Overnight fog rather more extensive and earlier than expected

Figure 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?

Figure 2 – Courtesy of the Met Office

Dunkeswell in fog at 20 UTC

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.

Figure 1

Tonights yellow alert for fog and the adapted Middle Wallop technique

Figure 1 – Courtesy of the Met Office

I was only saying complaining after the last yellow alert for fog that the Met Office issued, that a bit of advanced notice wouldn’t be a bad idea, and lo and behold, at least with this one, they have!

Coincidentally, I’ve recently been working on a Tactical Decision Aid [TDA] for the forecasting of fog. The idea is based on the Adapted Middle Wallop Technique which featured in an article in the September edition of the Weather magazine. I’ve written an application that downloads forecast data from the Met Office DataPoint web service and observational SYNOP data from OGIMET. This means that you can point the TDA at any of around 100 locations around the UK and check if fog is likely in the coming night. I’ve run out of steam with its development in the last couple of weeks, so it’s still very much a beta, all I need is to come up with a burst of enthusiasm to finish it off (fig 2).

Figure 2

As you can see, I still have work to do on the actual calculation of the forecast visibility. In this example for tonight at Yeovilton, I have it that will go into fog by 20 UTC with a temperature of 7°C, which looks way too early to me, so this is still very much work in progress. Let me know what you think of the idea and how useful it might be, I personally feel it’s just got to be better than doing it in a spreadsheet.


I have just come across a very interesting website which features a number of TDA online tools, one of them being for forecasting fog that uses the Adapted Middle Wallop technique. Isn’t it amazing what you can find find when you look!

Fog reluctant to clear over Ireland as pressure tops out at 1037 hPa

Figure 1

As if just to remind us that the clocks will be going back this weekend the weather has finally got round to conjure up what is quite an intense anticyclone (1037 hPa at 12 UTC ) over Ireland, on what I must say is a most beautiful late October day down here in mid-Devon, with hardly a cloud in the sky this afternoon (fig 2). I notice that the fog has been very reluctant to shift across Ireland today (fig 1) and I wonder just how widespread it will get tonight over the southwest England.

Figure 2

Late fog warning from Met Office

Figure 1

A late warning of dense fog for parts of England was issued by the Met Office early this morning. As far as I can see the warning wasn’t issued till 0540 AM when most affected stations, at least in eastern England, had been in fog since midnight. I can’t for the life of me see why this warning wasn’t issued much earlier.

Figure 2 – Courtesy of the Met Office

Fog warning

Figure 1

A good warning of thick overnight fog for Northern Ireland from the Met Office (fig 3). The only problem is that it’s lasting a little bit longer than the validity time of 1000 BST in the warning, with five of the eight stations still reporting 100 M visibility at 0950 BST (fig 1). Quite an extensive area of fog is still visible in the 09 UTC satellite image (fig 2). The Chief forecaster did say in his assessment that it might last till late morning, so why didn’t he simply make it valid till 1200 BST to cover that possibility?

Figure 2
Figure 3 – Courtesy of the Met Office

Looking back, the fog eventually cleared from Aldergrove airport between 1100 & 1200, and Portglenone the hour after.

Sea of fog

Snaefell on the Isle of Man, stands out in a sea of fog that covers the northern half of the Irish Sea this morning, as it should do, after all it is 2,037 feet high. Also standing out clear from the fog are the Lakeland fells over Cumbria.

Figure 1

This is the closest that I can get to a view from above the fog, from a webcam near the top of Snaefell. The sea fog in this part of the world was well forecast by the Met Office model yesterday, although the fog in the English Channel that they expected, didn’t materialise.

Figure 2 – Courtesy of the Isle of Man Government

The Ides of March and pesky stratus

Figure 1

Today the 15th of March is the Ides of March in the Roman calendar, and it’s on this day in 44 BC that Julius Caesar was assassinated. On the 15th March 2017 though, the stratus that has plagued the coastal areas around the south and west has been very reluctant to shift today. Its cleared though in mid-Devon this afternoon, but it’s still clinging to the south coast from Cornwall through to Dorset (fig 1). It’s not often that it’s warmer at Dunkeswell and Liscombe than it is at Exeter airport, but it is this afternoon. St Athan is in fog and cold, with a temperature of only 7.6°C at 14 UTC, whilst on the other side of the Bristol Channel in North Devon, temperatures are close to 15°C (fig 2) with blue skies and sunshine.

Figure 2

Fog in Po valley

Figure 1 – Courtesy of NASA/GSFC, Rapid Response

There was a lovely visible satellite image of the Fog in the Po valley earlier this morning (19 February) which is no real surprise at this time of the year (fig 1). What I did find surprising is that relatively few large towns that have sprung up along the River Po down through the centuries, and because of this there are absolutely no SYNOP observations (fig 2), which I just can’t believe. Maybe it’s because the Po has a sizeable floodplain alongside it, and it just wouldn’t be a very good idea to build along it, or maybe the Italians realised how fog tended to linger there the longest…

Figure 2


Fog in the southeast

Image 1 – Courtesy of the Met Office & EUMETSAT

It’s interesting to see the fog in the Trent valley dispersing this morning, as the edge to the more general area of fog and low cloud blanketing the southeast of England slowly edges northwestward, in the southeasterly that’s finally beginning to freshen across the south (fig 1).

Massive temperature rise

A lovely day down here in deepest Devon at the moment, in stark contrast to the fog of the last few days, with just a trace of cumulus now starting to form, it feels like there’s a real touch of Spring in the air. Massive temperature rise of 14.2°C at Exeter airport this morning from -5.2°C to 9.0°C in around six hours (fig 2).

Image 2 – Data courtesy of OGIMET

Meanwhile in the north of Scotland…

Slightly warmer than the 9.0°C at Exeter was the 12.6°C at Altnaharra.