Thundery wintry showers

I'm in two minds about preferred types of thaw. On general grounds I prefer a quick thaw to a slow slushy icy one with no hope of top-ups, but on the other hand, I would rather have a bright spell with gentle afternoon thaws in the sun than a wet and windy breakdown with a rapid thaw and widespread flooding. However we have to take what we're given and a wet and windy breakdown scenario looks imminent tonight. I agree that it was well worth getting up at 8:30am (as I also did, to take some photos).

Temp 3.6 here, snow is thawing on trees and roofs, but holding up quite well on the ground so far. It's back to the thing about an extensive snow cover having a high albedo and helping to reflect heat- if I'd woken up to just a couple of centimetres it would probably be almost gone by now.

Late-March 2012 had some remarkable diurnal ranges. I remember that in Cleadon I had minima of 3C and maxima of 20C which is extremely unusual within two miles of the North Sea coast.

About 12cm/5 inches on the ground here this morning- the precipitation stayed as snow throughout the night with a maximum temperature of just 0.4C at 5am, and then it fell to -2.9C around 8am as skies cleared. Some picturesque bright snowy scenes out there this morning. I expect some thawing today as it's set to be mainly sunny and the temperature is already up at 1.2C, but probably just shaving up to a few centimetres off the snow cover. Tonight's rain should wash it all away and will be of concern to those in flood-prone areas. Next week we may well be hearing, "lots of flooding, and if you're trapped out of your home due to the flood waters accompanied by high winds- well, don't worry, at least it will be mild!".

Snow intensity has increased to moderate-heavy again- I can't tell what's coming up on the radar because of the glitch over West Yorkshire so everything is a bit of a surprise at the moment. Temp has crept up but only to -0.5.

Strange how marginality affects different locations in different events- I'm at -0.6C with everything having fallen as snow so far, and some areas of the region are marginal and are seeing sleet/rain mixes. Yet some of those same areas had a sizeable top-up of their snow cover during last Sunday night's frontal event with temperatures close to or just below freezing while I was stuck up at +1C for most of the night on that occasion with no significant accumulations.

I think in view of this cold spell going out with a flourish here (9cm on grassy surfaces and 6cm on concrete) I'll have to upgrade this cold spell to a repectable 8/10- out of a possible 10, roughly 1.2 marks chopped off for lack of sunshine and 0.8 marks chopped off for the fact that there was never more than two inches on the ground here prior to the snow event associated with the breakdown. Otherwise pretty solid stuff, and there's been a good 10+ days of snow cover. Had I been in Tyneside during the cold spell from 25th Nov-10th Dec 2010 anything less than a straight 10 would have done it a grave injustice, but unfortunately I was in the infamous dry corridor in Norwich during that easterly. However the cold spells that I experienced from 17th Dec 2009 to 9th Jan 2010 and from 18th-26th Dec 2010 were a solid 9.5 as was the late-December 1995 spell. For some additional perspective I only gave the first half of February 2012 about 4/10 for where I was at the time- so this month's spell whopped that one out of sight.

Not much more to come judging by the radar, but about 9cm on grassy surfaces and 6cm on concrete- about twice the largest depths here earlier in this cold spell, and dropping to -0.4C at present so good signs re. the milder air catching up with the precipitation. The cold spell was rather disappointing in terms of snow depths here but has certainly gone out with a bang!

Checked my snow depths and they are indeed the highest of the cold spell- about 3-4cm on concrete and 7cm on the grass with more still to come! Especially considerring it's the last bout of the cold spell I feel greedy and fancy a good 15-20cm fall... lol.

It's going to be hard to call- the milder air is already overhead (850hPa temps of -2 or -3) but it will only penetrate towards the surface as the polar maritime airmass approaches from the west and we get some mixing of the layers. I have a feeling that over much of Yorkshire, if the mild air does get in before the precipitation clears, it will only be the back edge, but of course that could make the difference between 5-10cm of snow and 2-5cm of slush/ice for some of us. Tonight's GFS 18Z run seems to be suggesting that significantly milder air may not arrive until tomorrow night with maxes of just 2 or 3C tomorrow. I must admit that until recently I had largely written off this particular snow event but it's mainly because in my experience similar events have generally failed to deliver other than to limited slices of the British Isles- mainly because the west gets the milder air quickly and the east gets only light precipitation. Tonight's event is proving quite unusual for how much heavy precipitation is getting into central and eastern areas, but to be fair the GFS has been suggesting that for a while.

I'm just being patient for now- the heaviest stuff is to my south but is slowly inching north, temp still at just 0.1C, still coming down moderate to heavy at the moment.

I'm hoping for something akin to what I had in Norwich on the 23rd November 2008 (one of those rare cold-to-mild frontal events that delivered a lot where I was). Snow fell heavily for much of the morning until mid-afternoon and gave about three inches, and the milder air arrived just as the precipitation cleared (hence no issues with slush/ice) and the sun came out instead, so I had some good fresh snow to hang out with the UEA students in for the rest of the day, with the sun just trimming a bit off the depth. The snow then melted the following night. Could certainly do with the milder air holding off until after the precip clearance tonight- then tomorrow may be a day of proper snow cover, possibly my deepest of the spell, before the inevitable thaw tomorrow night, rather than an icy one (which is more likely to be the case if the milder air gets ahead of the back edge of the precipitation). Of course if the mild air lags behind the front at my location then it would imply a similar story at many other locations.

Looking increasingly likely that this frontal event may end up producing my largest accumulation of the cold spell- up to about 3cm already, with a temp of 0.2C so well on the cold side of marginal at the moment, and more to come on the radar. I'm a bit wary of that warmer air at 925hPa- but all snow so far. Shame it's waited until the end of the spell to do this here- but good to see it bowing out with a bang, especially as traditionally I don't often get much out of these frontal events coming in off the Atlantic.

Pulses of heavier snow to the south have finally crept overhead- getting some proper stuff now.

A bit irritating that the heavier stuff to the west is being blocked by the Pennines yet heavier stuff keeps also forming just the S and E- still, had more than some so far.

Not too marginal here yet- started off at 1.2C then fell to 0.4, about a centimetre of fresh snow on the ground, but rather light so far.

Some light snow this morning has coated most surfaces but the main stuff is still out to the west. I get a feeling that what comes in tonight will mostly be snow but will be rather more marginal- not convinced that much of it will settle near sea level.

There's usually a clash of "rights" when it comes to people being slow, say, at the front of a queue in a supermarket. There's the right of the people at the front to be leisurely and not be in a rush, vs. the right of the people behind to be able to progress in the queue without being heavily delayed. The need for consideration towards others works both ways and both sides can be guilty of being inconsiderate. We know about the impatient people who put pressure on those in front of them to hurry up, but there are also the dawdlers who feel that others should just let them take as much time as they like and have infinite reserves of patience and allow an infinite amount of extra time for their day-to-day activities- some of whom get a boost from watching others get annoyed in the queue behind them. I think all too often, the "dawdlers" get the benefit of too many doubts. There's a perception that people just need to slow down, be more relaxed, allow more time for everything and be more patient, and then it will be better for everyone, and thus that "dawdlers" are well within their rights. However, there's a difference between being slower because you aren't in as much of a hurry, vs. being slower because people dawdle more in front of you- the latter is a recipe for [i]more [/i]frustration and impatience, not less. There should be limits as to how much extra time people should be required to allow, and how much inconvenience and discomfort it is OK to subject them to. This issue is relevant to some motoring-related discussions that I've been involved in on this forum (the belief that people should be entitled to drive as slowly as they like, fuelled by the war against speed) and a similar argument can be put forward for the slow-walking people who walk 6 abreast down an alleyway. Personally I think that if possible, if you want to be slow it is good to occasionally let other people past. For instance if I'm walking down a pavement and someone is going for a jog, I'll step out of the way, I won't stand in his/her way and say, "stop being in such a rush!". Similar with people who want to drive very slowly- when holding up queues of 10 vehicles down a country lane it would be good to pull over once in a while instead of saying, "they should all have to bow to my right to slow everybody up". Of course, this often isn't possible in the likes of supermarket queues, in which case the only considerate thing to do is not to take a lot more time than you really have to.

I've quite often been thinking your bit in bold recently!

Philip Eden has England and Wales sunshine for 1st-21st January at 70%. http://climate-uk.com/ It is highly likely to go down as a very dull January here in the Thirsk/Northallerton area of Yorkshire. The mild anticyclonic spell brought mainly cloudy weather with the holes in the cloud mostly restricted to the south/east of here, and although the cold spell started off with some bright days, there has been hardly any sunshine since last Friday morning. I'll be surprised if my area has exceeded 25 hours of bright sunshine so far this month.

I remember 2001, 2006 and 2010 being very close to the 1971-2000 average. March and April 2001 were cold but were counterbalanced by a warm May, and in 2006, following a cold March, April and May were both slightly warmer than average. In 2010, slightly colder-than-average temperatures in March and May were offset by a warm April. Also none of those three springs were significantly (more than 0.5C) short of the 1981-2010 average either, contrasting sharply with the large number that were more than 0.5C above. April 2012 was not an exceptionally cold month because we didn't get any particularly long-draw northerlies- the prevailing pattern was generally cool and cyclonic- and excessive cloud cover, particularly in the second half, helped to hold the night-time minima up. The consistently low daytime maxima, lack of sunshine, frequency of grey windy weather and absence of any pronounced warm spells gave the impression that the month was a lot colder than the statistics suggest. I would be quite in favour of a cold bright spring for a change, but not another spring like 1996- March 1996 in particular was dominated by grey south-easterlies and some parts of NE England had 15 consecutive days without sunshine from the 11th-25th- which would be unusual enough in January, let alone March!

The last time I saw lying snow during the spring quarter was back in March 2009, remarkably when I was in Exeter and the south-west got hit by a localised snowfall on the 4th/5th. April 2012 came close in Cleadon but the winds off the North Sea held the temperature up at around 2C. I don't think there's much of a hard-and-fast rule regarding the association of cold temperatures with sunshine and rainfall during the spring months. A pattern with southerly tracking lows will usually be dull and wet towards the south but dry and sunny in the NW, a northerly or north-westerly type will usually be bright with wintry showers, while easterly and north-easterly types increasingly become grey and damp in eastern areas unless they are sourced from a long way north, as the continent warms up and the North Sea remains cool. As we head into summer northerlies become more commonly associated with grey damp weather as well, as any sort of modification from Scandinavia tends to stabilise the associated air masses, although it will still often be bright and showery if the winds are vectored from west of north.

One recurring feature of most recent summers has been the strong jet stream which has brought Atlantic depressions rapidly eastwards before hot southerly flows got much of a chance to establish- thus the main "thrust" of the Spanish plumes has been too far south and east. On the 28th June 2012 we managed to get widespread and, for some, unusually severe thunderstorms in spite of this, but that day was very much an exception. I remember a lot of thundery Spanish plumes over north-eastern England during the mid-1990s- they were particularly prominent in 1994, and July 1995 and the 1996 summer quarter also had a fair number. The key was that the Atlantic depressions often made only slow progress in from the west, with relatively strong high pressure to the east, and this allowed thunderstorms to develop widely along and to the east of the frontal boundaries. 1999 was a generally thundery year for most, with particularly prominent Spanish plume type events on the 27th/28th May and 26th/27th June. Spanish plumes don't bring significant thundery outbreaks as often during the spring months, but I remember one in Lancaster (not normally a particularly thundery location) on the 1st May 2005, as well as the aforementioned May 1999 one. The aforementioned Mays of 1992 and 1997 both had a high incidence of thundery activity over much of the country- I don't think we had any clear-cut Spanish plumes but both months had spells when hot and thundery regimes moved up from the SE. As Aaron rightly mentioned, unstable flows from the north-western compass are capable of bringing widespread thundery activity during the spring months, which can be accompanied by big hailstorms too- there were good examples in the second week of May 2005 and in the first half of April 2008 for example. March 1995 was particularly notable for a high incidence of hail in many parts of the UK due to frequent cold unstable west to north-westerly flows. In my experience cyclonic south to south-westerly flows, if associated with minimal frontal activity, can also produce a fair amount of thunder as we get into April and May, for example during the period 18th-24th April 2000 and towards the back end of April 1998.

Yes, March 1965 was exceptionally warm near the end, and in Whitby it was the hottest day of the year: http://www.wetterzen...00119650329.gif ...yet the beginning of the month had been exceptionally cold: http://www.wetterzen...00119650302.gif The 29th March 1968 was also exceptionally warm in many parts of the country with 25C widely over East Anglia. Unlike in the 1965 instance, a tropical maritime air mass kept the minimum temperatures high as well, though it meant cloudier skies in the north: http://www.wetterzen...00119680328.gif And then, into early April, we got this: http://www.wetterzen...00119680403.gif ...with widespread snowfalls and widespread maxima of 2 to 5C.

The polar vortex is indicated by an organised area of blues and purples on the pressure charts that show 500hPa heights. For example, here's the Netweather version of the GFS at T+72: http://cdn.nwstatic..../72/h500slp.png And the Wetterzentrale version, which is also popularly used: http://www.wetterzen...cs/Rtavn661.png A polar vortex, indicated by blues and purples, indicates very cold air at high altitudes and this encourages low pressure systems to form in those areas- this encourages a succession of low pressure systems tracking to the north of the British Isles with high pressure to the south, and thus mild westerly and south-westerly winds. The only route to cold snowy weather in that setup is if low pressure systems track NW-SE firing in frequent cold north-westerly winds, and that setup is pretty rare. If the polar vortex is weak (i.e. we don't have a lot of blues and purples showing to the north of the British Isles) then there is less chance of low pressure repeatedly tracking to the north of Britain and bringing in westerly winds. I mentioned this morning's ECMWF run which tones down the polar vortex at around day 9, when we end up with a fragmented vortex with one part over Canada and the other over Scandinavia: http://cdn.nwstatic..../ecm500.216.png However the GFS 06Z keeps the vortex pretty strong to our north, so there's a fair amount of uncertainty over this.