Model Output Discussion - Spring Has Sprung

[CoventryWeather]

Zonal winds look really good. 

[Mike Poole]

ECM clusters T120-T168:

The op is in cluster 2, which has the most rounded low anomaly at T120.  Bit difficult to see on these plots, but the other two clusters pass the low more southerly and quicker as far as I can see.  So I think UKMO solution might have some traction, but you’d need to see the individual runs to be sure.

T192-T240:

The build of heights is NW of the UK by T240 on all clusters.  None have a UK high at that time.  Cluster 3, which contains the op, does look to inflate heights to our south slightly courtesy the low to the far west which is deeper than on the other clusters.

T264+:

The extended is a downgrade because of the presence of cluster 3 (14 members), which leads to an Atlantic sourced airstream and re-inflates the heights to the south.  Clusters 1 and 2 have a strong block in the Greenland area by T360 - given the position of it, UK wind direction probably very dependent on which representative member they’ve chosen.  Both cluster 1 and cluster 2 have good potential as we firm up the detail.  We need to see cluster 3 sling its hook.

Edited February 4 by Mike Poole

[stodge]

Evening all

It would sometimes be nice, if boring, if all the charts said the same at T+168 and could all verify.

That may happen one day but not yet.

Quite apart from Thursday and Friday's drama (on which I'll leave others to muse though the UKM chart did cause even Mr Stodge, here in lowland East London, to raise an eyebrow), what we need I suspect is for the heights building to the north west behind the LP to move through cleanly and quickly into Scandinavia and not linger round the British Isles. If that happens, we'll get the nice Scandinavian HP we se eon GEM and JMA but both GFS OP and ECM are messier to say the least.

Plenty of angst and anguish to get through in the next 48-72 hours I suspect.

[Daniel*]

EPS goes very strongly with extensive high lat blocking further into February something is brewing here.

[Harsh Climate]

 AO-

In Holland you was always going to be on the milder sector of air Thursday to Saturday.

Also look at the long term outlook on those essembles, they are heading in the right direction which is colder.

Edited February 4 by Harsh Climate

[Battleground Snow]

Huge spread (especially for eps) for the 9th and 10th

Central England 

Edited February 4 by Battleground Snow

[Mike Poole]

 CoventryWeather Yes, bit of a bounce back on the SSW chances since yesterday.  GEFS 12z have 48% going for a SSW.

Blocking signal remains strong on the ECM 46.  The progression of the MJO, according to the actual data (grey line), has been progressing round smoothly for weeks as it now tiptoes into phase 8.  Once again, the model predicts a drunkards walk going forward, but then it’s done that every day there are charts still available for.

[WYorksWeather]

Been fairly busy this weekend, so not been posting as much. Time to make up for it I think this evening.

Anyway, first port of call is snow chances for next week. I see a lot of people talking about whether we're going to get snow or cold rain out of the low on Thursday, and whether if it does snow, it has chances of accumulating. Main focus here is going to be conditions from T+72 to T+120 on UKV.

First, temperatures. Here are the overnight temperatures for 6am on Wednesday, Thursday and Friday mornings. Pretty clear that through Friday, snow chances at low levels will be limited to Midlands and further north, if we can't even get temperatures below 0C by night.

Here are afternoon temperatures for Wednesday, Thursday and Friday (3pm).

Overall, except for Scotland and far north of England, this does look like the m-word, marginal.

Next, 850hPa temperatures. These are not of course an exact correspondence with snow chances, but I think it's fair to say that especially as we go deeper into February, anything above -5C is probably unlikely to deliver to low levels. Anything -8C or lower is probably close to near certain snow accumulations, and -5C to -8C is the grey area.

So, here are the 850hPa temperatures that UKV is predicting from T+60 to T+120, in 12 hour steps.

Through to Friday, it looks like we can summarise it something like this. Conditions are definitely suitable for snow in Scotland and the far north of England on Wednesday and Thursday, with marginal snow possible through Yorkshire and parts of the Midlands. By Friday, the conditions are definitely right through all of NW and NE England, and parts of Yorkshire, with marginal snow chances everywhere except the far south, and possibly west Wales.

Same again, but for dew points. We're looking for values below 0C here.

This looks less good for the south - never really any good chances south of a line from the Wash to the Bristol Channel - persistently positive dew points.

So, with that in mind, here are some of the snow events UKV is showing. On Wednesday morning, we have showers into parts of northern and central Scotland.

Then a band of mostly rain on Thursday morning.

An attempt on Friday just results in more rain for the south, and snow showers into the north.

 

If I were anywhere Midlands northwards with 200-300m of elevation, or down to low levels in Scotland, I'd be feeling quite good about this. But at the moment, with what UKV is showing tonight, it's just the wrong side of marginal for most of us. We need those temperatures forced down at least another couple of degrees.

Here's GFS 12z and the (incomplete) ECM 12z ensembles. We see again that there just isn't quite enough for near my location, going by the mean. 850hPa in the -5C to -6C range at this time of year is always going to have a certain amount of marginality. I have near 100m of elevation at my location and I'm still not that hopeful.

I think the key is timeframe. It's like looking for a heatwave in mid August - you need that bit more oomph in the 850s to get the temperature to 30C at the surface, nearer 15C rather than 10-12C given good surface conditions. Same here, an ordinary winter -5C is probably going to just come out the wrong side, whereas 2-3 weeks ago it might well have delivered.

Just anecdotally, it's becoming quite noticeable now that the seasons are getting ready to change again. I was out on Saturday and for the first time this year there was a very noticeable warmth to the sun. In just the last two weeks, we've also gained about 40 minutes of daylight, and by the period of interest on Thursday, we'll be close to an hour compared to mid-January. Yes, SSTs are still falling, but we need the initial airmass to be cold enough to tolerate a bit of warm air mixing as low pressure comes in.

So, for the moment, I'm expecting a ton of cold rain on Thursday if the low is over my location, possibly with a sleety element at times, but nothing more than that. I'd like to be wrong, of course.

It wouldn't take much, either way. 100 miles south with the cold boundary and we bring many more areas into play. 100 miles north and it would be pretty much a damp squib  - just snow over the Pennines and in parts of Scotland, which is standard fare in even slightly cooler than average conditions at this time of year.

Still time for this picture to change, and I will follow with interest over the coming days.

 

[ANYWEATHER]

As for the drama kings and Queens of winter synoptics,  it does look like a wet and windy spell ,by late week ,next weekend ,with snow on high ground in the North , by day ten ,musings of high pressure settling down across the nation...

[Paul_1978]

 WYorksWeather Now that's what you call a measured and informative post, versus the ones that seem to delight in telling us we're getting cold rain and adding laughing emojis. Top post WYW 

[stodge]

11 minutes ago, WYorksWeather said:

Just anecdotally, it's becoming quite noticeable now that the seasons are getting ready to change again. I was out on Saturday and for the first time this year there was a very noticeable warmth to the sun. In just the last two weeks, we've also gained about 40 minutes of daylight, and by the period of interest on Thursday, we'll be close to an hour compared to mid-January. Yes, SSTs are still falling, but we need the initial airmass to be cold enough to tolerate a bit of warm air mixing as low pressure comes in.

Just thought I'd pick up on this old chestnut. The saying "as the days get longer, the cold gets stronger" isn't entirely false.

As winter goes on, the sources of cold air (north and east) get progressively colder and for the far north and north east, it's still dark most of the time so not much to warm the air. Thus, an early December easterly often has modest 850s while by late February we can still see -20 850s and as you rightly say, the sea can be at its coldest.

MY cold nirvana is a SE'ly from a frigid and snowbound continent with the minimum fetch across the Channel - tonight's 12Z JMA at T+264 is nearly there but note the initial cold is often mixed out before the real cold arrives so it's often a waiting game to get the synoptics right before the real cold arrives.

[Chesil View]

 stodge very true Stodge.

The best snow I've ever seen. Feb 1978 was from a short fetch southeasternly from a frigid continent.

[WYorksWeather]

2 minutes ago, stodge said:

Just thought I'd pick up on this old chestnut. The saying "as the days get longer, the cold gets stronger" isn't entirely false.

As winter goes on, the sources of cold air (north and east) get progressively colder and for the far north and north east, it's still dark most of the time so not much to warm the air. Thus, an early December easterly often has modest 850s while by late February we can still see -20 850s and as you rightly say, the sea can be at its coldest.

MY cold nirvana is a SE'ly from a frigid and snowbound continent with the minimum fetch across the Channel - tonight's 12Z JMA at T+264 is nearly there but note the initial cold is often mixed out before the real cold arrives so it's often a waiting game to get the synoptics right before the real cold arrives.

Yep, definitely not trying to say at all that a further cold and snowy spell is impossible, and of course this is most obvious at the other end of the year in summer - most of our hottest days of the year are between mid-July and early August.

Definitely more chances to go, and winter is not over. To prove the point about SSTs, I'm not calling time on winter until this day 0 SST chart:

Is as cold or colder than this day 15 chart:

Based on the SSTs, a direct NE to ENE would be good as well - SSTs are only from 4-6C off the coast of Norway.

In short, I think we're saying the same thing here - a -5C 850hPa in mid-February won't be as cold at the surface as a -5C 850hPa in mid-January, but an identical synoptic might well give a lower 850hPa in mid-February, and hence the overall chance of cold doesn't begin to decline significantly until mid-February onwards.

I am wary though of some already starting to turn their attention to the second half of the month. Once you get to that point, it's not that winter is over, but the bar you have to climb increases. Especially for 'proper snow', which for me, means at least a few centimetre, staying on the ground for at least 24 hours without turning to slush.

Again, it's like looking for a major heatwave in the second half of August. It can happen, it breaks no laws of physics, and sometimes it does happen. But if you've not had a day over 35C (probably the recent average summer absolute max), you wouldn't put money on it with two weeks of summer left plus the first couple of weeks of September. Similarly, if we've not had a significant dumping of snow, I'm not betting on getting one in the second half of February or into early March.

Hence, I do think next week's chase is quite important - it's the last one before we start to enter last chance saloon territory. If next week goes wrong, the next significant attempt at a snow event has to land, or it's game over, see you next year.

 

[AO-]

 Harsh Climate

Not compared to this morning. It takes about two or three days longer to get the cold in. If anything it is not an improvement. 

[Ali1977]

No Move south from the icon, but it didn’t blow up the low this time!! If the GFS doesn’t move it south this run then I hold very little hope for the over nighters - stranger things have happened though!! 

[Chesil View]

It was quite expected that tonight's ecm would not be as good as this mornings. As IDO pointed out this morning it was an outlier.

That doesn't mean of course that this mornings ecm outcome might not be the actual outcome but simply that it was unlikely to be repeated tonight. 

Ideally you want  the jump south on this mornings ecm to happen at 48 hours rather than 96..

[Ali1977]

I guess by Friday the shift south is a little more noticeable- 100 miles or so 

[ICE COLD]

 Ali1977 had some hope after this mornings runs but it’s gone the wrong way on the 12z s . I’m more interested what happens after anyway with the height rises to the NW . Ukv still has some snow down south Friday tho . Probably a mixed slush fest tho

[CoventryWeather]

 Ali1977 did move south throughout the whole run - guess this will occur for the next few days. GFS is likely to start the backtrack now towards something of a mid solution. 

Plus people keep saying this mornings ECM was an outlier - it wasn't. Clearly supported by it's ensembles. Also somewhat supported by this evening's UKMO run.

[ANYWEATHER]

1 hour ago, stodge said:

The saying "as the days get longer, the cold gets stronger" isn't entirely false

Indeed, that's why Easter's  are more commonly known for being White than Christmas. ......

[Ali1977]

GFS a little better 

Edited February 4 by Ali1977

[Tim Bland]

Weds snow still creeping  south 

[CoventryWeather]

 Tim Bland Arome and Arpege ensembles also keen on the idea, what are others thoughts on this - is it possible as the cold air undercuts or unlikely? 

[ICE COLD]

ECM control coming along nicely. 

[andy989]

 WYorksWeather

Best post I’ve read on here in a long time. Very clear and easy to follow.