Black frost in mid Devon

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Another cold night across England and Wales with a moderate locally severe air frost. Here in Bradninch Devon we only managed -1.9°C, but at Exeter airport just 11 km to the south the AWS their recorded -6.3°C. That’s due to the fact that we are set up a little from the valley floor and the north northeasterly just kept running at about 5 knots all night, which is very typical here. It only dipped when the wind fell calm for short spells, for most of the time it was just above zero, and surprisingly thanks to the low dew point of the continental air, the humidity hovered between 77 and 90%, so little in the way of hoar-frost, and no scraping of cars – so a proper black frost in our little part of the world.

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The Met Office did much better last night than the night before with their forecast minimums, that is apart from the Northern and Western Isles where they over did it again.

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I think the same thing may have happened at other sites around the country have a look at this thermograph from High Wycombe.

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Benson to the west had a 18-06 minimum of -8.5°C whilst High Wycombe’s minimum was only -0.7°C due to the wind never falling out. This would have probably dried your washing if you had left it out overnight, but it maybe as stiff as cardboard when you brought it in!

Minus 6, minus 7, maybe even a -8 degrees

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Courtesy of the BBC

How many times do the weather presenters on TV use this old chestnut. I call it either the count-down, if it’s used in the winter for frost, or the count-up, if it’s used in summer for maximum temperatures. I believe there’s a whole chapter on this particular presentation technique in the “The Gamesmanship guide to Weather forecasting” which I’m still waiting to purloin a copy of. In summer there’s the classic “temperatures could reach 22°C or 23°C today, and in one or two places 24°C or 25°C, and I wouldn’t be surprised to see a 26°C from somewhere in the southeast”. Of course this five level count-up can only be used by the more adept presenter, but as you know it does happen. Anyway I digress, back to the overnight minima!

Certainly a moderate frost inland last night across most of England and Wales away from the coast, but not quite just the “minus 6, minus 7,  maybe even a -8 degrees” from this morning’s 06-18 minimum temperatures in the SYNOP reports, even though Leeming did dip to -6.2°C. Another curate’s egg of a forecast from the Met Office, excellent over the north and northwest of the country but the -7°C over East Anglia was out (-4.1) as was the -8°C in the south Midlands (-4.6), but the -5°C was never on in the southwest (-2.7) just too much wind as David Braine picked up on, and the -2°C just never happened in Northern Ireland (+3.3) and they remained frost-free. Out of the twelve ‘countryside’ minimum temperatures in the frame below, I reckon that at least four out of the twelve are just too low.

I prefer the old school definitions of frost by the way as you may have already noticed, and the definition for a moderate frost when wind speeds are less than 10 knots, are temperatures in a range between -3.6°C and -6.5°C. So in my opinion it’s not a hard frost, or a harsh frost (as I heard it called more than once yesterday on the BBC) but a moderate frost. BBC, please bring back Bill Giles and Michael Fish, it would be great to see them back on our TV screens with the latest graphics even if it’s only as guest presenters!

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Another cold night

Another cold night across the country last night, especially in Scotland, with the AWS at Aboyne in Aberdeenshire reporting -6.8°C in the 18-06 overnight period.

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Frost a little more widespread than forecast

It’s always very difficult to catch the BBC weather presenters out on the extent and intensity of any frost that they forecast the day after the event, but that doesn’t stop me trying! Yesterday is a case in point, petty but true. Here’s my flimsy evidence gleaned from Twitter:-

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Courtesy of Twitter

Even I think that graphic must be for midnight rather than 0500, but believe me I just couldn’t find one. And here are the stations that reporting a frost between 1800 and 0600 this morning (11 November 2016):-

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Frosts in December 2010

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I have been reworking my SYNOP anomaly application so that I can analyse temperatures over much longer time periods than I did before. I decided to give the application a dry run, and so here are the air frost counts for the very cold December of 2010. In theory I can now look back at any period that I choose which have SYNOP observations for, so that means the 1st of January 1973. Not only can I graph and plot the results on a map, I also generate statistics for each of the main synoptic hours as well as the daily extreme maximum and minimums.

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