You might be thinking it’s been quite a snowy end to 2017 wherever you live in the country, but spare a thought for those of us down here in the southwest who so far have yet to see a snowflake. In Cornwall none of the SYNOP stations have reported an air frost so far this Autumn, and even here in mid-Devon although we have had four air frosts, and only one of these was for a temperature lower than -0.2°C.
I’d like to do a similar thing with snow that I do with frost, by checking for the occurrences of snow in the present weather from the hourly SYNOP files. Not only would that mean opening thousands of hourly SYNOP files, but many of the AWS reports either don’t report a present weather, or if they do they’re not that reliable when it comes to the reporting of freezing precipitation. The same thing applies to the reporting of thunderstorms, I have yet to see an AWS report a thunderstorm, even though I know the more sophisticated Vaisala systems are capable of sensing them.
Temperatures fell to -13.0°C overnight at Shawbury (fig 1). Not a real surprise, because it’s a well-known fact that Shawbury plus a clear night and light winds, plus a snow cover equals a very low temperature. It still holds the record for being the coldest place in England, when almost 36 years ago now, the temperature fell to -25.2°C on the 13th of December 1981, when there was a similar depth of snow on the ground. As far as I can see this table of top ten coldest places in the UK from the Met Office blog is still correct (fig 2).
Having said all that last night was not a perfect radiation night at Shawbury as you can see from the observations (fig 3).
The wind never really dropped out, although this didn’t prevent them going into fog at 23 UTC, when the temperature suddenly dropped from -3.0°C to -9.2°C. Fog or freezing fog, as it may well have been, will slow or even halt the fall in temperature depending on its thickness, and if these observations are correct the minimum may have occurred around 05 UTC, because the next hour it rapidly warmed from -12.4°C to -6.9°C, before falling again (fig 3).
Looking back almost 36 years, here’s the 00 UTC chart for the 13th of December 1981 (fig 4). As you can see the minimum at Shawbury that night probably occurred close to midnight. It’s interesting to speculate that if the ridge of high pressure had just hung on for another 6 hours instead of collapsing like it did, the minimum temperature at dawn may have matched the -27.2°C extreme minima recorded in Scotland.
It’s a pity that our nor’easter across the south this morning hasn’t brought more of the weather that our American cousins associate with their nor’easters. Across southern areas it just means a biting cold wind, leaden skies and outbreaks of rain or wet snow. Low Xanthos is now a shrunken shadow of its former self across northern Germany, overnight developments have meant that the new kid on the block is low Yves over Brittany, its centre is much deeper than Xanthos was yesterday, with a minimum central pressure that’s already less than 960 hPa (fig 1).
A hard frost further north across the borders were winds were lighter and skies remained clear (fig 2).
Rather surprisingly, the whole meridional theme of the last couple of days is simply washed away in the next 36 hours or so, as we switch back into zonal mode across the UK.
I can’t see any logic in the yellow alert for ice that’s been issued this lunchtime by the Met Office for parts of London and the southeast (fig 1). I might be jumping the gun with this one, and they may will issue one later today for the Midlands and Wales, but these parts have seen 10 to 30 cm of snow today, surely this snow will still be around tonight, and any thawing of that snow would refreeze? So why no warning of ice for these places?
There has been freezing fog since 08 UTC this morning in Glasgow, and the temperature at 12 UTC is still -4.6°C. Why for goodness sake isn’t there a warning out for that? Perhaps they’ve been just too busy with the snow further south.
I thought that the Glasgow Bishopton was maybe playing up, so with the help of some Traffic Scotland website I’ve managed to find the offending freezing fog patch by the Erskine bridge on the M8 over the river Clyde (fig 3).
It’s a useful website made available by the Scottish government, but for goodness sake why do they restrict the website to show thumbnail images from their network of webcams?
Suddenly it’s all become clear, and now the Met Office yellow warnings of ice for tomorrow make perfect sense! Two and a half hours after they issued a yellow warning for ice for the southeast England, the forecasters at the Met Office have now just issued another yellow warning for ice (fig 4) that aligns with the earlier one to cover Wales, Midlands and East Anglia – cosmic!
My question to the Met Office is why the delay between the two? Why not just issue a blanket warning for ice that combines the southeast, Midlands, Wales and East Anglia, and then issue a separate snow warning just for the southeast corner? Of course the tricky bit would be to do all this at the same time, so that people who read the warnings get the impression that your approach was coordinated, which in itself would instill confidence with them that you knew exactly what was happening.
Meanwhile, north of the border in Scotland there’s a covering of snow in many places and there’s been a severe overnight frost. At Aviemore there’s 9 cm of level snow, and the temperature at 08 UTC is -11.0°C at Altnaharra and -11.1°C at Tulloch Bridge. Freezing fog has formed over the Clyde in Glasgow which could last a good while in the light gradient (fig 1).
This morning extended outlook for the run up to Christmas makes interesting reading for those of us who are looking for frost and snow, well at least for the first couple of weeks. I keep an eye on the extended outlook (fig 1) that they provide and usually it’s fairly bland and noncommittal, in this one I note a tone that the NWP backroom boys have latched onto something that might require its very own news item, or who knows even a mention in their regular forecast outlook to COBRA. So all you contingency planners out there – get some salt in – you heard it here first!