SnowStorm(Jamie)

Well 12Z data is out so time for another update regarding tomorrows storm. We see a frontal wave coming out of NE US/Canada which is interacting with a very intense jet stream as seen below: This serves to rapidly develop the frontal wave into a deep low pressure system which is forecast to run up just to the northwest of the UK. We will see a band of very heavy rain along with severe winds cross the UK, the NAE shows the rain to be especially heavy across Central and South Wales so flooding is also a risk: Theres potential for damaging wind gusts for parts of Wales as the storm is intensified by the strong jet stream coming across the UK. We can see this by looking at the GFS for tomorrow morning as it shows the area of high upper level winds crossing the UK: This is where the strongest winds will likely occur at the surface as shown on GFS 12z, this is the average wind speed: Taking this into account i think that Western/NW/SW coastal areas of Wales could see gusts of 70-80mph during this period. Will be interesting to view the wind speed observations tomorrow!

Hi Guys! Its great to come back and see all the posts/updates on the Welsh thread. Looking to do an update tomorrow, as during the next week the Atlantic will be very active and with all that energy in the jet stream interacting with the storm, the potential for severe winds is quite high. Longwave trough setting up just to the west of the UK gradually nudging eastwards allowing a colder/cooler flow from the West/Northwest which has been ejected out of Canada & has travelled over the Atlantic but nothing more than that in terms of cold for now. Main concerns will be precipitation distribution and the strength of the wind for next week.

Good to see some people in that SE corner of Wales getting snow judging by reports it seems to be falling to also quite low levels to which makes sense given the fact dew points are low and falling still. Chance for a good few more cm in SE Wales where the front is forecast to gradually die away by tomorrow morning: http://expert-images...012306_2212.gif Here in Swansea seems as if i'm a bit to far West right on the western edge of the band, one to keep an eye on though as is it may just edge far enough west to produce a slushy covering even here.

Certainly very interesting times looking through the charts id agree snow chances can really come from largely any direction when the cold air is present over us. Tuesday seems to be the one to keep an eye on as we could possibly be effected by small areas of low pressure bringing the increasing risk of precipitation. GFS 12z: http://cdn.nwstatic....2/42/ukprec.png < Tuesday Precipitation http://cdn.nwstatic....degisotherm.png < 0C isotherm quite low and falling lower as colder air gets pulled back over from the east. The result is we see a period of sleet and snow moving in to South Wales/Mid Wales: http://cdn.nwstatic....ctypeuktopo.png UKMO 12z: Simular sort of idea to the GFS for around the same time increasing risk of precipitation moving in from the south: http://www.meteociel...2-594.GIF?20-16 < 42hrs http://www.meteociel...8-594.GIF?20-16 < 48hrs With upper air temperatures around -4c or below: http://www.meteociel...U42-7.GIF?20-16 < 42hrs http://www.meteociel...U48-7.GIF?20-16 < 48hrs So again period of sleet and snow moving into South Wales. NAE 12z: The NAE model also has this feature and did show it on its 06z run, increasing precipitation swinging up on Tuesday: http://expert-images...012206_2012.gif < 42hrs http://expert-images...012209_2012.gif < 45hrs http://expert-images...012212_2012.gif < 48hrs Upper air temperatures around this time are around -4C down to around -6C: http://expert-images...012209_2012.gif Dew points below freezing apart from maybe the far SW: http://expert-images...012209_2012.gif Also SUB 528 DAM air is entrenched in: http://expert-images...012209_2012.gif Again the result is a period of sleet and snow intensifying as it moves very slowly (Slack flow) NE. If your caught under that band of snow and live away from the coast there's the potential for some good accumulations as looking at the charts i don't see where any fast progression of the front would come from. Of course caution must be taken as these features will be placed in different places as runs go by. Ice warnings also in force across Southern UK for Monday and Tuesday. For some reading Met Office forecast snow accumulations across the UK Sunday/Monday: http://www.metoffice..._snow_continues

Had some very light snow blowing around here so far today. Looking ahead it still seems possible that further snow will effect Wales but i can see the latest MO fax charts have moved the fronts slightly further south: http://www.meteociel...fax48s.gif?19-0 http://www.meteociel...fax60s.gif?19-0 The NAE brings some more general sleet/snow in to SE/E Wales in to Tuesday so we will have to see what further runs show.

Friday's snow was nice to see here in low ground Swansea we had a few cm's but higher up closer to 150m there was much more, was nice walking about and taking in the views. I still think snow opportunities are present over the next few days while colder air remains in charge for now. I see the NAE has been playing with the idea of Mondays front edging into parts of south wales however its latest run places it further south: http://expert-images...012112_1912.gif Something we will need to keep an eye on is Tuesday potential for more sleet and snow as shown on GFS and UKMO: http://www.meteociel...60-21.GIF?19-16 < @ 60hrs UKMO http://modeles.meteo...gfs-0-60.png?12 < 60hrs GFS Low pressure closer by with colder air present over the British isles, snowfall distribution will be determined by where these fronts/troughs pass through/if at all, but chances seem somewhat high for some more snow across parts of Wales at least during the early part of next week.

I think what may be altering the BBC forecasts (The latest update) is the NAE's angle of attack for Friday. You see the Upper flow of air is from the South/SW: http://expert-images...011718_1518.gif Now look at the upper air temperatures in the region where the flow is originating from: http://expert-images...011718_1518.gif To the SW of the UK we see upper air temperatures of +0c & above so further NE progression of the low pressure system/front will cause these higher temps to also move NE.

Indeed, i remember that well started as snow here on low ground Swansea then turned back to rain for most of the night before reverting back to snow in the morning giving a covering but i remember most higher parts of Swansea had snow right the way through. Possibly the same thing may happen again we'll have to wait and see.

GFS 18z seems similar to earlier if you ask me, i noticed during Friday the Zero degree isotherm is quite low: http://cdn.nwstatic....degisotherm.png More than likely this is because the cold SE surface flow off Europe: http://cdn.nwstatic....8/63/ukwind.png Very interesting as with some elevation the chances of snow will be higher (as always really) As the models currently show ECM, UKMO, GFS it appears most of Wales will see a period of snowfall Friday apart for the SW (Probably drawing a line from Swansea NW to Aberystwyth (as the rain/sleet area- snow at elevation 150-200m Perhaps) Where dew points will be higher: http://expert-images...1806_2_1518.gif Of course this is all subject to change and is just a rough idea of how things might go. By this time tomorrow Friday will be coming in to the NAE's range and i suppose there will be more than a few anticipating the mesoscale models guidance! Thursday night you can start to see the low on its way in from the Atlantic: http://expert-images...011718_1518.gif Notice the milder uppers to the S/SW and this is only on thursday night, wouldn't take much northward progression to move that over most of S Wales, vital that the upper flow can turn more SE or you'll see the warmer upper air temps advance to quickly. Worth noting on the NAE watch this little feature thursday: http://expert-images...011706_1518.gif < Precipitation http://expert-images...011706_1518.gif < Dew points http://expert-images...011706_1518.gif < Upper air temps Many parts could see a period of light/moderate snowfall if it does indeed swing through in the early morning: http://expert-images...011706_1518.gif

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.

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.meteociel.fr/im/8773/ECM1-72_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.meteociel.fr/im/843/ECM0-72_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 Steering flow is due to change indeed: http://expert-images...011500_1418.gif Going by current radar anything just over NW Wales/Just off the coast should make its way here then its whether its cold enough. I see the GFS is again showing a stalling front for Friday, I'll wait until its showing up on NAE guidance. The front could just end up being further north (Largely rain/sleet) or further south (Dry/Cold) or work out somewhat as the GFS/ECM/UKMO currently shows (Snow).

Was also just looking at that also, the event is now upon us and the NAE has probably placed the precipitation a little to far SW on this run in comparison to the radar. Dew Points lower on this run but reports of rain further east in Wales (Cardiff, Bridgend area) point towards a more rain/sleet outcome for Swansea/Lower land carmarthenshire. Ice the main risk after that as temperatures drop: http://expert-images...011506_1418.gif

Indeed looking very nice for inland Wales, its gradually sinking southwards must be a trough pushing through not sure whether it will miss us in Swansea to the NE at the moment but the MO forecast precipitation does bring in some more showers off the Irish sea again.

The precipitation current over N/NW wales will eventually sink southwards as the upper steering flow changes to a more northerly direction: http://expert-images...011418_1412.gif < @6hrs http://expert-images...011421_1412.gif < @9hrs http://expert-images...011500_1412.gif < @12hrs Dew Points over this period around freezing to just above: http://expert-images...011421_1412.gif http://expert-images...011500_1412.gif http://expert-images...011503_1412.gif With Upper 850hpa temperatures around -5C and sub 528DAM air over Wales i would imagine precipitation will be of at least wet snow away from the direct coast where mostly rain/hail and sleet will occur.

Had some wet/sleet snow here in Swansea yesterday before reverting back to rain. Tonight looks interesting as we pick up a NW Flow and a trough pushes through overnight shown on the fax charts for mid day tomorrow: http://www.meteociel...ax24s.gif?14-12 Looks like some inland parts will see snow provided precipitation is heavy enough, more so rain and sleet on the coasts as dew points will hover just above freezing. As per frontal snow events later in the week, id urge caution until in range of higher detail (mesoscale models) NAE, NMM, look at what the Met Office are saying daily for our region. ECM shows a flow from the South on its latest run: http://images.meteoc...CM1-96_iuf9.GIF So rain/sleet and snow pushing north. That being said from 72 hrs to 96hrs there is an incoming frontal system from the west so hopefully ahead of the front we have a flow from the SE, if its from the south id imagine dew points will remain above freezing. Snow/Rain distribution will change from run to run so lets wait and see.

Same is happening here, Met Office shows moderate precipitation over Swansea however it appears to be evaporating into the atmosphere. I agree the front appears to have arrived allot earlier than forecast, there is however precipitation over the Irish sea so i would imagine this will further develop and push eastwards, lets see what happens.

Met Office article regarding upcoming cold & snow for the UK. Also includes some snow accumulation maps for Monday & Tuesday: http://www.metoffice...d-snow-continue

Latest NAE is rolling out now and its not much different in terms of Snowfall distribution tonight. Lets look at the precipitation chart for this evening: http://expert-images...1321_2_1312.gif < @ 9hrs http://expert-images...1321_2_1312.gif < Dew points across Wales - Around freezing or below/Rising higher in the west as the front makes it's way through. Rolled forward to midnight: http://expert-images...1400_2_1312.gif < Precipitation http://expert-images...1400_2_1312.gif < Dew points Upper air temperatures rising slightly from the west from -5 to around -4C: http://expert-images...1321_2_1312.gif http://expert-images...1400_2_1312.gif Again you can see the area of dew points around freezing Mid/East/South Wales and the upper air temps starting at -5C before rising further ties in with my thinking of initial snow. Best chance of snow in mid/east Wales of course But initial snow for those inland away from the immediate coast as always really before reverting to rain: http://expert-images...1400_2_1312.gif < Rain/Snow Distribution chart

NAE 18z more or less the same with light precipitation Sunday evening/night with sleet/snow on its leading edge. We then see the Occluded front push in from the NW: http://expert-images...011412_1218.gif < Heavy Precipitation @ 42hrs http://expert-images...011412_1218.gif < Upper 850 temps around -5C http://expert-images...011412_1218.gif < Dew Points for the same time just above freezing over most of Wales at or below in east Wales. 528 DAM air present over Wales apart from the far SW- Granted it does start pushing SW again to cover all of Wales as colder air works in back around the low pressure - Which in itself will present the threat of snow showers for NW/W parts of Wales. http://expert-images...011418_1218.gif < Surface pressure @ 48hrs Very difficult to call in terms of Snow distribution, we'll have to keep an eye on it but it looks very close to me and if heavy precipitation is over us i wouldn't be surprised at all to see back edge snow on Monday. Quite a few wintry opportunities over the next few days as others mentioned earlier.

Clouded over here in Morriston, Swansea. Hopefully with a bit of luck a flake or two soon.

Cheers for that cant seem to find anything, will have to be more careful in the future Allot of talk now about the mild sector on Monday. I really think that any snow will come in the form of that frontal system Sunday evening. Lets look at the MO fax charts: http://www.meteociel...ax24s.gif?12-12 < 24hrs (Sunday afternoon) We see a warm front moving in from the NW with an occluded front behind it. It's on the leading edge of that warm front where i believe the sleet and snow will be, rain to coastal W/SW as i mentioned earlier. It then appears that the occluded front catches up and the warm sector is forced out as the front clears through and colder air floods in from the NW: http://www.meteociel...ax36s.gif?12-12 So some back edge snow possible from that front. At this current moment in time, snow accumulations seem unlikely away from the higher ground in Wales and perhaps Eastern Wales Lets see what the NAE 18Z shows us later anyway.

Had just written a whole post but closed the window by mistake Yes the NAE 12z does weaken the precipitation signal, but an initial period of sleet/snow looks likely away from far W/SW coasts. The lack of precipitation is one of the problems, i also believe another is the surface flow ahead of the front from the SW, mainly impacting the S/SW of our area causing an increase of dew points/temperatures. Wouldn't surprise me to see Met Office warnings pulled westward into Wales for snow, but we will need to see how further runs handle precipitation amounts, timing of the frontal system, etc.

Indeed, certainly very interesting weather for the next week. When looking at that 2nd band of more intense precipitation which is also going to assist you can see a slight mild sector still: http://www.wetterzen...cs/Rmgfs513.gif < 51hrs Precipitation http://www.wetterzen...cs/Rmgfs512.gif < Upper 850's They do lower as the front clears through so some back edge snow: http://www.wetterzen...cs/Rmgfs542.gif Of course this is only the GFS take on the situation so will be interesting to see what the NAE shows us later tonight for its 18z run. But i would agree that mild sector has been pushed somewhat SW over the last few days, so lets see if such a trend continues.

Looking at the MO fax charts & NAE 06Z you can see the occluded front arrive later on Sunday. MO Fax has SUB 528 dam air across most of Wales bar the far SW: http://www.meteociel...fax48s.gif?11-0 Similar for what the NAE shows for the same time also: http://expert-images...011400_1206.gif < 42hrs Dew Points gradually rising as the flow turns to the WNW: http://expert-images...011321_1206.gif < 39hrs 10m wind direction Dew points below freezing in the east of Wales rising above freezing in the west. http://expert-images...011321_1206.gif < 39hrs http://expert-images...011400_1206.gif < 42hrs http://expert-images...011403_1206.gif < 45hrs Upper air temperatures across wales are forecast to be around -4 in the West to around -5C in the east of Wales: http://expert-images...011321_1206.gif < Upper Air temps at 39hrs So some initial snow likely for central and east Wales where the conditions are more favourable. Some warnings have been updated on the MO now to include the risk of Snow to NE Wales.