Model Output Discussion - Happy New Year!

[stodge]

Afternoon all

Not much to add - the charts moving toward mid month are increasingly mobile varying from unsettled to downright stormy. The jet is moving at speed across southern Britain so plenty of weather on offer, none of it lasting very long.

Prospects for snow on Scottish hills and mountains look reasonable with PM incursions more frequent but further south it's fast moving rain, fast moving wind and hopefully noting else fast moving such as garden furniture, roofs and the like. 

Not sure where strat developments are taking us - the 06Z Control is interesting but not reliable given what has happened so far this winter. The OP suggests another round of warming at the end of next week but it's hard to see the TPV breaking down from that.

[Singularity]

Some words of caution for any snow-seekers taking the GFS precipitation type charts at face value during those polar maritime incursions - it has a low temp bias past a couple of day’s range, which from studying it’s performance, tends to be strongest in that setup.

Worth paying more attention if & when ECM shows sufficiently cold conditions within a week’s range. Or, I suppose, if GFS goes some way beyond the min requirements e.g -10*C 850s. Not out of the question for Scotland if one of those big lows moves in the right way and intensifies once already level with the UK (as this means less mixing out of cold during approach).

[Mike Poole]

I know this ridge we were discussing some days ago has faded out of the picture somewhat, but some could be waking to their first (and quite possibly, last) snow of the season on Tuesday as per the GFS 12z T66:

NE England favoured?

Edited February 1, 2020 by Mike Poole

[Interitus]

53 minutes ago, Singularity said:

Some words of caution for any snow-seekers taking the GFS precipitation type charts at face value during those polar maritime incursions - it has a low temp bias past a couple of day’s range, which from studying it’s performance, tends to be strongest in that setup.

Worth paying more attention if & when ECM shows sufficiently cold conditions within a week’s range. Or, I suppose, if GFS goes some way beyond the min requirements e.g -10*C 850s. Not out of the question for Scotland if one of those big lows moves in the right way and intensifies once already level with the UK (as this means less mixing out of cold during approach).

Don't forget in the deep lows the 850 height is much lower, the temps don't need to be as low.

[IDO]

Improvements again, the mini-ridge to the west favouring a better sourced colder flow from the NW so colder still than the 06z:

06z>12z>

Leading to:

06z>12z>

[Mike Poole]

GFS out to day 9, T216, and it is consistent with things we've seen recently including the clusters, well one or two of them anyway, see my earlier post. 

There are clearly two issues with this, stormy weather and the potential for any snow, however fleeting.  A stormy period seems to be massively increasing in likelihood, but re this run, will there be any snow at low levels?  With T850s lower than -8 I would feel hard done by if precipitation wasn't snow.  At -2C I'd be relying on certain things maybe evaporative cooling, and that won't happen in a raging gale, so even if the GFS -6 uppers are encroaching, it is marginal - and my definition of marginal is some places will see snow, some places won't.  

If this sort of thing makes it into the reliable, then we can start to make predictions about snow, and it will be fun to do so, but at the moment we are just waiting for this possible NW very windy flow to get into the reliable.  

[nick sussex]

Some changes over the last few days to the PV.

More disruption to that and pressure rising over the Arctic and ne north of Svalbard .

If you want the chance of some PM flows you need something to force the jet se near the UK and those pressure rises will help .

We need to see this consistency modelled . There is though the danger of a fast developing shortwave at the base of the main troughing that will deepen rapidly and move east .

These are the worst types of low pressure for wind strength , these small lows often wreak the most havoc .

In terms of snow , chances have improved especially for northern areas but still too far out given the GFS bias for cold uppers .

But more likely to verify if you have though pressure rises to the north and ne .

 

[IDO]

2 minutes ago, Mike Poole said:

 

If this sort of thing makes it into the reliable, then we can start to make predictions about snow, and it will be fun to do so, but at the moment we are just waiting for this possible NW very windy flow to get into the reliable.  

Yes, no winter wonderland but making the best out of an average synoptic. For us in the south cold rain mainly but potential Midlands especially higher ground. Scotland could get a pasting at times.

A repeating pattern that would have been even better without the euro heights preventing a Sceuro trough, so the UK right on that snow-line most of the run:

T270>

Another op run where we are getting wedges of heights at higher lats so the tPV looking less organised:

Need this to be modelled going forward, that bottled up cold just wants to sink south!

[feb1991blizzard]

2 minutes ago, nick sussex said:

Some changes over the last few days to the PV.

More disruption to that and pressure rising over the Arctic and ne north of Svalbard .

If you want the chance of some PM flows you need something to force the jet se near the UK and those pressure rises will help .

We need to see this consistency modelled . There is though the danger of a fast developing shortwave at the base of the main troughing that will deepen rapidly and move east .

These are the worst types of low pressure for wind strength , these small lows often wreak the most havoc .

In terms of snow , chances have improved especially for northern areas but still too far out given the GFS bias for cold uppers .

But more likely to verify if you have though pressure rises to the north and ne .

 

Agree with you about those shortwaves but it would be nice however unlikely if one of those would be the right side of marginal for snow here in the pennines but also with hurricane force gusts over 100mph so i could see a blizzard in the true sense of the world.

[nick sussex]

2 minutes ago, feb1991blizzard said:

Agree with you about those shortwaves but it would be nice however unlikely if one of those would be the right side of marginal for snow here in the pennines but also with hurricane force gusts over 100mph so i could see a blizzard in the true sense of the world.

The thing is Feb , the strongest winds would be on the southern flank of any shortwave and in the milder air . So perhaps just settle for the snow ! 

You might get blizzard conditions without the shortwave and in the PM flow , the winds look very strong even without the possible shortwave .

I personally don’t like these set ups as those developing shortwaves could go anywhere and I’m wind phobic ! 

The worst storms we’ve had down here have been in these types of set ups . Anyway that’s well into FI . Let’s see whether those pressure rises to the north and ne can survive .

[feb1991blizzard]

1 minute ago, nick sussex said:

The thing is Feb , the strongest winds would be on the southern flank of any shortwave and in the milder air . So perhaps just settle for the snow ! 

You might get blizzard conditions without the shortwave and in the PM flow , the winds look very strong even without the possible shortwave .

I personally don’t like these set ups as those developing shortwaves could go anywhere and I’m wind phobic ! 

The worst storms we’ve had down here have been in these types of set ups . Anyway that’s well into FI . Let’s see whether those pressure rises to the north and ne can survive .

Yes - the sting jet is always just south of the backbended front isn't it.

[Nick F]

18 minutes ago, Mike Poole said:

GFS out to day 9, T216, and it is consistent with things we've seen recently including the clusters, well one or two of them anyway, see my earlier post. 

There are clearly two issues with this, stormy weather and the potential for any snow, however fleeting.  A stormy period seems to be massively increasing in likelihood, but re this run, will there be any snow at low levels?  With T850s lower than -8 I would feel hard done by if precipitation wasn't snow.  At -2C I'd be relying on certain things maybe evaporative cooling, and that won't happen in a raging gale, so even if the GFS -6 uppers are encroaching, it is marginal - and my definition of marginal is some places will see snow, some places won't.  

If this sort of thing makes it into the reliable, then we can start to make predictions about snow, and it will be fun to do so, but at the moment we are just waiting for this possible NW very windy flow to get into the reliable.  

Not just T850s. Heights, thicknesses and dew points also need to be considered. Long sea track of Polar maritime flows from the W or NW that aren't direct from the arctic often struggle to have low enough dew points (0C or below) at lower levels on arrival to the UK to support snow to fall to low elevations, due to being well-modified by SSTs. However, low geopotential heights and thicknesses, which indicates a lower freezing levels, and heavy precip can compensate for this. But like you say, a howling gale doesn't help with evaporative cooling, need calmer conditions for that work generally.

You can have what looks like favourable T850s for snow with other set-ups, but if the surface dew point is too high, snow's not going to reach the ground.

[nick sussex]

Anyway let’s just say one of these shortwaves turns up . 

I think the interest is more likely to be on could it deliver snow. These set ups are often marginal because there’s not the depth of cold you might see if say you had a strong block and a low running into cold air in that situation .

So you’re likely to need some elevation and some evaporative cooling . So on the northern flank of that , and hopefully in a slacker flow which could happen .

But any snow can’t be forecast too far ahead given the marginal set up.

[carinthian]

Hi ,different run from GFS in the outer time span. Fragments the winter jet in mid-Atlantic and shows westward advancement of a big Siberian High is progress. Winters final fling with a beast from the east ? Now that would be the biggest surprise of all ! 

C

[MATTWOLVES 3]

Wild 12z ensembles for sure... Looks like a complete battleground of air masses... Warm air to the South and serious cold to the North, as to be expected has we progress into the final 3rd of Winter... I can see perhaps some interesting situations popping up at short notice moving forward... Something at least to keep an eye on. 

Edited February 1, 2020 by Mattwolves

[Kirkcaldy Weather]

30 minutes ago, Nick F said:

Not just T850s. Heights, thicknesses and dew points also need to be considered. Long sea track of Polar maritime flows from the W or NW that aren't direct from the arctic often struggle to have low enough dew points (0C or below) at lower levels on arrival to the UK to support snow to fall to low elevations, due to being well-modified by SSTs. However, low geopotential heights and thicknesses, which indicates a lower freezing levels, and heavy precip can compensate for this. But like you say, a howling gale doesn't help with evaporative cooling, need calmer conditions for that work generally.

You can have what looks like favourable T850s for snow with other set-ups, but if the surface dew point is too high, snow's not going to reach the ground.

Exactly, I had snow from this back in January 2018    with 850 hpa temps of around -5/-6 although usually -8 is a safer bet for snow but as you say temperatures and dew points will be crucial. Marginal snowfall events look possible certainly up here (possibly extending further south at times depending on the tracks of lower pressure)  

[Mike Poole]

GEM take on the potential incoming storminess, T240:

Seems there is consensus forming that' the flow will be north of west at least, but for many that will only mean driven rain with a few frozen bits in it.   But the interest remains as this one gets firmed up...

[nick sussex]

There’s still a divergence amongst the GEFS regarding the PV.

Some still keep the rounded PV blob to the north. And others have the PV more disrupted .

The latter is crucial to have any chance of some colder conditions . I’m going to start my t shirt print run . Say no to the blob ! 

 

[Cuban Zebra]

Out in FI you can pick up the changes in the pattern. 
I’m pretty sure in the next few runs we’re going to see some real coldie eye candy charts!!

[Singularity]

2 hours ago, Interitus said:

Don't forget in the deep lows the 850 height is much lower, the temps don't need to be as low.

Good point, admittedly I was working on the basis of an actual of at least -7*C 850 hPa, which I've found to be required here when the SLP is sub-980 hPa.

Further north the SLP looks potentially a good deal lower at times, such that as high as -5*C, maybe even -4*C could suffice for low levels (with high ground having even more leeway). Depends on how much vertical mixing has occurred, of course.

Regardless, the point of my post still stands - snowfall is unlikely to be as widespread as GFS keeps depicting.

I can see some decent falls, even accumulations in places, on high ground - but for low-levels, I remain to be convinced that there will be much to shout about, at least in England... Wales has a better chance and Scotland even more so. Could be some impressive accumulation rates up in the Scottish mountains - and some of the higher Welsh ones too.

Assuming, that is, the Euro high isn't being underestimated yet again and to the point that the flow turns out to be westerly, rendering all this discussion irrelevant - we've been there before! Oh how I miss being an optimist - years of hardcore science have weathered it away .

[Mike Poole]

ECM goes the warmer route, no cold mixed in with this, just the dross, T240:

Remember both this and the colder solutions were in the mix on the 0z clusters, for most of us in the south, it may be a question of wind driven rain vs wind driven rain with some frozen bits in it, further north and with altitude it could be a more important difference, more runs will hopefully firm this up...

[Nick F]

11 minutes ago, Mike Poole said:

ECM goes the warmer route, no cold mixed in with this, just the dross, T240:

Remember both this and the colder solutions were in the mix on the 0z clusters, for most of us in the south, it may be a question of wind driven rain vs wind driven rain with some frozen bits in it, further north and with altitude it could be a more important difference, more runs will hopefully firm this up...

The problem is a very strong westerly jet around an intense PV will always spawn secondary lows out west which will pull the upper trough axis out west too, pumping milder air in across the UK. Difficult sustaining Pm airmass with such an intense TPV. 

Edited February 1, 2020 by Nick F

[carinthian]

Well ECM delivers the worse winter chart of the season across virtually the whole of Europe (for lovers of cold anyway ) and there has been plenty. Just hope this is the extreme of its output.

C

[Mike Poole]

Well the ECM 12z mean is still in favour of bringing this tirade of utter crap from north of west, and that goes with GFS and GEM, but against its op run.  Mean and spread T240:

There's some uncertainty but not that much upstream to be honest, but as you can see what uncertainty there is has the UK in its sights, as almost always!!  The little kiggle on the SW of the uncertainty chart is what the op run saw I would guess, just enough of a dig in there out SW to have the jet SW- NE over us on that ECM op run, but at the moment that looks like the minority solution, the storminess with colder air more likely at the moment.

Edited February 1, 2020 by Mike Poole

[nick sussex]

The ECM is utter garbage for cold .

Flat as a pancake and one nasty PV blob to the north . At least as opposed to other winters we’re not seeing news items of snow everywhere else because winter in the NH as a whole hasn’t arrived .

After a bit more promise from the GFS the ECM has really harpooned hopes of at least some PM flows .