Wales - Regional Weather Discussion

[SnowStorm(Jamie)]

The colder upper air temperatures of -5C and the sub 528DAM line just about cover Wales on the GFS 06z run:

http://hw.nwstatic.c.../h850t850eu.png

http://hw.nwstatic.c...hgt500-1000.png

However not for long as some slightly milder air begins to filter in from the west for Tuesday. There is still uncertainty regarding the frontal wave or low that is running SE on Sunday - So changes can be expected as the models pin down details on this features intensity.

[keithlucky]

The met office fax should be interesting over the next few days to see how theHP develops over greenland and what track the LP takes Saturday Sunday as it crosses UK.

[Gorath]

There's a light covering of snow on the Carneddau range now, apparently. Not much, but it is nice to know that despite such a warm autumn, winter is on it's way finally.

[J10]

Continuing the previous theme.

If people wish to keep trends to see how things transpire.

This is Sunday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Monday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Tuesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Wednesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Thursday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Sunday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Monday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Tuesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Wednesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Thursday's thickness chart for 6am Next Mon http://hw.nwstatic.co.uk/gfsimages/gfs.20111201/12/90/hgt500-1000.png

The progression seems clear, with the 850Hpa -5 line and 528 dam thickness edging ever north. However this is more due to a slight delay in the cold edging south, moreso than the cold not finally pushing south. This does mean though any snow is less likely than yesterday's charts,as the colder air does not push through during the morning.

At the current rate, some wintriness possible for quite a few, hail, sleet and perhaps wet snow, if the cold air reaches by early early Monday morning.

Looking further ahead further chances of wintriness but too far away to look at seriously.

[Snowmadsam]

Continuing the previous theme.

If people wish to keep trends to see how things transpire.

This is Sunday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Monday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Tuesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Wednesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Thursday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Sunday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Monday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Tuesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Wednesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Thursday's thickness chart for 6am Next Mon http://hw.nwstatic.co.uk/gfsimages/gfs.20111201/12/90/hgt500-1000.png

The progression seems clear, with the 850Hpa -5 line and 528 dam thickness edging ever north. However this is more due to a slight delay in the cold edging south, moreso than the cold not finally pushing south. This does mean though any snow is less likely than yesterday's charts,as the colder air does not push through during the morning.

At the current rate, some wintriness possible for quite a few, hail, sleet and perhaps wet snow, if the cold air reaches by early early Monday morning.

Looking further ahead further chances of wintriness but too far away to look at seriously.

Would it be possible for western Wales, if a Pembrokeshire dangler was to form

[SnowStorm(Jamie)]

After checking the GFS 12Z it looks as if the cold thrust from the NW comes slightly later than the 06z run and there are differences on how they handle that frontal wave running SE on the 12Z its further North and we see allot of heavy rain moving in to Wales especially in the South while on the 06z run of the GFS it was further South.

Note the diffrences on the 12Z and 06Z precipitation charts for the same time:

http://hw.nwstatic.c...2/81/ukprec.png <12z

http://hw.nwstatic.c...6/87/ukprec.png <06Z

Again we see the colder -5C upper air come over Wales allong with the SUB 528DAM line:

http://hw.nwstatic.c.../h850t850eu.png

http://hw.nwstatic.c...hgt500-1000.png

Also adding in the dew points for later on Monday & as we head into Tuesday:

http://expertcharts....120518_0112.gif

http://expertcharts....120600_0112.gif

Generally around 0C in N. Wales and Mid Wales, above freezing around coastal areas - So if any sleet and snow showers are to be expected it will largelly be confined to N Wales and any showers that push in to Mid Wales, however the western side of the Cambrian Mountains will be most prone to showers in this airflow.

Edited December 1, 2011 by SnowStorm(Jamie)

[J10]

Wind direction is not Northerly enough for a true Pembrokeshire dangler to form, however some showers seems likely Monday am, some wintriness possible as per above comments. At this stage snow is odds against, but the odd flake cannot be ruled out at this stage, lying snow remains very unlikely apart from the mountain tops.

A more accurate Dewpoint chart is available in NW Extra and this is the chart http://nwstatic.co.u...2ed1fafa6cef66; (does this link work)

However this is also a function of Ground Temps,and GFS does tend to overstate coastal influences on temp, so that must be considered.

[SnowStorm(Jamie)]

A more accurate Dewpoint chart is available in NW Extra and this is the chart http://nwstatic.co.u...2ed1fafa6cef66; (does this link work)

Cheers for that, yes the link works and it gives a better view of the Dewpoints - Inland parts of NW/N Wales could well see some snow showers if those dewpoints remain low enough. Further South and West its looks more marginal

[J10]

Cheers for that, yes the link works and it gives a better view of the Dewpoints - Inland parts of NW/N Wales could well see some snow showers if those dewpoints remain low enough. Further South and West its looks more marginal

in which case

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew (noon)

http://nwstatic.co.u...c8ef;file=ukdew (3pm)

http://nwstatic.co.u...c8ef;file=ukdew (6pm)

http://nwstatic.co.u...c8ef;file=ukdew (9pm)

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew

http://nwstatic.co.u...c8ef;file=ukdew (06Hz run)

Certainly agree with the marginal comment. Things will change before Monday, and probably turning more marginal by the day.

[welshgritter]

in a nutshell.....................i this the start of winter? or is it just showing us its not too far away?

[Gorath]

I'm claiming it as the start of winter proper.

There seem to be a few likely blasts of cold wind for at least the next week. And will hopefully carry us on to the middle of the month, when a few forecasters believe this otherwise unseasonable warmth will at least start to fade away.

[Blackjack]

Wow. Is it me or are the the latest models runs throwing out a very wintery mix for next week?

On second looks it might just be me

Edited December 1, 2011 by Blackjack

[andymusic]

Wow. Is it me or are the the latest models runs throwing out a very wintery mix for next week?

On second looks it might just be me

nope it looks like winter has finally arrived and it's flippin cold out tonight too!

[welshgritter]

Happy Days!

[Cwmbran Eira]

proper chilly this morning. 1st real frost. Nice and white.

Looks very interesting over the next week or so. Considering many people thought that we couldn't possibly have a 4th colder than average winter it's looking like a real possibility.

[TonyH]

The overall pattern does not favour a cold December.

What January and February brings we will have to wait and see speculate

Certainly pretty cold early and again later next week. No freeze as maxima will be well above freezing, but frosty nights are likely. Snow however, does look restricted to high ground, say above 300-400 masl, and even there coverings will be temporary. Many of us in mid and north Wales could see the tops white for the first time this season in the next week though. Pretty typical December weather all in all.

Edited December 2, 2011 by TonyH

[DeepSnow]

It was a cold morning, low of 1.4C here and its now 6.5C! Much colder than of late. Even if us in south wales don't see much if any snow this month, I'm sure we will see something during the rest of winter!

[SnowStorm(Jamie)]

Met Office fax chart for Monday is shown below:

http://www.meteociel.../fax/fax72s.gif

A NW flow with sub 528 DAM air south of Wales, latest GFS runs 0Z & 06z have also shifted this slightly further southwards so going by this mornings Fax charts and latest GFS guidance for Monday showers will fall as snow over the hills perhaps as low as 250M in heavier ones with increasing potential for snow showers to lower levels of North Wales during the early hours of the morning.

[J10]

http://forum.netweat...t-2nd-december/ is the latest Snow blog for the next 7 days for the Alps with the usual synoptic detail.

Met Office fax chart for Monday is shown below:

http://www.meteociel.../fax/fax72s.gif

A NW flow with sub 528 DAM air south of Wales, latest GFS runs 0Z & 06z have also shifted this slightly further southwards so going by this mornings Fax charts and latest GFS guidance for Monday showers will fall as snow over the hills perhaps as low as 250M in heavier ones with increasing potential for snow showers to lower levels of North Wales during the early hours of the morning.

Providing the GFS doesn't downgrade further, which is a very big IF. But so far this cold spell has not downgraded as much as expected/suspected.

The odd flake of snow is possible just about anywhere, but probably a wintry mix more likely. But the best possibility moreso the further north you go and with altitude.

[J10]

It may be worth going to the November CET results threads as it makes good reading for some on here.

[Rich_Clements]

Afternoon, I just thought I would share with you that the Brecon Beacons National Park Twitter feed has posted that the top of Pen Y Fan had a coating of snow this morning, I can't back this up.

Edited December 2, 2011 by Rich_Clements

[J10]

Latest Update

This is Sunday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Monday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Tuesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Wednesday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Thursday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Friday's 850Hpa for 6am Next Mon http://hw.nwstatic.c.../h850t850eu.png

This is Sunday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Monday thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Tuesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Wednesday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Thursday's thickness chart for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

This is Friday's 850Hpa for 6am Next Mon http://hw.nwstatic.c...hgt500-1000.png

At 6am a bit better than yesterday, and generally not much change to my overall thought. One thing though the wind direction being a NW will push any showers further east than would normally be the case in a standard N/NNW flow.

[SnowStorm(Jamie)]

Sunday is now starting to come into range on the higher resolution NAE model, i thought comparing the thickness on the NAE @ 48hrs (Sunday) to the GFS 12Z for the same time might help show whether the latest GFS runs are allong the right lines with regards to the 528DAM line coming futher southwards to cover Wales.

NAE & GFS 12z thickness for same time shown below:

http://hw.nwstatic.c...hgt500-1000.png < GFS

http://expertcharts....120412_0212.gif < NAE

They are very simular with the SUB 528DAM line lying across Northern Republic of Ireland & N England.

A slight change in the flow however e.g. increasing westerly flow would make things even more marginal, but as it stands i think 200-250M even in the south could see snow showers perhaps some sleet and wet snow to lower levels (nothing settling) at times away from SW/W coastline IF the dewpoints are low enough and precipitation is present during night/early morning.

As for further out there's a chance we could see higher pressure in the Mid Atlantic ridge up towards south Greenland briefly setting us up for another shot of Polar Maritime air. It does remain very uncertain at this point though.

Edited December 2, 2011 by SnowStorm(Jamie)

[J10]

NAE now out

Dewpoints sub zero across Wales Monday 6am

http://expertcharts.weatheronline.co.uk/daten/proficharts/en/nae/2011/12/03/basis06/ukuk/taup/11120506_0306.gif

850Hpa at -6 Mid and N Wales, -5 S Wales

http://expertcharts.weatheronline.co.uk/daten/proficharts/en/nae/2011/12/03/basis06/ukuk/t850/11120506_0306.gif

Rain/ Snow Charts, mix of rain and snow

http://expertcharts.weatheronline.co.uk/daten/proficharts/en/nae/2011/12/03/basis06/ukuk/prty/11120506_0306.gif

In a nutshell, NAE synoptically very similar to GFS but going for lower ground temps esepcailly round coasts , which in turn reduces the surface dewpoint.

[soupsurfer7]

Still looking very marginal for Wales on Monday morning then...

There is a lot of precipitation coming onto the west coast of Wales at this time though, and with a west/north west wind, so I think the Cambrian mountains (just to my east) will get a good covering