Model Output Discussion. 3/12/2022. How cold will it get?

[Mark wheeler]

Uppers 144hrs UKMO , all snow Id imagine.

[Guest]

GFS 156 hrs threatens snow from the east

[Cheshire Freeze]

The windchill on that UKMO D6 chart…freezing cold.

[radiohead]

Just now, Mark wheeler said:

Uppers 144hrs UKMO , all snow Id imagine.

Yes, apart from the extreme SW there.

[Skullzrulerz]

2 minutes ago, Mark wheeler said:

Uppers 144hrs UKMO , all snow Id imagine.

Besides Cornwall!

We just manage to get the 0c into our lands! The shield still holds!

Edited December 7, 2022 by Skullzrulerz

[Kasim Awan]

29 minutes ago, MattStoke said:

 

Proving a right pain to predict. The Arpege and Arome give a widespread covering. The ICON and UKV give very little. The GFS gives nothing.

Here's my take on the upcoming snow risks:

In general, in an unstable flow, more features develop than appear in the modelling. This means that even if one model indicates it, there's somewhat of a decent chance it will verify in some shape or form. So I'd say the chance of an arpege/arome outcome sits around 65-70%, even though this group makes up roughly 40% of the high res suite. The other 30% just being some light flakes pass through northern england (very sporadic - barely detectable on radar).

If it does form -

It's speed will not be constant. This means a dusting to 1.5cm over the far north of england, slowing down as it approaches derbyshire, N Mids / Lincs area, possibly producing up to 7cm for a few lucky spots into the early hours of Friday as the onshore breeze picks up some North Sea convection. A dusting to 2cm more widely in this area. A cold surface and freezing level of ~500m means any marginality will be short lived inland but will come into play on the coast wherever the cold surface layer is not present.

The front reaches dissipation stage as it heads south into the Midlands & east England - back to a dusting to 1.5cm.

On Friday day time a small low with a westerly steering flow is likely to form over the Irish Sea - this could produce slow moving snow streamers into parts of NW England (S Cumbria, Lancs, Merseyside etc). The weakness of the steering motion means any precipitaiton may be limited to areas near the coast, with sleet on the immediate coast and snow >2 miles inland, in the 2-10 mile coastal distance some respectable falls of 2-7cm are possible locally.

The next focus looks to be Saturday night into Sunday as a little low breaks out over the channel and could provide some slow, moderate intensity snowfall to isolated areas into SE England early Sunday. Also watch out for some orographic enhancement over the moors of SW England on Saturday as the low develops within a mid level westerly steering flow.

Any marginality during all these events will occur where the surface cold layer that is being established is broken. This will allow the general 400-500m asl freezing level to influence snowflake progression. This means that inland & during night hours should be fine, it's during any daytime heating that altitudes below 100m may be affected by erosion of surface cold. This also applies to coastal areas that encounter an onshore breeze during precipitation.

Edited December 7, 2022 by Kasim Awan

[Snowy L]

UKMO the perfect widespread blizzard chart. No further North than that though please!

[bluearmy]

Just now, Weathizard said:

The difference coming out the eastern seaboard Farcical from the GFS

That’s the 18z against the 12z …..

[Snowy L]

Just now, bluearmy said:

That’s the 18z against the 12z …..

Still though, a polar vortex lobe forming one day and high pressure the next. Unforgivably bad.

[weatherguy]

More evidence of a battleground:UK scenario today.  Bring it on!

[radiohead]

Major differences between the GFS and UKMO at even 96 hours, which puts everything beyond that into question even more than usual....

Edited December 7, 2022 by radiohead

[danm]

2 minutes ago, Snowy L said:

UKMO the perfect widespread blizzard chart. No further North than that though please!

Agree, it’s just right but leaves little margin for error for those in the south. Squeaky bum time. 

[Jan 87]

Lovely GEM longer term. Could be historic if this came off, and at Xmas time too!

[MattStoke]

3 minutes ago, Kasim Awan said:

Here's my take on the upcoming snow risks:

In general, in an unstable flow, more features develop than appear in the modelling. This means that even if one model indicates it, there's somewhat of a decent chance it will verify in some shape or form. So I'd say the chance of an arpege/arome outcome sits around 65-70%, even though this group makes up roughly 40% of the high res suite. The other 30% just being some light flakes pass through northern england (very sporadic - barely detectable on radar).

If it does form -

It's speed will not be constant. This means a dusting to 1.5cm over the far north of england, slowing down as it approaches derbyshire, N Mids / Lincs area, possibly producing up to 7cm for a few lucky spots into the early hours of Friday as the onshore breeze picks up some North Sea convection. A dusting to 2cm more widely in this area.

The front reaches dissipation stage as it heads south into the Midlands & east England - back to a dusting to 1.5cm.

On Friday day time a small low with a westerly steering flow is likely to form over the Irish Sea - this could produce slow moving snow streamers into parts of NW England (S Cumbria, Lancs, Merseyside etc). The weakness of the steering motion means any precipitaiton may be limited to areas near the coast, with sleet on the immediate coast and snow >2 miles inland, in the 2-10 mile coastal distance some respectable falls of 2-7cm are possible locally.

The next focus looks to be Saturday night into Sunday as a little low breaks out over the channel and could provide some slow, moderate intensity snowfall to isolated areas into SE England early Sunday. Also watch out for some orographic enhancement over the moors of SW England on Saturday as the low develops within a mid level westerly steering flow.

 

Also, such small features often produce more widespread albeit very light snow than modelled outside of the main area picked up the models.

Edited December 7, 2022 by MattStoke

[Johnp]

Just now, Jan 87 said:

Lovely GEM longer term. Could be historic if this came off, and at Xmas time too!

That’s yesterdays. Check the time stamp top right. 

[Cheshire Freeze]

Just now, Jan 87 said:

Lovely GEM longer term. Could be historic if this came off, and at Xmas time too!

That’s yesterday’s run

[Tim Bland]

GFS is cold and mainly dry out to middle of next week. Let’s see what that low west of Ireland does…don’t have a good feeling though

[Mark wheeler]

Blimey Gem is difficult to navigate on meteociel this afternoon, This so far .

[chionomaniac]

2 hours ago, joggs said:

What could kick start that and do you expect it to?.

Tia 

There’s the difficulty - forecasting the MJO wave propagation and intensity

[radiohead]

1 minute ago, Jan 87 said:

Lovely GEM longer term. Could be historic if this came off, and at Xmas time too!

That's yesterday's 12Z. Today's 12Z is out to 108 so far.

[bluearmy]

Just now, Snowy L said:

Still though, a polar vortex lobe forming one day and high pressure the next. Unforgivably bad.

I wouldn’t want to look at continuity 24 hours apart from the other models over the past week at day 6/7 …

none have covered themselves in glory …..

[Kasim Awan]

12 minutes ago, Scott Ingham said:

Been watching this come and go but with direction and intensity mate. Whata your current take to lower levels? Im unsure under 100meters atm.

I always forget about marginality being at 470m ASL lol. Yeah probably will be some mixing possible below 100m east of the M1, the surface layer will remain cold so with DPs below freezing and a FL of ~500m, there'll only be a 300ft layer above freezing. Should be fine.

[Ice Day]

GFS at 180 - have you ever seen a messier chart?

Deep into FI now so anything shown should be treated with a shed load of caution.

[Scott Ingham]

Just now, chionomaniac said:

There’s the difficulty - forecasting the MJO wave propagation and intensity

THIS.... eyes firmly peeled on this atm for me.

Hows the strat looking today Ed?

[Jan 87]

2 minutes ago, CreweCold said:

That’s yesterday’s run

Thanks. Shame

Meteociel still not running properly and confusing us!