Model output discussion - The run up to Christmas

[Kasim Awan]

Xmas eve snow potential. Overall quite poor.

6 am to 8am. Relatively stable inversion present below ~700ft. This would allow wintry conditions to 50-100m early on across SE Scotland & Northumberland. Precip rates of 2-3mm/ hour locally producing a good dusting down to 20-80m. As the convective flow pushes southwards early morning the surface inversion erodes due to maritime influences.

See the retreat of the freezing line in the pics attached between 7 and 3pm. 

Between 12pm and 4.30pm showery precipitation will be gathering in the east. The surface flow is NNE but the 650hpa flow is due NE in the trough. This will fall as sleet and wet snow down to 0-50m with the settling snow line likely elevated to 200-250m. Therefore significant accumulations on the southern side of North York Moors ~7cm. A localized 0.5cm for around 10% of an area encompassing the east coast & ~25 miles inland though showers could reach the East Midlands due to the trough visualised nicely via the 850thetaE values. This producing localized heavy precip and therefore the risk of localized low level accumulation (1-2cm) during this time.

The base settling snow line will steadily fall not far from 100m after about 5pm. More % of the precip will be snow. Dew point 0c line roughly 5 miles inland & at 100m asl. This should produce isolated coverings of 0.5-2cm over 110m in Lincolnshire. Subsequently below ~ 100m altidude settling snow will be partially limited to rates >3mm/hour, nontheless dustings up to 1cm are possible from inland Norfolk, boundaries of the wash and central Lincolnshire.

Also note the possibility of flakes inland East Anglia later as the trough dives SE.

One thing to note is that the precip is too mostly light to erode the maritime warm layer. Therefore I fully expect coastal parts to stay the wrong side of marginal throughout.

Edited December 22, 2020 by Kasim Awan

[Scott Ingham]

7 minutes ago, Snow White said:

You must be looking at something different to me. I have been on here since 2004 and I could name 5 spells just since then that this WILL not compare to. Feb/Mar 05, Dec/Jan 10, Dec 10,  Jan 13, Mar 13 and Feb/Mar 18. 
There is potential for snow on higher ground but it’s not cold enough for disruptive low level snow.

I would love to be wrong but just don’t see it IMO.

Im talking avout the length of time of below average temperatures. Dont just look at next week look at what could potentiaply follow. 

No way mild air gets in before the middle of january at least. Backed up by the met who have forecast below average temperatures up until at least the middle of the month. The next round if amplification looks like being colder than next week and snow is looking increasingly to lower levels next week. I may be wrong and ive put my head on the line and if i am ill hold my hands up!

[Met4Cast]

8 minutes ago, Snow White said:

You must be looking at something different to me. I have been on here since 2004 and I could name 5 spells just since then that this WILL not compare to. Feb/Mar 05, Dec/Jan 10, Dec 10,  Jan 13, Mar 13 and Feb/Mar 18. 
There is potential for snow on higher ground but it’s not cold enough for disruptive low level snow.

I would love to be wrong but just don’t see it IMO.

Agreed. This isn't anywhere close to comparable to any of the cold spells you've listed, let alone to winters of past  A nice period of below average temperatures is on the cards & certainly a damn site better than anything we saw last winter, but to call this historic is taking it a bit too far lmao. December 2010 was 'historic".

High-res models will be the one to watch in the coming days, the latest UKV is already picking up potential for a small disturbance in the flow for Xmas eve! 

[northwestsnow]

Indeed Scott, I'm mindful not to overtake the model thread with Exeter talk but I forgot to mention  lower levels not restricted to the north !

[EML Network]

3 years since I last posted on here, goes to show how long it's been since there's been something exciting in the charts during winter. 

Hi All, really enjoyed snowkings informative post. 

 

It also helps explain why when I was out running along the South Downs on Sunday with air temperatures of 11 degree's we had a squall line come through and all of a sudden the rain had some sleetyness mixed in with it and the air temperature simply plummeted to the point where my face felt like it had been stabbed with an ice pick. 

Great to be back on here after so long away

[DanDorsetUK]

2 minutes ago, Scott Ingham said:

No way mild air gets in before the middle of january at least.

I agree with you Scott, obviously we have all got different opinions, but I have a feeling we could well be looking at a historic winter setting in. The potential when you look at everything on the horizon that could unfold has certainly got my attention!

[Battleground Snow]

6 minutes ago, Scott Ingham said:

Im talking avout the length of time of below average temperatures. Dont just look at next week look at what could potentiaply follow. 

No way mild air gets in before the middle of january at least. Backed up by the met who have forecast below average temperatures up until at least the middle of the month. The next round if amplification looks like being colder than next week and snow is looking increasingly to lower levels next week. I may be wrong and ive put my head on the line and if i am ill hold my hands up!

It will be very interesting to see if your call of a griceland high comes to fruition in the first week of jan, the 06z was close.

Will be watching the 12z GFS at 216 hours intently to see if we can get the potential Greenland high to shift south east by a few hundred miles.

Edited December 22, 2020 by Battleground Snow

[Scott Ingham]

10 minutes ago, Met4Cast said:

Agreed. This isn't anywhere close to comparable to any of the cold spells you've listed, let alone to winters of past  A nice period of below average temperatures is on the cards & certainly a damn site better than anything we saw last winter, but to call this historic is taking it a bit too far lmao. December 2010 was 'historic".

High-res models will be the one to watch in the coming days, the latest UKV is already picking up potential for a small disturbance in the flow for Xmas eve! 

Your basing it on only next week. This will last longer than next week with a ssw to come after. As mushyman said there is no end in sight to cold. Why not wait to see what happens?

Edited December 22, 2020 by Blessed Weather
Tweek

[Scott Ingham]

1 minute ago, Rapodo said:

I agree with you Scott, obviously we have all got different opinions, but I have a feeling we could well be looking at a historic winter setting in. The potential when you look at everything on the horizon that could unfold has certainly got my attention!

Agreed. Im taking a back seat and watching it unfold. If im wrong ill admit im wrong

[Frosty.]

Just before the 12z rolls out, a quick mention about the earlier ECM 0z ensemble mean which gradually trends colder again after Christmas as well as becoming very unsettled, something of a weather bomb swinging down from the NW!...the bottom line is, compared to recent Xmas periods, when I was already in despair with how abysmally the winters were unfolding..this time I’m filled to overflowing with hope regarding the chances of snow during the coming weeks!

 

ps...I’m glad I’m not popular and don’t get any personal messages and emails...I prefer the quiet life!

Edited December 22, 2020 by Jon Snow

[Scott Ingham]

2 minutes ago, Battleground Snow said:

It will be very interesting to see if your call of a griceland high comes to fruition in the first week on jan, the 06z was close.

Will be watching the 12z GFS at 216 hours intently to see if we can get the potential Greenland high to shift south east by a few hundred miles.

Im watching very interested

[Tim Bland]

9 minutes ago, Kasim Awan said:

Xmas eve snow potential. Overall quite poor.

6 am to 8am. Relatively stable inversion present below ~700ft. This would allow wintry conditions to 50-100m early on across SE Scotland & Northumberland. Precip rates of 2-3mm/ hour locally producing a dusting down to 150m. As the convective flow pushes southwards early morning the surface inversion erodes due to maritime influences.

See the retreat of the freezing line in the pics attached between 7 and 3pm. 

Between 12pm and 4.30pm showery precipitation will be gathering in the east. The surface flow is NNE but the 650hpa flow is due NE in the trough. This will fall as sleet and wet snow down to 0-50m with the settling snow line likely elevated to 200-250m. Therefore significant accumulations on the southern side of North York Moors ~7cm. A localized 0.5cm for around 10% of an area encompassing the east coast & ~25 miles inland though showers could reach the East Midlands due to the trough visualised nicely via the 850thetaE values.

The base settling snow line will steadily fall not far from 100m after 8pm. This may produce isolated coverings of 0.5-2cm over 100m in Lincolnshire. Below this altidude very locized dustings up to 1cm are possible from inland Norfolk, boundaries of the wash and central Lincolnshire >5miles inland. This really requiring heavy precip.

 

Great post Kasim, thanks for taking the time, hopefully you can do more like this over the next week or so!  

[tight isobar]

Over to the 12z.. which today/tomorrow are imo the all outs regarding how we progress into January.!!   Handbags .. toys.. prams..at the ready

[Valleyboy]

7 minutes ago, Scott Ingham said:

Your basing it on only next week. This will last longer than next week with a ssw to come after. As mushyman said there is no end in sight to cold. Why not wait to see what happens?

Agreed.  How can a comparison be made when the cold spell hasn’t even started yet!

Edited December 22, 2020 by Blessed Weather
Tweek to quote box

[sheikhy]

Massive move west at just 96 hours on icon and much more amplified eastern states/western greenland!crazy move so early on!

[V for Very Cold]

3 minutes ago, Scott Ingham said:

Agreed. Im taking a back seat and watching it unfold. If im wrong ill admit im wrong

If you’re wrong.... it’s Rotherham high st pt 2.... cartwheels! 

[weirpig]

2 minutes ago, sheikhy said:

Massive move west at just 96 hours on icon and much more amplified eastern states/western greenland!crazy move so early on!

Yep  noticed that    so much uncertainty still  

[Weathizard]

Early days but a considerably sharper ridge on the 12z icon at day 5

[goosey007]

 

14 minutes ago, Scott Ingham said:

Your basing it on only next week. This will last longer than next week with a ssw to come after. As mushyman said there is no end in sight to cold. Why not wait to see what happens?

Agree Scott ....totally understand we all have our opinions on the model output ...but to say this upcoming cold spell wont be comparible to those dates is some what premature perhaps...excluding Dec 10. If you are convinced its not going to be back it up with some data/charts and explain why it wont be at least. Its confusing for newbies otherwise. Thanks

Edited December 22, 2020 by Blessed Weather
Tweek to quote box

[Skullzrulerz]

5 minutes ago, sheikhy said:

Massive move west at just 96 hours on icon and much more amplified eastern states/western greenland!crazy move so early on!

Is this the low pressure? Not good news if so as less cold air would be in place?

[mushymanrob]

1 hour ago, Scott Ingham said:

Agreed. This will be historic imo for the length of below average temperatures. Im not saying a 63 (although potential is there with a ssw in our favour but thats def8nitely no guarentee) but a top 10 since the 40s is achievable 

Im not sure why some are using the "laughing" emoji for this... On my own page ive been reporting on the building of Northern blocking for a month now. A more irregular, unusual synoptic pattern has been evolving. Every proper cold spell has come about by Northern blocking so when its predicted then chances of a proper cold spell increases.

Ive worked outside through the winters of 78/9 and 84/5 and this year has the same vibe about it, and thats based on current expectations that suggest Northern blocking will be a feature this winter.

We are entering soon a period of cold and unsettled weather which alone is likely to produce snow. Then when you take into account the high chances of an SSW early next month, then a proper cold snowy spell later next month/into February, just like 78/9 84/5 is a realistic proposition. There is no sign, no real hint of raging zonality, nor uncle barty, lol, the outlook is colder then average and probably very cold at times.

These charts are possibly the most interesting ive seen in my 16 odd years here, im not a coldie, im not ramping cold, im a weather enthusiast.

Its also really great to read so many informative posts too, like @Scott Ingham who makes this site so great.

[sheikhy]

Lets hope the 12z follows in terms of amplification and not the move west!!dont mind low being over the uk as long as it slack with low thicknesses otherwise i want it further east!!

[phil nw.]

A lot of comments about depth of cold or not in the discussions lately which is understandable when we have a borderline pattern showing.

Normally if we have a continental east or north easterly with lows to the south then with that drawing bitter russian air towards us with low dew points then snow is a much safer bet.

In this situation with the Atlantic involved then it will be down to the wire as other factors come more into play such as dew points,wind flow,altitude etc and of course any mixing of less cold oceanic air as the trough heads south.

I guess i am saying it's too early to punt on snow chances yet .Small changes to the Atlantic ridging are still likely at quite short term which can change the orientation of the diving trough after Christmas.This will affect the angle of the cold air coming south and the amount of modification.

In this instance I am looking around day 6-8 as the low pressure drops down after Christmas.

A glance at the ECM 00z op shows a sharper trough just far enough east to encourage a somewhat colder feed more directly south compared to the 06Z gfs which shows a more rounded low over the UK with more modification and the coldest attack into the N.Atlantic to our west.

The key here seems to be sharper ridging on the ecm across S.Greenland as the energy off Newfoundland heads further south.

These are the sort of differences to look out for as this developing cold pattern evolves.There's no way any later modeling will have a handle on depth of cold or snow chances beyond the next 3/4 days.

A look again at the combined London 2m temp. graph

 

The cold forecast goes on.Plenty to keep us interested as wait for the 12s.

[Scott Ingham]

2 minutes ago, mushymanrob said:

Im not sure why some are using the "laughing" emoji for this... On my own page ive been reporting on the building of Northern blocking for a month now. A more irregular, unusual synoptic pattern has been evolving. Every proper cold spell has come about by Northern blocking so when its predicted then chances of a proper cold spell increases.

Ive worked outside through the winters of 78/9 and 84/5 and this year has the same vibe about it, and thats based on current expectations that suggest Northern blocking will be a feature this winter.

We are entering soon a period of cold and unsettled weather which alone is likely to produce snow. Then when you take into account the high chances of an SSW early next month, then a proper cold snowy spell later next month/into February, just like 78/9 84/5 is a realistic proposition. There is no sign, no real hint of raging zonality, nor uncle barty, lol, the outlook is colder then average and probably very cold at times.

These charts are possibly the most interesting ive seen in my 16 odd years here, im not a coldie, im not ramping cold, im a weather enthusiast.

Its also really great to read so many informative posts too, like @Scott Ingham who makes this site so great.

I have no idea mate. Its childish and patronizing. Im on exactly the same page as you. I wouldn't be so keen if there wasnt so much evidence to back it up

[Scott Ingham]

15 minutes ago, Valleyboy said:

Agreed.  How can a comparison be made when the cold spell hasn’t even started yet!

Exactly!

Edited December 22, 2020 by Blessed Weather
Minor change made.