Singularity

In a heavier burst, might have been some wet flakes in the mix here but that's as close as I've got. Seems the few 10s of metres asl difference between Downton and here was critical; snow is falling west of here as well, where there is also a little more height. Not sure how much longer into the night this feed of showers from WNW is going to continue; most models had fizzled it out by now.

As if I haven't been tormented enough already today with the radar overestimating precipitation rates and also showing snow 5 miles up the road from me for several hours now (although this may also be false - but it's devilish behaviour). Don't get me wrong, I always knew it was a long shot for here today, but the close proximity and constant signs of potential transition falling short have made it hard to shrug off even for someone as familiar as I am with being in the least snowy region of CS England (the dreaded southern half of the Avon Valley).

Interesting process appears to be occurring whereby the lying snow that's south of where the models had it causes lower DPs and air temps downwind than predicted, which turns precipitation to sleet and then snow earlier than expected there, which (in time) puts down at least patchy snow accumulations there, which lowers DPs and air temps downwind from there... and so on. That's my attempt to explain the current model versus reality discrepancies, and may also account for the snow line being misplaced on the NetWeather radar, depending on whether that's based on model parameters or observations...?

17.3 miles NE of here according to Google Maps. I sense a disturbance in the farce. Hmm, I've been staring at screens too much lately...

00z ARPEGE had snow fizzling by late Sunday. 06z has a lingering band well into tomorrow. What a devious tease by that model! Not much change in the LP behaviour from the 00z - there just seems to be better moisture availability on this run.

@legritter, my condolences, sad to hear of that. Glad to see you're enjoying some snow today To those surprised at snow settling after rain, in late Nov 2010 I witnessed heavy rain and 5*C change over to heavy snow and 0*C in the space of 10 minutes, with snow starting to build a continuous layer just half an hour after that. Admittedly it was a bit heavier that day than I can see in the Bristol area now for example, but it offers some hope for those currently seeing rain with the snow line not far away .

Still keeping an eye on this potential interaction of the flow around the French low with the old frontal boundary early tomorrow. Today... well, it seems the circulation is scooting east as fast as any model dared take it, with not much of a secondary low hanging back to prolong snow chances that way, so it really is a case of moisture supply versus the inherently drier cold air cutting in down the western flank of the main low.

Temp was meant to hit 6-8*C in far S this morning and then fall rapidly in the afternoon, the main issue today-tomorrow is less whether it turns cold enough and more whether there’s sufficient precipitation still falling to produce any lying snow once it has done so. Models are 50:50 on this so I’m not daring to expect much down here in the far S.

Looks on target to me - what site are you viewing them on as the time stamps on that site are an hour ahead of GMT?

Starting to look like even far-southerners may be a bit distracted from the longer-term by tomorrow evening . The cold pooling on the 12z GFS is considerable not far east of here. Were it not for the westerly bias of lower-res, I think we'd have had some fun charts to look at there. I suppose we actually did for Xmas Day (despite a less than ideal sliding low track) but it could easily have been quite a bit sooner. GFS takes quite a while to switch over to Aleutian ridging. I can see how a bit of toning down of the Pacific westerlies could bring it about a good few days sooner. The Aleutian Low/Siberian High combo does plenty of work on the stratosphere beforehand, though - so it may be best if that's not cut off too soon after all? Judging by IF's tweets in the model tweets thread, the Met Office are already adjusting their timing accordingly (via GloSea5 behaving itself); the longevity of the more zonal signal is being played down more today than was the case yesterday.

http://www.meteociel.fr/modeles/arome.php?ech=3&mode=142&map=0 Okay so I've finally had a look. Interesting indeed with snow-rain-snow events on offer for locations as far south as me overnight Sun-Mon and all snow for places just a little N of me (say, 20+ miles inland from the coast?). The brief transition to rain occurs where the 'warm' sector of the LP just edges inland a touch in a shallow wedge formation. That region does see heavier precipitation as a trade-off but it only takes a bit of rain to mush some nice lying snow into a nasty slushy later that then freezes into ice when further snow starts falling. This region, i.e. CS England less than 20 miles from the coast, is within a minute (by modelling standards) S shift of an all-snow event, but equally so of an all-rain event. Talk about nerve-wracking! This is why I was actually more relaxed when the snow prospects were minimal this far south . AROME, linked above, actually brings the snow south by Sunday afternoon in a sweeping motion that's seriously mesmerising. Seems this wrap-around of cold has increased with each new run today as the elongation of the overall trough structure to the west has been diminished to the point of insignificance. WRF-NMM 2km 12z is not so 'sweeping' in its ways but does have an interesting boundary line setting up that transitions to snow by Sunday evening as the cold air cuts in; I can already see the forum posts complaining about the wet ground making it take so long for the snow to start accumulating .

Been too busy with non-weather things to keep track of the models today (shock horror!) but as interesting as the slider low adjustments are and that potential storm on Monday for that matter, what has caught my eye most today has been the huge discrepency between the model projections of two days ago that I saved for verification purposes and the actual observed MJO; I have overlaid below with the old runs as those fainter blue lines. No need to worry which model is which as they've all had a total 'mare . Seriously though, this means a lot more forcing toward amplification and HLB to our N and NE than the models have been working with lately. Might take a day for the corrected signals to work through fully but GFS looks to already be smelling the first fumes from the coffee. There could even be increased sharpness to the ridge-trough pattern Thu-Fri this coming week but that might be too close in range given the typical lag time for tropical forcing to propagate across to the Atlantic sector.

When it comes down to it, we have in the 8-10 day range a not all that strong or flat jet (compared to what it can be... as we're seeing for early next week) coming up against some significant cold pooing in what looks likely (as of this evening at least) to be a pretty slack setup to the E and NE, which has an increasing amount of aid of background forcing as we move between mid and late-Dec. So not surprising to see the models trying out some trough disruption with the Atlantic being held off. Whether this can actually be achieved without the Atlantic westerlies ever really getting in will depend on a combination of the pattern continuing to look supportive of deep cold pooling next Sat-Mon plus enough of a nudge in the right direction from the tropical teleconnection. There is a Bay of Bengal tropical cyclone that could complicate matters, but today has seen wind shear impeding the system and keeping it weak (https://www.accuweather.com/en/hurricane/indian) which, given an expected poorly-conducive environment for development in the days to come, reduces the likelihood of much impact on the extratropics .

Based on recent model trends, I'm surprised so little is being made of the Monday potential by the Met & BBC. The latest consensus has more favourable conditions than Sunday due to the undercut of colder/low dewpoint air from the E/NE. I suppose though it's a bit early to call the trend dependable, as the storm's very existence only really gained consensus this morning, with much question over the intensity and resultant ability to draw that colder air into the circulation.

Blimey, didn't work here earlier despite rain rates of 10 mm/hr - shows how much the WBs are coming down in general as well.

Are you sure, the wind's not that strong so I'd expect most Xmas lights to be okay. Okay, that didn't quite work but whatever, at least I'm trying . Showers struggling to get much past the Bristol Channel at the moment, but some heavier ones are now over S. Wales and as the 850's also drop, this may further increase vertical instability to aid shower penetration inland.

Shift S from WRF-NMM 0.05* model for Sun-Mon. Result is... eyebrow-raising to say the least. Sorry, I've gone and raised the bar too high now haven't I? Don't shoot the messenger!

A blizzard warning, surely

Making a call on Sunday is going to cause headaches today I'm sure... the question is, to trend or not to trend? As in, extrapolate the overall multi-model trend southward. As for Monday, it can be seen on the GFS 06z how crucial it is that the LP to the S develops enough of an independent circulation from the one to the N to draw the cold air in from the east. It helps if the decaying form of Sunday's low positions itself more or less east of the one to the S as well. Should the low turn out to be weaker than this run shows, that'll also be important as there will be less of a wrap-in of the cold air, with the snow line not tucking in so far south behind the low. The ECM charts on the US site show mostly mixed rain/snow from the 00z version of events, which reflects on just how marginal the event is looking although that is with not quite as much cold.low DP air drawn into the circulation as the GFS 06z goes with.

Yes I'm just into the New Forest from there. Not far from a 100m hill which I now wish I was on top of... coffee break couldn't come soon enough for this one

Showers of such intensity have distinct updrafts and downdrafts and I wonder if that made all the difference with this one; updraft = rain (or soft hail if you're lucky), downdraft = snow as cold air descends from aloft. Oh well. Maybe Monday will make up for it...

About 10 minutes down the road from you and it was 75% heavy rain and the rest large flakes. Can't believe it really; model consensus, TV forecasts and general theory all support snow here today based on projections but it seems something isn't quite what it was meant to be this morning.

Good morning to you too Shower near me has turned very heavy on radar over Salisbury. So near yet so far. Yes Sun-Mon continues to toy with us. The track of the Sun event will affect the cut-in of cold air on the Mon event. Best case scenario for snow would be the Sun event adjusting near 100 miles south yet the Mon event staying on a similar track... that'd be quite some trick now wouldn't it?

Gives the impression some intensity and duration of precipitation is needed today - assuming, that is, that the rain was light - as it appeared on radar?

Classic ruler-on-the-screen radar watching today. Already had a moderate shower pass tantalisingly close to the SW although it did transition to sleet on the radar just as it reached my latitude which makes me wonder if I'm just a bit too low in elevation (a measly 10 m asl!). Nasty feeling a heavy snow shower is soon to pass just north of me, giving Salisbury a good show while I'm stuck in this office unable to chase .