Thundery wintry showers

Widespread falling and lying snow is possible in October but is pretty rare. The 28th October 2008 was the most outstanding recent example, as a trough moved in from the NW and brought sleet and snow showers and some longer outbreaks of wintry precipitation, accompanied by thunder in some places, and some parts of the Home Counties had two or three days with lying snow. Around the 20th October 2010, sleety showers affected eastern coastal areas as far south as Scarborough with a dusting of snow for Aberdeen. However, other than that, lying snow in October has been very rare. In 1993 the Aberdeen area had a snow cover on the 16th, and in 2000 parts of Lancashire and Yorkshire woke up to a snow cover on the 30th, but as a general rule October northerlies bring mainly rain showers at low levels with sleet and snow over the hills. October snowfalls were more common in the 19th century. When I trawled through the synoptic archives at Wetterzentrale I found about half a dozen years when the -5C 850hPa line was well south around the 11th October, and I remember reading that lying snow was widespread over Cumbria on the 11th October 1896 with thundersnow at Dartmoor. Statistically though lying snow at low levels has always been rare except near the end of the month.

[quote]High pressure will be dominant over central and northern Europe during the first half of September, which will bring plenty of warm dry sunny weather to most of southern and central Britain, although Scotland and Ireland will always be more prone to banks of cloud. During the second half of the month, low pressure will take up residence to the west of the British Isles giving us a changeable but rather warm south-westerly type. Dry, sunny weather will dominate over most of England and Wales on the first three days but with more cloud over Scotland and Ireland. A weakening belt of cloud and drizzle will head south-eastwards over England and Wales on the 4th, with brighter weather following from the north-west, and bar a few isolated showers over western and northern Scotland, it will become dry again. Between the 5th and 9th September, the weather over Wales, together with central, southern and eastern England, will be consistently sunny and dry, with generally warm daytime temperatures, though not exceptionally so. Most places will see highs between 21 and 24C. Scotland, Ireland and Cumbria will be prone to more cloud and some light rain, particularly on the 6th and 7th, although these areas will be dry and sunny on the 5th. High pressure will start to pull away between the 10th and 15th which will allow a changeable south-westerly type to establish over north-western Britain. This will bring some rain belts interspersed with brighter showery weather, with the majority of the showers confined to northern and western Scotland. For most of central, southern and eastern England, though, there will be long dry sunny periods and rainfall amounts will be very small. Temperatures will continue mostly above normal, although daytime temperatures may drop a little below normal at times over western Scotland and Northern Ireland. Around the 16th/17th we can expect a large depression, containing the remains of a tropical hurricane, to approach the British Isles, and this will herald the shift towards more unsettled conditions. A bout of wet and windy weather is expected, with gales possible in western areas. After that, the winds will be mostly southerly or south-westerly and this will bring belts of rain interspersed with brighter showery weather, with some of the showers heavy and thundery, particularly in the west and south. Temperatures will continue rather above normal except over western Scotland and Ireland. During the last week of September lowest pressure will transfer north-eastwards and give us a more "traditional" westerly type, with temperatures returning to normal, and the majority of the rain will affect north-western parts of the country, with small amounts over central, eastern and southern England. September 2012 will be a warm month. I am predicting a Central England Temperature of 15.4C, with temperatures generally ranging from 1.5 to 2.0C above the 1981-2010 average in eastern England to 0.5-1.0C above in Ireland and western and northern Scotland. Rainfall totals will be slightly above normal over western Scotland and Northern Ireland, but elsewhere it will be a generally dry month with rainfall shortages of 20-40%. Shortages of over 50% are expected quite widely over the eastern half of England and also in south-east Scotland. Sunshine totals will be 10-20% below average in western and north-western Scotland, but near average over most other parts of Scotland, together with Ireland and Cumbria. Elsewhere it will be a sunny month with excesses of 10 to 30% in most places. Sunshine is likely to be 40-50% above at some places across a belt of eastern England from Northumberland down to East Anglia. [/quote] I was pleased with how the June, July and August forecasts went, but my September forecast wasn't one of my better ones. The first 10 days of the month went much as predicted, as did the change towards less settled conditions in the middle third of the month, but the weather turned out somewhat cooler than I expected after midmonth and we did not get a large depression around the 16th/17th. That prediction had been based on the likelihood of an ex-hurricane approaching the British Isles, but in reality its remnants passed by harmlessly to the north of Scotland. A second ex-hurricane then swung across the country on the 24th-26th and gave those exceptionally large rainfall totals in northern England. It goes to show how much of a difference these depressions containing remnants of tropical storms can make to the UK's weather, and they can certainly provide forecasting headaches especially at long range. As a result of the above, temperatures were generally a degree or two down on the values that I had forecast. Rainfall totals were looking set to be similar to what I had predicted before the big depression on the 24th/26th raised totals above average over many parts of the country, while sunshine totals were quite similar, maybe a little higher than I expected in N and W Scotland and lower in eastern England. The saying, "you win some, you lose some" certainly applies to long-range forecasting!

Looks like my Penzance prediction isn't guaranteed to come off then! The easterly outbreak of the 11th-14th January 1987 was the coldest of the twentieth century, but it does show that Penzance can get sizeable snowfalls given an exceptionally cold easterly coming off the English Channel- I do recall reports of thundersnow from the extreme south-west in late November/early December 2010 also. It does require an exceptionally cold easterly type though. I remember having similar feelings in Tyne and Wear on the 9th-12th February 1998 when we were hearing about the warm sunshine that was extending up from the south-east, while stuck under dull, dry, mild conditions with a strong south-westerly wind. The sunshine extended further north on the 13th to cover Tyne and Wear, and I went over to Carlisle that day where it was also generally sunny, but Lancaster recorded just 0.2 hours of sunshine indicating that some parts of NW England stayed cloudy.

I'm going to make some extremely bold predictions for the upcoming winter: Daylight will steadily decrease, reaching a minimum around 21st/22nd December, and will then increase afterwards. Each of the three main winter months will be colder than this upcoming October. The sun will shine for less than 50% of the possible total in all parts of the country. Somewhere at low levels will see a covering of snow at some point. If we get snow in November, the winter will feature repeated posts referring to the old saying, "Ice in November to bear a duck, the rest of the winter will be slush and muck", referring to the 2010/11 season as proof of the amazing accuracy of the saying. Hastings will have more than twice as much sunshine as Lerwick. The mean global temperature will be above the twentieth-century average in all three months. Penzance will have very little snow.

11.6C- I think it may warm up after next weekend as high pressure pulls away to the east.

The latest GFS runs are reminding me of early October 1995, which started with a week of windy and showery west to south-westerlies, and then a southerly incursion on the 8th/9th which brought unusual warmth, and plenty of sunshine to most places. The GFS is indicating similar temperatures for next weekend, with 21-24C over a wide area on Sunday when you account for the GFS's traditional underestimation of maxima: http://cdn.nwstatic....180/h500slp.png http://cdn.nwstatic....6/ukmaxtemp.png However I don't think it is very likely to come off, as the UKMO and ECMWF are going for a very different picture- we still get a ridge of high pressure, but we get a cool bright showery west to north-westerly regime on Thursday/Friday which would set us up for a dry sunny cool weekend with overnight frosts. Before that, next week looks like being showery but also quite bright, with a slow moving low pressure giving us relatively little frontal activity, although as always in these setups there is potential for disturbances to turn up nearer the time and turn sunshine and showers into a cloudy wet scenario from time to time.

It says in the "asterisk" information at the bottom that the Woodford data is estimated.

Some good points earlier. I mentioned North Sea convection and the way central and western areas often get more snow from frontal battleground type setups, but I omitted to mention the arctic maritime setups with winds vectored from west of north that bring snow showers off the Irish Sea into the Cheshire Gap area, as well as parts of Wales, SW England, Ireland and western Scotland. I remember seeing about the south-west getting unexpectedly hit by heavy convective snowfalls on the 25th November 2005, with a midday temperature of only 1C at Plymouth. Those setups with snow showers off a polar maritime westerly or north-westerly are pretty dramatic on the rare occasions when they are cold enough- early March 1995 was probably the starkest example in my lifetime, as I am too young to have experienced the Januarys of 1978 and 1984. The main issue with them is that it's rare that they are actually cold enough south of the Scottish border.

One scenario that hasn't been mentioned yet is the situation where we get embedded fronts and troughs in an arctic or continental airstream, which can bring belts of organised snowfall in an otherwise showery regime. This happened widely on the 5th/6th January 2010. The snowfalls over SE Scotland and NE England on the evenings of the 26th and 27th November 2010 were similarly enhanced by weak occluded fronts out in the North Sea. Such disturbances are often still associated with pools of comparitively warm air, but nothing like the warm airmasses that get into the mix around depressions associated with Atlantic fronts. The 27th January 1996 was a good "easterly" example- many of us saw sunshine and snow showers on the 26th, and then a weak front moved over on the 27th and gave mostly cloudy weather with snow for southern Scotland and the northern half of England. However many of the biggest snowfalls in central and western Britain, which are sheltered from North Sea convection, have historically arisen from "battleground" events with Atlantic weather systems pushing in and then stalling against cold arctic and/or continental air. In those situations areas on the poleward flank of the fronts can pick up large amounts of snow, although to the south and west of that it will often turn milder with rain, so we end up with euphoria for some snow lovers and disappointment for others depending on location. In most places near the North Sea, though, frontal battlegrounds tend to produce rather less than convection off the North Sea.

For me, as a fan of convective type weather and sunshine, I prefer the scenario of sunshine mixed with heavy snow showers- they may be more hit-and-miss but they provide dramatically-changing conditions, and more spectacular cloud formations. I feel that it's a shame that the weak winter sun doesn't generate much convection inland, with showers often restricted to coastal areas, as I think the sort of showery northerlies that we get in April, but with maximum temperatures close to freezing, would be very exciting to watch. I wouldn't say "no" to a major frontal snow event though, even if it involved snow turning to rain. My main concern is that when we get "marginal" frontal snow events, sometimes the precipitation ends up as rain or sleet throughout and the weather ends up grey, raw and, to my mind, rather depressing. If a showery setup ends up on the wrong side of marginal the result tends to be a mix of sunshine and hail/sleet showers.

The 16th December also brought the biggest snow event of the winter to the Tyne and Wear area. A small band of rain moved northwards overnight 15th/16th, ahead of the main frontal belt that affected Stoke, and then it retreated southwards, turning to snow as it did so. As a result, Cleadon had a few centimetres of snow, with more than that in some inland places and on higher ground. Showers followed behind off the North Sea although they turned to hail and sleet as a pool of slightly milder air moved in, and this trimmed away some of the snow cover. Nonetheless, there was more than 50% snow cover at Cleadon on the mornings of the 17th and 18th.

Re. last winter, December contained numerous marginal snow events in the north but snow cover was generally short-lived at low levels except in parts of western and northern Scotland. January was largely snow free at low levels, while February had two significant snow events over much of England, but much of Scotland, Ireland and parts of Wales and northern England largely missed out. In Tyne and Wear there was a notable "ice-storm" on the 4th February, with an increasing tendency for snow further south into Yorkshire. The autumn was remarkably snow-free, while the spring had a few marginal snow events but no widespread snow cover at low levels. On my "Winter Snow Events" index the winter scored 28 which put it on a par with 2003/04 and 2004/05, but it was easily the least snowy since 2007/08.

Dull and wet in Sandhutton, with 56mm since yesterday morning- up until yesterday it looked like being a very dry September here, but after just one day, it now looks certain to be wetter than average! A minimum of 10.3C, contrasting with recent cold nights.

2nd consecutive frosty morning at Sandhutton, N Yorks, 1.6C minimum yesterday and 2.5C minimum today. Yesterday was sunny all day but today has started foggy, and I think with deep lows sweeping in it will be a while before we get another frost here.

Re. having to clear your pavement in front of your driveway, the different laws on this are probably a consequence of the relative frequency of snow. Over much of Germany, winter snow sometimes sticks around for prolonged period and accumulates to large depths during cold winters, so people will struggle to get around on foot unless the paths are cleared, particularly after the snow is repeatedly trampled on and compacted to such an extent that you're left with solid ice. (Yes, I've had conversations on this topic with a couple of people who have lived in Germany for significant periods). In the UK, away from high ground, we aren't used to seeing prolonged spells of snow cover so I imagine that the prevailing view will be that it isn't worth making an effort to clear snow away when it will probably be gone by the next day. As is often the case, it boils down to the issue that we don't prepare very well for prolonged snow cover due to its rarity. I agree, though, that having laws against clearing the path in front of your house is pretty stupid. The winters of 2009/10 and 2010/11, and to a lesser extent 2008/09, probably caught out a fair number of experienced drivers as well as inexperienced ones, particularly in the milder parts of the UK, for we had a long run of mild winters from 1988-2008 during which some drivers wouldn't have experienced major snow-related problems. Those drivers should hopefully have accumulated more experience of driving in snow by now but new drivers are always going to be vulnerable.

There is a significant difference between the UKMO and the GFS/ECMWF for this Sunday at 00Z with low pressure close by to the south: http://cdn.nwstatic..../96/h500slp.png http://cdn.nwstatic..../ecm500.096.png http://cdn.nwstatic....9/00/met.96.png This is worth watching as the UKMO then blows this up into a vicious depression over SE England on Monday which would bring wet and windy weather into the SE much earlier than the GFS and ECMWF show. The surface weather that we get from next week's low is uncertain. The GFS shows a straightforward sunshine-and-showers setup, and with it being late in the season, inland areas may not see many showers, but the UKMO and ECMWF both strongly hint at secondary low development which would promote active rain belts especially for the west and south of the country. My gut feeling is that the UKMO/ECMWF will probably be nearer the mark with this. Although the general outlook for the next few days 'looks' quiet we have a slow-moving frontal system which will affect Scotland and northern England tomorow and will then spread into southern areas on Friday.

At the weekend GFS had quite a deep low for Thursday while UKMO/ECM had a much shallower feature, and it is looking probable that UKMO/ECMWF will be right about this. However, there could still be a pretty active rain belt sweeping SE with some heavy rain over Scotland, northern England and Northern Ireland, though fizzling as it approaches southern England. Other than that, a fairly quiet week ahead- some scattered showers about tomorrow in a chilly NW airstream, but most places should be dry with sunny intervals on Wednesday and again on Friday. With winds consistently coming down from the north-west temperatures will consistently be on the low side of the long-term average. A touch of ground frost is likely in inland parts of the north on the nights of Tuesday/Wednesday, Thursday/Friday and Friday/Saturday, with the night of Tuesday/Wednesday perhaps seeing a slight frost in parts of the south. There is pretty strong model agreement that low pressure will dominate most of next week's weather, with the low sliding down from the NW, although at this range, it is not impossible that the models may tone down the low as we get nearer the time.

I'm not sure I'd be keen on a repeat of the second week of February 1998 because warm sunshine didn't establish widely over northern England until the 13th and the weather prior to that was generally mild and muggy- if high pressure had been centred further north and east giving a south to south-westerly airflow it would be a different matter. I would certainly welcome a repeat of the second week of February 2008 at some point during the winter though, with warm sunshine by day and chilly misty nights. As for early February 1996, that would certainly be welcome.

It can be extremely hard to forecast- I remember being caught out by this in mid-March, predicting a "sunny" high only for banks of cloud to turn up on one of the evenings. One general rule of thumb is that the more humid the airmass is (as measured by relative humidity), the more likely it is that low-level cloud will form, particularly when the wind is coming off the North Atlantic or the North Sea. This low cloud then gets trapped underneath a layer of stable, sinking air associated with the high pressure, and spreads out into a thick stratus and/or stratocumulus sheet. Hence high pressure to the south often means a lot of cloud for northern and western Britain in particular. High pressure to the west or north tends to bring cloudy easterlies into eastern areas, although in the summer half-year, winds from south of east sometimes fail to produce much cloud over the North Sea if associated with dry continental air. High pressure to the east tends not to bring much cloud in off the English Channel, so anticyclonic/southerly types are almost invariably sunny in the summer half-year, though in the winter half-year we may import stubborn banks of cloud from the continent due to the weak sun failing to burn them off. In the summer half-year, the stronger sunshine tends to burn off such cloud sheets more effectively than in the winter half-year, and thus high pressure is a more reliable source of sunshine in late spring and summer than it is in winter. However, that isn't always the end of the story, because when we are under moist airmasses, solar heating generates convection which produces low-level cumulus, which in turn spreads out into stratocumulus- this can give us sunny mornings and evenings but cloudy afternoons. I generally think that in the winter half-year, the most reliable route to a "sunny" high is an incursion of dry polar or arctic air followed by a build-up of high pressure. Imports of dry continental air with high pressure centred to the east are comparably reliable in the summer half-year, but in the winter half-year it all depends on how cloudy it is over the continent, and thus "southerly" anticyclonic spells in winter range from the remarkably sunny (e.g. 8th-20th February 2008) to the overcast (e.g. much of February 1993).

I vaguely recall a surprise thaw in Cleadon near the Tyneside coast overnight 19th/20th February 1996, following a very snowy day on the 19th. I'm not sure if it was mainly down to the strong NE winds lifting the temperature near the coast or mainly a "dry windy thaw", but we woke up to about 1-2cm on the morning of the 20th after having seen a good 2-3 inches on the ground during the previous evening. I remembered John Kettley's forecast referring to a "finger" of showers in NE England late on the 20th, but frequent heavy snow showers unexpectedly developed over NE England after the forecast was issued and restored the snow cover to about two inches again. The radar outputs from the forecast on the 19th show how widely the snow showers developed to the west of the Pennines- perhaps a combination of the strong winds bringing the showers well inland plus a modest amount of solar heating adding a homegrown element to the convection (like also happened in the northerly outbreaks of late-February 1993 and 2004). Lancaster reported two inches of lying snow on the morning of the 20th.

One of those rare cases where I come out similar to the majority it would seem. Somewhere within the range of 20 to 25C suits me best, nearer 25C when idle and nearer 20C when active.

It was a rather mild damp month in Tyneside- I remember a cold bright spell in the first week with hazy sunshine, but after that, a lot of mild cloudy weather, and that exceptional frontal rainfall event immediately before the cold snap. However, although the month was dull in the northeast, most central, western and southern areas reported above average sunshine.

Here in North Yorkshire, Saturday was mostly cloudy but since then it's been generally sunny and with temperatures on the warm side of average. There's been some interesting cloud formations about at times, so not too boring either. It is all dependent on the positioning of the high pressure though and I always suspected that some parts of northern and western Britain would be rather cloudy.

The issue is simply that climate science is very complicated. Climate scientists are reasonably sure that global temperatures will rise overall during the 21st century (but with considerable debate still ongoing re. the likely magnitude of the rise), but many of the feedback processes that come into play are still poorly understood. The prevailing theory re. impacts on atmospheric circulation has always been that a warmer world would lead to a northward movement of the jet stream giving us milder wetter winters and hotter drier summers. However, the recent southward movement of the jet stream, coinciding exactly with record low Arctic sea ice extent, has forced the mainstream climate scientists to reconsider their position, with an increasing amount of research going into the impacts of reduced Arctic sea ice on the position of the jet stream. I don't think these complications change the overall picture regarding global warming, but there is mounting evidence that the next IPCC Assessment Report will have to revise the "ice-free Arctic summers" projections forwards. As for the "they told us X, and now they're telling us Y", there are some valid criticisms here, which stem mainly from the mis-handling of the politics of climate change rather than the science. When the subject gets political there is always a temptation for people to simplify and replace, "is indicated if current trends continue", with "will happen".

Perhaps surprisingly, September 1995 came out with a near-average mean temperature in the end, despite a cool and, for some, exceptionally wet start, and some chilly north-westerlies in the last week. Sunshine totals were also generally close to average except in the phenomenally wet east and north of Scotland. There was a spell of fairly warm and quiet weather in the third week which probably helped bring the average up a bit. The Septembers of 1992, 1993 and 1994 were all much cooler than average though, as well as being dull and wet for the majority. I remember September 1993 being particularly dull and wet following the warm start. Septembers 2001 and 2008 were cool by day, but high overnight minima prevented those months from falling far below the long-term normal. There has indeed been a lack of cold dry autumn months in recent years. October 2003 springs to mind as a rare example of one.