Wales Cymru Cold Spell Regional Discussion

[TonyH]

In my defence m'lud I present this quote from my weather guide issued Sunday just-

The trough bringing the rain and showers early in the week clears through on Tuesday night with cold northerly winds behind it, so a possibility of showers turning to sleet or snow in places before Wednesday morning?

[georgiedre]

some heavy showers around now here in nw wales and yes some sleet and hail mixed already... hope we get snow!!!!!!!!!!!!!!!

[swales]

2.2c here with a DP of 0c.

Showers incoming about 10 miles away, hopefully might see a flake or two but I imagine temp will start to rise as it approaches

[mikeocarroll]

I use Snipping Tool, comes free with Windows , just get what you want on screen, and save it to JPG or whatever.

Or you can just hit the save button above the images.

I call that 15-0 to Tony H.

Much easier.

Thanks!

[Marcus_surfer]

Bits of hail in these showers 3.5C.

[mikeocarroll]

Thought I'd post the GFS 12z ensemble charts this evening as they are quite interesting IMO:

As you can see there is a very wide spread beyond day 5-6 which just shows how we can't really have any firm idea about what will happen after that. The runs seem split about 50:50 between fairly mild and extremely cold. Not quite sure what evolution is happening in the crazy purple (edit: might be brown actually) run - starts of milder than the rest and then in deep FI dives towards crazy cold.

Deep cold is a flip of a coin then, which is much better odds than usual, but still nothing like nailed on. In the favourite phrase of weather enthusiasts everywhere, more runs needed!

Edited December 4, 2012 by mikeocarroll

[marclt]

A few intense showers here, with some soft hail at the moment. Temps 3.4c.

[TonyH]

Plain heavy rain showers here should be a little more interesting past the midnight hour.

[J10]

I think tonight ECM is a warning call for everyone to be honest.

A bit of an Ouch.

[marclt]

I think tonight ECM is a warning call for everyone to be honest.

A bit of an Ouch.

really... it's a bit far out... ?

[andymusic]

really... it's a bit far out... ?

It doesn't matter - all models are showing EASTERLIES - EASTERLIES - EASTERLIES - these are massive great big warnings that we are about to get the big one with snow and freezing temps - anyone can see that surely!

edit:- opened door to take away guy earlier - it was perishing cold - like opening the door to my freezer - so when these showers get here - wouldn't like to guess what we're gonna get - could well be something wintry - up here in the crows nest - aye aye Jim Lad - ha ha ha ha - Polly want a cracker?

Looks like we got all of Wales on here tonight + a few sheep I wouldn't mind betting ha ha ha ha lol!

Edited December 4, 2012 by andymusic

[mikeocarroll]

I think tonight ECM is a warning call for everyone to be honest.

A bit of an Ouch.

I assume that the 50% of GFS members going for mild (or at least non-cold) have an evolution similar to the ECM. Will be interesting to see the ECM ensembles later.

Re: rain/hail reports, the precip across west Wales is much more intense than was forecast - by the NMM at least - didn't look to closely at the others. Doesn't signify anything I don't think, except to show that modelling precip is difficult even at less than 24 hours. Would be great if we got more precip than expected either tomorrow morning or tomorrow evening, as both look good for some sleet/snow otherwise.

[TheWeatherGirl]

Am in Caerphilly, any chance of some cold white stuff here? Or are we too far south?

[whiskers]

do you really think easterlies?or just winding us up? if we did would we get snow for xmas? whats the odds

[Ukwoody]

It doesn't matter - all models are showing EASTERLIES - EASTERLIES - EASTERLIES - these are massive great big warnings that we are about to get the big one with snow and freezing temps - anyone can see that surely!

edit:- opened door to take away guy earlier - it was perishing cold - like opening the door to my freezer - so when these showers get here - wouldn't like to guess what we're gonna get - could well be something wintry - up here in the crows nest - aye aye Jim Lad - ha ha ha ha - Polly want a cracker?

Looks like we got all of Wales on here tonight + a few sheep I wouldn't mind betting ha ha ha ha lol!

Not when you're this far West Andy!

[SnowStorm(Jamie)]

Well its about time to do the full update with regards to Wednesday mornings possible snow event over Wales.

In this analysis i will try and factor in a few models including NAE, GFS, UKMO + FAX charts (12Z data).

So lets take a look at the setup as shown on the NAE. We see how todays flow has come from the NW:

http://expert-images...120415_0412.gif

By Midnight tonight that area of low pressue drops southwards introducing an even colder source of air from the NE, this low is also our source of precipitation shown on the NAE by midnight:

http://expert-images...120500_0412.gif < Note the colder upper 850hPa air moving in towards our north.

During the early hours of the morning we see the occluded front push through so an enhanced area of precipitation likely as shown on the NAE charts below:

http://expert-images...120503_0412.gif < 15h

http://expert-images...120506_0412.gif < 18h

http://expert-images...120509_0412.gif < 21h

Notice how the front is heavier to the east over east Wales something which the NAE was showing yesturday. Is this consistent with current GFS model guidence?

Lets take a look at the GFS precipitation charts (12z) for the same timeframes:

http://cdn.nwstatic....2/15/ukprec.png < 15h

http://cdn.nwstatic....2/18/ukprec.png < 18h

http://cdn.nwstatic....2/21/ukprec.png < 21h

And the UKMO 12Z precipitation chart:

http://www.meteociel...8-594.GIF?04-18

Looking at the above data NAE & GFS 12Z i think theres is good enough consistency to say that the front will be heavier towards the east and less organised towards its western flank. UKMO signal not as clear as this is not run at higher resolution but it does show the general idea of a front pushing southward.

Precipitation is alsways hard to pin down and can change so it is also worth watching the radar. Now what about the upper 850hPa temperatures and are they at or below -5C which is what is generally the figure we need to look for when discussing snow possibilities.

Again using the NAE 12Z data for the same timeframe as precipitation moves through:

http://expert-images...120503_0412.gif < 15h -5c to -4C upper temps into N & E Wales

http://expert-images...120506_0412.gif < 18h lowering further with -4C temps across south Wales -6/-5C across Mid, N, E

http://expert-images...120509_0412.gif < 21h By this point -5C upper air covering most of Wales.

GFS and UKMO agree with the -5C upper air temps moving across Wales:

GFS @ 21H : http://cdn.nwstatic..../h850t850eu.png < -5C upper air right across Wales

UKMO @ 18H: http://www.meteociel...U18-7.GIF?04-18 very simular with the -5C line lying roughly across South Wales.

Looking at the sub 528 Dam air during the same period on NAE:

http://expert-images...120503_0412.gif

http://expert-images...120503_0412.gif

http://expert-images...120506_0412.gif

As you can see the colder air floods more or less south and west by early morning and the whole of Wales is in sub 528 dam air by 21hours (Early wednesday morning)

GFS in agreement also: http://cdn.nwstatic....hgt500-1000.png

We must then look at the dew points that the NAE is modeling for the exact same period as precipitation moves through in the early hours:

http://expert-images...120503_0412.gif < 15h - Dew points above freezing for Wales although notice the lowering to NE.

http://expert-images...20506_0412.gif <18h - 0C down to -1C in E/NE Wales when Precipitation is present.

http://expert-images...120509_0412.gif < 21h - Below freezing -1C to -4C across Wales while again precipitation is passing through - Remember heavier precipitation focus is shown towards east Wales.

So what about the temperatures by early morning (21hours) on the NAE:

http://expert-images...0509_2_0412.gif

As you can see Sub Zero central & East Wales/ 1C around N Wales/ 1-3C around southern Wales roughly then higher towards the SW at around 4C.

And of course lastly the MO fax chart for tomorrow:

http://www.meteociel...ax24s.gif?04-12

By this stage you can see the occluded front has pushed south of the UK and we are left with a cold North flow with a ridge of high pressure building in from the west.

Taking all of the above into consideration the greatest chance of Snow will be in the E & NE Wales probably a covering in some places, even some snow falling in inland parts of SE Wales. For South Wales i think a wintry mix more likely under what is modeled as light precipitation perhaps snow to higher ground, Simular story for West Wales where tempeartues are slightly higher so mostly rain with snow to higher ground.

[andymusic]

Not when you're this far West Andy!

admittedly as you're in pembs it could - and i say could be more difficult - but not impossible - once the cold air is in then any precip from any direction will be wintry (snow hopefully) + once the cold air is in - any half hearted attempt by the atlantic to throw a front against the cold will result in copious amounts of snow for us in Wales (usually what happens) and this can be reapeated a number of times as long as the block holds on in place - and strong blocking is progged - so we all have a chance to see snow in these set ups! I've seen snow streamers in the past as well make it all the way to Wales from Eastern England - very heavy snow too - so that's possible also - showers are knocking on my doorstep - will let you know what comes out of them shortly!

[alijoe]

Idon't like this rollercoaster.... seems like your given something good in one hand and then another output takes it away :-( all bit far out i know, but would love to be at the point where it all looked great and we could just sit back and count the days or hours to all the good stuff. Feeling like it may end up in a dissapointing way this winter..... really hope not. good luck to everyone tommorow though

[alijoe]

Watching football and the snow is falling in croatia lol..... mind you very very wet snow and rain, maybe we will do better lol

[Wales123098]

Sleeting here right now. I'm up my gfs in Llantrisant about to head home soon. Car says 2c. I expect it's a degree colder where I live. Very heavy

[Gavla]

Is this chance of snow tommorow our main chance in wales this week? Isnt there a more organised band of ppn progged for us thursday? Surely this would more likely be snow with the cold already in place. Hopefully someone can correct me. Looking good long term just eager for snow now its been too long lol.

[alijoe]

Snow update..... hammering it down in croatia , cant hardly see the pitch now lol. oh i really really hope we get some this winter, really am such a big kid and find snow amazing :-)

[PeteB]

2 degrees here and pouring down with rain. Wouldn't be surprised to see The Clwydian range covered in snow by the morning.

Pete

[andymusic]

gonna have to admit defeat on this one right now - it's rain - yet reports of sleet just up the road lower down in llantrisant is weird! - but I'll be patient - snow is not far away I can "smell" it

[alijoe]

Hmmm. dont admit defeat andy, your my only hope lol