Wales Cymru Regional Discussion - January 15th 2013>

[Snowmadsam]

Just looking through some of the 12z data for Friday, if you ask me the Atlantic push seems to now be modelled a little further northwards, potentially allowing for more widespread snowfall across Wales/West Midlands however also introducing milder sectors into the SW of Wales.

I think what we have to look at here is where is the flow going to be coming from is it the SE/S/SW?

On Friday GFS shows a surface flow from the SE which is good in terms of keeping the low dew points as colder air is getting pulled across from Europe:

http://cdn.nwstatic....2/66/ukwind.png

But what about the upper flow? at the 850hpa level we see a flow from the South- more so originating from the Atlantic so this would also causing a rise in the upper air temperatures and in the past in these frontal situations your really looking for -1C and below:

http://expert-images...011806_1512.gif < Upper Flow

UKMO 12Z brings in more of a SE flow and the result is ahead of the front we have SE flow and colder air- brining snow to its northern edge:

http://www.meteociel...W60-7.GIF?15-18

Still its a case of watching the Models for trends northwards/southwards, upper temps, dew points, directional flow both upper and lower as we await it to come in range of the NAE. Expect Met Office warnings to be fine tuned as the days go on as details become more clear.

---

Just editing my post to include update on ECM 12Z

http://images.meteoc...CM1-72_axh5.GIF < 72hrs

You can see how the atlantic push comes further North and East thus introducing slightly milder upper air over the SW/South Wales:

http://images.meteoc...CM0-72_wra7.GIF

So we have differences already but the GFS and ECM do seem to be somewhat similar to me in the shorter timeframe which i am focusing on at least.

Would upper air temperatures matter due to DAM thickness?

[Elnonio]

Shame the dangler consisted of rain not snow though.

True!!!

Snow on the way though.......

[SnowStorm(Jamie)]

Would upper air temperatures matter due to DAM thickness?

Yes, SUB 528 DAM air does not play a large roll in these frontal situations, however upper air temperatures & dew points will. If you have upper air above freezing then snow would be melting in the upper levels and turning to rain/sleet.

[Snowmadsam]

Yes, SUB 528 DAM air does not play a large roll in these frontal situations, however upper air temperatures & dew points will. If you have upper air above freezing then snow would be melting in the upper levels and turning to rain/sleet.

I know i'm going on but evaporative cooling could take place....its gonna be now-casting really

[keithlucky]

Just looking through some of the 12z data for Friday, if you ask me the Atlantic push seems to now be modelled a little further northwards, potentially allowing for more widespread snowfall across Wales/West Midlands however also introducing milder sectors into the SW of Wales.

I think what we have to look at here is where is the flow going to be coming from is it the SE/S/SW?

On Friday GFS shows a surface flow from the SE which is good in terms of keeping the low dew points as colder air is getting pulled across from Europe:

http://cdn.nwstatic....2/66/ukwind.png

But what about the upper flow? at the 850hpa level we see a flow from the South- more so originating from the Atlantic so this would also causing a rise in the upper air temperatures and in the past in these frontal situations your really looking for -1C and below:

http://expert-images...011806_1512.gif < Upper Flow

UKMO 12Z brings in more of a SE flow and the result is ahead of the front we have SE flow and colder air- brining snow to its northern edge:

http://www.meteociel...W60-7.GIF?15-18

Still its a case of watching the Models for trends northwards/southwards, upper temps, dew points, directional flow both upper and lower as we await it to come in range of the NAE. Expect Met Office warnings to be fine tuned as the days go on as details become more clear.

---

Just editing my post to include update on ECM 12Z

http://images.meteoc...CM1-72_axh5.GIF < 72hrs

You can see how the atlantic push comes further North and East thus introducing slightly milder upper air over the SW/South Wales:

http://images.meteoc...CM0-72_wra7.GIF

So we have differences already but the GFS and ECM do seem to be somewhat similar to me in the shorter timeframe which i am focusing on at least.

The most important factor as in 1978 we keep the S easterly flow ant switch back to a south to south westerly game over ,the forecast seems to keep the gale force S easterly .so forget damn line etc .At this time even S East Ireland is under threat of blizzards.

[Panayiotis]

True!!!

Snow on the way though.......

For Friday or earlier?

[bradymk]

I know i'm going on but evaporative cooling could take place....its gonna be now-casting really

A huge thing to stress regarding to this set up is dew points, evaporative cooling, 850's and dam not really the biggest factors. You really want a south easterly wind for any snow as this brings in very low DP's off the continent. As soon as you lose the SE'ly you lose your Dewpoints. So the location where snow turns to rain will determine on wind direction which will be determined by position of the front and how much trough disruption occurs. ECM shows snow for all of Wales Friday morning under strong SE'ly winds however after 12pm, the wind starts to change direction in the west with snow changing to rain here and this making steady progress eastwards. All we need in Pembrokeshire is a 50-75 mile shift west of current output and it would stay as snow most likely everywhere in Wales otherwise snow to rain with this more likely in the SW.

The most important factor as in 1978 we keep the S easterly flow ant switch back to a south to south westerly game over ,the forecast seems to keep the gale force S easterly .so forget damn line etc .At this time even S East Ireland is under threat of blizzards.

Yes this is key, if Wales stays under the south easterly then it will stay as snow throughout, if not, then its more likely to be snow-rain.

Edited January 15, 2013 by bradythemole

[Elnonio]

For Friday or earlier?

Friday says Derek and since he is a national institution I have complete faith in him!!! Then again, who really cares about Pembrokeshire - I just want to know what's happening in Cardiff!

(Only joking Pembs )

[Stevetynant]

From being completely in the firing line now looks possible we could miss out in S Wales in the short term- though the way things are evolving its probably best to hangfire until tommorrow before really getting hung up on it one way or the other. Fingers crossed still all to play for.

[Panayiotis]

Update on the potential on Friday from the ECM's point of view, which looks good IMO..

These charts are for Friday and Sunday:They show the upper air temp and precipitation (which correlate with each other), most of Wales when there is precipitation are in -5C uppers, which IMO is enough for snow and with the continental feed, dew points will be low, which is even better for snow.

Edited January 15, 2013 by Panayiotis

[Snowmadsam]

A huge thing to stress regarding to this set up is dew points, evaporative cooling, 850's and dam not really the biggest factors. You really want a south easterly wind for any snow as this brings in very low DP's off the continent. As soon as you lose the SE'ly you lose your Dewpoints. So the location where snow turns to rain will determine on wind direction which will be determined by position of the front and how much trough disruption occurs. ECM shows snow for all of Wales Friday morning under strong SE'ly winds however after 12pm, the wind starts to change direction in the west with snow changing to rain here and this making steady progress eastwards. All we need in Pembrokeshire is a 50-75 mile shift west of current output and it would stay as snow most likely everywhere in Wales otherwise snow to rain with this more likely in the SW.

Yes this is key, if Wales stays under the south easterly then it will stay as snow throughout, if not, then its more likely to be snow-rain.

You can just tell this is gonna be a now casting event...I also suggest that people get wind veins etc so we can have an accurate measure of wind direction as this will be a crucial factor...*goes to look for a DIY wind vein*

EDIT:- Found one! http://www.metoffice.gov.uk/education/kids/things-to-do/weather-station/wind-vane

Edited January 15, 2013 by Snowmadsam

[bradymk]

Friday says Derek and since he is a national institution I have complete faith in him!!! Then again, who really cares about Pembrokeshire - I just want to know what's happening in Cardiff!

(Only joking Pembs )

watch it! Friday looks a good possibility of seeing snow however I do think it is a snow-rain event AT THIS STAGE for most of S Wales although mid wales and NE likely to see all snow. But i must add, this is not down to what i want to see but i do expect a correction SW'ards because this does happen quite often regarding frontal incursions, hopefully this one moves south west by around 75 miles, then we will be happy bunnys.

[J10]

A few charts from best case scenario. (UKMO)

In Comparison to GFS shown in Jamie's post above which has shown in the charts above have uppers close to 0c.

ECM has uppers below zero, but at 12Hz they are close to zero for a time before dropping back later. Wind flow more of a southerly than SE.

GEM also looks promising

Tonight though UKMO the best charts which would give a snow event for virtually all, while GFS 06Hz would have much less snow for most.

Potential is still there, but this can go wrong is so many ways.

Edited January 15, 2013 by Jackone

[Bonjangle]

I know this is a forecast for the SW , but look at Wales getting a hammering .http://news.bbc.co.uk/weather/hi/news/newsid_7760000/7760862.stm

[Cwmbran Eira]

I know this is a forecast for the SW , but look at Wales getting a hammering .http://news.bbc.co.uk/weather/hi/news/newsid_7760000/7760862.stm

Looks fantastic. Wonder why our Derek didn't show anything near as interesting.

[TheWeatherGirl]

Caerphilly mountain was NOT fun this morning! An hour to get from Abertridwr to Llanishen when it usually takes 20 mins?! Looked stunning though! I felt really Christmassy despite it being 3 weeks too late!

I think Derek is a mildie ...

[Cwmbran Eira]

Caerphilly mountain was NOT fun this morning! An hour to get from Abertridwr to Llanishen when it usually takes 20 mins?! Looked stunning though! I felt really Christmassy despite it being 3 weeks too late!

I think Derek is a mildie ...

I think he's made some bad calls in the past so is very cautious. I remember seeing a very sheepish Derek after we had 20cm of snow here when none was forecast. Very difficult though. I'm sure all forecasters have made similar mistakes.

[soupsurfer7]

I think he's a realist or maybe slightly leaning mildy.

[Stevetynant]

That forecast for the West is certainly "high stakes" as he calls it

[bradymk]

I think he's a realist or maybe slightly leaning mildy.

While i have been following him on twitter, i would say he is a coldie definately

[Wales123098]

I've noticed with Derek he likes to avoid the snow forecasts. I can remember when we've had snow and hes got his forecast completely wrong. He doesn't like to venture there at all. Ian on the other hand clearly loves the cold and snow and will not shy away from telling the public what might happen.

[soupsurfer7]

I agree. He's probably a coldie at heart but doesn't want to delve into it too much because we live in one of the most difficult countries in the world to forecast snow.

[Cwmbran Eira]

While i have been following him on twitter, i would say he is a coldie definately

Think he's just biding his time for the big forecast tomorrow evening and an even bigger one on Thursday. Very dramatic in true Derek style

Very cold tonight. Mislaid my thermometer though after building work so have no idea of the actual temps. Very frustrating

Edited January 15, 2013 by Cwmbran Eira

[dyl232]

So is this snowy period this coming friday pretty much nailed on then? Consider it less than 72hrs away now, pretty much all of wales under the white stuff from derek's forecast,what your views, which areas of wales is likely to get most?

[Jackfrost]

On the subject of TV forecasts, am I the only one who finds ITV Wales forecasts a bit on the depressing side?

The presenters can never do enough to emphasise how dangerous/miserable/inconvenient any cold weather is, with use of phases such as "unfortunately", "don't venture out unless you absolutely have to" and "bitterly, bitterly cold", all said with a very glum face and a tragic kind of voice.

Watching Derek is a positive joy in comparison.

Ian's forecast for the Southwest is very exciting. Snow beginning in the early hours of Friday and still going strong at 22:00, while the three day outlook shows snow through until Sunday. I worry that it won't quite pan out like that, but it's fun to see a forecaster being so gutsy.

Edited January 15, 2013 by Jackfrost