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Thundery wintry showers

Long range forecast team
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Everything posted by Thundery wintry showers

  1. Yes, it could have been, as the hourly temperature readings from Exeter Airport suggest a rapid temperature drop to 3.1C, which is just about low enough for the odd bit of half-melted snow to survive on its way down: http://www.weathercast.co.uk/world-weather/weather-stations/obsid/3844.html
  2. In the long run I think yes, but I think it will be a slow and erratic process, as it would seem that for every X amount of warming in the Arctic, our northerlies only warm by a very small fraction of that amount. I reckon we'd probably need at least another 2 to 3C of global warming, even taking into account the Arctic amplification, to make it close to impossible to get widespread lowland snow from a northerly, and probably close to 5C of global warming to nuke those rare but intense "Beasts from the East". After all as you mention in your next post we managed to get widespread snow (even including an instance of lying snow here in Exeter) in late January/early February this year, from air masses that weren't originating from the east, or even from particularly far north. I can foresee Britain continuing to get widespread lowland snow from northerlies throughout the next half-century, but with the frequency of northerlies that are cold enough gradually becoming fewer and further between, and increasingly outnumbered by the northerlies that just bring rain. The same goes for easterlies too, as while the coldest easterlies tend to be colder than the coldest northerlies, the majority of our easterlies are also pretty marginal for snow. There is a chance that we might not warm by enough to make it impossible to get widespread lowland snow off a northerly, because the amount of warming that we'd need for that would be likely to have destructive knock-on effects in various parts of the world, notably including the Arctic itself, hopefully spurring humans into action to try and avoid dangerous levels of climate change.
  3. Yes, I think the Arctic climate encountered a step-change in 2005 when the main driver of warming in the region shifted to being warm sea surface temperatures and lack of sea ice. Between 1990 and 2004, much, though not all, of the Arctic warming could be explained synoptically, and the same was also true of our relatively mild and snow free winters in the UK, as when we did get northerlies they weren't significantly less potent than they were earlier in the 20th century. There was a paper on this subject by Erik Kolstad (Marine cold-air outbreaks, Climate Dynamics) which showed no significant decline in the potency of northerlies between 1961 and 2000. It would be interesting to see an updated scientific analysis of marine cold-air outbreaks for the period 2005 onwards, as I expect that it would give very different results. I have a suspicion that the Arctic might have passed another "tipping point" into a warmer base climate state in 2016 driven even more strongly by SSTs and sea ice than in 2005-2015, although we'll need at least a couple of years more data to be able to have as much confidence in this as with the 2005 shift. Although the greatest warming from 2005 onwards has occurred in the "Arctic Rim" at 70-80N, which is most sensitive to sea ice changes, these climatic shifts are also evident in the ERA reanalysis for the Arctic north of 80N: http://ocean.dmi.dk/arctic/meant80n_anomaly.uk.php
  4. Yes, and all of this is happening despite relatively favourable synoptics for sea ice growth for a large part of the autumn so far. I think the exceptionally high sea surface temperatures on the Eurasian side of the Arctic, extending across towards Alaska, may be largely to blame, following record breaking temperatures there during late July and August after an unusually early melt-out. I recall looking at the 1995 Arctic melt season (which at the time saw one of the two lowest minimum extents on record, the other being 1990) and sea ice was slow to form on the Eurasian side of the Arctic because of persistent strong southerly winds in that region in late September. However, as soon as the southerlies abated, the ice quickly reformed and by 20 October a large majority of that region had iced over. Things have clearly changed a lot up there since then!
  5. Copernicus (using the ERA5 reanalysis) has September 2019 as nominally the warmest September on record, just ahead of 2016, and has 2019 on course to be the 2nd or 3rd warmest year globally. Surface air temperature for September 2019 | Copernicus CLIMATE.COPERNICUS.EU
  6. I tend not to look forward to winter because of the lack of daylight. I don't think I suffer strong enough "light withdrawal symptoms" to officially qualify as having Seasonal Affective Disorder but I seem to have a mild version of that kind of thing. On average it doesn't have a big effect on my quality of life but I tend to find it easier to be in high spirits in spring and summer than in autumn and winter, all other things being equal. One marked instance of where all other things weren't equal was in 2010, when I found the darkest months of November/December/January more enjoyable than many of the lighter months, for reasons that many of you may be able to guess.
  7. At one time (back in the early 2000s) I was one of those who dismissed January 1987 as chiefly a south-east event, mainly because I had access to weather stats for Lancaster and they just had a centimetre from it, and because the archive charts show very high pressure across the north. But my present-day impression is that most areas had a fair amount of snow, with sheltered western areas tending to be the exception, as the air mass was so cold that it was able to generate plenty of North Sea convection all the way up to eastern Scotland despite the very high pressure. Another area that was heavily hit was, unusually, southern Cornwall, with massive falls in places like Penzance, as the air mass was so cold that even the far south-west peninsula was cold enough for snow, and it presumably got hit by snow streamers running along the English Channel.
  8. I was in South Tyneside during that February 2012 spell and remember an ice storm on 4 February and some freezing rain on 9 February, but I was just to the north of the freezing rain/snow boundary. The ice melted quickly on the 5th, but I remember travelling down to Birmingham by train around the 6th/7th and finding that there was a fair amount of lying snow from Durham southwards, though not in Birmingham itself. I saw pictures from the University of East Anglia suggesting that the Norwich area had fairly deep snow which stuck around for a while. I also remember January 2012 having an anticyclonic spell in the middle of the month with some stunning sunsets, reminiscent of the anticyclonic spell of 8-20 February 2008. Otherwise nothing else sticks out as particularly noteworthy. The winter of 2011/12 was also notable for insane warmth in the Russian and Norwegian Arctic with seasonal temperature anomalies locally in excess of 15C.
  9. It depends on what dataset you're using, as NSIDC still has the 2019 sea ice extent above 4 million square km: https://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/ NSIDC also has 2019's sea ice minimum as the second lowest, though only very marginally ahead of 2007 and 2016. My initial thoughts were that, yes, it was surprising that August ended up as the Arctic's warmest August on record at 925hPa, but when I think deeper about it, it's not really that surprising. Temperatures over the main ice pack were often close to the long-term average, especially late in the month, which restricted the decline of the sea ice extent, but the 850hPa temperatures over the Eurasian side of the Arctic - where all of the sea ice melted out by midmonth - were often exceptionally high. Barring favourable synoptics there's a good chance that the refreeze north of the Eurasian continental mass will be unusually slow this year.
  10. Here's some old classics from a NW or WNW direction, these brought plenty of snow to much of the North West: https://www.wetterzentrale.de/maps/archive/1955/era/ERA_1_1955011712_1.png https://www.wetterzentrale.de/maps/archive/1958/era/ERA_1_1958011912_1.png https://www.wetterzentrale.de/maps/archive/1973/era/ERA_1_1973021400_1.png https://www.wetterzentrale.de/maps/archive/1978/era/ERA_1_1978011000_1.png https://www.wetterzentrale.de/maps/archive/1981/era/ERA_1_1981011500_1.png https://www.wetterzentrale.de/maps/archive/1982/era/ERA_1_1982121700_1.png https://www.wetterzentrale.de/maps/archive/1995/era/ERA_1_1995030200_1.png This one, although brief, was pretty well timed: https://www.wetterzentrale.de/maps/archive/2004/era/ERA_1_2004122512_1.png This westerly brought severe snowstorms to many parts of Scotland and Northern Ireland, I don't think snow generally lay for long at low levels across the north of England though: https://www.wetterzentrale.de/maps/archive/1993/era/ERA_1_1993011112_1.png I was in Lancaster in the early 2000s so became pretty familiar with the search for these setups. However, my luck was out during that spell - the only decent snowfall that Lancaster had during my time there was on Christmas Day 2004 (from the second-to-last north-westerly linked above), while I was away! Actually, come to think of it, Lancaster had falling and lying snow from a west-north-westerly as recently as... this year, and it stuck around for a few days, so even in the current warmer climate it is possible. I remember Lancaster University tweeting about it:
  11. It could very easily have been Jan 1984 - that was an unusually snowy "westerly" month from the north Midlands northwards. The WNW'ly type delivered widely around the 15th in particular and then there was a frontal snow event around the 21st-23rd which had similarities with that of early February 1996. https://www.wetterzentrale.de/maps/archive/1984/cfsr/CFSR_1_1984011506_1.png I remember the snow from a westerly on the evening of 11 February 2014 - I was up in North Yorkshire at the time and remember a dusting that evening, but it had largely gone by the next morning as milder air moved in. It was the only lying snow of the entire 2013/14 season, which stuck out as the most snowless season that north-east England has had in the past century. Yes, one can draw parallels between 2013/14 and 1987/88 as the winter of 1987/88 similarly marked the end of the cold winters of 1985-1987 (and the more generally snowy period of 1978-87). However the winter of 1987/88 was followed immediately by more exceptionally mild winters in 1988/89 and 1989/90, whereas 2013/14 was followed by the closer to average winter of 2014/15, which I recall had fairly widespread snowfall from westerlies around 14 and 29 January.
  12. Some interesting stationary waves at around 3:05 - is that what you meant? I have often been intrigued by those, how the clouds seem to be moving and yet staying still at the same time. They were quite common when I was living up in Tyne and Wear, but less common down here in Devon.
  13. Yes, it was. The last third of December 1987 was generally dull, drizzly and mild with a persistent tropical maritime SW'ly, but on Christmas Day we had an incursion of returning polar maritime air which was still fairly mild and brought plenty of sunshine: https://www.wetterzentrale.de/maps/archive/1987/era/ERA_1_1987122512_1.png It wasn't as mild as some of the tropical maritime air that we had either side of Christmas Day but it would probably have felt warmer in the sunshine. I don't remember the day specifically, just remember browsing some climate stats some years ago and seeing a long run of sunless days in late December 1987 interspersed with ~6 hours of bright sunshine on Christmas Day.
  14. It's hard to understand why there is a patch of ice around Spitzbergen as that region has consistently had above-average temperatures through the summer - perhaps ice has been transported down from the north? Certainly the ice patch is reflected by the fact that the capital Longyearbyen had its first lying snow of the season a few days ago, which is unusually early for recent years (in most recent years it hasn't snowed and lay there until October, although last year there was a bout of lying snow near the end of September). Over the past year it's especially been over the other side of the Arctic, especially around and northward of the Bering Sea, that we've seen exceptionally high temperatures and seen ice struggling to take hold even in winter, in a region that has historically tended to be at least partially ice covered all year round. The fact that we're unlikely to record our lowest annual minimum is a reflection of how extreme August 2012 was for its rapid melting, assisted by an intense low early in the month. It's still possible that 2019 could record the lowest annual mean sea ice extent if the refreeze is sluggish during the rest of autumn.
  15. Examining the global temperature stats from the main centres, it would appear that 1979 was when global warming got underway after the slight drop in global temperature between the 1940s and 1970s. 1980 and 1981 were both very close to being the warmest on record at the time, and from then onwards it kept warming up. I don't think Britain's climate showed any evidence of warming until around 1988-89. Winter 1979/80 was indeed fairly mild but there were several very cold and snowy winters after that, notably 1981/82, 1984/85, 1985/86, also January 1984 in the north, and the exceptional easterly in January 1987. There were also several cool summers during this period. The shift to milder winters started with the winter of 1987/88, while the shift to warmer summers started in 1989. I think we will run into cycles of cold winters again. I remember Philip Eden remarking on a 22-23 year cycle of cold winters around 1895, 1917, 1940, 1963, 1986, and 2008-2013 was a bit delayed relative to the earlier recurring cycle but not by a lot. If this cycle keeps up we might well run into some more cold winters around 2032-2035. But as the global temperatures continue to rise, each batch of cold winters will typically be less cold and less snowy than the previous one.
  16. Yes, we have a pool of anomalous warmth extending from Siberia into the Barents/Kara Sea region and towards the north of Greenland at present, which may be largely responsible for the accelerated melt: https://www.wetterzentrale.de/de/topkarten.php?map=2&model=ecm&var=34&time=0&run=0&lid=OP&h=0&mv=0&tr=24 The loss should slow down again in the next few days though as a low with cold circulation develops close to the pole, but it's looking increasingly unlikely IMHO that the minimum will be 5th or 6th lowest now - it will almost certainly be between 2nd and 4th, and if I had to place a bet it would be on 2nd lowest.
  17. I generally think of a "washout summer" as a summer with significantly above average rainfall, with emphasis on the frequency of rain rather than necessarily the quantity, combined with significantly below average sunshine. In recent years 2012 is the big standout for me, and 2004 is a contender as it was very wet, but not on a par with 2012 for lack of sunshine. In the archives, the summers of 1912 and 1954 particularly spring to mind. The stats for Durham for the summer of 1912 are shocking: all three months much cooler and wetter than the relatively cool 1961-1990 average, and with less than 50% of the normal sunshine, which would have contrasted particularly starkly with the summer of 1911.
  18. August 2000 was pretty decent in Tyneside, especially the second half, but July was distinctly dreich with maximum temperatures about 1.5C below the average and about 60-70% of the normal sunshine. June was a mainly dry cloudy month but with over a month's worth of rain on the 3rd/4th and a heatwave in the third week which raised temperatures slightly above the long-term average. And 2004 was a very, very wet summer in that part of the country, although with near or just slightly below average sunshine in all three months. Not sure what those two summers were like in the Exeter area. 2019 will go down as the strangest summer that I have experienced so far - lots of cloudy wet weather, but also a dry sunny first half of July, and apart from that, every time we've had a significant bout of warm/hot sunny weather it has broken temperature records across Europe and sometimes the UK.
  19. A sharp levelling off is evident in the NSIDC sea ice extent charts: http://nsidc.org/arcticseaicenews/ I was hopeful that the melt rate might slow down once the scattered ice patches detached from the main ice cap had melted out, but I didn't expect the slowdown to be as dramatic as this - it appears that the main organised clump of ice has melted very little over the past week. There is still potential for further reductions in sea ice extent during September as we saw in 2005 and 2010, which is most likely to happen if we get warm southerly incursions from Siberia melting the edge of the ice to the north of Eurasia and pushing it towards the pole. But it is looking extremely unlikely now that we will beat or even come close to the 2012 minimum. Indeed, there's even a slight chance that we could see little or no further melting from now, as happened in the 2006 and 2015 melt seasons, which would place 2019's minimum at only 6th lowest. I think between 2nd and 4th lowest looks most probable though, and I have a gut feeling that a melt event may happen around mid-September and push it up to 2nd lowest. Nonetheless, this isn't a major cause for celebration - for most of the spring and summer we've been tracking lowest or second lowest, we just failed to get a repeat of the exceptional August melting that occurred in 2012. 2019's annual average sea ice extent still could end up as a contender for the lowest on record.
  20. Really enjoyed watching the weather today, plenty of hefty showers in Exeter, the occasional rumble of thunder at 3-4pm and more frequent thunder at around 5-6pm.
  21. Not much shows up on the lightning detector but I got woken up in the Exeter area at 3:10am by strong winds, torrential rain and three flashes of lightning.
  22. I think it owed a lot to above-average temperatures over north Africa combined with a few days of southerly winds originating from that region. In addition the north African air mass was somewhat hotter than it has tended to be in previous heatwaves, as is particularly evident from the 850hPa charts, which show much of north Africa with 850hPa temperatures between 30 and 34C. In previous heatwaves north Africa has tended to have 850hPa temperatures mostly between 25 and 29C with some small pockets of >= 30C. This was reflected also in the 850hPa temperatures that we got across Europe with the 25C isotherm getting through a large part of France and the 20C isotherm extending up to the Scottish border - these values were even higher than anything that we saw in the August 2003 heatwave. It was a similar story with the late June 2019 heatwave also, which given the time of year was even more exceptional at the 850hPa level, but an undercut of cooler air off the North Sea prevented Britain from seeing record breaking temperatures on that occasion.
  23. In the UK it is the other way round at the official MetO observing network - maximum temperatures have generally increased faster than minimum temperatures. I get a sense that this shift occurred in the 1990s and 2000s, associated with a decrease in cloud cover, and that we may see the maxima and minima both go up by a similar amount from 1981-2010 to 1991-2020. That said, in many of the expanding populated areas of the UK the mean minimum temperature has risen more quickly due to the urban heat island effect. Edit: I see Relativistic beat me to it!
  24. The PDF doesn't say why the station over-reads in bright sunshine. It could be that the sensors are accurate but that it is in a sheltered exposure in someone's back garden. I have a Davis Vantage Vue running in my parents' back garden (and Davis are as reputable as they come for personal weather stations) and their garden frequently gets about 2C warmer than the nearest official MetO sites on sunny days in the summer half-year.
  25. Regarding the London sunshine stats, remember that Heathrow moved to an electronic Kipp-Zonen sunshine sensor in September 2005. The 30-year sunshine averages (whether you're using 1961-1990 or 1981-2010) are based on Campbell-Stokes sunshine sensors, which in the UK tend to record 10-15% more sunshine in the summer months than Kipp-Zonen sensors. So to make it a fair comparison you'd have to shave ~12% off the 30-year averages for June/July/August and then compare the resulting figures against the sunshine data for 2006 onwards. If you do that you'll find that at Heathrow, since August 2011 the only significantly duller than average August was in 2015, with the others all close to or a little above the long-term average. It's true, though, that even if you allow for the ~12% difference, no recent August has been as sunny as those of 2003 and 2005 at Heathrow, or for that matter 1989, 1990, 1995 and 1998.
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