Model Output Discussion - Colder but how cold and for how long?

[Joe Bloggs]

30 minutes ago, Kasim Awan said:

Yes but with a slack flow the coverage of these features will be relatively poor, slack flow also means they will struggle to develop into larger features. December 2022 and November 2023 spring to mind. We need the low from Iceland & the one to our South to make better inroads for anything really significant otherwise a slack flow will just generate a lot of very dry cold weather with snow limited to a few coastal areas.

Hey Kasim  

In my experience slack flows are actually better at generating convective showers and streamer features? It’s an ingredient I look for when trying to judge if we’ll get westerly snow showers here. If there’s a strong wind it’s often a fail.

Anyway - the uncertainty remains this morning. Hopefully ECM has this pattern nailed. 

[Kasim Awan]

2 minutes ago, snowking said:

Kasim come on, I appreciate you’re commenting at face value on the exact precipitation output shown in this single deterministic run, but you’ve been here long enough to know how poor modelling of precipitation is at such range under such conditions.

———

This next part is not aimed at you because I appreciate you try to provide a face value overview direct from modelling. But I do think in general these forums in the morning might provide psychologists with the best possible data source they could have for the effects of sleep deprivation.

Nothing has changed from where we were yesterday. Deterministic runs are still just picking scenarios at random from the range offered in the ensemble suites over the last few days. Usually at the sort of ranges we’re talking you would start to err towards the view that deterministic runs, with their superior resolution, should be getting a handle on things. But this is such a difficult setup to compute, far from the usual west - east flow one would expect locally (never mind globally) that I don’t think the deterministic runs are any more use to us right now than the rest of their respective suites.

And whilst it’s a fun exercise in imagination, there is absolutely no use in looking at any form of precipitation chart beyond (if I’m being really generous) 90 hours other than for a brief fanciful glance if you really want to torture yourself.

Yes lots to be resolved and we could be very lucky or very unlucky. All part of the chase. If we miss the Icelandic low shunting from the NW around 120h aswell as the low to our South then (we will be unlucky) plus any showers will be limited to the immediate coast with winds maxing out at 5-10knots. So we've got 2 main chances in the next 8 days as far as I see it, and as TillyS says the trend has been somewhat negative in terms of the low over the past 24 hours with a trend southwards, and most populated areas don't really have a convective flow to fall back on for snow streamers etc, away from the North / North West.

 

1 minute ago, TillyS said:

This is very true.

It’s the synoptic trend which concerns me more at the moment.

There’s no escaping the fact that the past 48 hours the models, all of the big three anyway, have been backing away somewhat from 1. deeply intense potent northerly and 2. powerful under-cut low across southern Britain.

It may all pep up again but I’m not liking this trend. It usually only means one thing.

We can't be three times unlucky, one has to deliver I guess, that would be rather exceptional. 

[Anthony Burden]

Morning all,Lots of uncertainty and various scenarios this morning ECM the the pick of the bunch for the extended cold,but reliability past 96hrs/120 hrs looking the form horse due to polar vortex being hammered.Interesting times ahead but as I have said before most of the UK will see snow within nine or ten days.

[Kasim Awan]

3 minutes ago, Joe Bloggs said:

Hey Kasim  

In my experience slack flows are actually better at generating convective showers and streamer features? It’s an ingredient I look for when trying to judge if we’ll get westerly snow showers here. If there’s a strong wind it’s often a fail.

Anyway - the uncertainty remains this morning. Hopefully ECM has this pattern nailed. 

Hi Joe - my answer is, slack yes but not too slack - a 20knot wind with some convective energy is perfect, not a low centered over the UK with 5/10 knot winds, the latter will just produce rogue showers and the odd confined trough.

[Nick123]

Gah headache central this morning. Unfortunately from what I can see ( amateur here but have been following weather and forum for years) have to agree with Kasim and tilly. I think the main opportunity from this spell was that low coming into play. Now we are in real danger (as its gone south) of getting a bog standard cold but no fun type event. Which I personally hate!!

[Nick F]

No point squabbling over how dry it will be, too far away to pin down where troughs, convergence zones or lows will track next week that may bring snow

I think the key to the longevity of next weeks cold spell will be how long the TPVs over Canada and N/NE Europe are kept apart by ridging mid-N Atlantic and Greenland. 

GFS/GEM ops are more bullish to merge to 2 TPVs over the Atlantic later next week, turning the flow more zonal / milder / unsettled. While EC det keeps the two upper vortices apart. However, as already posted, the mean of both GEFS and EPS do join the two together by day 10, with the more zonal look taking over.

But the smoothed out mean may not be the best guidance at handling upstream developments and how the upper flow and surface lows over the Atlantic interacts with the cold air entrenched over northern Europe

Edited January 11 by Nick F

[Duane S.]

20 minutes ago, Astral Goat Juice said:

Snow and cold hasn't even arrived and folk are complaining about a lack of snow

Yes, it does make me laugh how once someone states it will be dry, they then have to go to great lengths to ‘prove it’.

Surely the irony of desperately trying to prove a point, based on something (that hasn’t yet even occurred) that will be missing all sorts of macro details at this far out stage, isn’t just lost on me? 

 

[Nick123]

Just now, Duane S. said:

Yes, it does make me laugh how once someone states it will be dry, they then have to go to great lengths to ‘prove it’.

Surely the irony of desperately trying to prove a point, based on something (that hasn’t yet even occurred) that will be missing all sorts of macro details at this far out stage, isn’t just lost on me? 

 

People are just sayin' what the models are saying problem is folk don't like it lol

[alexisj9]

1 hour ago, winterof79 said:

Thank god someone else reads it like that.We were doing post mortems earlier and looking to February.Very cold next week and impossible to predict snowfall yet.

And slack does NOT mean no snow with very cold air off the Irish sea

No it doesn't, in fact slack often means there's room for a trough to form.

[Kasim Awan]

Just now, Nick123 said:

People are just sayin' what the models are saying problem is folk don't like it lol

Yes I'm not saying it will indefinitely be dry just that the models look dry with a lack of fronts / showers this morning. Not sure what is so bad about that?

[bradymk]

UKV has an organised area of snow moving through Northern Ireland and into NW England late Monday. It then looks to pivot slightly and moves into N England and into Ireland during the night.

Pressure is also lower on UKV at 120 than compared to both ECM and GFS. It has the 1011mb contour through the midlands at +120 whereas GFS has 1019mb.

Thought UKV did well with the recent cold pool that crossed Southern areas this week so worth adding it into the mix the next few days for the initial northerly hit.

[Nick123]

Just now, Kasim Awan said:

Yes I'm not saying it will indefinitely be dry just that the models look dry with a lack of fronts / showers this morning. Not sure what is so bad about that?

Well that's how I'm reading it too unless my glasses are broken  

[Ali1977]

27 minutes ago, Kasim Awan said:

Yeah only Kent and North York Moors got anything significant out of December 2022. Looking at the charts one might think instability would be extensive with features popping up regularly:

When in reality the lack of thermal gradient in the slack flow only results in very localized (but intense) features that don't last particularly long either, often only covering one or two counties. 

For the type of trough development many on here are suggesting is possible, i.e. covering large portions of the UK, a far more unstable flow is required. For example, this flow from November 2005. Or progression of a larger trough / low such as the one from Iceland / to our South West could provide the extent of convection required for more widespread snowfall.

Now I'm not suggesting that there wont be any snow chances in the upcoming cold spell. Just that if we end up with a quiet area of low pressure under slack winds then likelihood in building widespread heavy troughs is quite low, as proven by the previous cold spell and December 2022. This is proven by the accumulation charts shown by the GFS/ECM/GEM etc. These are fair in giving an indication of potential and if the slack flow indicated was indicative of heavy trough development then these charts would reflect this and show more extensive snow accumulation. This could still change though. We may still source an active and larger area of low pressure which is certainly possible.

Dec 22 slack flow was great for Gloucestershire - about 6inches or more in places 

[Sparky68]

Just now, Kasim Awan said:

Yes I'm not saying it will indefinitely be dry just that the models look dry with a lack of fronts / showers this morning. Not sure what is so bad about that?

The way the models have been flip flopping these last couple of weeks nothing would suprise me regarding next week. Could be freezing cold and dry as a bone or some places could see a good dumping of snow!

[Penrith Snow]

1 hour ago, Harveyslugger said:

Ur more knowledgeable than me surely you know disturbances will pop up even 24hrs before the event. And remember how wrong the last SE snow models predicted some showers but in reality it was a mass of snow.not heavy snow I know.but goes to show models can get these features wrong even at a nowcast situation.so I expect many features to pop up in the closer time frame

Absolutely, during the early December cold spell Cumbria was forecast to be completely dry for the duration, in the end the Lake District got 30cms - 40cms with 5cms - 10cms further east in the County.

Get the cold in first, then...

Andy

[alexisj9]

42 minutes ago, Kasim Awan said:

I don't think there was any such streamer in early 2009. 

There was a famous one, but it came from the east and literally shut SE London down for three days.

[Nick123]

Just now, alexisj9 said:

There was a famous one, but it came from the east and literally shut SE London down for three days.

Oh I remember that. Feb 2nd 2009 I believe?

[Essan]

32 minutes ago, Kasim Awan said:

Yeah only Kent and North York Moors got anything significant out of December 2022.

Actually, here in SE Worcestershire, December 2022 gave us the best snowfall since 2010     From a small feature that wasn't forecast at all.

[TSNWK]

11 minutes ago, Kasim Awan said:

Yes I'm not saying it will indefinitely be dry just that the models look dry with a lack of fronts / showers this morning. Not sure what is so bad about that?

Hello.. I guess there are plenty of us that read and understand model op runs and offer a view verbatim to what they say (I freely admit that’s my limit  in essence at present ) the real skill comes when people can use more than one source of info to form a view for example ensembles / trends / local knowledge / precedents/ teleconnections / sea surface temp / as examples  w it’s a. Little choas and then holistically box it all together to form a view… if we just use ops runs then we are simply human versions of weather apps

Edited January 11 by TSNWK

[Mike Poole]

ECM clusters this morning, just one cluster T120-T168, T192-T240:

I think these are an improvement on the 12z suite, because the block looks more resilient, particularly on clusters 2 and 3 - the op is in cluster 2 with  15 members.  Cluster 3 moves the block too far west, though.  Cluster 1 has the block weakening towards day 10, but retains a southerly track to the jet.

T264+:

Massive uncertainty here, but basically a mobile theme, as the teleconnections have been suggesting for towards the end of January, again the merest hint of something building towards Scandi on clusters 1,2 and 5 but no more than that at this stage.

[ICE COLD]

Not had chance to read through the forum. I looked at the models this morning in the order of - 

The GEM - Rubbish 

The GFS op - Rubbish 

The GEFS - not to bad 

UKMO- not to bad 

The ECM - lol what a excellent run 

ECM mean/eps - upgrade 

us coldies have been dragged through the mill this winter . The NWP modeling has been abysmal from the strat to this to that . Anyone who says it’s not a stress ? well I’m pulling my hair out . Please please be right ECM . 

 

[Drifter]

22 minutes ago, Duane S. said:

Yes, it does make me laugh how once someone states it will be dry, they then have to go to great lengths to ‘prove it’.

Surely the irony of desperately trying to prove a point, based on something (that hasn’t yet even occurred) that will be missing all sorts of macro details at this far out stage, isn’t just lost on me? 

 

…and then they end up with the most snow when the time comes! Always the way. 

[near northampton]

43 minutes ago, Kasim Awan said:

Yeah only Kent and North York Moors got anything significant out of December 2022. Looking at the charts one might think instability would be extensive with features popping up regularly:

When in reality the lack of thermal gradient in the slack flow only results in very localized (but intense) features that don't last particularly long either, often only covering one or two counties. 

For the type of trough development many on here are suggesting is possible, i.e. covering large portions of the UK, a far more unstable flow is required. For example, this flow from November 2005. Or progression of a larger trough / low such as the one from Iceland / to our South West could provide the extent of convection required for more widespread snowfall.

Now I'm not suggesting that there wont be any snow chances in the upcoming cold spell. Just that if we end up with a quiet area of low pressure under slack winds then likelihood in building widespread heavy troughs is quite low, as proven by the previous cold spell and December 2022. This is proven by the accumulation charts shown by the GFS/ECM/GEM etc. These are fair in giving an indication of potential and if the slack flow indicated was indicative of heavy trough development then these charts would reflect this and show more extensive snow accumulation. This could still change though. We may still source an active and larger area of low pressure which is certainly possible.

Incorrect, the Northern Home Counties and Gloucestershire where I live both had significant snowfall in December 2022, was over a foot of snow in the high Cotswolds and 6 inches here in Cheltenham which lay on the ground for a week. It wasn't forecast and occurred in a slack flow. You are taking the precip charts at face value here. 

[Nick F]

00z UKMO 'current laying snow' chart animated through next week until Thursday suggests northern areas look to see greatest chance of laying snow, probably from that low that forms near Iceland and drops SE and also from showers, but also a chance in the southeast as one or two lows track east close to the south.

Although it's too far off to forecast snow for now, seems a reasonable assumption, for now, to think Scotland, N England and N Ireland stand to see greatest chance of snow, lower chances further south, unless the Atlantic lows track further north, but the low from the southwest more likely ending up further south into France.

[Harsh Climate]

57 minutes ago, frosty ground said:

Not sure how many more time you can basically write it’s going to be dry.

i think we get it now.

we've gone from storm of the century to dry as a desert, i now forecast change with new data but maybe just maybe we dial it back a bit.

looking at a few operation 5 days and dismissing unexpected features about 6 times in one morning is a bit much.

I'm not seeing it being dry at all. UKMO would deliver a hell of a lot snow Northern England northwards. I have a feeling we will have a few systems coming in from the NW - SW next week delivering a lot of snow over quite a wide area. This area is looking like being North Midlands/ Central Northern England northwards at the moment but in reality could be hundreds miles either way. 

Again next week looks far from dry!