Model output discussion - cold spell approaching?

[Climate Man]

51 minutes ago, sub zero said:

I really don't see a prolonged very cold spell from the chats atm, yes I see a snowy spell with maybe some severe temperatures at times lasting a week maybe 10 days from these charts, which in itself is amazing to see and has me glued to this forum and meteociel..

But the only chance we get of seriously cold uppers, is from channel lows passing under the block and giving us a brief easterly, the rest of the time the general wind direction is a northerly , which will be cold enough for snow but not severe, as too long a sea track...

It seems there is only one outcome (as far as I can see) as the cold pool makes its way towards us then floods into the Atlantic, ruining the amega block by cutting off the waa into Greenland and giving us a west based NAO..

I don't see how we can get long sustained cold unless we can get heights over Iceland or scandy giving us more of an easterly feed...

Are there many times when the trough stays out to the east (with no heights to the north or east) staying put and delivering  cold for the uk for long periods, or do we need to see height rises to the north/east...?

an unusual set up and intriguing to say the least..

Don't get me wrong I'm not trying to put a dampner on things , I just want to put things in perspective..

I'm a coldie through and through .. honest...!

 

The thing about snow cover is that we can generate our own cold. With any wind between NW and SE the 850s become far less important with snow cover in place. Certainly if you want severe surface cold.

[Trom]

All seems very bullish on here today.

The phasing or not of the two lows seemed extremely tight and led to very different medium term outcomes i.e. UKMO vs ECM/GFS.

It really seemed razor tight whether they phased or not.  I'd like to see a little more separation on the 12Z runs to be confident.

Additionally, as usual, there's been a lot of cognitive dissonance, in dumping runs that don't show the preferred outcome.  Of course this is a human nature, resulting from conformation bias.  We all seek information that confirms our desired result and have a bias to ignore information that doesn't.  I'd feel more confident if it was the same model being dumped in each run but it's not, each model seems to have moments as a hero and villain at the moment.

So I'd advise a little caution moving forward until we see some intra run and cross model agreement on a more consistent basis.

Fingers crossed - I'd love some snow as much as anyone.

Edited January 12, 2021 by Trom

[Bogman]

1 hour ago, winterof79 said:

Yes the "Pumpathon" over the Pacific has to be balanced out by the atmosphere hence very shortly there will be a "Dumpathon" over our side. 

The Pumpathon was a damp squid for me last night. Alas, too many interruptions.

[MidnightSnow]

4 hours ago, I remember Atlantic 252 said:

for fun of course, but normal for these days, lows track too far south, South of M4 for snow, unlike 90's where north of M4 for snaw

Too far south for you.  IMBYism 101

[Singularity]

2 hours ago, Nicholas B said:

all important for snow chances and so often the difference between rain and snow for low levels, from the 21st the dew points are looking good too!  

This is a very good point to make - airmass origin is of high importance when you have a possible battleground setup in the works.

The Arctic / polar continental origin later next week means that even after some mixing over the sea, there's a good chance dewpoints will be widely subzero across the UK.

This then means that where precipitation falls, the air temp will tend toward zero or below if it wasn't down there already. 

Consequentially, you can feasibly have an air temp of 4 or 5°C yet ten minutes later be subzero with falling snow. I've seen that a fair few times in Feb-Mar.

It also makes possible a strange situation where the 850 hPa temps are above freezing, yet precipitation falling below that altitude has lowered the air temp sufficiently for snowfall. In fact, that's how some of the heaviest snowfall occurs, as available moisture tends to be at its highest (higher air temp aloft, more capacity to 'hold' water).

 

Of course, all this depends on getting that air in to begin with. Ideally with the least possible mixing. The ECM 00z has rather a lot of it but still just about manages to keep the dewpoints low enough. Given the model's typical enthusiasm for developing a lot of 'shortwave' lows, this could be taken as a good sign of you're seeking widespread snow chances.

[Badgers01]

Not sure who indicative Preston is for many other areas though 

[Speedbird]

Sorry if this has already been posted.

Astonishing

Edited January 12, 2021 by Speedbird

[Radiating Dendrite]

1 minute ago, Speedbird said:

Sorry if this has already been posted.

Astonishing.

EribFkhXAAIRYDZ.jfif 391.38 kB · 26 downloads

Not sure I want to risk downloading that! You are not going to ask me for Bitcoin?

[Battleground Snow]

Icon still gets nail bitingly close to phasing, but look at the difference between the 12z v 00z

[Weathizard]

The marketing team at the ICON hit the jackpot by making it come out before the rest didn’t they, much better than this mornings run

[Speedbird]

2 minutes ago, Radiating Dendrite said:

Not sure I want to risk downloading that! You are not going to ask me for Bitcoin?

sorry, try now

[Severe Siberian icy blast]

2 minutes ago, Battleground Snow said:

Icon still gets nail bitingly close to phasing, but look at the difference between the 12z v 00z

Thats some huge difference there, the greenland highs cut off too so no sinker but really don't think that's an issue this time round lol

[Singularity]

8 minutes ago, Badgers01 said:

Not sure who indicative Preston is for many other areas though 

Preston's about halfway up the UK so reasonable for a broad idea.

Here's London for a view down south. Still a good stretch of subzero mean, plenty of scatter but that's to be expected at this range.

You can browse other locations via: 

Wetterzentrale.de - Diagrams

WWW.WETTERZENTRALE.DE

---

Forecasted 2m Dewpoint from GFS, 06Z

 

[Notty]

and we're off

GFS 06z T+6 hrs

[Weathizard]

Atlantic dead and buried on the ICON, but the large difference inter run and how dangerously close it came to phasing them lows mean caution is once again, word of the day. 

 

[SLEETY]

Can we have the gfs op go down to minus 15, at least, to get this place really buzzing 

[winterof79]

Well boys and girls I have reached the point where I am happy to sit back and let this play out and its not often I have said that. Yes there will be ups and downs for many depending on locations but attacks from the North/East and South will happen. Enjoy the ride they don't come along every year. 

Here's the beginning 

 

[Windysun1]

2 minutes ago, Weathizard said:

Atlantic dead and buried on the ICON, but the large difference inter run and how dangerously close it came to phasing them lows mean caution is once again, word of the day. 

 

Is it more likely we will get a north to north east at times rather than an east this potential cold spell?  Thanks.

[fujita5]

11 minutes ago, Speedbird said:

Sorry if this has already been posted.

Astonishing

Certainly ties in well with the idea of a strong Greenland high. Abnormal warmth going to into NE USA, eastern Canada and Greenland, cold over much of Europe....

[Singularity]

Interesting point raised by this run - we don't necessarily need the cut-off low to hold position for very long, through 18th might be sufficient if the low heading toward the UK moves fast enough.

It also drops an hint of that most infamous type of complication; cold air spilling west of the UK and seeding development of a secondary low.

This is perhaps a higher risk of the cut-off low makes a move sooner rather than later, as it slows then stalls the trough earlier.

So, it seems we should hope for it to stay put at least a day longer, through 19th.

[mountain shadow]

1 minute ago, Singularity said:

Interesting point raised by this run - we don't necessarily need the cut-off low to hold position for very long, through 18th might be sufficient if the low heading toward the UK moves fast enough.

 

Certainly a lot cleaner without those low phasing. Lets see what UKMO does with the phasing.

[weirpig]

1 hour ago, Severe Siberian icy blast said:

The midlands are slowly but surely becoming a threat to see snow, the latest met video has it snowing in Cambridge Thurs, another 50 miles west and the central spine will be having snow fall 

Indeed

[Kasim Awan]

3 minutes ago, mountain shadow said:

Certainly a lot cleaner without those low phasing. Lets see what UKMO does with the phasing.

The lows eventually phase though which expands the low and pushes the colder sector further west. A frustrating scenario under the ICON we would be under a cold unstable low with marginal snow events.

[feb1991blizzard]

22 minutes ago, Speedbird said:

Sorry if this has already been posted.

Astonishing

Yes, makes a change from recent years where those charts have shown practically the whole world red, one for @BLAST FROM THE PAST

[cyclonic happiness]

23 minutes ago, Speedbird said:

Sorry if this has already been posted.

Astonishing

Good stuff, so long as the eastern seaboard of the US and Canada remain warmer, we're in with a good shot.