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Thundery wintry showers

Long range forecast team
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Thundery wintry showers last won the day on November 12 2012

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About Thundery wintry showers

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  • Gender
    Male
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    East Exeter, Devon
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    Weather (of course!), chess, music, computer gaming, social events, football, tenpin bowling, environmental issues
  • Weather Preferences
    Sunshine, convective precipitation, snow, thunderstorms, "episodic" months.

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  1. Thundery wintry showers

    snowfall temp

    As 4wd suggested it depends significantly on the temperature of the higher layers of the atmosphere: if the precipitation has to fall through a large layer with temperatures >0C then it is more likely to turn to sleet or rain than if there is only a shallow layer of >0C temperatures near the surface, as it takes time for snowflakes to turn to rain. Another factor is the relative humidity - the lower the relative humidity, the greater the tendency for snow at above freezing temperatures to evaporate rather than turning to rain, and the process of evaporation cools the air around the snowflakes cold. A general rule of thumb is that if the average of the dry bulb temperature and the dew point, or alternatively the wet bulb temperature, is around or below zero then it will probably snow, but it doesn't always work as a lot also depends on how shallow the >0C layer is. Being near the coast with an onshore wind often means greater relative humidity than further inland, and also the temperature tends to be raised due to the warming effects of the sea. I've seen snow showers in the spring months with a temperature as high as 8C, and occasionally even in February. This is typically due to a combination of low relative humidity and a shallow layer of solar-heated >0C air near the surface, typically if we get a sunshine-and-showers setup from a northerly, or (more rarely) cold zonality as happened repeatedly in March 1995. In heavier showers the colder air further up tends to be dragged down to the surface through the aforementioned evaporative cooling process, which can lead to some pretty sharp temperature drops. On Christmas Day 1999 I saw wet snow fall with a temperature of 5C in a chilly westerly regime, but that seems to be the upper limit for December. As 4wd pointed out if you get a temperature inversion you can get freezing rain, with rain falling at temperatures of around or below 0C, which freezes on impact with the ground. More rarely you can get ice pellets, where snow turns to rain and then starts to refreeze again as it approaches the surface, and these tend to broadly resemble hailstones.
  2. Thundery wintry showers

    Winter 2018/19

    Yes, I've been reminded of mid February 1998 recently, which interestingly was in a year with a very strong El Nino, contrasting with the weakly positive ENSO state of this year. I had a feeling that this mild spell was also likely to be accompanied by plenty of sunshine in many parts of the country, which is relatively unusual at this time of year, and so far it has proved that way. Mild weather accompanied by bright sunshine may also be widespread in about a week's time, but it does depend on the positioning of the high to the east. The current setup has the high pressure further north/east which means we're not getting quite as warm an air mass as on 13/14 February 1998 but on the other hand the clear sunny weather has pushed further north today thanks to the more southerly component to the airflow (on the 13th February 1998 it got into much, but not all, of northern England, resulting in maxes of around 17C in the Tyne and Wear region, while in the south it exceeded 19C in some places, but Scotland and Northern Ireland stayed cloudy). The February 2008 spell had the high pressure further west than this which led to the widespread high sunshine totals and colder nights. I have fond memories of that latter spell, which I spent in Norwich, where there were some stunning sunsets. It's hard to see a route to anything significantly colder before the back end of February now, but indeed, it could change pretty quickly as we head into March.
  3. ENSO has behaved much as forecast prior to the winter as far as I can see, with indices between +0.5 and +1.0. When I looked at the ENSO analogues back in November 2018 it seemed that a transition from neutral to weakly positive (+0.5-1.0) heading into the winter months was more strongly correlated with reduced westerlies and northern blocking in February than a strong El Nino (strong El Nino winters have included the exceptionally warm February of 1998 and the fairly warm one in 2016, as well as the cold north-easterly February of 1983). But indeed, for whatever reasons the atmospheric circulation has not followed suit this year, despite that plus the favourable SSW and MJO signals that Nick F referred to. I still see a bit of potential for something colder from the east arriving during the latter part of February but the odds against something that could bring widespread snowfall is increasing - a moderately cold south-easterly at this time of year would be more likely to bring predominantly dry cloudy weather to the east and sunshine to sheltered western areas.
  4. Thundery wintry showers

    February 2019 C.E.T. and EWP forecast contests

    Looks like my 2.6C is a bust as well - until a few days ago I had been hopeful that the recent westerlies would be a blip and that the high would eventually head N/NE drawing in colder easterlies as many of the longer-term signals had suggested for February, but this now looks increasingly unlikely, in spite of the weak El Nino combined with the Madden-Julian Oscillation heading into phase 8. A head-scratcher!
  5. Thundery wintry showers

    February 2019 C.E.T. and EWP forecast contests

    CET 2.6C, EWP 47mm. Probably lots of easterlies mid to late month, hence the low guess, but no prolonged spells of extreme cold.
  6. I doubt 2018 will be behind 1998 because 2018 was by far the warmer year of the two in the Arctic, and even HadCRUT4 (which does not interpolate over the Arctic) has 2018 running about 0.05C warmer than 1998. The Met Office article's figures includes values from several sources and has 2018 averaging 0.13C warmer than 1998, putting it 4th warmest. ERA-INTERIM even has 2018 as provisionally the third warmest year, probably mainly because 2015 was a cold year in Antarctica and it was less warm in the Arctic than several recent years, and in NASA's GISTEMP 2018 and 2015 are currently just 0.01C apart for January-November. My feeling is that 2019 will end up a little below their central estimate but warmer than 2018, and a lot depends on the strength of the El Nino.
  7. Thundery wintry showers

    January 2019 C.E.T. forecast and EWP contests

    Having had some more thoughts I'd like to bump my CET prediction up to 4.2C please. Still going with 48mm for the EWP.
  8. Thundery wintry showers

    January 2019 C.E.T. forecast and EWP contests

    CET 3.9C, EWP 47.6mm. Overall quite mild in the north and cold in the south. Probably some wintry weather around midmonth from the N or NE aided by the sudden stratospheric warming event but my suspicion is that the main wintry spells of the winter will fall in February instead.
  9. Thundery wintry showers

    Antarctic Ice Discussion

    A scary rate of decline recently, which has just edged ahead of 2016 and 1979 as the lowest Antarctic sea ice extent for the time of year on record. Anomalously high melting on both sides of West Antarctica appears to be to blame, with large areas of open water where we would normally have ice. Around the Antarctic Peninsual and off East Antarctica the sea ice extent is near average.
  10. Thundery wintry showers

    Winter 2018/19

    January 2013 had a long cold spell from the 12th to 25th and here was a snowy breakdown at the end of the spell with many places seeing an all snow event prior to the arrival of milder westerlies. I recall that satellite imagery on the morning following the breakdown showed a snow cover over a large majority of Britain though with large areas of the south-west missing out. So it's not that long since we saw a widespread cold snowy spell in January. And indeed, much of January 2015 from the 13th onwards was cool zonal in the north and west with some fairly snowy polar maritime incursions, and January 2017 was quite cold in the south.
  11. CET 5.8C, EWP 103mm. I reckon that mild and wet weather early and late in December will outweigh a cold spell in the middle.
  12. Thundery wintry showers

    The hunt for cold - Model discussion (late November)

    Historically this early in the season cold weather via northerlies has been a lot more common than from easterlies in late November and early December, although there have of course been exceptions like 18 November 1985, 20-23 November 1993 and 5-7 December 1995. Sub -10C 850hPa air is somewhat rare from either north or east at this time of year although sub -8C is not that unusual. This is partly because the continent and North Sea still have a fair amount of cooling to do, and partly because blocked easterly types with a persistent Scandinavian high are less likely to happen at this time of year. The late Nov/early Dec 2010 instance saw the cold come from a mix of north and east winds but the easterly spell was brought about by a Greenland high ridging across to Scandinavia, and the coldest day in the CET area (28 November) arose after five days of northerlies, just as the easterly was starting to kick in. In many recent years the warmth of the Arctic has meant that it was a struggle to get northerlies that were cold enough to bring lowland snowfall, but the Atlantic side of the Arctic has cooled down quite a lot this November and is currently relatively cold for recent years. Of course there are regional differences - an easterly type is on average somewhat more reliable at bringing cold and potentially snowy weather to most of central and southern England, whereas over much of Scotland and north-east England it is the other way round - but taking the country as a whole the equation tends to be more in favour of northerlies early and late in the season with easterlies causing a higher percentage of significant cold snowy spells in January, February and early March.
  13. Thundery wintry showers

    Aren’t Windows updates a pain?

    I haven't had many problems with Windows 10 updates on my desktop but they have often been a pain on my laptop, probably partly because it is relatively rarely used and was upgraded from Windows 7. Windows will force-feed the laptop updates at an inconvenient time and if you close the lid overnight or when travelling on a train or a plane (the latter two being bad times to update due to internet connection issues, the first being bad due to disrupting sleep) it will automatically switch back on after a short while to stop you from circumventing the automatic update. Not good if it then gets very hot. Also, on the laptop, updates tend to reset a lot of my preferences back to the Microsoft defaults (this has happened somewhat less often on my desktop computer) and this isn't just the bi-annual feature updates - it happens quite often after minor system updates also. Examples include resetting my picture viewer back to Photos, my music player back to Groove Music, re-enabling Automatic Folder Type Discovery and then resetting my preferred Details folder views back to the defaults. Although updates generally play nicely with the settings on my desktop, here was one time on my desktop where an update to Office 2016 reset the Developer tab in Excel back to the default of disabled, so for a while I was left wondering where it had disappeared to. If you have Windows 10 Pro you have a fair amount of customisability with updates, but if you have Windows 10 Home you generally have no choice but to update as and when Microsoft deems suitable, with the exception of the bi-annual feature updates which can be deferred. I am not against forced security patches, but I am against forced system and feature patches. It's often said that getting the latest feature updates "gives the best user experience", but a lot of the time new features are thrust on users when they are still buggy and incomplete and degrade the user experience, and they only become improvements after a while of ironing out bugs in subsequent mini-updates. Most cases of updates tinkering with default settings are probably unintentional, but there are exceptions, such as when I disabled OneDrive and one of the feature updates re-enabled it, reset all of my OneDrive settings back to their defaults and then introduced an ad for OneDrive that popped up every time I opened Windows Explorer. Generally the cynic in me thinks that Microsoft will feel they don't have to put as much effort into leaving people's settings alone now that updates are compulsory. In the past they had more pressure on them to make sure that updates were right or else people would disable them altogether and leave their systems insecure. And when it does go wrong, well, it serves as a neat little nudge towards the Microsoft defaults which could help increase user compliance with the defaults as the path of least resistance, and the more people comply with the defaults, optimising defaults for the vendor's revenue streams becomes a more effective policy. Microsoft still hasn't managed to get most Windows 10 users to use Edge, though.
  14. It got pretty close in Exeter but not quite close enough - there was a period of light rain with a temperature of 3C.
  15. Thundery wintry showers

    Winter 2018/19

    In the early days of Netweather it was Joe teddy beari, and then changed to Joe laminate floori! There was also a new town called Sprunehorpe.
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