Model output discussion - cold spell approaching?

[Ninman]

10 minutes ago, Tim Bland said:

We have gone from a Greenland high to a 945 low

This is what the GFS appears to do when it can't see a clear outcome. It is like a child eating up their sweets and then realising they have no more. Do they ask for more or accept they have eat enough - don't know how to handle this so will try and destroy something.

I expect even if these lows appear in reality, they will be much less pronounced

[Ninman]

1 minute ago, Battleground Snow said:

Hmmm there is an amber warning out now for the north, but no adjustments further south of the yellow warning

I can only see this being a north/north east affair with a bit of altitude. Looking at the dew points/wet bulbs etc, low levels will be rain with some sleet mixed in. Even if it does turn to snow, I doubt it would stick at low altitude.

[Matt H]

There’s a significant amount of scatter within the GEFS 06z ensembles from the 19th onwards, there’s probably a perturbation to satisfy each member on here as there’s so much uncertainty. So it’s far too early to be calling this one way or another, we’ll just have to see where we end up after the 12z runs later but I’m not going to spend my day stressing out about it. Have a good day everyone.

[london-snow]

30 minutes ago, snowking said:

as @Nick F suggested earlier, probably best not to concern yourself with too much more than +144 for now.

Points of the morning,

Their is no definitive clear trend beyond d6 which takes us to the 19th, Now forgive me if i am incorrect but wasn’t the implications post the ssw to be felt after the 20th possibly a few days further? Add to this we have also seen a further warming which effects could be felt towards late January. All leads me to feel that we are in with a very decent chance however those dice has not stopped rolling on the table. 

[mountain shadow]

28 minutes ago, Battleground Snow said:

Very slight improvement on the mean.. 

I'm still optimistic for the end of January, especially once we get that pesky MJO to behave.

 

Yesterday, we were confident a cold spell would start the middle of next week. 

The problem is, as ever, when we start kicking the can down the road until tomorrow, tomorrow never arrives.

[Battleground Snow]

Just now, mountain shadow said:

Yesterday, we were confident a cold spell would start the middle of next week. 

The problem is, as ever, when we start kicking the can down the road until tomorrow, tomorrow never arrives.

Indeed, it is disappointing to have lost that Atlantic push into Greenland for a faster route to cold, but more opportunities are on the table. Volitilaty is still high. It will be extremely frustrating if we don't get a least one cold spell over the next 6 weeks

[Ninman]

2 minutes ago, mountain shadow said:

Yesterday, we were confident a cold spell would start the middle of next week. 

The problem is, as ever, when we start kicking the can down the road until tomorrow, tomorrow never arrives.

Sounds like a James Bond film parody where 007 goes undercover as a meteorologist!

 

I'm curious as to what happens with the dip in 850s after 20th in the short ensembles. Most likely a 20c scatter but hopefully the mean continues on a downward trend!

[johnholmes]

For what it's worth, an update on the 500 mb anomaly charts!

Looking at the ECMWF chart, see link below

http://www2.wetter3.de/Fax/00_ECMWF_ENS_p0_500hPa+144_240.gif

These show a generally westerly(slight n of w) at 500 mb, and the -5C 850 mb temperature showing no sign of colder air penetrating the UK from the upper trough over Scandinavia, two pronged at first, part into Europe and part towards the UK but with no pretention of –ve 850’s, the trough then swings more towards the UK but with no real lowering of the 850’s for the uk?

On the EC-GFS output, yet again they show a marked ridge over Greenland and a marked trough over the uk (sub 528 DM, but with little penetration again into Europe.

Noaa has a fairly similar pattern on both its 6-10 and 8-14 charts, quite meridional.

So where does that leave the UK weather. I wish I knew. We have two outputs from EC both rather different. The anomaly charts, all 3, show, as they have for several days, meridional with the ‘cold’ trough over the UK. So where is the cold air, the synoptic charts, taking the 120h, as that is as far as UK Met go to allow comparisons with all e major models, none of them show any cold let along major cold. Beyond that then, to varying degrees, EC and GFS do show the probability, not consistently, of ‘colder’ air feeding south behind a low system at the surface with signs of surface pressure rising in the Greenland area. These tend to back up the persistent meridional outputs from the anomaly charts.

It does not, to me ‘hang together’ coherently enough for me to say cold weather is going to win out. I sit on the fence for a day or three.

Enjoy the roller coaster from the synoptic models, take the snow charts as a possible general guide but for your sanity ignore the amounts.

ECMWF/GFS DAY 8-10 MEAN 500MB HEIGHT COMPARISON

WWW.METEO.PSU.EDU

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Edited January 13, 2021 by johnholmes
adding a link

[pyrotech]

Its not good for me, but Saturday looks like transient Snow for Brecon Beacons, then as it moves East  snow likely to lower levels from around line (Beige). Welsh Marches to West Midlands. This will only settle on some hills. Further East again (Orange line) Approx East of Northampton to Brighton, Snow is likely to fall and in lower elevations settling is possible. Ignore precipitation amounts, map just utilised to show where snow on Saturday is more likely.

[Tim Bland]

Huge 20c scatter by the end of the ensembles ...more runs needed

[Jason M]

2 minutes ago, Tim Bland said:

Huge 20c scatter by the end of the ensembles ...more runs needed

Huge rainfall spikes on that chart. If we end up on the wrong side of this pattern it will be a real 'rain maker'.

[Cuban Zebra]

We shouldn’t really be surprised by the major changes we’re seeing, what with all the volatility in the air! The second warming is well under way so that’s probably causing the issues!

Allowing the run to run changes to affect you is a one way ticket to a nervous breakdown!!

[Paul]

Have moved some more posts into the chat thread, would be great not to have to though

Please just keep it to discussing the specifics around the model output in here. For everything else:

 

 

[Penrith Snow]

1 hour ago, General Cluster said:

Here's something we ain't seen for a while -- and hopefully won't be seeing for a good while longer:

    

Just when you thought it was safe to go in to winter, a smiling Uncle Barty turns up with a large trunk of luggage  

[weathermadbarnsleylad]

6z ens South Yorkshire. Don't discount anything past the 17th.This is not over for coldies yet. 

[weathermadbarnsleylad]

Just now, weathermadbarnsleylad said:

6z ens South Yorkshire. Don't discount anything past the 17th.This is not over for coldies yet. 

I expect the 12z to be an upgrade on the cold. In my personal opinion. I still think something is lurking. 

[sheikhy]

Again judging from the pressure charts ecm 06z has snow line midlands!!looks very much like euro4!

[Frosty.]

I’m going to stick my neck out and say there a more juicier cold members in the GEFS 6z compared to the 0z (can’t post them all!)...the cold ebbs and flows and there are a scattering of milder members but i think there continues to be plenty of wintry / wintery potential during the next few weeks...so, I’m not giving up on snowy nirvana visiting our little island in the not too distant future!!

[goosey007]

Afternoon all,

Taken we a few hours get my head around what the models have presented us overnight and into this morning. Even though I knew deep down that the models could flip at any any moment, I am still disappointed as a part of me always believes that this time they wont and things will firm up....just hard to fathom out sometimes. But not all is lost there is still a better chance than most winters of seeing something more widespread and significantly white before Feb is out.

SSW has thrown a curve ball the models are really struggling to get to grips with as we know ...much still to be decided. The drama will continue and I wouldn't be surprised to see the models present a different route to cold tonight or even flip back completely to the route we have been seeing...who knows.

 ...we cant even be sure whats happening tomorrow with the snow tomorrow both GFS models cant even agree totally at 36 hr range....

stay positive all there still a chance!!

GFS  PARA                                                 GFS 

 

 

Edited January 13, 2021 by goosey007

[mb018538]

Just looks like a chilly deluge of mainly rain for many:



I'd be more worried about flooding than anything else at the moment, especially in the West and Northwest.

[Kasim Awan]

1 hour ago, Ninman said:

I can only see this being a north/north east affair with a bit of altitude. Looking at the dew points/wet bulbs etc, low levels will be rain with some sleet mixed in. Even if it does turn to snow, I doubt it would stick at low altitude.

This post is not quite correct, the consensus is for a 1-3 hour spell of heavy wet snow tomorrow down to lower levels across the North Midlands, Northern England producing fairly widespread accumulations of 1-6cm. There will of course be an element of marginality related to the coast, the western extent of the cold air and intensity regarding evaporative cooling. So yes, many places in these areas will be very dissapointed but that doesn't take away from the growing confidence of an area of colder uppers with heavy ppn producing conducive conditions.

[Cold Winter Night]

The interesting thing about the output the last few days is that the short term has not been worked out properly yet. Models are underestimating the heights to our East in the earlier timeframe (48-96h), which could still throw up surprising developments. I think that is what @carinthian has been hinting at too.
Keeping an eye on that, what seems to happen to our West in the 120-240h timeframe has changed compared to two days ago.

Most have now woken up to this particular Greenland High scenario probably not working in our favour.
The High, as in the output today (and tbf yesterday) simply does not develop in the right place for us, whether it's an official West based -NAO or not. Not all Greenland Highs are a guarantee for a winterfest.

The EC at +120h below illustrates what I mean. WAA (Warm Air Advection) comes out of Newfoundland, directed at West Greenland. In my opinion, we need WAA for a proper Greenland High (that does deliver the goods) to be more or less East of the black line.

I have looked at the development of many decent or legendary cold spells, and so far I haven't seen any that started with WAA in the Newfoundland area. Some were reinforced from there later on, yes, but it was not the starting point.
If anyone knows of historic cold episodes that did start this way, please let me know.

In the second picture, I have drawn where, as I see it, the High pressure should ideally originate (and where not).

1. A UK/East Atlantic/Western European High. Retrogresses towards Greenland. Classic example: Nov 2010
2. A Scandi High, retrogressing to Greenland. Developed in situ, or split off of a Eastern European or Russian High. Classic examples: Jan 1947, Dec 1962
3. An Arctic High extending Soutwest, retrogressing through Scandinavia towards Greenland. Usually assisting no's 1 and 2. I can see this one, combined with no.2, happening in late January and into February. Look at that area in the output the coming days and weeks. Perhaps delayed SSW influences and MJO effects could help us here. As of now, the extended output shows this to some extent, but not convincingly yet.
4. A West Greenland High, as we see in this morning's output. Too far West for us, tendency to retrogress to Ellesmere Island, seeking to connect to Pacific Highs.

 

[Paul]

1 hour ago, Kasim Awan said:

This post is not quite correct, the consensus is for a 1-3 hour spell of heavy wet snow tomorrow down to lower levels across the North Midlands, Northern England producing fairly widespread accumulations of 1-6cm. There will of course be an element of marginality related to the coast, the western extent of the cold air and intensity regarding evaporative cooling. So yes, many places in these areas will be very dissapointed but that doesn't take away from the growing confidence of an area of colder uppers with heavy ppn producing conducive conditions.

What you're saying is possible, but equally so is Ninman's view - it's all on a knife edge. I'm not sure what you're meaning when you say there's a consensus on the snowier outcome, as tbh I'm not seeing that. Some models are more bullish than others, but I'd say that the most likely outcome isn't for widespread lower level snow. 

I don't know if this is applicable in this instance, but a lot of people seem to be taking some of the snow accumulation maps at face value from models such as the Arpege, GFS etc. But the issue with these is that many of them are showing a water equivalent snow accumulation, based solely the precipitation rates and not taking melt or the moisture content of any snow into account.  Typically on those charts the water equivalent snow amount is multiplied by ten to get a depth, but that multiplication is what dry snow would bring. On this occasion in particular, even assuming everything was snow, it's not going to be dry, so immediately, even if all of it settled you could be looking at needing to perhaps halve the values shown on those maps. And on top of that, you also have to take into account the snow (and maybe other frozen/semi-frozen precip types) which fall but don't settle.

I'm not saying lower level snow isn't possible, I'm not even saying that the accumulations you're describing aren't possible, but equally they're not a certainty, and I think the uncertainty around all this is where the true consensus is right now. 

Edited January 13, 2021 by Paul

[Scott Ingham]

1 minute ago, Paul said:

What you're saying is possible, but equally so is Ninman's view - it's all on a knife edge. I'm not sure what you're meaning when you say there's a consensus on the snowier outcome, as tbh I'm not seeing that. Some models are more bullish than others, but I'd say that the most likely outcome isn't for widespread lower level snow. 

I don't know if this is applicable in this instance, but a lot of people seem to be taking some of the snow accumulation maps at face value from models such as the Arpege, GFS etc. But the issue with these is that many of these are showing a water equivalent snow accumulation, based solely the precipitation rates and not taking melt or the moisture content of any snow into account.  Typically on those charts the water equivalent snow amount is multiplied by ten to get a depth, but that multiplication is what dry snow would bring. On this occasion in particular, even assuming everything was snow, it's not going to be dry, so immediately, even if all of it settled you could be looking at needing to perhaps halve the values on those maps. But on top of that, you also have to take into account the snow (and maybe other frozen precip types) which fall but don't settle.

I'm not saying lower level snow isn't possible, I'm not even saying that the accumulations you're describing aren't possible, but equally they're not a certainty, and I think the uncertainty around all this is where the true consensus is right now. 

I feel the areas in a long period of +1 hour of 3mm+ precipitation will see these values due to evaporative cooling and areas who miss this will see rain or sleet. I think Kasim does cover that though

[Methuselah]

Not the most exciting GEFS temp ens... But he, ho they are what they are:

    

NH profiles don't look too bad, and should be less unstable than individual GFS runs?

    

    

And lastly, a 'deep and meaningful' afterthought... Picture the weather as a perfect straight line, reaching from here to eternity; now imagine the models as a pack of blootered zombies trying to follow that line: wouldn't those zombies be just like the models -- weaving, waving, stumbling and tripping their way forward, but never quite getting it right?