Paul T

GAMECHANGER...GFS is backing down. What a difference in temps and snow for Saturday

Its less the track of the "original" low as most models have that shooting west of Ireland, its more the development and progression of the shortwave(s) as it nears the UK. Look at 144hrs gfs (18z v 00z). They paint a fairly different picture all driven by the treatment of the shortwave across the UK. The GEM 18z v 00z has changed towards a potentially more snowy and cooler friday/saturday. The MO v ECM differences (attached) at 120hrs are down to the treatment of the shortwaves...MO going for channel low development and a further one over the Slovakia area whilst ECM is not to fussed and therefore brings a milder southerly. Given that shortwave development can change pretty drastically right up to 24 to 48hrs we are someway off consistancy across the models. Although it must be said that even the fairly "mild" GFS 00z solution has significant snow on Friday for many (incl. the south) and temps on sat are hovering around zero from the Midlands North...

I like to spend a little bit of time comparing the fax charts as the update as they are good to spot trends or shifts - they also have the input from the MO forecasters. With regard to the last 2 updates of the fax charts for next wednesday (12z) it shows the low as it approaches spain increasingly flattening on the NE side. Further forward, the GFS has the position of this low stalling south of Ireland (Friday AM) and then moving east across the UK on Saturday. In the next few updates/runs, and after reviewing the ensemble quite a bit, I would still suggest that it could very much stall between Cornwall and NW France and move up the channel. Well, the 12z is out now so lets see what the trend is...

My take on the next 4 or 5 days for the south west... MONDAY Very cold start and temps then hovering around zero all day. Very isolated snow showers. TUESDAY Bloody cold again. Light to moderate snow in Bristol from 6am for a few hours. This will be moving into Devon a few hours later. Showers then possible for anywhere into the evening. So a dusting likely. WEDNESDAY Temps not getting above zero. A more organised band of snow is forecast to skirt the south coast of Devon and Cornwall from midnight and could last into the afternoon. Personally I think this could produce some decent accumulations if indeed it does skirt along the coast and nudge inland..its 50/50... Bristol could have an occasional snow shower not much more. THURSDAY and FRIDAY So, heres the biggy. Its very different depending on if you're in Jannerland or not... Plymouth will have heavy snow showers and as Thursday evening progresses it will turn to full on frontal snow. It will turn to rain at some point (i mean, it is Plymouth afterall)...I think it will change first thing friday morning after you've had a few inches from the full on frontal snow. Bit rude. For my neck of the woods in Portishead its a similar theme but its not set to turn to rain until midday Friday, if all at. Current accumulations set to be around 8 to 10 inches. If that happens I will be making a 10 foot snowman with my son, sticking a scottish hat on it and rugby tackling it as hard as humanly possible to help me get over yesterdays game.

Yes, the Op is higher res; my point above was that when comparing all of the ensemble members with the control (also in low res) the theme across the board was a shift S and E. This therefore highlights the potential that, with a tweaking of the input, it suggests a trend consistantly towards a more southerly and easterly track. Thats pretty much all they are useful for..

With regard to the GFS evolution of "that" low next friday - the stamps confirm that every single run has the low placed further south and east than the control map, barring P14...therefore the progressive nature and dilution of the 850's and placement out to the west of the low is perhaps overplayed a little on the contol. In my opinion, placement in the channel and then an intense weakening is a fairly likely outcome, backed by many ensemble members.

Snow Sunday evening is likely for Somerset and Dorset, overnight tonight will be rain

HGT 500-1000 looks great for Friday and the 850's -9 widely across the SW. If the showers aren't snow with that set up you might aswell give up. Positioning of the low will change a fair bit for Sunday. What I would like to see is the 850's a little cooler, but either way the sea is pretty warm still so inland and altitude will be particularly important.

Pretty tastey charts - Brian isn't a massive storm but its a spicey one that might delivery a fair punch... I think the spring tide tomorrow PM in the Bristol channel could bring a bit of water higher than usual - no real shakes, but certainly of interest.

Question: Where will the centre of the depression (or "eye") be when it makes landfall on Ireland? Well, comparing latest radar tracking with the high res models (12z) it suggests it could be between Bantry (SW tip of Ireland) and Cork. This would be an Easterly shift of around 50 miles as most models suggest the very tip of SW Ireland being where the "eye" will be positoned. It will be a proper nowcast event tonight!!

With regard to the Bristol Channel surge potential... Its large tidal range actually makes its ability to "cope" with a storm surge better than areas with limited tidal range. The "perfect storm" for a detrimental storm surge would be a spring tide (lets say 14.5m at avonmouth) with the additional of further hieght from a surge. Therefore, focussing on Monday, we have a 11.8m high tide, so even a storm surge of say 1 meter, along with some higher waves at high tide would still probably be within tolerences... In summary, if it was a spring high I would be more concerned but one to watch...

Oh come on! The event was never on, NAE 48hr high res suggested nothing but rain, GFS only hinted at sleet and the Met agreed. Today has been exactly as we should all know it would have been...a chilly NW'rly moving in with alot of cold rain. HOWEVER....Its all a red herring ! Firstly, and excitingly, the showers tonight will be giving it big-guns across the whole SW; Keep an eye out, as some areas will have a nice few CMs by tomorrow morn. Secondly, this pattern will continue over the next 48hrs... Check out the HGT 500-1000 maps. I can almost promise snow when they are below 522 hpa/mb. Thirdly....next week: Cold cold cold from the East, with weather systems trying to form and push in = nice combo!

10.8

This low gave 6 inches on Dartmoor, and it snowed down to 100mtrs...850's were -2 or -3...however, there was continental cold in place prior to its arrival.... Compare that to the current set up, its hugely similar (but rain!)

There is no continental cold to tap into with the channel/undercutting lows... For example, the set up on saturday into sunday would 100% be snow if there was significant continental cold.

Winsford is 200 mtrs above sea level...

Watch out of Sunday Morning...it has potential! NAE ppn charts will give a clue later today.

A change is coming....GFS pub run has shown what is possible with a shift in the jet by 500 miles south...the consistantly regressive way the GFS has treated that low next Tues backs it up...strong Easterly next week is a significant possibility.

The rule I have always worked to is that you need the following in place before I even consider the possibility of the white stuff: 1) Are the Upper 850's below -5oC? YES/NO 2) Is the HGT 500-1000 below 528? YES/NO If the answer to those is yes, then you have an awesome chance of the white stuff. If its close to the above paramiters, then the next question is: 3) Is there entrenched cold present (Daytime temps hovering around 1 or 2 oC) ? YES/NO If thats a no, then you havent usually got a much of a hope, at sea level at least. If all three are 'NO' then I dont even consider snow a possibility - and that has pretty much always been the case for this weekend unfortunately. If im pushed to have a hope for snow over the coming 4 or 5 days, then I would say Saturday Night into Sunday Morning is the only chance, but it requires upgrades... Paul

Blustery start to the day in North Somerset, nothing out of the ordinary so far...just a typical winter low pressure system. Max gust was at midnight of 50mph.

Don't over-do the St.Tropez Ian!

GFS was correct with the band into SW 10pm until 1am, nae and MO got it correct after that. I call it a draw. -1 each.

Looking at latest radar - the GFS is bang on the money... Pretty embarrassing for the Met Offices forecast app and general interpretation of the situation via the NAE high res. Shame.

Massive difference in the GFS and NAE for 3 am Friday... worth seeing who wins, as it impacts on which model we should trust:

I think it will be 100% rain and im hoping it clears at least North Somerset as I have the day off to start my Garden Project!!