I heard Eddie Mair going on about the temperature in Phoenix Arizona in yesterday evening’s PM program on BBC Radio 4, so I thought I’d keep an eye out on the maximum temperatures and see what turned up. Well to trump Phoenix (no pun intended) the maximum temperature reported at 00 UTC from Nuevo León in Mexico was 49.7°C (121.4°F), and a shade (I can’t help it) higher than the 48.3°C in Arizona. Excuse the contouring of temperatures is far too smooth and not accurate.
Jersey airport ended up being the warmest place in WMO block #03 as suspected with 32.4°C, but Le Mans was the hottest place in France with 36.8°C this afternoon. That air over France will start to feed up across the channel as the gradient starts to veer overnight and possibly produce an even hotter day tomorrow across the south.
Jersey looks like taking the crown today as the warmest SYNOP station in WMO block #03, with a temperature just over 90°F at 14 UTC (fig 1).
Here in Bradninch mid-Devon, the temperature has been hovering around 30 or 31°C for much of the afternoon, so to escape the sun that I’d string some code together and look at a couple of thermographs since Saturday for Exeter (fig 2) and Heathrow (fig 3).
Not bad going for Devon, when you consider that Exeter is always starting several degrees cooler than Heathrow each day. I think the sea breeze just kicked in time to prevent the temperature at Exeter airport possibly exceeding 31°C at 14 UTC, as it did here in Bradninch. My Vantage Pro has been recording temperature since September 2004 and this afternoon’s max of 31.3°C makes it the warmest June day in that time.
There seems to be no exact definition of what constitutes a heatwave, either how long the spell should last, or how hot it should be to be classified as one, either here in the UK or anywhere else come to that from the different rules adopted by different countries. Looking at the daily CET series and the reported temperature observations of the current ‘heatwave’, I reckon a mean 24 hour temperature of 24°C or above might be a good threshold to use here in the UK.
The above graph (fig 1) are the hourly temperatures from Heathrow Airport since the start of June. The yellow outlined series is the 24 hour centred moving average, and the red line is 24°C, that would mean that we are in day four of the current one.
Of course you could use the daily anomalies for a station, which would make it more flexible, but that would be more difficult to compute if you did it hourly, because you would also need hourly anomalies, although it could be done if you could access the data from the AWS.
That 24°C threshold wouldn’t do for the summers in the south of Spain though, because the entire month of June so far has been more or less one continuous heatwave, so perhaps 28°C or even higher might be more appropriate here (fig 2).
The latest 06 UTC model run must be showing signs that the breakdown of the current hot spell is not going to be a quiet one.
It looks like the Met Office are still having problems with this new warnings web page of theirs. The map is a great improvement on the old one, but some of the locations plotted on it are blatantly in the wrong place. I reported this to them a couple of weeks ago, and it really should have been fixed by now. At worst its misleading to the general public, at best it just doesn’t look professional, I am amazed that it wasn’t picked up at testing.
There’s quite a steep thermal gradient across the country this evening, with dewpoints as low as 6.4°C at Stornoway in the northwest, to as high as 19.3°C at Yeovilton in the southwest.
I count 26 stations with 30°C or higher today, and tomorrow, particularly in the southwest it may be even a little hotter again (fig 1). With temperature as high as 32°C, which they’ve been in the London area this afternoon, which could trigger one or two isolated thunderstorms in places.
2017, continues to move a little higher up the league table of warmest years to date (the 1st Jan to the 18th June), it’s now joint 4th and is within striking distance of both 1990 (0.02°C higher) and 2014 (0.15°C higher), and the way this current hot spell is going it could will go clear as the second warmest start to any year since 2007 before the week is out, in the daily mean temperature record that started in 1772. This is of course based on provisional values for this month from the Met Office.
This is a listing of the largest diurnal range across the British Isles, well to be precise the difference between the 18-06 minimum and yesterdays 06-18 maximum, I can’t plot the results on a map, so the table will just have to suffice for now (fig 1). Yesterday, Topcliffe in North Yorkshire, tops the list with a range of 18.7°C or 33.7°F.
At the opposite end of the table the minimum and the maximum on the Bealach Na Ba where both 7.7°C (fig 2).