Model output discussion - into the start of Winter

[Skullzrulerz]

20 minutes ago, Frosty Winter said:

Not as good as previous runs.

It is not Frosty enough for you ?

[northwestsnow]

GEM ends lovely...

[BlueHedgehog074]

1 minute ago, northwestsnow said:

GEM ends lovely...

Yep. Dry, chilly, and festive. A UK High being something I would choose over what the 12Z GFS shows at a similar time frame of bringing the Atlantic back in. 

[SMU]

So Whats the net change in the last 24 hours ?

Well there has not been a run where Shaky hasn't popped up & said its trending SE! By now you would expect the system to be in Greece !  

All joking to one side those 10-20 mile increments have added up to a fairly substantial change to a colder theme giving way to a higher threat of snow.

The updated JMA easily highlights that as the 84 chart thats just arrived compares with the 108 chart from yesterday.

Today first > Huge spacing between the isolines with more energy seperation & a small shallow low sliding into the SE highlighting the possibility of snow in its NW flank-

Interesting stuff.

12z Looks like another failure to amplify the jet similar to the other day before the 18z switched back.... The mean charts about the same-

[johnholmes]

Nice explanations above by DRL especially for newcomers on how to create a forecast from the relevant charts., and  from Steve re the snow factors that can have marked effects on the probability of snow.

[Anthony Burden]

After 8 days of cold unsettled weather that will be very difficult to forecast regarding 

where the white stuff will fall.Gem at  216 hrs brings in high pressure to the north and 

the dream scenario of east winds,following the met office forecast.

[I remember Atlantic 252]

48 minutes ago, sheikhy said:

What more can we ask for of you looking for a surprise snowfall somehere at the end of the week!!ukmo and gfs further east now and the lows are not as deep!!in a col situation with low thicknesses i expect temperatures to get pretty cold especially by night!!

don't want it further East! 12Z is further east, meaning snow risk is, 06 v 12, know which one I want, not the 12, but all FI as far as snow risk goes

 

[Updated_Weather]

1 minute ago, I remember Atlantic 252 said:

don't want it further East! 12Z is further east, meaning snow risk is, 06 v 12, know which one I want, not the 12, but all FI as far as snow risk goes

 

Can it move slightly east again 20-50miles or so, so I have a chance of seeing the good ol’ white stuff!

[Geordiesnow]

GFS12Z run is marginally better in terms of cold but for me, a trough dropping southwards into - 4 upper air is unlikely to be cold enough for much wintry weather away from high ground although I do accept a slack flow and low thicknesses does help a little bit. If the initial WNW'ly was that bit colder then I would be more hopeful(upper air temps of - 6 or lower) for more widespread wintry weather. 

[johnholmes]

I think everyone needs to remember that predicting ppn is very difficult even in summer when it is just rain that will fall. Think back to how many times the amount, timing, and area it fell in, was not correct even at 24 hours, even nearer T+oo. Assuming the model/forecaster gets the timing correct he/she is then confronted with 8 other variables to get right for any one location, some of which Steve outlined.

[johnholmes]

6 minutes ago, johnholmes said:

I think everyone needs to remember that predicting ppn is very difficult even in summer when it is just rain that will fall. Think back to how many times the amount, timing, and area it fell in, was not correct even at 24 hours, even nearer T+oo. Assuming the model/forecaster gets the timing correct he/she is then confronted with 8 other variables to get right for any one location, some of which Steve outlined.

This link may help for each 'back yard!

Remember to factor in your height.

[SMU]

So whats been the trends of the day

* The snow potential for the end of this week seemingly drifting SE towards the South Midlands / Cotswolds sort of zone

* Surface temps more suppressed than originally forecast across the days - with some central zones end of week maxing out maybe 1-3c

* Amplification may not be quite as strong in the atlantic day 8-9 however is compensated by the movement west of the Scandi block..

( I dont think the ENS have got a good grip on the mid term yet around greenland )

[Scott Ingham]

18 hours ago, Beanz said:

Now that’s actually an interesting point, not that I claim to be an expert but I’ve often wondered if cold at that level is always the be all..  

For me they are important in a convective snowy set up like an unstable easterly but if you have systems and troughs dropping into air that's got a good freezing level and dew points (which you can create from your own cold pool) you can get away with it with uppers -3 upwards 

[Iceaxecrampon]

On 29/11/2020 at 15:24, Jon Snow said:

Looking at the GEFS 6z I think winter is coming guys..dec 1st for sure!...joking aside, there is some snow / snaw potential to..and too be honest, that’s all I care about!!!!!   

Where are you Frosty? - big Ramp on the Horizon - need your input.

[Eskimo]

There's a trend to move the centre of the low eastward down through the North Sea, which should put us on the colder side of the low.

Yesterday

 
Today

[SMU]

ECM 72 into 96 really does look pretty wintry - its just pinpointing the snow - UK on the cold side of the low

 

[weirpig]

If it doesn't snow   its got nothing to do with  thickness levels 

[Tim Bland]

Can’t wait to pop open those ECM snow depth charts later ...so everyone can berate how unreliable they are uppers -3 to -5 and Mega low thickness...it’s going to be on a knife edge ...

[MattStoke]

1 hour ago, johnholmes said:

This link may help for each 'back yard!

Remember to factor in your height.

Decent chance at 5 foot 9?

Hate being short!

[sheikhy]

Fantastic ecm between 72 and 120 hours!!deep low all but gone!!bring on some frost and maybe a bit of snow!

[Tim Bland]

A chance for the south later in the weekend perhaps ️

[weirpig]

5 minutes ago, Tim Bland said:

Can’t wait to pop open those ECM snow depth charts later ...so everyone can berate how unreliable they are uppers -3 to -5 and Mega low thickness...it’s going to be on a knife edge ...

-5  really is borderline  I think for here   altitude certainly will help   at the moment I plump for snow above 250m   were ever it falls 

[Daniel*]

Cold air aloft upgraded. 00z > 12z increasing snow risk later this week.

 

[Allseasons-Si]

The ECM is the best out of the three at 144 in terms of amplification in the Atlantic

[Eskimo]

Some run-to-run consistency from the ECM to bring snow initially to much of Scotland and then down through the spine of the country. 

Edited November 30, 2020 by Eskimo