Ireland looks like getting pasted!

Perfect example of this was sometime in 2004 (may have been 2003). I had an afternoon meeting just north of Stoke. When I set out from Manchester city centre, it was snowing and just beginning to settle. Decided to take the scenic A34 south instead of the M6 and it was a fantastic journey, snowing heavily all the way and snow settling deeper. About 5/10 miles short of Stoke and the traffic ground to a halt. After sitting there a good 5 minutes, I learned that busses & lorries were stuck all over the place at the bottom of hills with Stoke & surroundings gridlocked. Called the client to put the meeting back to the following day, then turned round, thinking of making the most of the snow back home. Snow still bucketing it down, about 12cm deep where I was.

Crawled back toward the M6 at J17 and, almost as I reached it, the snow became sleetier and thinner on the ground. This only about 5 miles west of the A34. A few miles north on the M6 and it was a sleet/rain mix with only a thin slushy dusting, and that's how it was all the way home.

After a whinge on TWO, it was explained to me that a warm sector to the west of the low had skirted down the west of the UK. The boundary between deep snow and nothing was literally just a few miles - a rough guide that day was west of the M6 = sleet; east of the M6 = snow

I actually think there'll be an element of this for the Wed-Fri period

Yes they're an absolute bugger - particularly as they can look so enticing but usually have a sting in their tail. I'm thinking us lot down at low level in the NW could be looking at a lot of those polystyrene balls as opposed to the fluffy snow we crave - as you mention the transition in marginal air is usually around the M6. Still positive about Weds eve though. I too will be very suspicious of any organised feature appearing on the models/radar given the 850s! 

Anyway all that discussion should probably be on the dedicated thread 

RE the output, GEM at 240 looks nice, but it's been all over the place so probably best ignored. 

Just for fun...?

The mysterious 'NetWx-MR' model makes a lot more of Thursday night's embedded troughs than any other output I've seen:

This output seems to be based on NMM (see lower-right corner) but with a lower resolution than usually seen on sites like Meteociel.

The enhanced precipitation amounts are a curious feature. Perhaps there is some modification by the professional forecasters working for the parent site.

Anyway, it makes for entertaining viewing given that most of it falls ahead of the less cold air feeding down from the NW on Friday.

Any idea of what that mysterious model gives for the 850's in the above timeframe? And does it do DP's?

a fergie post on NW -------------  Arguably the key mesoscale development we are watchful for is showing within EC-ENS Mon-Tues, with low development running SE from Iceland to SW UK. Recent EC runs have hinted at this and we give 30% PROB currently. This possible, but still low-likelihood outcome, is reflected well in ENS spikes for PPN in Reading and Exeter plumes and a number of stamps both yesterday and again in 00z suite. 

Interesting - I'm going to be in North Devon over the weekend and have to drive back across Exmoor on Tuesday.

Hope the GFS 12z run brings the high pressure back at the low res end of the output, the 6z looked like the model woke up in a foul mood this morning.

The 06z NMM still giving Central and North Wales a lot of snow, still can't understand why it is not in Met warning.

http://modeles.meteociel.fr/modeles/wrfnmm/runs/2015012706/nmm-1-49-0.png?27-13

Rain for the SW though so can see why they have been excluded - according to this anyway.

dp's just not good for the South:

http://www.theweatheroutlook.com/charts/gfs/12_45_ukdp.png?cb=361

What does fall on Thursday south of Manchester looks to be wet rather than white.

Although better by lunchtime:

http://www.theweatheroutlook.com/charts/gfs/12_48_ukdp.png?cb=928

All relative of course, but to guarantee snow if charts show -2 (as well as other parameters falling into place) it should be white rather then wet.

Er...no. Worse by lunchtime

That is the kind of dp chart we want:

http://www.theweatheroutlook.com/charts/gfs/12_135_ukdp.png?cb=992

http://www.meteociel.fr/ukmo/runs/2015012712/UN144-21.GIF?27-17

UKMO is better than GFS. Looks like cold will be sustained

Nice chart - lots of potential ...   for frost down here.

The GEFS snow row for my lat/long gives 100% snow risk for tomorrow afternoon and evening.

The MetO forecast says heavy rain at lunchtime with 6C followed by dry and cooling off to 2C - and they they have dropped the S word completely.

Now which do I believe?  It's a tough call 

We still end up with a cold surface high. Could have been a lot better had it not been for one spoiler shortwave

http://modeles.meteociel.fr/modeles/gfs/runs/2015012712/gfs-0-240.png?12

I've got 90%, 25%, 80%, 90%. 65% from Wednesday evening through Thursday.  I'm wondering also.

Very rare have i seen a snowshower from a northwesterly.  I remember a period in the 1990s' - probably around 1998ish?  and i remember leaving school and seeing snow showers drifting in down the road.  it would go very misty in the distance then like a curtain approaching us woud deliver about 20 mins of very dry small snow flakes.

Down the road in chester they had proper 50p sized clumpy snow flakes.  Coastal areas never get true snow showers.

That we can agree on!

I've had settling snow from a positive DP at 0.3c air temp of 0.8c not up a hill and 4 miles from the sea.its not the be all and end all.

The dew point is the temperature to which the air temperature has to fall in order for the air to saturate.

Saturation tends to be associated with precipitation, so the dew point gives a good idea as to what the air temperature will become provided precipitation is persistent enough. For this, a value of around zero is usually sufficient provided it is as cold or colder at higher altitude.

The dew point has its limits as a predictor though - the drag caused by precipitation on the air can pull colder air down from higher altitude, simultaneously lowering both the dew point and the air temperature. This requires the precipitation to be on the heavy side to be effective all by itself.

Evaporation of precipitation in drier low-level air can lower the air temperature, this being the 'evaporative cooling' process that gets mentioned from time to time. Of course you then need further precipitation to mix out that dry air and bring the rain or snow to the surface.

Downdrafts associated with strong convection can bring colder air down regardless of precipitation rates, but this is less common in the winter months.

For tomorrow night into Thursday, no two models seem to agree on what the dew points will be from Bristol southward. 

GFS is close to zero for the most part except for right along the coasts, Euro4 is generally a degree or two lower, but NMM is degree or two higher!

In other words... inconclusive 

Not when combined with this precip chart it ain't!

http://www.theweatheroutlook.com/charts/gfs/12_135_precipratec.png?cb=680

Age old prob down here -   Cold enough to snow and no "moisture".  The second it's too warm to snow and we get a deluge