from last night you will get some evidence, the current charts are not showing it but steve said to look at the NH charts for a better view of the bigger picture.

[Bristawl Si]

More of the same for the foreseeable....according to the model output - that HP to the south of the UK is being a right pain!

I notice GP is reading - any update thoughts Stewart? The NW forecast for the Winter was only updated 2 days ago - do you think we're still 'on track' re late Jan?

[Robbie Garrett]

Looks pretty cold in the eastern USA at 120hrs!

http://www.meteociel...map=1&archive=0

Overall good agreement across the models for a typical mixed bag of weather, a few swipes of colder air more especially for the north, interspersed with milder interludes.

The GFS makes more of the Azores high, the ECM looks to keep this mainly displaced a bit further to the west and south.

The ECM 240hrs is an improvement in terms of cold or should I say less horrifying for cold and snow lovers in here with a slightly better NH pattern, overall I'd sum up the output as pretty typical winter weather for the UK.

If I win the Euromillions I'll hire a couple of jets and take us all over to Canada in time for that deep cold plunge shown at 120hrs!

I can always fly my Cessna 172 across the Pond, but the idea of flying a single over the North Atlantic doesn't bare thinking! Might cost a bit too, and many stop offs (only got 5hr tanks) To be honest, it's good fun model watching but the weather pattern we have at the moment is providing a lot of flying day's when each LP system goes by it drags clearer air behind it, which means some lovely flying days.

I just had a look at the outputs from last year on Meteociel, and I can see why people say don't look to far into FI, ECMW didn't show any potent northern blocking until at least 192hrs out from it actually happening, and at least 3 days before this started happening it was about as bleak as it is now.

My question is though, you say we are looking for an NW/SE angled jet? to allow any heights to rise to produce SSW for Greenland providing a HP northern block. Can you draw this to show what you mean? on top of one of the charts or something? Or is this something that must happen upstream to allow for a amplified jetstream once it reaches the UK shores? I am confused but my generation will learn better from Visuals!!!

Also what is the significance of that HP cell in the Arctic?

[J10]

As expected the GFS is a bit of an outlier, not so much in terms of temps which it is generally milder than the mean, but more in terms of pressure in which it is a High Pressure outlier for Southern Britain and North West Europe.

http://hw.nwstatic.c...prmslLondon.png

http://hw.nwstatic.c.../t850London.png

the 850Hpa shows the Interspersed PM and TM air, with the op run showing less PM than the ensembles.

So in summary, zonal, ranging from cool to mild.(ECM showing a similar pattern)

The cool zonal periods will give wintriness, as an example some snow is expected over part of Scotland in the next 24 hrs.

[Frosty.]

Also, the GEFS Ensembles do paint a colder looking picture for early next week, and stormier compared to the operational runs.

[Cheese Rice]

Low at T114 needs to be watched, not only will it bring strong winds but also a chunk of GFS members bring snowfall risk to large parts of the country.

Each image represent a different member, although the timing is still to be decided.

Edited December 29, 2011 by Cheese Rice

[nick sussex]

I can always fly my Cessna 172 across the Pond, but the idea of flying a single over the North Atlantic doesn't bare thinking! Might cost a bit too, and many stop offs (only got 5hr tanks) To be honest, it's good fun model watching but the weather pattern we have at the moment is providing a lot of flying day's when each LP system goes by it drags clearer air behind it, which means some lovely flying days.

I just had a look at the outputs from last year on Meteociel, and I can see why people say don't look to far into FI, ECMW didn't show any potent northern blocking until at least 192hrs out from it actually happening, and at least 3 days before this started happening it was about as bleak as it is now.

My question is though, you say we are looking for an NW/SE angled jet? to allow any heights to rise to produce SSW for Greenland providing a HP northern block. Can you draw this to show what you mean? on top of one of the charts or something? Or is this something that must happen upstream to allow for a amplified jetstream once it reaches the UK shores? I am confused but my generation will learn better from Visuals!!!

Also what is the significance of that HP cell in the Arctic?

I still haven't figured out how to attach a small image to one of my posts so I'm going to have to try and explain things in written form.

The reason a nw/se tilted jet is important is for two reasons, firstly this brings lower pressure into central Europe and stops the Azores high from edging east into that location, also as the energy from the jet is forced se'wards it often promotes higher pressure developing to the ne.

The much talked about SSW hasn't actually occured at the more important 30hpa level in the stratosphere, we have a minor warming but this at present doesn't look like it will provide the knock out blow to the PV.

What a second warming might do is slow the jet sufficiently and weaken the PV so that at least gives the chance for some potent colder shots, again though you're unlikely to sustain cold without a proper Greenland high,if you remember last winter many of the easterlies progged in FI were shortened because the background signal was to develop blocking over Greenland, so we saw short easterlies then northerlies.

You can get a very cold easterly without a background signal for northern blocking but its unlikely to sustain for very long as the jet will sink the Scandi high so we're always brought back to looking out for northern blocking.

You can get some decent PM shots with a nw/se jet but for what many people want to see in here it's really essential to have northern blocking.

In terms of upstream patterns generally a positive PNA or more amplified pattern in the USA can often help bring colder conditions to Europe, in this instance even though we get that eastern US trough because the PV is limpeted in western Greenland we don't have a chance of a northerly toppler.

The Arctic high is nice to see but unfortunately isn't much help at the moment because of the location of the PV, before we can think of any major NH change that really needs to be displaced from there with a proper split.

Hope that helps.

Edited December 29, 2011 by nick sussex

[phil nw.]

Also, the GEFS Ensembles do paint a colder looking picture for early next week, and stormier compared to the operational runs.

Yes there will be brief mild incursions, but balanced out by days where polar air comes south and east behind the cold fronts,thereby we see an average looking graph on the Gefs.--going slightly below later which shows the Op.run one of the milder members by then.

The T72hrs chart is tyoical of what type of conditions we should expect for the next week or so.

Rain bands bringing in alternate milder then colder air,quite windy at times,especially further north where there is likely to be some brief spells of snow,especially over the hills.

[TonyH]

Wonder if the colder sectors will be moderated by short waves as with the past 2 days resulting in another generally mild week?

[Robbie Garrett]

Thanks for that nick, does wonders at explaining exactly what we are looking at and what we want to see. I am guessing the green lines on this chart are the jet? or where it would try follow? The big question is what comes first? SW or Jetsteam tracking south, with mild air track north (Northern blocking), which distrupts the PV.

[Bristawl Si]

Update from GP in last few mins in the Winter Forecast Thread - here's an extract - hope this is OK to post here:

"Clearly the AO and this cold vortex event are a big deal and will not be overcome easily however this was expected, and the repeat warming waves in the stratosphere, allied to the idea that because this event started early, will end mid month (60 day rule), allied to the exceptionally good MJO analogues, all point towards a transition in both the NAO and the AO during the mid to late January period.

So no reason to amend or alter a forecast (if it aint broke, don't fix it)."

Interesting stuff - probably means that models will not show anything for another couple of weeks yet.

"

[syed2878]

Guys what i don't understand is that if all the main models not forecasting any blocking how come then most membors keep on going on about this cold an snow from mid jan?

[Grimsby Snow Lover]

Guys what i don't understand is that if all the main models not forecasting any blocking how come then most membors keep on going on about this cold an snow from mid jan?

Have a read through GP'S latest post on the winter thread. This should explain the northern blocking after mid month.

http://forum.netweather.tv/topic/71680-winter-forecast-now-available/page__st__100

Edited December 29, 2011 by Grimsby Snow Lover

[bluearmy]

many comments on how the models are differing. however, at day 10, compare the polar representation of the ecm ens mean and parallel GEFS

spot the difference in upper heights ???? i suggest, given this agreement at T240 that to look at the GEFS mean a while later may not be too unreasonable.

T384 mean and spread

part of the vortex lifts out of scandi a little to the northwest as the p/v tightens as it is likely to do on a deep fi mean chart plus the alaskan chunk heads off to eastern siberia to join forces with the small segment already there. note the alaskan chunk of p/v is replaced by a mean ridging which i think will prove significant if we are to get our cold final third of the month. the spreads are indicative of a fairly strong flow around the globe with plenty of ridges showing - quite amplified which shows perhaps the vortex losing some of its strength. the large spread west of iceland - another likely toppler for us around mid month - maybe a few days as per the weekend before xmas.

i am using the parallel GEFS as i know if to be an improvement on the existing GEFS in terms of resolution etc.

[Cheese Rice]

Guys what i don't understand is that if all the main models not forecasting any blocking how come then most membors keep on going on about this cold an snow from mid jan?

A select few members use more complex methods for future forecasting. While alot of other members are jumping on the bandwagon because more experienced posters see cold

[Frosty.]

three hours of wet snow; that is my story,

That's 3 hours more than I have seen then, you lucky bleep bleep

The models tonight are showing a very unsettled zonal spell for the next 7-10 days, especially further north, a few colder incursions are likely with the 528dam line sweeping across the uk by next monday and a chance of it returning but inbetween the colder intervals it will be mild and it looks very windy at times.

[Jason M]

The 18Z opp run is so awful its actually funny.

Post 300 hours (which is obvoiusly complete la la land and therefore hopefully won't verify), the high moves East into the 1988 position over the near continent.

Looking through the earlier ensembles there were again some interesting synoptics, however the problem then arises that the 850s are generally too high as there is no cold pool.

My view is that the existing pattern will not break as such, it will simply shift North with the jet. I suspect by mid month we will have the high sitting directly overhead with the jet running over the top.

The interesting point that arises from this is that lack of rainfall will be a serious problem for parts of the SE and East Anglia given the scarcity of any rain over recent months. This could become a really big story over the next couple of months imo.

Jason

[Robbie Garrett]

It's still a pattern change though, but hopefully it doesn't verify!