LomondSnowstorm

I almost did the same thing Catch wasn't going to do the other day with liking the post when he didn't 'like' the post. It's tough to see a way out unfortunately, all the mild air or even the non frozen air remains out in FI with no sign of it arriving soon. Hopefully the blocking will shift to our latitude sometime in the first half of April to allow a gradual warm up to average or above but incredibly the slightly jokey post I made a few weeks ago about a perpetual winter has so far been much closer to the mark than I ever could have imagined. This month is yet more evidence to me that our synoptic pattern has completely reversed from 2007 and that we really are in a new phase of generally cool, wet summers and cold blocked winters. I just hope things improve in the near future for you. Another thing I didn't realise - the Edinburgh Botanic Garden series has been running since 1956 and in that time it had never recorded a colder December than 2010. The station at the Observatory, which stopped taking recordings in 1960, was consistently slightly lower than that at the Gardens, yet in its entire history running back as far as 1760 there has never been a colder mean December temperature than the 2010 Botanic Gardens reading. This means that, while we only have enough data for a 100-odd year Scottish mean series, we can say that in all likelihood for Scotland December 2010 was the coldest December in over 250 years.

+240, still in the cold air, signs of the 'great easter blizzard of 2013' coming into view: Will it break the pattern down though? Well it can't go on forever, surely?

If I saw a chart like this in the depths of winter, my immediate reaction would be 'cold locked in for another 7-10 days': There is literally nothing other than the date on that chart to indicate any sign of temperatures getting above 5C in the near future, never mind 10C.

Debatable as to where the front itself would lie, not sure there's much in it between the three of them to be honest, worth a look at the ECM precipitation charts when they come out. Anyway, overnight into tomorrow the NMM throws up the prospect of a trough moving into eastern parts from north Fife up to about Aberdeen, say 2-4am landfall, which could be quite interesting and give a decent covering to some parts.

Maybe the best ensembles of the season in the reliable, would suggest no real breakdown until the 30th at least provided we don't see any direct westerlies. Even 0C uppers are enough to keep snowcover intact on the ski runs.

Ian Fergusson talking up the chances of a major snowstorm in addition to the one on Friday/Saturday 9 days away i.e. Good Friday, with mention of blizzards and drifting snow, but with signal for milder air after that. I think a good snowfall or at least a decent easterly with really cold uppers again this weekend followed by some colder drier days with maybe a slight northerly incursion into next week before a really major snowfall would be a nice way to end the month and the cold spell. Ideally the blizzard would be a three dayer to the evening of the 31st with the trough neutrally tilted a la February 1996 before the block sinks southeastwards, the milder air comes up from the south and we're sunbathing by the 3rd of April

Somehow I didn't notice this, Saturday 12pm, a mere 72 hours away: If that does coincide with the front nudging into central Scotland then it's going to be a more severe and prolonged rerun of Monday! (not Saturday) night.

I think NAE is being a little overprogressive with the front if I'm honest, I can see it making here but probably not as quickly as it does. On face value though it looks promising. Surface wind is the only issue which has struck me as being at all worrying about the frontal incursion: It is easterly for some but since the fetch looks to be almost non-existent south of the Tay(the winds veer southerly the further east you go) and with uppers sub -8C north of there it looks like away from the immediate coast that it wouldn't be too much of an issue (certainly slight corrections to a more southerly wind vector wouldn't go amiss though). The vital metrics if there's no wind are the dewpoint being below 0C, the 850 and 950 hpas being below 0C and the temperature sitting no higher than about 1C. This ticks those boxes so it would almost certainly be snow away from exposed coasts and by that I mean Angus and Fife coasts rather than the Lothians(whether the precipitation would get to us is a different story):

Looks to me like the pub run of the classic 'August 2003' model. 150cm on the upper runs for the equinox at Cairngorm, with no sign of any easing until the end of the month at the earliest: http://www.snow-forecast.com/resorts/Cairngorm/snow-report Maybe not that far off after all...

Sure, the gist of it is that you need -8C 850hpa temperatures in an easterly flow for lying snow to occur in lowland eastern Scotland. It's not based on anything other than past experience of these events but so far the rule has held up pretty well. For anything other than easterlies or southeasterlies -5C upper air temperatures are usually fine and higher than that can still sustain snow under some circumstances (up to 0C even in a southerly flow with cold embedded at the surface) but without -8C or lower uppers the coastal marginality tends to lead to slushy coverings at best.

It's always a tough call with showers, usually often the models underestimate their intensity though in this instance it doesn't look like it's likely to be all that problematic. Skew-ts are suggestive of not a huge amount of capping up to tomorrow afternoon/evening but not really suggestive of major convective activity for southeast Scotland, for Aberdeenshire however it does look quite a bit more interesting overnight and some fairly heavy showers could pep up : The best profile for snow in the next 3 days is Friday night for Renfrewshire, which is pretty textbook for a big frontal snowfall:

Haha, it was more a retrospective rant about today. If the front makes it the wind will probably be southerly enough to avoid the worst of the marginality (if it's southerly then it's a different story because you have a continental type surface flow which counteracts the increased humidity associated with it so I'm kind of neutral on whether I want the front to get here or not.

From my perspective the output is win win if you like cold - if it reaches us we get a hell of a blizzard but if it doesn't we stay in sub -8C uppers with winds from the east so a similar setup to what we had yesterday evening. I know I've probably learned this lesson before but fronts and easterly winds are not a good mix under ANY circumstances for the east coast or low lying areas within 10-15 miles of the east coast. The precipitation from the fronts tends to be overdone, as much as the convective stuff tends to be underdone in fact, and that leads to a build up of expectations which is almost never met. The best thing that can happen when encountered with one is to have a relatively quick encounter on its northernmost edge so that the effects are relatively minimal and we can get back to the nice convective stuff. In the end it was the showers which delivered the most as always, and not the front that the MO put out the orange warning for, which I think is why I had a bad feeling about the warning - they tend to only be put out for frontal stuff since the MO usually miss the convective potential and being in the frontal zone tends to lead to disappointment. Now why is frontal worse than convection when dealing with a maritime flow? 1. For convection to occur in winter with SSTs relatively low in the North Sea the upper air temperatures must be pretty damned cold by definition to sustain it. This also leads to the nice effect that, in general, the heavier the showers the colder the airmass. However, with fronts uppers can be anything you like and in fact the strongest fronts have more pronounced warm sectors, with those which don't being fairly weak. 2. Convection gives you clearances between showers, which in the middle of winter during the day and at all times at night causes the temperature to drop away. The absolute worst condition assuming an all snow event at night is either very light or non existent precipitation coming from a large organised cloud bank. Temperatures are held up by the cloud cover but without the redeeming feature of the heavier precipitation to bring temperatures down towards the dew point. 3. The airmass changes significantly. Whereas before you were looking at a nice clean cut Arctic Continental airmass being slightly modified by the North Sea you're now talking about an almost entirely modified airmass with a 'dynamic' rather than convectional skew-t. On the ground this means that, whereas before on the coast you were looking at very low dewpoints with slightly higher DPs inland where temperatures were lower and precipitation more intense (and hence higher humidity) you're now talking about a base level humidity of around 90%. After 10pm last night most of the east coast south of Dundee was reporting DPs above 0C and for most of today almost all locations in central or eastern Scotland had DPs above 0C in spite of the low temperatures. This has a very dramatic effect on the ground conditions, turning the most pristine snow to slush and stopping any further snow accumulation even in spite of relatively high intensity snowfall. DPs above 0C can be countered if they are temporary, temperatures are 1C or lower and there's limited mixing but if not things just start to become very damp. 4. Temperatures will always be held above 0C no matter what until it clears, barring exceptionally cold starting conditions AND limited wind speeds. In December 2009 and January 2010 we saw a few quasi-frontal events during the great cold trough period and after, but crucially wind direction was not due east for the most part. The one event we did have with easterly winds and a front early on the 2nd January was very close to a disaster near the coast for snow cover, with temperatures going from -10C widely to 1-2C in a matter of a few hours and snow from the front itself failing to lie. This was with uppers around -6/-7C and wind which was not exactly strong. However what followed behind was a fantastic spell of convectional snow with a classic Forth-Clyde streamer event, leading to the now definitive -8C rule, which for convective snowfall remains a kilted thread absolute for forecast guidance (Shuggee must take a large part of the credit for this monumental discovery during 2009/10). 5. Convective snowfalls are often just as good for the west coast as frontal snowfalls from the east. Ayrshire was reporting lying snow last night from the initial northeasterly convective stuff and Lanarkshire has on numerous occasions been utterly pasted by nothing more than a North Sea snow blower. With frontal snow marginality is often absolute and not just confined to the immediate coast because conditions under the blanket are generally much more homogenous than the localised immediate North Sea marginality. Also, you're now speaking to the new secretary of EUSNA (or Edinburgh uni SNA as it's now officially unofficially known) so you know who to talk to for all your Edinburgh Uni nationalist needs

In spite of the radar it's just light sleety garbage here at the moment. At least BT might get his trip up the Braids!

Not really, the fundamentals are the same, the only difference on the ground is the increased solar output. The main difference is that cold setups are rarer as winter turns to spring and into summer with the cold sources generally diluted. Here we've had the same basic setup as we've had for much of the winter and because of the persistent cloud cover temperatures haven't been any different to typical winter maxima for this kind of profile at around 2-3C. If it comes in in the middle of the day that would nudge temperatures a bit higher than what they otherwise would be but if it's overnight or early morning it's exactly the same ball game as if it were January. I think I did a post a few days ago also about the futility of the 528 line in breakdowns. It's a different story when the cold air is incoming but basic physics tells you that it's tougher to shift the cold air from ground level than it is from the upper air (cold air sinks) and that if the cold pool at lower levels is well enough established, as it will be by Thursday, it requires either a mild maritime surface flow or uppers which simply are too high to sustain snow to dislodge the cold pool. For central and northern Britain neither of those conditions are a given and therefore any breakdown of the pattern can't be taken for granted at this stage.

I just wonder if the band that's currently over the Borders is going to push northwards through the afternoon/evening. Temperatures may have dropped enough by then for at least some parts to see further accumulations. Temperatures aren't exactly high at around 1-2C and the main issue seems to be that the humidity is too great, which was not an issue when we were just looking at convective stuff. However then the problem would've been sunshine melting the snow through the day so in fact it's hard to win on that front at this time of year! Anyway, if temperatures kick down a degree or so when we get to 5-6pm things might start to look interesting again. NAE earlier progged about an additional 5-10cm of snow for this evening for the Lothians and Fife, though with a risk of further melt near the coast (if anywhere at the coast still has cover) too. Friday and Saturday are up in the air at the moment, though my preference would be for the front to stall across us with an eventual disruption rather than for it to simply not make it as far as here, because the potential if it hits at the right time is quite something. In terms of keeping the March temperature average down I think as long as the pattern doesn't break down completely the temperatures will be very much suppressed, especially given the upland snow cover and further snow potential from the south or even the east. To ride out the next 12 days without an end to the cold remains possible, and in fact the ECM 0Z shows the -8C line over us for pretty much the entire run, so temperatures by day will really struggle to break 4-5C at best and by night frosts could be very harsh away from the east coast. We're starting from an anomaly which is around average for the first ten days (as expected given these are usually the coldest of the month) but with the next ten days likely 4-5C below their average so a similar anomaly is probably required in the final ten days to really start chasing sub 2C and even sub 1C. And after the month ends I'm going to start chasing warmth because I think 6 months of winter is probably enough

Similar story, though not quite as bleak, snow holding on the surfaces it was before and had a brief forray onto the hard surfaces but basically wet there still. Anyway, I'm offski, hope things hold or improve temperature wise and that the front delivers big time overnight.

Thundersnow, possibly, in Freuchie now. So far nothing confirmed by the NW lightning map but since it corroborates with Dundee reports it might not just be the bins getting taken out

Yeah, it's a risk, not sure if it's worth taking (it almost never is) but we have to gamble on it anyway. Uppers will get up to about that for your area but you'll cope with your elevation, boundary between -6C and -10C becomes very sharp through tomorrow and I have a horrible feeling it might end up being the Forth that divides the two but we'll see. Pepping up a little, temperature starting to decrease a little bit in town (2C to 1C at 'Edinburgh City' on wunderground) and threatening to lie on tarmac now, once again. This event wouldn't have played out any differently in January or December with the same profile for all those who are visitors to the thread, absolutely classic marginal Arctic sourced easterly profile with a frontal unknown chucked in for good measure.

Ici: After this winter I understand your frustration BT, it's not simply the marginality but the fact that the heavy stuff just seems to avoid us altogether even when the radar looks like it should be immensely snowy.

It just looks rather disjointed on the radar, with the 'curl' due east of Newcastle broadly in the same position as the analysis front's western end was at 5pm (which to my mind would make more sense). It sort of makes sense though, cheers, the front curl is now D+G southwards with the rest to the east of here feeding in and that curl out in the North Sea will at some point 'link on' when it reaches land.

Potentially quite a big one, moreso because there's no real marginality issues there either so could make for a hell of a rush hour on the mate Still snowing here at a moderate rate, if it picks up a bit we might be in business but nothing on the scale of West Lothian, Fife, Dundee or Angus at the moment, though this at least backs up my map

I've spent the last 24 hours trying to work this out but it's not an easy question Many possible fronts around, none of the different FAX charts agree, so honestly I don't know but I think the 'main' event is going to be in the morning.

I'm waiting for that heavy stuff out at Duns to make a move before heading off and waking up early to catch the really heavy stuff, if the models are correct.

Correction on my earlier comment about the front - NMM shows heaviest precipitation, and hence (probably) THE main occlusion, coming in around 5am as expected, with intensity much greater than currently across Fife and the Lothians (which will be quite something). Greatest marginality at the coast when it hits before we see temperature heading back down again through the morning. Remember the orange warning isn't in effect until 5am and so opportunities remain for those who've missed out so far.