LomondSnowstorm

Could've been the 27th - rather similar to the charts for this Thursday: I've got a slight break between exams at the moment, with astrobiology Tuesday afternoon and maths on Thursday, so I'll not be posting much in the next week, and after that I'm off to Prague (which will depressingly will be as mild or even moreso than Scotland next weekend). Some quite impressive convection likely to build up out in the Atlantic - this is the Skew-t for Tiree - so with even warmer Atlantic SSTs than the surface temperature progged here there could be some hefty squalls moving inland from the west. Cloud bases are progged at around 900hpa and capped at 400hpa, so the profile is ripe for Cb development: Uppers aren't that impressive, mostly just -5Cs according to the latest GFS, but with such low air pressure it won't matter that much because 850hpa isn't particularly 'high' compared to normal. Wet Bulb Freezing levels are probably a better indicator, and at 300m maximum that's absolutely fine for snow: 925hpa temperatures are borderline but again pretty impressive given such low heights and the fact that we're talking about midday in a convective type setup: Surface temperatures are progged at 3-4C initially across Central Scotland although more like 0C with even fairly modest height further north, and freezing levels will lower rapidly in any showers. Looking at January 1993 as a rough guide to temperatures in this kind of regime shows surprisingly high maxima given fallen snow was recorded almost every day from the 7th to the 20th: http://www.tutiempo.net/en/Climate/Glasgow_Airport/01-1993/31400.htm For the main event the maximum temperature for the 11th was 3C and 4.2C the next day. Further east, Edinburgh Airport was, as expected, slightly lower, with maxima of 2.2C and 3.2 respectively: http://www.tutiempo.net/en/Climate/Edinburgh_Airport/01-1993/31600.htm For the December 1990 thunderstorm maxima were similar at 3C for Edinburgh this time: http://www.tutiempo.net/en/Climate/Edinburgh_Airport/12-1990/31600.htm Anyway, my point is that decent one off low ground snowfalls can occur with temperature not all that much below average, and while Thursday doesn't look quite like a repeat of January 1993 I wouldn't be at all surprised to see accumulations pretty much anywhere in Scotland. This is one of those setups which favours central Scotland in particular and I think we could be in for a treat if we don't see too many downgrades on the strength of the cold pool in the next 96 hours.

Sylvain could correct me if I'm wrong but I believe that it's some kind of flaw with the data which means that air pressure below 950mb isn't showing up for those models on meteociel. Wetter has it at 935mb: I was mentioning on the regional thread the similarity of this synoptic setup to January 1993, which was a generally mild month and probably not all that notable for the south but included what I believe was the deepest Atlantic low pressure recorded in modern history, the Braer storm, which brought the most almighty blizzard to central Scotland, with upper air temperatures no lower than -6C and a similarly dominant Polar Vortex: I can certainly see some similarities between the above and this from GFS in FI: Of course Nick is right about shortwave scuppers occuring frequently etc. but for Scotland, Northern Ireland and northwest England these aren't necessarily the worst setups in the world if you're looking for snow.

Hard to believe we've had people on the MT writing off the entire month of December when this is showing up at D6 for the 19th. January 1993-esque charts for Christmas Day:

This was originally posted in the Scottish regional thread but I felt it was also worth putting in here as well, if for no other reason than to 'bump' this thread up and maybe encourage some more of the usual excellent posts on here: There are hints of cool/cold zonality as we go towards Christmas, with the Euro high increasingly likely to be flattened and troughing digging south via height rises on the other side of the pole again. This from Joe B from EC control for the 22nd shows how we can maybe cash in from that intense North American based cold - note the Atlantic ridging starting to divert the jet southeastwards: Talk of similarities to the late December 1983 severe cold outbreak over the pond (their coldest December on record) which is interesting for us because of the month that followed here: Note the Aleutian ridge as well - as I discussed with last week's setup it's critical to shunting the vortex off Greenland and allowing Canadian sourced northwesterlies in. Normally this kind of setup is somewhat speculative but my thinking is that, with the extreme depth of cold that will continue to build in the North American continent in the next 10-15 days, there's a much better than average chance of that kind of setup delivering. I think the Euro high might still be too dominant to stop anything other than a more bog standard zonality up to Christmas (with still the odd hint of high ground snow potential if we're in a 'cold front' phase of the pattern) but after that, with the Euro height anomaly steadily decreasing and the Aleutian high gaining traction, the possibilities are intriguing (albeit that's not a particularly inspiring mean on the face of it): What I most like about this solution is that it's synoptically 'big' and elegant, and also could also segue nicely into a January which is increasingly dominated by a more southerly tracking jet and the first proper HLB (all speculation at this stage but there's at least a bit of interest starting to show up on the strat thread as well which should help down the line). So, in summary, HP less likely, full on storminess/troughing/rain zonality also more likely but the real shift in probability is towards a cooler zonality in the longer run, although with the evolution pretty slow, painful and potentially resulting in a dreich, sodden and cool but not quite cold enough for snow Christmas period.

There are hints of cool/cold zonality as we go towards Christmas, with the Euro high increasingly likely to be flattened and troughing digging south via height rises on the other side of the pole again. This from Joe B from EC control for the 22nd shows how we can maybe cash in from that intense North American based cold - note the Atlantic ridging starting to divert the jet southeastwards: Talk of similarities to the late December 1983 severe cold outbreak over the pond (their coldest December on record) which is interesting for us because of the month that followed here: Note the Aleutian ridge as well - as I discussed with last week's setup it's critical to shunting the vortex off Greenland and allowing Canadian sourced northwesterlies in. Normally this kind of setup is somewhat speculative but my thinking is that, with the extreme depth of cold that will continue to build in the North American continent in the next 10-15 days, there's a much better than average chance of that kind of setup delivering. I think the Euro high might still be too dominant to stop anything other than a more bog standard zonality up to Christmas (with still the odd hint of high ground snow potential if we're in a 'cold front' phase of the pattern) but after that, with the Euro height anomaly steadily decreasing and the Aleutian high gaining traction, the possibilities are intriguing (albeit that's not a particularly inspiring mean on the face of it): What I most like about this solution is that it's synoptically 'big' and elegant, and also could also segue nicely into a January which is increasingly dominated by a more southerly tracking jet and the first proper HLB (all speculation at this stage but there's at least a bit of interest starting to show up on the strat thread as well which should help down the line). So, in summary, HP less likely, full on storminess/troughing/rain zonality also more likely but the real shift in probability is towards a cooler zonality in the longer run, although with the evolution pretty slow, painful and potentially resulting in a dreich, sodden and cool but not quite cold enough for snow Christmas period.

This is the GEFS 10m wind forecast for somewhere along the mate corridor (around Airdrie way) just as an example: http://modeles.meteociel.fr/modeles/gens/runs/2013121112/graphe7_1000___-4.528301886792452_55.91093117408907_.gif I'm not 100% sure if this is gusts or sustained, but either way it's pretty bad, and if it's sustained (which I suspect it is) it has the potential to be worse than any of the storms we've seen in the last few years.

I'm not entirely sure of how many levels it has but it definitely does model at least the lower strat - Recretos on the strat thread posted a CFS strat forecast at some point so I reckon it goes to at least 1mb. I'm not sure what its record would be compared to the ECM/GFS RE forecasting warmings but while it nailed the very cold March it only seemed to flip to this after the SSW had already occurred. Better than if it were showing a positive AO though!

Transient it may be but we saw just last week how quickly cool zonality can morph into a full blown northerly (albeit then back towards a toppler on verification). We could do with lower heights for a better chance of snowfall if we were being picky but given the slim pickings that have been on offer in the last few days beggars certainly can't be choosers.

I think as a general rule having high confidence in any model solution post +168 and certainly post +240 is rather foolhardy - while we may speculate as to the outcome and while we can give a reasonable estimate on the probability of an outcome depending on the degree of support from the longer range EC ensembles, MOGREPS, the EC 32 dayer etc. we always have to be wary of chaos theory even in what may seem like a relatively straightforward progression with a fairly large margin for error for the general weather pattern i.e. the current train of SW/Westerlies fuelled by a strong Greenland centred tropospheric vortex, a cold stratospheric vortex and a euro high. We can have somewhat higher confidence than normal in the general weather type for the British Isles for say D6-D10 than normal, given good model agreement for a mobile westerly pattern (albeit with varying degrees of amplification and Pm airmasses into Scotland depending on your model of choice) but even today we've seen one or two charts in FI which hint at the possibility of something more interesting via troughing digging that bit further south, encouraging ridging of heights northwards into Scandinavia. While I think a full blown easterly is very much an outside bet at this stage I wouldn't be surprised to see more cold solutions in the coming days as the models toy with the next phase of our winter, but equally the outlook remains pretty unspectacular for sustained HLB in general and, for the foreseeable at least, any cold is likely to be squeezed out of favourably positioned mid latitude heights rather than stonking great Greenie highs. edit: I started typing before reading Ian's post so the use of foolhardy in both is purely coincidental, honest

You're right enough, last year March was the best (well actually January was pretty incredible if you live in SS/CMDland) for snow and cold generally, in 2012 April saw the biggest snowfall of the winter, in 10/11 November/December saw the deepest snow and cold while in 09/10 December was the snowiest in Scotland, although the first half of January was also very cold and quite snowy and the rest of winter certainly wasn't bad by any means either (second coldest ever in the Scottish timeseries). We're overdue a properly cold February, 2009, 2010, 2012 and 2013 all showed promise at points but none fully delivered, least of all 2012. February 2007 had one decent snowfall and 2005 had a few good 'uns late month and other than those mentioned the only Januarys that stand out in my lifetime are 2011 (purely because of the Arctic westerly setup of the 7th/8th which were locally exceptional for snow with 9 fresh inches and giant flakes after an incredible December but rather disappointing elsewhere) and 2009, but the latter is purely because of the number of near misses from battleground setups where transient warm layers scuppered numerous 'nailded on' dumpings. I think we're overdue a decent late January/February cold spell and we've got a reasonable shot at it this winter but of course the same could've been said for any of the last few winters at this stage in the game.

I doubt we'll hit 8.8C - we had a slightly below first week including that 36 hour period Thursday night-Saturday early morning where almost nowhere was above 0C, it's going to be mild to very mild this week into the start of next and after that it's likely to go back to closer to average in all probability with maybe hints of a transient northerly around or just after Christmas (or at least a mid latitude high giving surface cold). I think average to slightly above is a decent bet for this month as a whole but probably waiting until mid January before the strat gives us a shot at more prolonged cold. Sorry, I missed the models today, it's actually an undercut type setup (or at least cold troughing) we could be looking for in the longer term? Interesting stuff indeed.

Some impressive WAA on that chart, sadly most of it's heading over us!

Snow back on here, slightly more intense than before but with more like snow crystals than the usual dandruff. temperature still -0.2C with the DP at -2.7C so no immediate risk of a thaw. Will be interesting to see where exactly the snow/(freezing) rain boundary ends up by morning with Fife as very much the boundary. Oftentimes the Lomonds are the boundary line in these setups which would put us and Dundee in a good position to remain with the snow until the warmer air finally breaches into the lower levels:

Must be gutting that one of those places is right over your house Anyway, not really much to add, a pretty poor pattern all in all and pretty high confidence of upper air temperatures too high for even high ground snow for the foreseeable (how far that is, of course, is open to discussion, as while Nick can only see up to maybe D10 at most Ian's staring a repeat of 88/89 down for the next two months). Someone on our regional thread picked out this as the best chart of the entire output, which for Scotland at least is both true and extremely depressing from a cold POV: In my view, up to D15 we have such poor teleconnections for sustained HLBs that we're reliant on either a UK/slight more northerly Sceuro high type setup or, for a slight chance of northern snow, a shift of the core of the heights from Europe to the Azores to shift the jet on a better, NW-SE, trajectory (which was effectively what brought us the stormy cold snap we've seen in the last few days). I think the former is more likely but the latter may be a possibility if we can get a bit of amplification upstream, as the above chart shows. Still, this is simply straw-clutching in the extreme!

This Fax chart is actually a better guide than the NMM has been - what we saw there was a decaying warm front, which is why it didn't bring any milder air but also didn't bring much in the way of precipitation either. The warm front won't push in until at least midnight but in the interim we've got a few showers forming in the very slight upper level westerly flow: When the line with the roundy bits on it passes over your house the fun ends and we all turn back into pumpkins for the next week or two at least.

Odd to see the precipitation so far north and east at this stage, the NMM had the precipitation just moving into western parts at this time so we're really in the dark about what comes next. Seems to be more brewing out west so perhaps this is merely an added bonus but I find it a bit bizarre when mesoscale models are so far out at such close range.

Don't get me wrong, I would too, but getting to say 'I told you so' is a decent consolation prize This is possibly the least intense snow I've ever seen accumulating, or at least since January 2010. Getting marginally more intense but you can still see the individual snowflakes on the ground.

Seems like one of those times when the radar isn't exactly providing an accurate picture of events (tends to happen in drizzly/snizzly setups like this one). NMM suggested the bulk of the precipitation coming in from 9pm-3am so we might get something more substantial then. There has been on/off snizzle but the current moderate intensity looking band over East Lothian and the Eastern Borders looks much like a false return. Still -0.2C but the DP is up to -2.9C. edit: it is actually snowing here, extremely light to the point where I didn't even notice until I went outside but it's better than nothing.

We went through that last week with the northerly downgrade, now it's more like boredom, a very unexciting output after an exciting but all too short cold snap. I'm not all that bothered by it for two reasons - 1) it keeps my LRF on track and 2) I've got exams from the end of next week to the 19th so I wouldn't want to spend too much time on here, which I undoubtedly would do if we were set for an interesting spell of weather

Back in Fife now, currently -0.2/-3.3 so plenty of wiggle room temperature wise. Going to be 6am before the milder 950s push in but more like 3am for those Glasgow westwards. Precipitation on the radar looks light but with slightly heavier pulses and it is pretty far east already (if the radar's accurate) so I'd be expecting to see some lying snow here if and when it does reach us - maybe a nanometre or two! Equally, I'm not regretting booking at break to Prague just before Christmas - this may be the first genuine 'Bartlett' setup during my time on the forum if it comes off. This is also why this particular spell of cold is worth making the most of - with the current charts as they are we're at least 8, and perhaps even more like 15+, days away from seeing a significant risk of lowland snowfall again: This is for Aberdeenshire, which gives you an idea of just how poor the outlook is at present - no runs below -5C after tomorrow until the 16th: Some longer term positives are that Wave 2 activity is forecast to propagate reasonably well into FI (D8-D9) which could assist amplification upstream (although that doesn't necessarily mean cold but maybe more of a 'battleground' setup or a UK high type setup): Some signs too that the MJO may manage to make progression through the poor phases and back round to the 6-7-8-1 phases that we like. However, the MJO forecast have been lacking skill so far to say the least so I don't have much confidence, but hopefully the high amplitude will remain and give us a chance of getting another cold snap at least before month's end:

Aye, a strong flow combined with low heights and massive temperature gradient (-12C uppers now into the far north) is providing exceptionally good convective conditions, which will ease somewhat unfortunately this evening when the colder 500hpas move eastwards, but still some fun to be had this afternoon: The skew-t for Aberdeen shows CAPE to be massive, almost thunderstorm levels, with a cloud base around 900hpa and not capped until 500hpa, so major instability there. A look at the radar shows what might have been if we'd managed greater amplification - November 2010-esque convection out in the North Sea where the 500hpas are sub -40C and conditions for Polar lows are optimal. Looks like Glasgow is taking a direct hit from a shower now though...

It's snowing in Northeast Fife apparently so I'd imagine it'll be the same when it reaches you. Was on a night out yesterday so I was only briefly awake around 7-8.30 (listened to the cricket before taking an executive decision to suspend brain activities for the morning) but looking at the gust speeds recorded it could've been even worse given what the forecasts were showing yesterday.A red warning was necessary because of the timing alone IMO - any event which shuts down the ENTIRE rail network surely worthy of a take action warning. Had it been in the southeast it would easily have been red but because we have higher average wind speeds and storm frequencies commuters on the motorways or trains are meant to be much better placed to deal with fallen trees on the road or all the trains stopping running.Anyway, I'm looking forward to seeing some snow this afternoon and some more persistent stuff tomorrow (although north of the Grampians seem to be taking enough of a pasting now) but more on this later. Just to say for the moment that a stalling front on the edge of a very cold surface layer ( sub 0C at the surface all day tomorrow in central and eastern parts) brings a risk of lying snow for some. edit: Some horrendous typos in there to the point where bits of it didn't make sense (damned iPhone) Corrected now hopefully

Was St Jude's the wee breeze you had in October? Seriously though, 80mph gusts are progged for Glasgow and Edinburgh for Thursday morning, we have had a few of these in the last few years (2011 was particularly bad for storms) but hurricane-force gusts in major cities and along busy (and quite elevated) motorways between the two are still pretty concerning.

I think it's mostly topographical - when the winds are westerly there's not much stopping the flow of air from the Atlantic (or at least the Clyde estuary) right through to East Lothian, whereas generally the Northwest, Western and then Southern Highlands tend to shelter lower parts further east. I suppose part of it is also just the modelling though, because at the resolution of the GFS the above, rather simplified, version of events is what will show up most clearly rather than a more nuanced picture. For example, the summit of Cairngorm almost always gets the highest wind gusts due to its elevation and individual sites vary hugely depending on very local topographical features.

One thing I have been monitoring, other than the back edge potential Thursday lunchtime for central areas, is the 'breakdown' on Friday night when a warm front approaches from the west. Now, the main problem of course with a warm front is that it introduces uppers which are above 0C, but on the front edge with very little mixing and temperatures going, or remaining, sub zero on Friday night, we might just have a chance at seeing some of the white stuff: The timings on this vary, with the above probably a bit more progressive than the GFS/NMM solution, but it gives you a general idea of the frontal setup as we head into Friday night - a slow moving warm front drifting eastwards. At 3am the NMM global model shows this: With temperatures at the same time remaining near 0C for most: While the precipitation does look light it's likely that whatever falls between midnight and 4am for most central areas will be as snow and likely to lie (although with the caveat that we don't have the 950s so freezing rain or sleet may be a possibility) with uppers not getting above 0C for most of Saturday: By morning the colder air at the lower levels will gradually be squeezed out from above so I wouldn't expect to necessarily wake up with any precipitation but if you fancy an allnighter you may be able to catch a bit of proper snowfall if Thursday doesn't deliver (although Thursday still looks reasonable for a bit of falling, if not lying, snow on the backedge down to relatively low levels with some impressive totals for the mountains.