Model Output Discussion - cold spell to end Autumn

[Snowmadsam]

1 minute ago, PLANET THANET said:

as long as it doesnt go t*ts up

Or B*lls up...

[Frosty.]

Anyone despairing about the progressive Ecm 12z operational really shouldn't..it goes against other models and the Met Office..see what the mean shows if you see what I mean..about 30-45 mins to go.

[Derecho]

Hello again.

So we have good agreement now that we will get an undercut. A complex situation to forecast because small changes have big differences further down the line.

Here is a simplified depiction



The black line represents the jet and anywhere a bit to the east and north of that low stands a chance of snowfalls. Its all academic at this point though given its far out from here. The slightest nudge west and the UK could get a lot of snowfall, especially in the south. A nudge to the east and the weather will be miserable with lots of cold rain.

From here a further three situations may develop (could be more but these are most likely), each one rated with their chances given a percentage.

8-8.5/10 GFS, 25%                                    7-7.5-10, ECM, 35%                               Worst case scenario, 10-15%

 

 The GFS is excellent and if the undercutting was a little bit further east, the snow potential on this run would be very impressive. If the arctic high recedes from the Svalbard area the Scandi low can move west and high pressure can take its place.

Alternatively we could have more transient northerlies from the Azores high expanding north, the polar vortex lobe however could be quite persistent so may be harder to get a deep arctic feed.

The final scenario would take us back to standard UK winter fare but seems to be the minority option at the moment at least.

The arctic high could play a bigger role but I haven't seen that in closer time frames that much (though the 06z op showed it)

Personally I think its a tough call between the GFS and ECM path. Also have to mention that storm on Friday with the ECM looks quite concerning... I really hope it isn't that deep.

Generally the repeated northerlies make me think the last option is unlikely. So I would expect the first two patterns to have the greatest chance of occuring. Some may be disappointed though if the undercutting moves east, yet some could be rewarded if its further west. That's the risk ya take!

Edited December 4, 2017 by Quicksilver1989

[bobbydog]

the key point is at +168. the low pressure system exiting canada behaves differently between the ECM and GFS

on the ECM, it runs with the jet and blows up as it approaches us. the GFS has it further south and allows more amplification. i would expect adjustments in our favour as i think the ECM has that low a bit too intense.

thought i should add, whichever way it goes, in previous winters, we would have seen this as our 'big chance' for the winter. this time round, its just going to be one of many...

Edited December 4, 2017 by bobbydog

[Winter Hill]

9 minutes ago, Frosty. said:

Anyone despairing about the progressive Ecm 12z operational really shouldn't..it goes against other models and the Met Office..see what the mean shows if you see what I mean..about 30-45 mins to go.

Hi Frosty.

Can you tell me why you think the ECM 12z is progressive?   What if it is bang on the money ?

[Chesil View]

27 minutes ago, Broadmayne blizzard said:

Two things to note from the 12z ECM. Firstly the slider has corrected southwest slightly and as other have noted this is often seen with sliders. From  40 years experience

of monitoring synoptic developments I would expect further corrections over the coming runs as the slider moves into the more reliable time frame.

Secondly as Damians Law states in his post above please can we get past this rubbish about uppers having to be between minus 5 and minus 10 for every case of snowfall.

If you want an example of just how much snow you can get from much higher uppers then google the great southwest Blizzard of February 1978 look at the pictures of the twenty foot drifts and take on board the fact that this colossal fall came with uppers of just minus 2

In fact here,s a pic to show you what minus 2 uppers can deliver.

[Frosty.]

17 minutes ago, Winter Hill said:

Hi Frosty.

Can you tell me why you think the ECM 12z is progressive?   What if it is bang on the money ?

Because it changes the meridional pattern (Northerly flow) back to a flatter less cold / milder westerly zonal flow with depressions pushing in from the west and I think that goes against the general background signals which as far as I know still indicate generally more blocked and colder weather until at least mid dec..if not further ahead..i'm not saying the ecm op is wrong, just that it's unlikely.

Edited December 4, 2017 by Frosty.

[blizzard81]

Ecm mean looks to have better Atlantic ridge towards day 10 compared to the 00z mean. 

[Winter Hill]

7 minutes ago, Frosty. said:

Because it changes the meridional pattern (Northerly flow) back to a flatter less cold / milder westerly zonal flow with depressions pushing in from the west and I think that goes against the general background signals which as far as I know still indicate generally more blocked and colder weather until at least mid dec..if not further ahead..i'm not saying the ecm op is wrong, just that it's unlikely.

Thanks for the reply.

[blizzard81]

Does anyone know if the ec46 updates tonight? 

[andymusic]

3 hours ago, Dafydd Tomos said:

Same here in Tenby although 10C is possible on Saturday, so much milder than the ensembles show. Well at least apart from a rainy Sunday we should get plenty of winter sunshine  it's better than mild, wet & windy imo mate

can't see Tenby or Porthcawl managing 10c from that with a wind chill also

Edited December 4, 2017 by andymusic

[Daniel*]

I do think some folk over stress the impacts of a warming arctic and the lack of sea ice on the potency on northerly airstreams. These 850hPa temps on GFS 12z for Friday are pretty exceptional, -9C uppers south of the M4. All precipitation will fall as snow away from the coast at least a white day for some.

Edited December 4, 2017 by Daniel*

[Man With Beard]

Something that went under the radar on the ECM was the 100mph gusts over Northern Scotland on Thursday.

[I remember Atlantic 252]

1 minute ago, Daniel* said:

I do think some folk over stress the impacts of a warming arctic and the lack of sea ice on the potency on northerly airstreams. These 850hPa temps on GFS 12z for Friday are pretty exceptional, -9C uppers south of the M4. All precipitation will fall as snow away from the coast a white day for some.

Yes good angle too from the Cheshire Gap, -9 should be okay, although -10 needed off convective NW'ly for my location

[Man With Beard]

2 minutes ago, Daniel* said:

I do think some folk over stress the impacts of a warming arctic and the lack of sea ice on the potency on northerly airstreams. These 850hPa temps on GFS 12z for Friday are pretty exceptional, -9C uppers south of the M4. All precipitation will fall as snow away from the coast a white day for some.

...and this cold pattern is also helping cool the seas around us, which will it turn lead to colder weather as the winter goes on.

[snowbunting]

1 minute ago, Man With Beard said:

Something that went under the radar on the ECM was the 100mph gusts over Northern Scotland on Thursday.

Eeek dont say that. Together withheavt snow showers we might get snowed in and .... ok I will stop!

[Frosty.]

Tonight's Ecm 12z ensemble mean shows a good looking arctic blast and thereafter it stays unsettled and generally on the cold side with further wintry ppn and frosty / icy nights..looks a much better profile than the increasingly flatter zonal less cold operational.

Edited December 4, 2017 by Frosty.

[I Cumbria Marra I]

4 minutes ago, Daniel* said:

I do think some folk over stress the impacts of a warming arctic and the lack of sea ice on the potency on northerly airstreams. These 850hPa temps on GFS 12z for Friday are pretty exceptional, -9C uppers south of the M4. All precipitation will fall as snow away from the coast at least a white day for some.

Id imagine it would fall as snow even right on the coast.

[bluearmy]

Just to keep everything clean, the extended eps back end week 2 continue the theme from previous runs with the Canadian lobe edging east and driving the jet ever further east at a slightly higher latitude with the Atlantic upper ridging pushed very close to the uk - bound to be plenty of spread by then and this does offer some support the gfs op far off fi idea of building a ridge up into Scandinavia. 

i would say that the later gefs means/anoms are decent wrt the eps 

[Guest]

7 minutes ago, andymusic said:

can't see Tenby or Porthcawl managing 10c from that with a wind chill also

Was thinking the same! Not sure where 10C came from  It's shaping up to be a bitter end to the week 

[northwestsnow]

2 minutes ago, Frosty. said:

Tonight's Ecm 12z ensemble mean shows a good looking arctic blast and thereafter it stays unsettled and generally on the cold side..looks a better profile than the increasingly flatter zonal operational.

Fabulous ec mean matey 

[tight isobar]

2 minutes ago, Frosty. said:

Tonight's Ecm 12z ensemble mean shows a good looking arctic blast and thereafter it stays unsettled and generally on the cold side..looks a better profile than the increasingly flatter zonal operational.

The mean is a world apart from the op!!

Much-much better...

[ANYWEATHER]

Evening! A potent shot of artic air for all during Friday and Saturday, both ecm and gfs have a messy scenario after that with the Atlantic having some influence .Certainly not mild though as the jet stream even at T+240 time frame shows the jet stream way south of the uk. A few things to note on this upcoming scenario, don't believe the snow charts, expect the unexpected , and computer models will be in a frenzy with any detail.....

[Daniel*]

3 minutes ago, Man With Beard said:

...and this cold pattern is also helping cool the seas around us, which will it turn lead to colder weather as the winter goes on.

As 62/63 has posted the seas around us have cooled considerably, since early November courtesy of several quite potent northerlies. A good thing as it reduces marginality for those on the coast or with close proximity to it, and has a limiting effect probably very slight on the moderation of cold air from the north or east. However, the vigor of convective snow showers may be impacted thus requiring even colder upper air temps to override the cold SSTs. 

[Iceberg]

The ec members eps are even better for Sunday. The control has snow for everybody away from the sw on Sunday 5-15cm and a majority of the members have snow from Devon upwards.