Model Output Discussion - cold spell to end Autumn

[Nick123]

12 minutes ago, nick sussex said:

Everyone here started off on the net as a likely beginner and trying to understand about this complicated weather in the UK. So you shouldn't feel worried about asking questions and theres lots of different threads and a learning area to help you along the way.

Thank you so much! I was a little worried because I really don't understand a lot of what people are saying on here. But I will take a look around and hopefully improve

[Dennis]

next week more cold weather

[bobbydog]

1 minute ago, CK1981 said:

Thanks for the insight, Nick. It’s really useful and makes this situation all the more interesting!

its worth remembering that this 'slider' which is modelled to be quite complicated, therefore difficult to predict details, even for the professionals, doesn't even exist yet....

[Paul_1978]

24 minutes ago, Nick F said:

Extended EPS mean does paint an increasingly mobile / zonal picture out to day 15, as the Euro trough de-amplifies and heights rise toward SW Europe as the trop PV over eastern N America expands east over NW Atlantic. The signal for height rises to the NE rather faint too. As I mentioned earlier this afternoon, the flattening of the +PNA ridge is creating deamplification of the H500 flow downstream and allowing low heights to spread east out of Canada and more jet energy to flow and de-amplify the flow across the N Atlantic.

This from the CPC prognostic discussion today:

http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html

However, the extend ens means are prone to change and the 12z GEFS mean indicates H500 mean ridging over Norwegian Sea and Svalbard, so there is still chance yet of this height rises to the NE scenario unfolding in the run up to Xmas.

Anyway, lets enjoy the cold and snow prospects on offer the next 4 days and hopefully, in the meantime, the medium-longer term outlook will improve from EC/EPS over next few days.

Well as someone said, that's a dramatic shift from what everyone was saying this time last night. 

But on the plus side we've still got GP's and Tamara'a background signals which are apparently very good if you are of the cold persuasion. 

[alexisj9]

4 minutes ago, bluearmy said:

00z run 

Yeah read that after, but anaysis still stands. 

[bluearmy]

18z a little north at T48 with precipitation and jet - will this manifest with a more northerly snow line on Sunday? 

[MKN]

4 minutes ago, bluearmy said:

18z a little north at T48 with precipitation and jet - will this manifest with a more northerly snow line on Sunday? 

As expected if so. I haven't seen it but 06/18z have been further north than 00/12z of late

[winterof79]

10 minutes ago, bluearmy said:

18z a little north at T48 with precipitation and jet - will this manifest with a more northerly snow line on Sunday? 

Yes but it pivots a smidgeon too

Edited December 7, 2017 by winterof79

[nick sussex]

8 minutes ago, bluearmy said:

18z a little north at T48 with precipitation and jet - will this manifest with a more northerly snow line on Sunday?

The jet was a bit more amplified upstream but the issue is the phasing with that trough. I can't remember the last time I saw this type of slider set up that was so complicated.

[Snowy L]

North Wales area looking at getting 30+ hours of non stop snow based on the 18z. The hills are going to be buried.

[winterof79]

3 minutes ago, Snowy L said:

North Wales area looking at getting 30+ hours of non stop snow based on the 18z. The hills are going to be buried.

I would say Southern pennines too.

[Stephen_Mcr]

18z certainly holding steady for the North West. Manchester is always terrible for snow and has been wavering all week, but looking pretty solid - I use the PPN maps as a guide to the conditions being right for snow rather than location which will still probably change - even then, its normally touch and go

Just had a huge crack of thunder in South Manchester too

 

 

[bluearmy]

Beeb 10pm forecast showed the occlusion pushing further north later Sunday though emphasised that the set up could be further north or further south

[Singularity]

I do reckon we're seeing a bit of climatology trying to take over during the transitional period as one strong set of signals (for the EPO ridge etc.) lets go while the new HLB signal (near to NE) is not being very well latched onto at this stage and so is not very evident in the EPS/GEFS yet. Not sure why EPS is so much less interested than GEFS though.

There is one possibility though; I have noticed that the MJO propagation to phase 7 has gained a bit of a stall in the model predictions, particularly those from ECM, before a resumption of eastward motion. This may have widened the window of simulated time (i.e. what the models go with) during which a more zonal flow is able to get going before the push toward the new HLB phase kicks in. Worth watching out for any sign of HLB gaining support late in the EPS over the coming day or two.

Thing is though, that MJO stall may well be erroneous in itself, in which case the output will backtrack toward what runs such as yesterday's 06z depicted i.e. a quicker transition to HLB near to the NE with the attempt to increase the zonal flow across the N. Atlantic derailed. Not sure it will ever be quite as quick as that run showed though, but you get the idea.

[Richard Fisher]

3 minutes ago, Stephen_Mcr said:

18z certainly holding steady for the North West. Manchester is always terrible for snow and has been wavering all week, but looking pretty solid - I use the PPN maps as a guide to the conditions being right for snow rather than location which will still probably change - even then, its normally touch and go

Just had a huge crack of thunder in South Manchester too

 

 

Quite a bit further North. Most of the Midlands missing out based on this run.

[bluearmy]

Ec46 looks pretty pos  NAO out to end week 4. Then possibly troughy across nw Europe but that's a long way off. 

[Southender]

At this rate it’s going to be a North Wales/Cheshire/Lancs/Yorks event on Sunday.

What drama!

[nick sussex]

Quite amazing to see what happens with the low at phase point, you can see the track more se at T48hrs and T54hrs then phase happens with the trough to the east at T60hrs and you get that shift eastwards the low centre deepens slightly to 970 which edges this ne causing the pivot then the shortwave to the sw runs se causing a south push to the sw and like those weighing scales you get a push north towards the east of the UK.

For that reason its the areas towards the nw which get into the cold are just far enough west so that the pivot towards the east still keeps that area in the cold.

I know I'm making this sound very complicated but it really is!

[Cheshire Freeze]

10 minutes ago, Singularity said:

I do reckon we're seeing a bit of climatology trying to take over during the transitional period as one strong set of signals (for the EPO ridge etc.) lets go while the new HLB signal (near to NE) is not being very well latched onto at this stage and so is not very evident in the EPS/GEFS yet. Not sure why EPS is so much less interested than GEFS though.

There is one possibility though; I have noticed that the MJO propagation to phase 7 has gained a bit of a stall in the model predictions, particularly those from ECM, before a resumption of eastward motion. This may have widened the window of simulated time (i.e. what the models go with) during which a more zonal flow is able to get going before the push toward the new HLB phase kicks in. Worth watching out for any sign of HLB gaining support late in the EPS over the coming day or two.

Thing is though, that MJO stall may well be erroneous in itself, in which case the output will backtrack toward what runs such as yesterday's 06z depicted i.e. a quicker transition to HLB near to the NE with the attempt to increase the zonal flow across the N. Atlantic derailed. Not sure it will ever be quite as quick as that run showed though, but you get the idea.

The NWP has a habit of tending to overreact to a zonal signal in situations like we could see unfold later this month. 

It could well be one of those situations where something tends to pop up out of the blue at the day 7/8 range, rather than ticking down from 10 days + This especially tends to be the case with Scandinavian height rises.

[Paul_1978]

The funny thing is if we were watching this run 4 weeks ago, we'd all be marvelling at the state of the Atlantic and WAA into Greenland at T+150. 

It's easy to forget what we're seeing before our very eyes. 

GFS is out to T+150 and the output is fantastic - a potent snow event on our doorstep for some of us, then OK, north westerlies, but by the end of the week we're back to northerlies again. 

After that who knows, but I'm detecting a bit of despondency and I don't really know why. This is the best model watching we've had for years!

Edited December 7, 2017 by Paul_1978

[Frosty.]

The Gfs 18z shows persistent heavy snow for some areas on sunday which would make for a very snowy drive to work next monday..potentially severe weather on the way for somewhere across the central swathe of the uk..plenty of snow showers piling into western and northern areas before then with sharp frosts, especially over the snow fields..hope I get to say that plenty more times this winter!!

[ribster]

6 minutes ago, Southender said:

At this rate it’s going to be a North Wales/Cheshire/Lancs/Yorks event on Sunday.

What drama!

Don't think it's a done deal yet, will probably correct south again in the morning...

[snowbob]

The rate this is moving north don’t bode well for the cold to sweep down the uk

surely we need south corrections 

[blizzard81]

4 minutes ago, CreweCold said:

The NWP has a habit of tending to overreact to a zonal signal in situations like we could see unfold later this month. 

It could well be one of those situations where something tends to pop up out of the blue at the day 7/8 range, rather than ticking down from 10 days + This especially tends to be the case with Scandinavian height rises.

Good point Crewe. I have also noticed this over the years. It always happens during the more classic winters. Here's hoping. 

[sorepaw1]

Lots to talk about these coming days .

I'm struggling to load up the 18z gfs.

I keep getting intermittent power cuts with the strong winds here.

I've got as far as T+126 hrs.

Is it still looking potentially cold beyond that.

Sorry to be a nuisance.