Hill fog and periods of heavy rain and drizzle made this a very nasty kind of day down here in the southwest, especially along the south coast, hopefully things will improve tomorrow.
It’s arguably just as foggy first thing this morning (fig 1) as it was yesterday (fig 2) in many places across the south of the UK, but the difference is that today there were no yellow warnings in force from the Met Office about it. All I can think is that must have lost all the enthusiasm for the subject after making such a song and dance about Monday and Tuesday. It’s probably to do with the fact that yesterday’s was radiation fog, but today’s is more advection fog covering higher ground – but it’s all fog.
I don’t know exactly why, but the fog that formed well before midnight across southern areas (fig 2), thinned quite quickly from many places in the second part of the night (fig 3). There certainly was a little more in the way of low cloud north of Birmingham later in the night, and the gradient may have picked up across other areas, but it’s now quite patchy across southern England at dawn, and in some areas such as the southwest of England and east of London, fog was reluctant to form at all. The thinning may have had something to do with warmer air aloft advecting up from the southwest and permeating down to lower levels, I notice for example that the temperature difference between Dunkeswell (252 M amsl) and Exeter airport (27 M amsl) at 09 UTC here in Devon was 6.2°C.
Certainly the earlier yellow warning of fog which lapsed at 06 UTC was quite accurately forecast by the Met Office (fig 4).
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.
PS It’s still foggy on the M8!
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).
The overnight fog arrived much earlier and was a little more extensive than the Met Office warned of their yellow warning issued yesterday afternoon (fig 1). The warning was for the period starting 02 UTC this morning (fig 2), but there were visibilities of 100 metres or less at Exeter airport from as early as 21 UTC, which must be quite embarrassing for forecasters, when the airport is such a well-known frost hollow and fog trap. In fact by 20 UTC, under an almost full moon you could see the Culm Valley where we live 8 km to the north filled with fog. The main rail line to London and the M5 also run up the Culm valley towards Taunton. Fog did take longer to form further east, but the Met Office had to extend the area at 0720 UTC this morning to cover areas to the west of London. I wonder if the TAF for Exeter airport required amending?
Dunkeswell have gone into fog at 20 UTC with a temperature of 4.7°C (fig 1). Maybe my adapted Middle Wallop fog TDA had the right idea after all! Certainly the yellow warning for fog that the Met Office issued this afternoon seems to have already gone awry, because the validity time doesn’t start till 02 UTC! Of course technically it may not be true radiation fog, and could well be upslope stratus, but 100 metres visibility is still an F in the Beauforts in my book.