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!

How long will it last?

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Courtesy of the Met Office

Lovely clear skies across the bulk of England and Wales this morning after a frosty start, but just how long will the skies remain clear? I suppose it all depends on how long we can keep an east or southeasterly low-level flow from the continent and keep the cloud to the northwest at bay. It maybe that the cloud will fill in later tomorrow according to the latest forecast, but that won’t prevent another frost tonight.

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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Met Office see a cold start to the winter…

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Courtesy of Met Office

I don’t know why I’m getting carried away with the latest news from the Met Office about a cold start to the beginning of winter 2016/17, but I must admit I am a little. It must be the little boy in me that just wants to see the world turn white, at least for a few days or so, preferably over the Christmas holidays. I love the infographic they use in their long-range forecasting it says very little in effect, but apparently because the QBO is in an easterly phase and totally out of phase, this is expected to weaken the westerlies over the North Atlantic and allow blocked conditions to occur more and hence more winds from the north and east. One thing about the Met Office is it knows how to take advantage of social media in all it’s forms, I can just see them getting warmed up down at the Daily Express at this very moment!

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Courtesy of the Met Office

 

December continues the anticyclonic theme

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The anticyclonic theme thats been so common through much of October and November this year, is set to run into at least the first few days of December. The three main NWP models all have an anticyclone across the country aligned NW to SW. This kind of setup can mean fog and frost in December, but it’s all cloud dependent, and if today is anything to go by, there may be a good amount of it.

Tropical Arctic

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Here’s a chart of temperature anomalies that I’ve calculated from the NCEP reanalysis data for the first 24 days of November 2016 for the Arctic region. And again, it’s showing massive positive temperature anomalies across the board, it’s no wonder that the sea ice is struggling to increase in extent this Autumn in the Arctic. Below is a bar chart of temperature anomalies for the grid point at 77°30’N and 15° E (close to Ny-Ålesund on the Island of Jan Mayen), and as you can see they have been generally between +5°C and +10°C for much of the time since September 2016. Obviously there is a lot of warm air finding its way into the Arctic from further south, but I think the anomalies may be even larger around Jan Mayen because this winters sea ice has been so slow to form (see bottom image), and temperatures over open water (even though the sea surface temperature is close to zero) are obviously going to be much warmer than they would be over frozen sea ice.

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Courtesy of the NSIDC

Mild air returns to Deeside

After some pretty sharp frosts this last week, mild air has now returned to  the north of Scotland and particularly Deeside today, with temperatures getting  up to at least 12°C late this morning.

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Not just quite as mild on the other side of the Cairngorm mountains on Speyside though.

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A triple warm sector – not something you see everyday!

The boys down at Exeter have really outdone themselves today with the 06Z analysis – a triple warm sector – I kid you not, three distinct warm sectors, embedded one within the other, between Iceland and Norway.

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There is no doubt that warmer air aloft – above 4000 feet at least – has spread down from the northwest over northern Scotland since midnight, take a look at this thermograph of hourly temperatures from the AWS on Cairngorm [1237 M].

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At least the low cloud cleared from all but parts of Yorkshire today, so yesterday’s forecast was correct after all. We have had seen some thick cirrus (from the frontal system over central France) to the south for most of the day in Devon, but I notice that’s now finally starting to edge away this afternoon.satellite-image-1330-utc-on-fri-25-november-2016

The Greenwich Lightvessel

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The Greenwich Lightvessel Automatic to give it’s full title, is anchored in the middle of the English Channel at latitude 50°24″ N and longitude 0°, and that’s why it got it’s name – something I hadn’t realised until I came to write this article. The ship currently on this station is solar powered, as you can see from the above picture, and was built in 1946 for Trinity House, and has been in active service at various stations since 1947 as Lightvessel No. 5 – good old Wikipedia! I think I am right in saying that it must have been manned for many years until it was finally automated, some lightship men have probably spent a whole lifetime of service on vessels like this one.

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Courtesy Google Maps

This week has been a real roller coaster ride for Lightvessel No 5 in the channel, first the hurricane force southwesterly that storm Angus generated on Sunday morning, and then a complete flip, as an almost straight anticyclonic easterly set in from Wednesday, with gale or near gale force east northeasterly winds for over 36 hours. This week is nothing exceptional though, and I’m sure that there have been periods when it exceeded these strengths and for much longer. But at least now I know just a little more about the Lightvessel No. 5 with the callsign 62305 as it appears in the SYNOP reports. Here is a plotted grid of observations from the automatic weather station:

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And here’s my pseudo anemograph for the Greenwich light vessel since Sunday:-

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When I added this graphic I noticed that the winds slumped at main synoptic hours (00,06,12 & 18). The raw SYNOP data reveals that the AWS for 62305 reports in knots as it should do, but occasionally at main synoptic hours it reports in metres per second [MPS]. I had forgotten to check the wind units in my code and failed to make the conversion from MPS to knots. It’s very odd though, and it may well be worth reporting to the Met Office, but in all truth I think it’s probably a conversion problem at OGIMET (the wesite that I get my SYNOP data) who convert data in BufR format to SYNOPs. If not, you’ll know the next time that you listen to the shipping forecast why the wind in the channel seems a bit on the light side!

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The 1 in the fifth character position of the time group in the raw SYNOP code indicates that wind speeds are in MPS rather than 4, which indicates knots. I’ve fixed the code in my application and here’s the correct version of the anemograph for the Greenwich Lightvessel with all wind speeds in knots!

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 Just for the more curious amongst you – here is a graph of wave heights from the Lightvessel for the same period:-

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Low cloud more persistent that the BBC may have thought

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Today’s persistent low cloud over parts of England and Wales – a mix of stratus and stratocumulus – has been a little more persistent than the BBC weather presenters would have us believe – and ultimately what the Met Office NWP model forecast. Despite TV weather presenters Carol Kirkwood, Darren Bett and Chris Fawkes all promising how the low cloud would readily break up over England and Wales, it’s been stubbornly persistent, although there have been some breaks along the south coast and in the far southwest.

Meanwhile, yet again for the bulk of Scotland (apart from the far north), Northern Ireland, Northwest England and the West of Wales it’s been another beautiful day with gorgeous blue skies and another sharp frost tonight.

The BBC are forecasting more or less clear skies across England and Wales for tomorrow – let’s hope they get that right. Apparently the model is forecasting a cloudy weekend, but the way it’s performing at the moment I wouldn’t bank on it!

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