Model Output Discussion - 12th December Onward

[jonnybradley]

Not sure where you saw that. Must of the alps are in for a good dumping, 30 to 50cm on friday across most parts, which is alot, but obviously not rare in the mountains at those heights. I can't see anywhere that is getting 1meter though.

I suspect the snow levels will decrease across the alps if the UKMO is right with the track of the storm, I think those snow levels are assuming it takes a track closer to the channel.

Yep spot on kmanmx. Sorry that last part wasn't meant to be taken to seriously. Saw it on the weather-forecast.com site, there 06 posting. Think they may have been on the GFS ott juice? (not certain they use GFS but I suspect)

As you say any snow fall is subject to the path of that low on Friday, which clearly is some way off being know at this point.

Edited December 12, 2011 by jonnybradley

[kmanmx]

I'm a subscriber to snow-forecast.com so I can view there 9day weather forecasts. Probably not really worth it thinking about it, anything over 4days out is hardly accurate. But it does seem to update 4 times a day, so yes i suspect it does use one of the more common runs, most likely GFS at a guess.

I'm off Skiing in January, so i'm rooting for the channel track for Fridays storm. Terrible snow amounts over most of the alps at the moment. Go back 2 weeks and there was pretty much nothing.

Still fairly FI at the moment though, I don't know half of what most people on here know but it's pretty obvious there is quite a lot of disagreement in the models. Seems pretty up in the air whats going to happen.

Edited December 12, 2011 by kmanmx

[Harve]

I'm a subscriber to snow-forecast.com so I can view there 9day weather forecasts. Probably not really worth it thinking about it, anything over 4days out is hardly accurate. But it does seem to update 4 times a day, so yes i suspect it does use one of the more common runs, most likely GFS at a guess.

I'm off Skiing in January, so i'm rooting for the channel track. Terrible snow amounts over most of the alps at the moment. Go back 2 weeks and there was pretty much nothing.

You can see 9 day weather forecasts for free by just using weather-forecast.com. For example:

http://www.weather-f...orecasts/latest

It functions exactly the same, with the GFS, except it focuses on settlements (though it shows a lot of them) and thus you can't specify the altitude. Though this one is for 1850m.

Edited December 12, 2011 by Harve

[damianslaw]

Meto suggest a continuation of the rather cold conditions and NW/W flow next week - no suggestion of heights building from the south and a raging southwesterly - indeed the models have had to continuously postpone any rise of heights from the south during recent days - wouldn't be surprised to see the models downplay significant height rises from the south next week in the coming days.

But before we get to next week we have tons of weather beforehand which will have a major bearing on things next week. The situation appears to change every day at present - models will continue to play around with different options beyond the reliable timeframe.

Back to thursday/friday - won't be until wednesday before we know with any real certainty the path of the storm.

[ribster]

We have a strongly +ve NAO going into next week and HP to the NE will not be coming into play other than to perhaps form an elongated High with the jet running over the top.

As I said earlier, the scenario shown on the GFS and ECM at T240 is one that takes weeks to come out of generally speaking.

Exactly a week ago today Ian, you told us that exactly the same thing would be happening at T144/T168, yet here we are again... Now you're looking at 240, keep calling it and you might be right at some stage!

[OldMetMan]

I keep on seeing people say "due to the complexity" of Fridays system. Could anyone elaborate a bit more on the complex factors involved? Would be nice to try to understand and follow some of these factors building into it.

Hi Jon, perhaps you were referring to what I said above. The models have been changing over the last day or so to depict the developing low for Friday as a more complex feature, rather than a single centred depression. The UKMet chart I attached above has what is essentially a warm frontal wave, and this doesn;t quite look right.

The following definition of a warm frontal wave might serve to explain it better:

"A secondary disturbance, often accompanied by a shallow closed-low circulation, that forms at some point on a marked warm frontal boundary a good way (at least 1000 km) from the parent (occluding) depression. Once formed, it moves quickly away from the parent depression (in the Northern Hemisphere east or southeastwards). Although not common, they are often responsible for considerable forecast errors, and are of particular importance in winter (snow-situation) forecasting as mild, maritime air attempts to displace a cold, continental blocking anticyclone."

I think the models seem to be suggesting this as a posssible outcome, but as the definition shows, this is very tricky from a forecasting point of view. One notorious instance of this was the October 1987 storm I referred to, when the models completely missed the development of the LP that caused all the damage. Granted, forecasting wasn't so sophisticated then, but I think we might be facing this situation Thursday/Friday.

We are looking at a potentially explosive situation here in my opinion. The baroclinic zone where this low is developing is very strong and development will be accompanied by an intense jet, so frontal disturbances will be fast moving and very difficult to accurately model. That is why i think the models so far today are giving mixed signals.

I think on balance the NOGAPS looks more realistic - at the moment - as if this low does turn out to be complex, then the final low in the chain is more likely to be the major one, as it engages the upper trough and deepens, accompanied by a rapid pressure rise behind it.

This is why I keep on about the satellite images as these will be key in identifying exactly how this frontal boundary is developing.

[bluearmy]

Looking through the ECM postage stamps, I'd say about 50/50 for very potent winds across the southern half uk on thursday night/Friday.

Beyond that at T168, a 20% chance that th mid Atlantic ridge will hold up the zonal train.

Looking at the Dutch ens, the op was a mild outlier by day 10 and it looks a fairly cold lead up to Xmas Over the near continent. will Ian be right for xmas weekend? I doubt it looking at the ens mean and spread. Shallw euro trough seems likely.

[NorthernRab]

I'd rather FI was showing mild weather for the run up to Christmas in comparison to cold, seeing as the opposite tends to happen anyway!

Anyway, looking just slightly outside the reliable time frame (Thursday / Friday into the weekend), it's looking actually quite good for cold fans and there's also something in the offering tomorrow when the cold sector moves in - not too bad for the "blowtorch" weather we were promised for the first two weeks of December!

[DAVID SNOW]

Thanks Both Nicks.

OK son your nicked.

[casparjack]

We have a strongly +ve NAO going into next week and HP to the NE will not be coming into play other than to perhaps form an elongated High with the jet running over the top. As I said earlier, the scenario shown on the GFS and ECM at T240 is one that takes weeks to come out of generally speaking.

'Weeks to come out of' - says who and why - you can't come out of something you're not already in? Sounds like pattern matching again to me, (or something worse), unless you provide justification for your thinking with charts, which would be a novelty for the members in here.

If the high to the NE does come into play, can you explain how you foresee the jet running over the top as you keep describing, surely what you mean is that there will be no link and the jet will continue to run between the two.

As ever you're trolling the thread trying to wind people up, you've been calling what you rather poorly explain above since the end of November in a number of threads, yet here we are on the evening of the 12th December and we are yet to see what you describe, with the models only really hinting at its development by T216 - acknowledged by a majority of experienced players as real FI.

You always appear to be so certain in your statements, yet they don't become reality as far as I can remember; go on prove me wrong with evidence of past success...

Edited December 12, 2011 by casparjack

[Summer Sun]

ECMWF ensembles are getting better for Friday up to 990mb for Birmingham now

http://expert-images.weatheronline.co.uk/daten/proficharts/en/ecmwfts/2011/12/12/basis12/pslv/03534_1212.gif

987mb for Glasgow

http://expert-images.weatheronline.co.uk/daten/proficharts/en/ecmwfts/2011/12/12/basis12/pslv/03140_1212.gif

990mb for London

http://expert-images.weatheronline.co.uk/daten/proficharts/en/ecmwfts/2011/12/12/basis12/pslv/03772_1212.gif

[Fozfoster]

This is why I keep on about the satellite images as these will be key in identifying exactly how this frontal boundary is developing.

http://www.yr.no/satellitt/europa_animasjon.html

this is a good satellite link.:-)

[Liam J]

ECMWF ensembles are getting better for Friday up to 990mb for Birmingham now

http://expert-images.../03534_1212.gif

987mb for Glasgow

http://expert-images.../03140_1212.gif

990mb for London

http://expert-images.../03772_1212.gif

In what sense are they 'getting better' ?

[Summer Sun]

In what sense are they 'getting better' ?

They've gone from possible severe storm force winds to somthing much less so.

[BurwellWeatherWatch]

Lots of people feeding the trolls tonight!

Weather watching doesn't come much more varied and exciting than this week though. Thurs still far from resolved - I think a pressure reading Alone is too simplistic though and there will be more factors than this which determine the windiness.

(null)

[Optimus Prime]

They've gone from possible severe storm force winds to somthing much less so.

As expected now we are nearing reliable territory. 1987 is an interesting example not to get complacent with these thingsm storms are very difficult to forecast correctly more than a day out at times.

It needs watching.

[phil nw.]

Looking through the ECM postage stamps, I'd say about 50/50 for very potent winds across the southern half uk on thursday night/Friday.

Beyond that at T168, a 20% chance that th mid Atlantic ridge will hold up the zonal train.

Looking at the Dutch ens, the op was a mild outlier by day 10 and it looks a fairly cold lead up to Xmas Over the near continent. will Ian be right for xmas weekend? I doubt it looking at the ens mean and spread. Shallw euro trough seems likely.

Yes some doubt wrt to the placement of the Azores ridging after the Friday low.

GEFS show s that the 12z operational was milder at the end.

http://www.wetterzen..._London_ens.png

Pressure rising in Xmas week so you would deduce that High pressure is favoured to be close to or over the UK,keeping rather cold surface conditions,perhaps retaining some Pm air in the mix from this week.The 2m temps are certainly near average for London.

A look at the Postage stamps at T240 show some differences in the pressure build around the UK.

http://www.wetterzen...nspanel2401.gif

You would have to favour the Azores high being a big player next week but it doesn`t always mean mild conditions if ,as the GEFS suggests, it builds far enough North.

Edited December 12, 2011 by phil n.warks.

[Nick L]

They've gone from possible severe storm force winds to somthing much less so.

Just because the pressure has increased slightly doesn't mean the winds can't be damaging.

[Frosty.]

Cold snap this weekend? discuss...all the comments are to do with the downgraded second storm or whether mild sw'ly winds will return next week but nothing about the cold and wintry weekend coming up, given a choice between strong winds and snow, snow wins every time for me.

[chionomaniac]

Lots of people feeding the trolls tonight!

Weather watching doesn't come much more varied and exciting than this week though. Thurs still far from resolved - I think a pressure reading Alone is too simplistic though and there will be more factors than this which determine the windiness.

(null)

Yes the gradient is just as important as the GFS is about to model with the secondary dropping along the south coast on Wednesday evening.

Edit it just fills after reaching Ireland, but could still be nasty!

Edited December 12, 2011 by chionomaniac

[Uncle_Barty]

This is why I keep on about the satellite images as these will be key in identifying exactly how this frontal boundary is developing.

Also worth looking at the WV images too. The presence of a dark streak (i.e. dry, cold air} behind the developing storm 'head' could be fuel for the 'bomb'. This was clear as Bawbag developed last week.

[OldMetMan]

http://www.yr.no/sat..._animasjon.html

this is a good satellite link.:-)

Thanks for that. Very smooth animation, makes a change!

Need to watch the GOES-East satellite over the W Atlantic in the next couple of days to see how this LP develops.

Also worth looking at the WV images too. The presence of a dark streak (i.e. dry, cold air} behind the developing storm 'head' could be fuel for the 'bomb'. This was clear as Bawbag developed last week.

Yes indeed, the GOES-East have a variety of different images, needs close watching I think.

[lorenzo]

Thanks for that. Very smooth animation, makes a change!

Need to watch the GOES-East satellite over the W Atlantic in the next couple of days to see how this LP develops.

Yes indeed, the GOES-East have a variety of different images, needs close watching I think.

Here is another with excellent overlays http://www.eumetrain.org/eport/euro_18.php?width=1280&height=800&date=2011120718

[A Winter's Tale]

Simon's latest update is very interesting!

He looks at another stormy week and the potential for strong winds on Wednesday aswell as the cold spell for the weekend. Although crucially the canadian models are showing signs of the "Keeling High" which would result in a cold, dry period to and including Christmas. He's feeling pretty confident but other models disagree. I wonder what I would prefer, the atlantic to continue with potential for snow from polar maritime air or to sacrifice the snow for a cold and dry Christmas. Certainly if this were to happen, it would ultimately contribute to a lower December CET and contradict to an extent part of RJS's forecast for late December.

[syed2878]

Hey guys ian keeps on going on about this mild just had alook at the bbc's monthly outlook they don't say much about it unless i red it wrong.