Can't understand ...I thought we were in for a prolonged cooler spell... has this completely evaporated now?

Shame on you, cherry picking one days chart from one model     But the GEFS Control does have a nice Scandi High developing a couple of days later ....    

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During the last 'cold' spell, the Met Office forecast maps were also useless.

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Amidst all the talk of snow, when it ends, big disagreement between models at +240h etc, I think a look at the ensembles is a sensible step. These suggest that from midweek, a Northerly plunge will cool things down for us all.  Snow details etc - no point in looking at predictions more than 24 hours out, and even that can be pretty uncertain.

Anyone who takes any precipitation map and gets excited about it days before the event needs to have a word with themselves 

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 The reason I did was because increasingly this winter I've seen a few posters cherry picking cold charts from the ENS. Perhaps I should have added a  to my post. 

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Exactly, we are still 3 days away from the start of the next cold spell and already everyone is anguishing about how and when it will end ....

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As if that ever happens here 

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I don't think so Neil. I have been looking for a couple of minutes and cannot see one.

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A couple of minutes......

 

Liar.

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Afternoon all. Been a regular viewer and visitor of this site and I've got to say, it's a great read and very informative. 🙂 however there are a few windup merchants & sometimes it is best to ignore certain implausible unreasoned biased ones. Anyway, keep up the good work 👍 🙂 With regards to wed night onwards...it will without doubt, turn much colder & the fact that warnings ⚠ are already out..(3 to 4 days in advance) confirms the changes ahead. There is also mention on t.v forecasts, so all I would say is keep tuned to the forecast, for details and developments. There will without doubt be instability within the air flow, so significant disturbances are more than likely to crop up, on the northerly..so due to the inability of being able to accurately pick these up yet, these will be identified by Tuesday evening-ish. All I would say, is that the whole country is at risk of seeing some ❄ . it may be in the form of showers, but the spine of the country is probably at highest risk. For those that don't see any, at least the weather is turning interestining, unlike last years bore-fest of a snowless Winter! U can't make everyone happy, so just enjoy what u get, instead of looking for an end to what hasn't even occurred yet! Hopefully northern blocking enters the model output, over the coming days & results in more excellent analysis here. I, probably like most, enjoy the unpredictable and severe weather, when It occurs, so let's hope this week pays dividends. J

IMBY alert - a cold (yes cold) WNW'ly is as good as it gets for here. 

But yes, it needs to be cold enough. I'm not convinced yet. 

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It's interesting how a lobe of raised theta-e and 850ts gets trapped on the NE flank of our developing low next week and then gets directed round and down across the UK on Fri/Sat.
This could scupper potential snowfall although it may enhance ppn so one to watch.

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http://www.wetterzentrale.de/pics/Rtavn1201.gif  

Yes it's looking far more potent than last weeks limp affair with a very unstable and cold PM airmass which should delive some considerable snow amounts for many in the NW, more so those with elevation. 

Just having a quick skeg through the charts while I'm waiting for the dinner to be ready.

Is it too soon for me to say that the latest GFS output does have snow potential dripping off it? Can you hear that squeaking sound? That's the sound of me backpedalling and admitting that perhaps, just perhaps I'll be getting to see some wintriness between the 5 to 10 days range (or at least I have better luck than the last time).

Of course, it begs the question on how long that cold snap will last before high pressure takes a hold as we go into the second week of February but I am falling into the trap of trying to seek a breakdown to a cold snap that is yet to take place in the first place!

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I imagine this is what a lot of my non-weather pals think of when I start going on about 'weather models'.

 

As far as the computers go, I'm keeping an eye on this little feature embedded in the deep cold flow Wednesday night, as should anyone across the far south who would enjoy waking up to a bit of lying snow Thursday morning:

No point going into details as the track could change. The past 6 or so GFS runs have shown some notably enhanced precipitation rates for this sort of time, and always across the same region - right across all of the southernmost counties.

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I have been wondering about that area of 850's on Friday/Saturday too Neil. It's not a warm sector being acquired, as there's no developing LP involved, so it will come down to how well it influences surface conditions. Dew points peak at 0*C for the majority on Friday so evaporative cooling in any heavier precipitation could do the trick.

Saturday depends on whether we see an Atlantic shortwave interfere with things across England and Wales as per the GFS 06z op run. The 12z still has the feature but it tracks further south, creating a rain event across Cornwall and Devon with a marginal snow event extending SE from Wales as of +144 hours. Three hours later it's snow for the vast majority of locations across the SW'rn third of the UK.

That happens with 850's of -3*C or so... goes to show that other factors - particularly dew points and theta-E - serve as better indicators.

 

Now although the details are not to be taken seriously, the GFS 12z can be used to make a very good point about next weekend:

Theta E is the equivalent potential temperature and a great parameter for identifying different air masses.

Here, the wedge of light blues brushing the SW/S of the UK is the warm sector of the shortwave from the Atlantic, which we really want to avoid being underneath. Yet being on the periphery can work out well for heavy precipitation falling as snow.

For this, the 12z evolution is far better than the 06z because not only does it track further south, it doesn't develop so much, so the northern edge of the warm sector remains flatter i.e. drawn out west to east with little intrusion northward.

The cold air to the east is then able to be drawn in to the north of the shortwave, providing the undercut needed to keep precipitation as snow - that cold air may not seem to be up to much in terms of 850's, but if you trace it back to its origin, it turns out to be a mix of the polar maritime air from the NW with a fair bit of cold continental air from Central Europe - with the low dew points needed for an effective undercut event.

 

Worth noting how compared to earlier this week, the LP has far better orientation for encouraging that cold air to feed across the UK from the east. That was sorely missing during our last round of potential.

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It is also interesting to see that the GFS 12z op run so far is much more like earlier ECM output than previous runs have been.

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http://www.meteociel.fr/ukmo/runs/2015012512/UN144-21.GIF?25-17

Decent again from UKMO

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Indeed Michael

http://modeles.meteociel.fr/modeles/gfs/runs/2015012512/gfsnh-0-210.png?12

At this point on the GFS6z we had the Atlantic running in

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And much closer to the 06GFS control. Could have the first Scandy height rise on the OP in low-res.

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Yes, although it did not really happen on this run I think it may be something to watch out for in the output in coming days.

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The whole ukmo run is very good and it's the best GFS for awhile stays cold until day 12. 

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No ignoring the continued disagreement between GFS and UKMO regarding the extent to which the LP is organised next weekend.

GFS is a lot messier but delivers a good amount of precipitation that largely falls as snow, while UKMO looks better for a less stressful ride but perhaps rather lacking in precipitation away from windward coasts - but not necessarily.

Or perhaps we'll see a bit of both... a fairly extreme example on offer from GME this evening:

The LP is notably deeper by +84 hours than GFS has it (brings one heck of a cold blast from the west!) so a little hard to take seriously, but it shows how small features can develop in the cold, unstable flow (just look at all those kinks in the isobars!).

 

I've been thinking a bit more about the situation with the 850hPa temps seeming a bit on the high side for a northerly at this time of year. Among other things, the deeply unstable conditions seem a likely explanation; there's a lot more vertical mixing of the air, which means there's less of a temperature change between the surface and the 850 hPa level.

Combine this with the 850 level being closer to the ground thanks to low heights (drops a hint as to what low heights actually means), and the 850hPa temps are likely to be a fair bit closer to the 2m temps than you'd expect in a 'classic' northerly, which tends to see a a ridge building in quite fast, reducing the instability.

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