Model output discussion - deep cold inbound?

[ianmm94]

JFF but peturb 2 looks insane at 120

[Nick L]

5 minutes ago, Scott Ingham said:

Yeah completely agree and its this micro scale abilities that make these my models of choice for streamers and showers. 

Excited for friday night and saturday mornings runs.

Yes the lack of instability keeps the flow cleaner, stops the formation of very small troughs in the flow cutting off the longevity of the easterly winds whilst we have just enough instability to create cloud tops capabale of proucing 75%/25% moderate snowfall but for a long period of time.

Dps being very low along with temperatured gives us a better moisture to snow ratio and even light showers will instantly stick

North midlands south yorkshire - 20-30cms

North east and North Yorkshire 20-30cms

Midlands and central southern england -20-30cms

South east and london - 30-40cms (due to a stalling front saturday night sunday morning)

All of this close of play tuesday with battleground snow to follow

Come on. The output is looking good but not THAT good. 

We can expect 10-15cm quite widely for East Anglia and parts of the SE. Let's not get carried away here.

[weirpig]

4 minutes ago, Scott Ingham said:

Yeah completely agree and its this micro scale abilities that make these my models of choice for streamers and showers. 

Excited for friday night and saturday mornings runs.

Yes the lack of instability keeps the flow cleaner, stops the formation of very small troughs in the flow cutting off the longevity of the easterly winds whilst we have just enough instability to create cloud tops capabale of proucing 75%/25% moderate snowfall but for a long period of time.

Dps being very low along with temperatured gives us a better moisture to snow ratio and even light showers will instantly stick

North midlands south yorkshire - 20-30cms

North east and North Yorkshire 20-30cms

Midlands and central southern england -20-30cms

South east and london - 30-40cms (due to a stalling front saturday night sunday morning)

All of this close of play tuesday with battleground snow to follow

I think we are in danger here of going a tad OTT   im sure there will be places that receive some snow  and im sure those eastern areas  may well get around those values.   but all of those regions  bordering on a foot of snow?.    highly unlikley 

[Cloud 10]

Polar Vortex in a state of extreme distress on the 18z as Randolph Scott rides into town.

 

[GeordieX9v]

Pub run low is on it's holiday to Portugal

Bowling tournament in the UK on the 12z

[Kasim Awan]

1 minute ago, Nick L said:

Come on. The output is looking good but not THAT good. 

We can expect 10-15cm quite widely for East Anglia and parts of the SE. Let's not get carried away here.

There's a difference between what we could expect vs what is likely to happen

If we plotted a histogram of probabilities of outcome vs severity of that outcome I would say your prediction sits at 30% on the probability axis which is conservative territory

I'm going with 50% atm which is more > 20cm quite wildey

 

[Scott Ingham]

2 minutes ago, Kasim Awan said:

I'd agree on all of that, in addition I'd say the 20-30cms will be a 40% coverage in the central / northern zone due to streamer localization. Get an alternating wind direction and the streamer coverage will be widespread as the spatial extent reflects the scope of the wind direction variation. This is looking possible too though at slightly lower scales due to the more stable flow - so I'm giving a rough figure of 40% coverage of streamer enhanced very high totals. For the SE - I'd say we're in historic territory right now.

The reason why i have widely given east midlands to north east england these amounts replay back the arpege. A streamer sunday night sets up north midlands south yorkshire. It slowly heads north through to tuesday giving each region roughly 6 hours of streamer snowfall with snowfall more spatial whilst out of this streamer.

What i can say is this is only one run and will change and your 40% coverage is most probably nearer the mark as i see convergence becoming stuck over one area a lot longer than forecast.

Of course there is always one 20 mile area unoucky who only get 4 or 5cms such is the nature of showers

[Eastbourneguy]

Meanwhile, over the pond...

 

Back to the UK... 3/4 days of a potent easterly followed by war with the Atlantic. I don't think anyone can ask for too much more!

ps: For cold and snow lovers anyway!

Edited February 4, 2021 by Eastbourneguy

[Captain Shortwave]

Pretty impressive to see the mass of very cold air over Scandinavia bleed out towards the U.K. (modifying slight over the Baltic and North Sea.

Pretty representative from the GFS. 850s falling to around -11c (-12 or slightly lower across Scotland and parts of East Anglia).

 

Couple this with fairly low heights then the should be plenty of showers pushing inland in many parts of the country. I wonder whether we can eek out slightly lower 850s and heights by T0. 
The GFS tends to dry out by the end of Wednesday with a widespread severe frost before fronts try and push in from the west. A very good run with snow possible near enough anywhere over the next seven days.

Like others have said there are some rather impressive maxima as well, ice days likely across northern areas with a decent covering of snow and across the south where winds are coming from the continent.

Edited February 4, 2021 by Captain Shortwave

[East_England_Stormchaser91]

6 minutes ago, Frosty the Snowman said:

Looks like a serious battleground snow event emerging for the west of the country around T150 - and barrels through to the east so quite possibly a truly nationwide snow event (a rare thing indeed) , a good way to deal with the Atlantic low I suppose. 

 

 

 

Big question is whether it remains mild afterwards or cold returns. 

This run for the East is as far from mild as it gets. The uppers are warmer than the surface in East Anglia on the 18z, which is holding onto cold from what looks to be a bone chilling continent. I’ve got a feeling we may start seeing these Atlantic lows slide, more especially if we see the cold creep further down into France. 

[Nick L]

Just now, Kasim Awan said:

There's a difference between what we could expect vs what is likely to happen

If we plotted a histogram of probabilities of outcome vs severity of that outcome I would say your prediction sits at 30% on the probability axis which is conservative territory

I'm going with 50% atm which is more > 20cm quite wildey

 

There certainly is. But there is no evidence in either case to suggest the snowfall depths that were suggested there. There is no way that we're going to see in excess of a foot of snow through London and the SE on Sunday. If people want to post the evidence from the models that suggests otherwise then be my guest. EC has totals no higher than 10cm, GFS closer to 15cm, UKV could see closer to 20cm in places. Absolutely no evidence that I'm seeing to suggest in excess of a foot.

I'll be writing the forecast for TfL later, so if anyone wants to provide evidence for it I will gladly change my mind! 

[ancientsolar]

look at the difference over Germany  , there must be a 10 degree difference between the 12z and 18z .. and that cold has an impact right through to us in the UK ~ 
a huge difference.. ~ we will have to keep a very close eye on what happens in the atlantic.. if the low breaks up anymore, gets weaker.. and also if the cold air coming in from Scandinavia reinforces itself on other runs. (Doesn't look like the East will have a thaw anytime soon based on this chart)

 

 

Edited February 4, 2021 by ancientsolar

[weirpig]

The only concern i have  and to be fair its not really that a big deal   but if the uppers are so low  we get that  alpine type powdry snow   which in my opinion is bloody awful.  You can have a foot of the stuff and the ground is clear  but up the corner of some terrace house it upto the upstairs bathroom. 

[Scott Ingham]

6 minutes ago, Nick L said:

Come on. The output is looking good but not THAT good. 

We can expect 10-15cm quite widely for East Anglia and parts of the SE. Let's not get carried away here.

On current output not factoring in streamers and troughs i agree but from experience in this set up some locations i feel will hit these amounts. 

Not everywhere but a decent size area caught in this i would honestly not be surprised.

We will see come tuesday night i guess!

[Kasim Awan]

1 minute ago, Scott Ingham said:

The reason why i have widely given east midlands to north east england these amounts replay back the arpege. A streamer sunday night sets up north midlands south yorkshire. It slowly heads north through to tuesday giving each region roughly 6 hours of streamer snowfall with snowfall more spatial whilst out of this streamer.

What i can say is this is only one run and will change and your 40% coverage is most probably nearer the mark as i see convergence becoming stuck over one area a lot longer than forecast.

Of course there is always one 20 mile area unoucky who only get 4 or 5cms such is the nature of showers

I share this POV tbh, as we've seen 6-8" from 12 hours of a flow with say 1.5x more instability in 2009

The upcoming flow > lasts say 36 hours at 1x the instability

12 hours x 1.5 intensity = 18 units. 18 / 7.5 inches = 2.4 units to an inch

Upcoming flow > 36 hours x 1 intensity = 36 units. 36 units / 2.4 = 15 inches

 

[bluearmy]

5 minutes ago, Nick L said:

Come on. The output is looking good but not THAT good. 

We can expect 10-15cm quite widely for East Anglia and parts of the SE. Let's not get carried away here.

 

5 minutes ago, weirpig said:

I think we are in danger here of going a tad OTT   im sure there will be places that receive some snow  and im sure those eastern areas  may well get around those values.   but all of those regions  bordering on a foot of snow?.    highly unlikley 

Yes - rather over excited 

widely 5/10 cms up the eastern side of England ....locally 15/20 cms, especially in coastal counties 

But those 5/10 cms could easily end up 2/5 cms .....that’s just how snow is .....

[Ice Day]

I would be more than happy to take that run as gospel, enjoy a bitterly cold week with plenty of snow opportunities for most areas, before heading contentedly towards spring.  However, I genuinely suspect any mild spell (if it even happens) may just be a brief interlude before another cold spell comes along. 

We shall see, but maybe, February 2021 will be talked about alongside Dec 78, Jan 87, Feb 91 and Dec 10 in years to come.  

[Nick L]

1 minute ago, Kasim Awan said:

I share this POV tbh, as we've seen 6-8" from 12 hours of a flow with say 1.5x more instability in 2009

The upcoming flow > lasts say 36 hours at 1x the instability

12 hours x 1.5 intensity = 18 units. 18 / 7.5 inches = 2.4 units to an inch

Upcoming flow > 36 hours x 1 intensity = 36 units. 36 units / 2.4 = 15 inches

 

Can I ask what you're using as a measure of instability?

[Scott Ingham]

12 minutes ago, CentralSouthernSnow said:

Hmmm underwhelming really for south west. 

The south west will hopefully benefit after tuesday during a battleground period. Its very hard for the south west to do as well as the east in a south easterly

[Kasim Awan]

1 minute ago, Nick L said:

There certainly is. But there is no evidence in either case to suggest the snowfall depths that were suggested there. There is no way that we're going to see in excess of a foot of snow through London and the SE on Sunday. If people want to post the evidence from the models that suggests otherwise then be my guest. EC has totals no higher than 10cm, GFS closer to 15cm, UKV could see closer to 20cm in places. Absolutely no evidence that I'm seeing to suggest in excess of a foot.

I'll be writing the forecast for TfL later, so if anyone wants to provide evidence for it I will gladly change my mind! 

There was not much evidence in 2010 for excess of a foot. This Pov is formed not by model values, but by awareness of model bias and potential with the set up

Of course, I'm not guaranteeing 12"+, just stating the possibility here

[stainesbloke]

13 minutes ago, Scott Ingham said:

Yeah completely agree and its this micro scale abilities that make these my models of choice for streamers and showers. 

Excited for friday night and saturday mornings runs.

Yes the lack of instability keeps the flow cleaner, stops the formation of very small troughs in the flow cutting off the longevity of the easterly winds whilst we have just enough instability to create cloud tops capabale of proucing 75%/25% moderate snowfall but for a long period of time.

Dps being very low along with temperatured gives us a better moisture to snow ratio and even light showers will instantly stick

North midlands south yorkshire - 20-30cms

North east and North Yorkshire 20-30cms

Midlands and central southern england -20-30cms

South east and london - 30-40cms (due to a stalling front saturday night sunday morning)

All of this close of play tuesday with battleground snow to follow

Maybe take the 0 off those figures, probably more likely then Made me chuckle, anyway and who really knows?

[weirpig]

Just now, bluearmy said:

 

Yes - rather over excited 

widely 5/10 cms up the eastern side of England ....locally 15/20 cms, especially in coastal counties 

But those 5/10 cms could easily end up 2/5 cms .....that’s just how snow is .....

Im not saying  some areas may do really well   and maybe some areas that you would not expect  such is the nature of showers  streamers etc.      anyway  at least its something exciting to look out for 

[Kasim Awan]

1 minute ago, Nick L said:

Can I ask what you're using as a measure of instability?

500mb heights & parcel trajectory. Maybe there is a better method.

[Djdazzle]

3 minutes ago, Nick L said:

There certainly is. But there is no evidence in either case to suggest the snowfall depths that were suggested there. There is no way that we're going to see in excess of a foot of snow through London and the SE on Sunday. If people want to post the evidence from the models that suggests otherwise then be my guest. EC has totals no higher than 10cm, GFS closer to 15cm, UKV could see closer to 20cm in places. Absolutely no evidence that I'm seeing to suggest in excess of a foot.

I'll be writing the forecast for TfL later, so if anyone wants to provide evidence for it I will gladly change my mind! 

Prior to the February 2009 snow event, they were predicting 10-15 cm. South of London was quite widely in excess of 20-25cm.

[sheikhy]

Any news on the gefs??!