Cold Spell Discussion

[Stu_London]

much is made of the days being at there shortest at this time of year and therefore that being best for cold spells, however I would say that the relative humidity being generally higher at this time of year (and therefore dewpoints are higher) more than offsets the benefit of minimal solar heating.

Case in point - last night - frost and sub zero temps followed two hours later by rain. I doubt that would happen in mid to late February as dewpoints would likely be at least 1 or 2 degrees lower in that set up. 

I think the actual sweet spot is probably last week of January and first week of February - if you can get the right set up then - BINGO. 

[I remember Atlantic 252]

2 minutes ago, Stu_London said:

much is made of the days being at there shortest at this time of year and therefore that being best for cold spells, however I would say that the relative humidity being generally higher at this time of year (and therefore dewpoints are higher) more than offsets the benefit of minimal solar heating.

Case in point - last night - frost and sub zero temps followed two hours later by rain. I doubt that would happen in mid to late February as dewpoints would likely be at least 1 or 2 degrees lower in that set up. 

I think the actual sweet spot is probably last week of January and first week of February - if you can get the right set up then - BINGO. 

best for beast I'd say mid Feb to mid Mar, coldest seas too

[Stu_London]

2 minutes ago, I remember Atlantic 252 said:

best for beast I'd say mid Feb to mid Mar, coldest seas too

For mid-March you need really exceptional uppers to offset the solar influence. 

1991 was very well timed - 2nd week of Feb - 2 weeks in the freezer. 

Edited December 28, 2020 by Stu_London

[pureasthedriven]

First reference to potentially ‘very cold’ from Exeter this afternoon. Still not having ‘exceptionally cold’ mind But the reference to very cold suggests the possibility of daytime 2m temps around freezing I would suspect. 

[damianslaw]

4 hours ago, Stu_London said:

much is made of the days being at there shortest at this time of year and therefore that being best for cold spells, however I would say that the relative humidity being generally higher at this time of year (and therefore dewpoints are higher) more than offsets the benefit of minimal solar heating.

Case in point - last night - frost and sub zero temps followed two hours later by rain. I doubt that would happen in mid to late February as dewpoints would likely be at least 1 or 2 degrees lower in that set up. 

I think the actual sweet spot is probably last week of January and first week of February - if you can get the right set up then - BINGO. 

Optimum time for cold second half of January, that for me is true mid bleak winter, still dark enough to feel that lighter days are a long way away still, by mid Feb you begin to notice lengthening daylight and sun strength and whilst temps can and often are at there coldest then, the winter feel begins to ebb. Northerlies usually pack their coldest punch end of Feb and into March when the arctic is at its coldest, however, the sun can quickly get to work on any snow cover by midday.

Easterlies are usually at there coldest in February, but not always, as proven in Jan 1987.

High pressure overhead though usually delivers coldest conditions in late December through to mid January when solar heating is more minimal.

Its been a long time since we had a notably cold snowy period  second half of January, can't think the last time..

[Stu_London]

1 minute ago, damianslaw said:

 

Its been a long time since we had a notably cold snowy period  second half of January, can't think the last time..

The last third of Jan 1992 was sub zero - from memory I think it was largely due to freezing fog as I recall my entire clapped out ford fiesta freezing whilst driving south on the A1

The period 5th Jan 1985 to 20th Jan 1985 was pretty noteworthy at -1.5C, although the cold relented in the last week of the month.

 

[damianslaw]

9 minutes ago, Stu_London said:

The last third of Jan 1992 was sub zero - from memory I think it was largely due to freezing fog as I recall my entire clapped out ford fiesta freezing whilst driving south on the A1

The period 5th Jan 1985 to 20th Jan 1985 was pretty noteworthy at -1.5C, although the cold relented in the last week of the month.

 

Yes, latter part of Jan 1992 was cold, it was dry and very frosty but little or no snow as I remember. Latter half Jan 1991 also quite similiar. Jan 20th onwards in 1996 was very cold and snowy.

[Mapantz]

Here are the last 4 runs of the UKV, it's consistent..

[ancientsolar]

• some seriously heavy sleet coming into the North East England , looks like it's already turning to Snow , East of Manchester according to NWRadar 

[Weather-history]

Snow cover really lightens up a night

 

Edited December 29, 2020 by Weather-history

[Chris Smith]

Nasty sleety mess in Durham this morning. To be expected I guess, from returning returning returning Polar Maritime.

[Met4Cast]

UKV is so far south even the S Coast remains dry tomorrow.. eeek.

[kold weather]

15 minutes ago, Met4Cast said:

UKV is so far south even the S Coast remains dry tomorrow.. eeek.

Look how fast it is as well! Thats WAY too fast.

Its basically 3-6hrs ahead of any other model! Only one that is close is the equally far south Euro4.

So we have an interesting battle here where nearly all the high resolution models are to the south, where as the globals and the ensembles are somewhat further north.

I'd probably put more weight onto the high resolution, it fits with the normal southward trend and it should be entering their zone so to speak, however there is alot of uncertainty yet and I'd not feel confident until it comes onto the radar.

I suspect UKV/Euro4 is too far south because of how fast it shoots it eastwards.

Edited December 29, 2020 by kold weather

[MP-R]

17 hours ago, damianslaw said:

Its been a long time since we had a notably cold snowy period  second half of January, can't think the last time..

January 2013. Although not impressively cold, notably snowy between the 16th and 26th.

January 2006's coldest weather was also in the second half, in fact the final third, after a milder middle third. Very frosty, although largely snowless.

[swfc]

I'd be of the opinion the cold spell is only just getting started and evolve. The cold air will become entrenched and even slack. Dew points will be low even with average 850s.be looking for upgrades this afternoon esp 12z ec

[Catacol]

Feels like we are in a lull at the moment. Trough in place....waiting for the next stage. So time to take stock a bit having trawled the data today.

1. Latest EC data doesn’t quite split the vortex though the SSW is on course. While Chio may well be right in not seeing this as vital (I am a mere R2D2 on his Xwing...) it was an important part of my thinking. To see modelling moving away from a split and moving more firmly to a displacement in the first third of January is a disappointment.

2. Timing. I’m trying to get a hold on NWP timing and not quite reading it today. Momentum products had me thinking of a relaxation in early Jan....but this isn’t being modelled. Instead we seem to have a relaxed pattern in the modelling kicking in around Jan 5 and running to the end of the EC run...and given the significant EAMT and pacific jet running through the New Year I’m a bit perplexed. Will need to keep checking the data - and try to get a handle on it.

3. The less amplified phase when it comes (5-7 Jan according to current runs) has a knock on impact on trop forcing on the strat, so we see a resultant fall in both wave 1 and wave 2 forcing. This was always going to happen - totally not a surprise...but again timing has come out of sync here with my thinking and so instead of a rise again in wave forcing come Jan 7 we have a lesser pattern.

 

Lots of use of the word “timing” here - because in the end it is all about timing. If, as seems likely we end up with a displaced vortex over Russia come Jan 7 then fresh thinking will be required. Assuming the next amplified phase has to happen soon after that (impacts of NY Pacific jet) then blocking will rebuild and downwelling impacts of the SSW and likely reversal will begin to back Asian cold westwards....but the longer term picture then gets cloudy. In some respects forecasting beyond a split and shattered vortex would have been easier....but a displacement I think adds more uncertainty.

Fascinating watching it all unfold. Time to sit back and watch the picture develop for a few days. One way or another though the January outlook remains a cold one.

Edited December 29, 2020 by Catacol

[Sweatyman]

Good looking met update

[Weather-history]

Just a slight thaw today now gone icy again, you can see snow slip off the bungalow's roof

 

Edited December 29, 2020 by Weather-history

[noseyparker]

Hello All Newby here.

 

I've always been interested in the weather since I was a school boy, so I know the basics.

We've been in this coldish spell for a while now and I notice the Beeb shows the winds turning in to the East over the weekend.

The only thing I don't get is, even though the wind is in the north,  Lerwick and the Stornoway Isles are going to be 6 c. How comes that? If the wind is coming down straight from the North I'd expect it to be  colder than that? Plus the beeb shows Easteries but with temps up to 7c. It's January almost. It doesn't make sense to me?

 

Can anyone explain please?

 

 

[chionomaniac]

15 minutes ago, noseyparker said:

Hello All Newby here.

 

I've always been interested in the weather since I was a school boy, so I know the basics.

We've been in this coldish spell for a while now and I notice the Beeb shows the winds turning in to the East over the weekend.

The only thing I don't get is, even though the wind is in the north,  Lerwick and the Stornoway Isles are going to be 6 c. How comes that? If the wind is coming down straight from the North I'd expect it to be  colder than that? Plus the beeb shows Easteries but with temps up to 7c. It's January almost. It doesn't make sense to me?

 

Can anyone explain please?

 

 

Most likely wrong but islands surrounded by warmer water than the air above will often be warmer because of this warm sea air modification

[summer blizzard]

12 hours ago, noseyparker said:

Hello All Newby here.

 

I've always been interested in the weather since I was a school boy, so I know the basics.

We've been in this coldish spell for a while now and I notice the Beeb shows the winds turning in to the East over the weekend.

The only thing I don't get is, even though the wind is in the north,  Lerwick and the Stornoway Isles are going to be 6 c. How comes that? If the wind is coming down straight from the North I'd expect it to be  colder than that? Plus the beeb shows Easteries but with temps up to 7c. It's January almost. It doesn't make sense to me?

 

Can anyone explain please?

 

 

The islands are actually falling under a toppling high which brings milder uppers. Likewise (city temps but still) the uppers are somewhere around -5C for the easterly so not massively cold.

[chionomaniac]

09z ukv precip 12z prediction vs actual

 

looks a tad further north

[Weather-history]

Foggy all day and virtually no thaw

 

[davehsug]

I've not been an avid winter model thread reader for several years now, but I've been reading the last few days, due to the interesting aynoptics. I've noticed several new "respected" posters, but the garden path remains unchanged it seems.

[Weather-history]

This morning's snowfall around Irlam