Nick F

Can see the arctic air (dew points below 0C) over NW England right on the northern edge of rain moving SE from Wales ready to undercut and bringing some back edge snow tomorrow morning

I'm sure they do fairly often with certain set-ups, this is not your usual zonal Atlantic stuff, plus we are more intensely scrutinising each run with snow involved than we would with rain. In the warmer months, those that are interested in thunderstorms will often bemoan the models handling of areas of storms when they miss us, because models often struggle with simulating areas of convection.

The models are really struggling with these shallow lows and waves moving east across the south from later tomorrow through Wednesday into Thursday. 18z GFS quite similar in track to 12z for Thursday/Friday low, but it's GFS/UKMO with the more northerly track compared to EC/GEM/ICON/ARPEGE taking it further south.

Any meso low or wave that forms along the front, which may be happening over Wales right now (given the heaviness), will help delay the front's southward progress and also maintain heaviness and evaporative cooling.

Yeah, will help if the rain/sleet over Wales, which is heading towards SE England along the cold front, remains heavy when it reaches us later.

18z GFS back with the back edge snow early doors tomorrow Certainly looks like heavy extensive rain sleet and hill snow Wales at the moment:

Great deal of uncertainty over the track of the low across the UK later on Thursday and overnight into Friday morning. Quite a few GFS ensembles take the low further south. 06z EC was further south compared to 12z GFS for 00z friday 12z ARPEGE, below, on a more southerly track

Just covering their backsides in case it snows more than models anticipate. Plus just a few cms on higher routes can cause mayhem down south.

06z GFS making more of the back edge snow as the cold front slowly clears tomorrow UkV too, slow to clear the front allowing colder arctic air to catch up

No wonder it was cold today, even with some flurries, -8C 850 mb temps across SE this evening on 18z EC run snow threat still there for Wednesday on 18z EC

Still too much model variance and run to run changes to be overly confident on potential snow event across S England during Wednesday, 12z EC and UKMO / 15z UKV quite similar, but could easily end up too far south. E.g. ICON over France. More runs needed until I get too excited.

Storm Otto named by Danish Met Service WWW.METOFFICE.GOV.UK A low-pressure system which will bring high winds and rain to parts of the UK has been named Storm Otto by the Danish Meteorological Institute (DMI). Better post something model related. Only just looked at the 00z EPS extended mean, suggests milder in the south from late week maybe only temporary, the Iberian heights signal is lost through next week, days 11-15 look colder than average.

There's not been one storm named yet by Met Office / Met Eireann, first time this happened since storm-naming began in 2015 (I think the right year). Think Met Office have given up naming them, even though there's been a few worthy ones for Scotland IMO - instead they let other European agencies name them, such as Storm Otto by the Danish, that brought damage, travel and power disruption to parts of the northeast back in February.

Looking at a EC snow (10:1 ratio) chart for T+90 posted on another forum by Knocker, it shows snow across much of S England and far south of Wales, but greatest amounts over SW England, so suggests it will be cold enough to snow, but whether it settles another matter, high ground favoured, i.e. SW Moors, Mendips, Downs further east.

06z ECM brings channel low threat to S England Wednesday night with chance of snow on northern edge of precipitation swathe.

Difficult trying to keep up with the nuances of each model for each run for each day next week from Tuesday. 18z GFS seems to have pepped up the snow on the back edge of the front clearing S England Tuesday morning, but often overdoes the snow signal on back edge of fronts. 18z ICON has a snow event across far S Wales and S England on Wednesday, GFS S England south of M4 Wednesday night. Not even worth going any further, can't cope!

So, next week: for the south, a few cold, dry and bright days before turning wet and windy on Friday. For the north, cold and dry for many inland, snow showers around coasts and perhaps occasionally inland too, then snow event Friday (Caveat - could still change for better re: snow for the south)

Thursday's low moving into the SW approaches looks weaker on 18z GFS so far, so a more southerly track looking likely. That deeper dartboard low further west out over the Atlantic not so good news

Window does seem to be narrowing, for now on 00z EC and now 06z GFS, for next week's cold spell, may just about squeeze it out to the end of the week in the south, the north Sunday. Our modern foe the Iberian high seems to be ruining things again, despite strat-trop coupling leading to Greenland high following the SSW and supposedly favourable lag MJO trop forcing over the Pacific. But we still have at least a few days of snow potential, not really worth looking at beyond Wednesday, but 06z GFS showing potential for some back-edge snow along the cold front clearing south early Tuesday morning UKV hints at it too ...

Not sure the reason why it happens exactly, but these shallow lows moving in from the west against cold airmass more often than not make a beeline to track along the English Channel or northern France then into the Low Countries, see it so many times. So think 06z GFS track seems plausible for next Thursday. if it was a rapidly deepening low, then this would be a different matter, but it doesn't look to undergo RACY.

06z GFS doesn't pump the Iberian heights like the 00z EC / EPS, then again the 00z GEFS mean doesn't either. The heights tendency over Iberia in the medium range looks crucial to the longevity of the cold spell, too strong and greater risk of milder air flooding at least the south, some uncertainty in this area IMO. But at least one thing I've noticed in favour of prolonging the cold is the tendency for the trop PV to stay close to northeastern Europe on 06z GFS and 00z EC rather than bouncing back to Greenland as GFS was keen on previously, which makes sense - given the MJO going into high amplitude 8-1 and the continually drip down of the strat reversal following the SSW. Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815002

06z GFS doesn't pump the Iberian heights like the 00z EC / EPS, then again the 00z GEFS mean doesn't either. The heights tendency over Iberia in the medium range looks crucial to the longevity of the cold spell, too strong and greater risk of milder air flooding at least the south, some uncertainty in this area IMO. But at least one thing I've noticed in favour of prolonging the cold is the tendency for the trop PV to stay close to northeastern Europe on 06z GFS and 00z EC rather than bouncing back to Greenland as GFS was keen on previously, which makes sense - given the MJO going into high amplitude 8-1 and the continually drip down of the strat reversal following the SSW.

2nd warming downwelling into trop and MJO 8-1 high amplitude combo you would think reinforces high lat blocking for a while, so would expect any Atlantic milder ingress to be temporary if at all.

So, that's both 12z EC and 18z GFS with cold (sub -5C T850s) locked in until day 10. Seems to be delaying the Atlantic milder air flooding in. With the MJO heading into v high amplitude phase 7-8, which promotes higher heights and blocking to our NW, will we see the trop PV kept over NE Europe rather than bouncing back to Greenland as models were previously keen on?

I think too many are getting way too judgemental of what's going to happen and finding fault with every run, e.g. uppers not cold enough, flow too slack, sun too warm, only coastal showers the list goes on. Lets see what actually happens next week when it comes, it's going to get cold, cold enough to snow even to lower levels, some may be pleasantly surprised, some maybe disappointed, we can't predict for sure what will happen this far off. Just enjoy the fact it will turn cold enough for snow. It doesn't happen very often, especially in March.