Model Output Discussion - The Run In To Christmas

[East_England_Stormchaser91]

Yes pretty good agreement across the output this morning so far with any cold being very transient behind a deep low.

Is it time to call any cold spell for December dead?

I will wait for ECM and then GFS this evening and UKMO and JMA and the ensembles and maybe tomorrow...

 

Seriously though, it doesn't look likely now.

Still time for so many things to chop and change. A movement of the breakoff of that shortwave 300 miles further South would see a huge difference on where that storm will blow up. Thats even if it does of course! This space needs to be watched incredibly closely!

[Cheshire Freeze]

That storm looks extremely severe across the GFS and UKMO this morning. Something like 90mph gusts would occur should it play out as the GFS P suggests. Nasty but intriguing all the same. Damage would be fairly widespread in that scenario I would imagine.

Usually such features downgrade come closer to the day however.

Edited December 21, 2014 by CreweCold

[Eugene]

Very good set of 00Z's from NAVGEM, UKMO, GFS P for cold weather fans.

[snowangel32]

Still time for so many things to chop and change. A movement of the breakoff of that shortwave 300 miles further South would see a huge difference on where that storm will blow up. Thats even if it does of course! This space needs to be watched incredibly closely!

Yh true it has potential to cause a lot of damage and I expect it to deepen more. Its the track that's going to be a severe headache to the mo, I would say currently its not really a snow issue because we are on the wrong side of marginal in my opinion. But it would only take a small tweak and it could be blizzards so nothing is off the table. Let's see how the ecm handles that low and I bet the mo are watching it very closeley.

[Abyss]

GFS pushes system east quickly while the GFS(P) stalls on the East coast of Scotland then dives directly South which helps cold uppers stay in place for longer.

 

Gfs operational at t144

Gfs(p)

GFS (O) 

Gfs(P)

Come T174 GFS(O) Is centred just to the North of Poland

While the Gfs(P) is the low countries

 

At t192 gfs(o)

Gfs(p)

[alexisj9]

GFS pushes system east quickly while the GFS(P) stalls on the East coast of Scotland then dives directly South which helps cold uppers stay in place for longer.

 

Gfs operational at t144

Gfs(p)

GFS (O) 

Gfs(P)

Come T174 GFS(O) Is centred just to the North of Poland

While the Gfs(P) is the low countries

 

At t192 gfs(o)

Gfs(p)

Although the P seems better for cold, I would prefer the O because the track and strength is a bit safer for the east coast and the low countries too, it would be better if it doesn't develop at all. Keeping a close watch, hoping it disappears. 

[West is Best]

 

Is it time to call any cold spell for December dead?

 

 

You're being a bit of a wind-up merchant tbh Mucka. I'm not sure of your definition of cold spell, but these two screenshots are not exactly mild now, are they? Have you checked the 850hPa temps? On the GFSP, for instance, there is a sustained cold 'spell' that lasts over a week.

 

We're starting to see good agreement for 27/12 across GFS, GFSP, UKMO and GEM. UKMO is particularly tasty and that inspires great hope in me. I await the ECM prodigal with bemusement.

 

Edited December 21, 2014 by West is Best

[Iceberg]

Some fantastic lower strat movement from GFS OPS at the lower range, resulting in a very nice trop pattern..ALL along way off in FI, looking to hit the UK 2nd week in Jan. Before then  there is every chance for a few folks to see snow, cold and some interesting weather. Might be a quick 48 hrs of cold, with snow limited north of the boarder, could be more longer snow for a few areas, with the cold a higher chance of lasting longer under any falling high. UKMET is far better with the WAA allowing the ridge to develop far enough north at T144 to limit west to east progression of energy. Not much support for it from the GFS ENS though.

[West is Best]

So the ECM now gives us the best Christmas Day chart of the lot! It's close to the GFSP for the same T96, only even better:

 

[Captain Shortwave]

Still ECM/GEM vs UKMO/GFS by day 6

ECM

GEM

 

UKMO

GFS

Parallel

 

Lets see how the ECM develops as the only difference between the GEM and the others is the timing of the colder spell which on all the output so far is brief., that said the ECM seems to have shortened the milder spell as the Atlantic low does cut off again at day 7. Out of the 5 main operationals, it looks like none of them will establish a pattern that will ensure a prolonged cold spell and instead just involve a sinking Atlantic ridge.

Edited December 21, 2014 by Captain shortwave

[SLEETY]

Gfs looks a complete mess.Huge differences between ecm its laughable now

[LomondSnowstorm]

Interesting set of models this morning so far. GFS broadly the same as yesterday, upstream not amazing but would trend towards a mid-latitude high after a potential 'winter storm' which would likely deliver at least some low ground snowfall. UKMO manages to both track the storm further east and get decent ridging into Greenland, representing what looks like the happy middle ground we're likely to end up at. ECM looks a bit nicer for Christmas Day (potentially white for much of Scotland on that), still keeps the low further west but also looks like it remains consistent on building a GH.

[Matty M]

wow, this is model uncertainty I haven't seen in a while.

 

How does one forecast this

 

Nevermind Boxing Day, the forecast for Christmas Eve is appallingly difficult with the ECMWF giving some parts of Scotland

a dump of snow and mountain blizzards.

Edited December 21, 2014 by Matty M

[Duane S.]

Yes pretty good agreement across the output this morning so far with any cold being very transient behind a deep low.

Is it time to call any cold spell for December dead?

I will wait for ECM and then GFS this evening and UKMO and JMA and the ensembles and maybe tomorrow...

 

Seriously though, it doesn't look likely now.

 

Poor comment. The story of the past few days is model output variability and that continues. There are 10 days left in December last time I checked.

[bluearmy]

Whilst you have this upstream at day 6, I wouldn't bother trying to work out where we're headed

some seem happy with the 00z. From a chilly and frosty/foggy perspective, I'd be interested. From a snow perspective, I'd be depressed wrt to the previous suites (ops and ens although ECM ens not available as yet)

looks like too many varied clusters moving forwards to have much confidence in any solution. Even Xmas eve into Xmas Day now seems a bit uncertain for the scots.

Edited December 21, 2014 by bluearmy

[Polar Maritime]

The GFSP continues to show the Winter Storm tracking South over the UK around the 27th, Bringing severe gales and heavy rain with blizzard conditions in places and Snow to lower levels even down South. An atrocious spell of weather on the way, But interesting all the same for us weather enthusiasts. I would say until this storm is out the way the Models will continue chop and change, So expect further wild swings from the out-put over the next day or two.

 

Edited December 21, 2014 by Polar Maritime

[karlos1983]

image.jpg

Whilst you have this upstream at day 6, I wouldn't bother trying to work out where we're headed

some seem happy with the 00z. From a chilly and frosty/foggy perspective, I'd be interested. From a snow perspective, I'd be depressed wrt to the previous suites (ops and ens although ECM ens not available as yet)

looks like too many varied clusters moving forwards to have much confidence in any solution. Even Xmas day into Boxing Day now seems a bit uncertain for the scots.

Never understood those charts....

[tinybill]

The GFSP continues to show the Winter Storm tracking South over the UK around the 27th, Bringing severe gales and heavy rain with blizzard conditions in places and Snow to lower levels even down South. An atrocious spell of weather on the way, But interesting all the same for us weather enthusiasts. I would say until this storm is out the way the Models will continue chop and change further into the run, So expect further wild swings.

 

i.e  the people on the east coast will need to keep a eye on this beast with the possible big tidal surge which could come down the east coast  ,and looking at the latest models the east coast could  easy expect  heavy snow on the 27 at the moment

[bluearmy]

Never understood those charts....

Karlos, the darker the shades, the less variability exists from the mean. Therefore huge confidence in the upper long wave pattern. As the shades lighten, there is a lack of confidence as there are ens members which diverge significantly from the mean in that area. That day six chart shows that there is a big variance off the ne seaboard of n America at day six with heights. this means there are flat ens members and there are amplified ones. The odd member that's very different wouldn't skew the spread like that. What happens in this area is crucial as to whether the Atlantic high gets flattened quickly or becomes a more n Atlantic/s greeny feature. Clearly, that dictates how amplified the jet becomes and whether it's flattish and pushes the whole pattern east or amplified and sinks the trough well into Europe.

The spreads can also be useful to spot clusters on ECM, given that we don't have access to these charts.

[karlos1983]

Looking through the GEFS Purbs, what is clear to me is that a deep low is pretty much nailed to be near or over the UK at 144 or thereabouts. All but 3 Purbs at 144 show this. UKMO also agrees

[Polar Maritime]

i.e  the people on the east coast will need to keep a eye on this beast with the possible big tidal surge which could come down the east coast  ,and looking at the latest models the east coast could  easy expect  heavy snow on the 27 at the moment

 

Yes Tinyb, Some heavy snow model'd for the South, With sever gales for the UK. 

 

Edited December 21, 2014 by Polar Maritime

[IDO]

Having seen that the ECM 12z was a temp outlier it is no surprise that the 0z moves towards the GFS with just transient ridge and trough in a less amplified pattern. The Greenland height bias anomaly on the ECM (last 5 runs) has been extraordinary, so it is impossible to take any block in that area seriously:

 

 

D10 on the ECM is similar to a major cluster the GEFS have been showing for a while: 

 

 GFS P: 

 

As the mean has been suggesting this was only likely transient, a variation on the current pattern. The real pattern changing potential was always if the Pacific ridge developed (around D9) and the following upstream wave to our sector. With the US likely to dig a cold and wintry trough there is a good possibility we would get an associated ridge in our locale. Unfortunately the GEFS are downgrading the longevity of the Pacific Ridge and it looks like they are continuing with the amping up of the PV. The mean at D15:

 

 

That is a fair resemblance of the clustering in the GEFS and it looks like Dr Cohen's 3-4 week analysis where the Pacific Ridge fails and we head into a neutral AO and positive NAO is showing up.

 

So wintry wise little away from the December norm. The real concern is the potential storm around D6. The LP system looks like being a smaller feature but the main cluster is fairly represented by the op:

 

 

One to watch. As for snow for the south on the back edge as per the GFS P, the ensembles have this as a 10% risk and remains unlikely.

Edited December 21, 2014 by i'm dreaming of...

[dragan]

I have a question please: the low around the 27th looks different all the time. Will the final placement of it have a major impact on the weather after it, depending where it tracks?

[karlos1983]

Karlos, the darker the shades, the less variability exists from the mean. Therefore huge confidence in the upper long wave pattern. As the shades lighten, there is a lack of confidence as there are ens members which diverge significantly from the mean in that area. That day six chart shows that there is a big variance off the ne seaboard of n America at day six with heights. this means there are flat ens members and there are amplified ones. The odd member that's very different wouldn't skew the spread like that. What happens in this area is crucial as to whether the Atlantic high gets flattened quickly or becomes a more n Atlantic/s greeny feature. Clearly, that dictates how amplified the jet becomes and whether it's flattish and pushes the whole pattern east or amplified and sinks the trough well into Europe.

The spreads can also be useful to spot clusters on ECM, given that we don't have access to these charts.

Cheers ba, that probably makes my previous post (which I wrote before seeing your reply) a bit redundant then if there is uncertainty at D6 up there. Edited December 21, 2014 by karlos1983

[TEITS]

Forget about snow, cold spells as im now more concerned about severe gales and more importantly storm surge for those living on the N Norfolk coast. Now the UKMO is predicting such a storm it must be taken more seriously especially as the next frame of the UKMO would see low pressure move SE and deepen further!

 

As for the potential cold spell and the ECM/GFSP are nowhere near as good as yesterdays 12Zs for the longer term. However its futile to discuss the longer term when the shorter term remains unresolved.