Mist & Fog



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.

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.

Exeter catches the BBC out again in more ways than one…

The -5.2°C overnight minimum at Exeter airport last night caught out not only David Braine in the Spotlight SW weather forecast at 6.55 PM, but also John Hammond in the later national forecast at the BBC.

Figure 1

It’s always very difficult gleaning evidence after the event in any BBC forecast from the previous day, suffice it to say the -5.2°C (fig 1) was considerably lower than either presenter forecast.  Even the forecast temperatures for 08 UTC this morning left a lot to be desired (fig 2 & 3).

Figure 2 – Courtesy of the BBC

Figure 3

Fog all day at Exeter

What annoyed me with David Braine last night is the fact that even though Exeter Airport had been in fog all day on Tuesday, with visibilities of 100 or 200 metres and a maximum of 1.8°C (as had we in Bradninch), he never even bothered to mention it. The plot grid (fig 4) is especially for David as a reminder that it might be a very good idea to have a look at a handful of observations from across the southwest before going on air. Even Holly made a quick reference to the fog in ‘southeast Devon’ in the weather at 1.40 PM. As for the Spotlight news team, they were probably too busy having another go at the NHS to mention any travel disruptions at a distant airport, but I digress…

Figure 4

I can’t believe that hundreds of people weren’t inconvenienced by not being able to fly where they wanted to yesterday (and in the last week) from Exeter. Surely that’s newsworthy to the people of the southwest? When David did mention fog in his presentation, it was with a passing reference to Dorset and Somerset. Curiously the fog that had blighted the airport for days cleared by the early hours by drier air that had been advected up from France.

Minimum Temperatures

As for his stab at the minimum temperatures they were wildly on the high side, he was too busy going on about how cold it will feel on Thursday when the wind picks up, the increased wind chill in the strong SE’ly wind, and what a shock to the system it will be.  And I do know that Exeter Airport is a well-known cold spot, which doesn’t excuse the insertion of an extra low value on the chart to cover this possibility.

Plymouth Centric Spotlight

It may have been much milder in Plymouth, but for a number of mornings in the last week I’ve been scraping the ice of our car, so I know how cold it’s been in our part of Devon. All I can conclude is just how Plymouth centric both his, and the rest of the Spotlight news teams thinking really is.

At 08 UTC this part of mid-Devon was covered white in frost as the sun was rising and the sky was a gorgeous Mediterranean blue, the temperature at Exeter Airport was a full 12°C colder than it was at Plymouth, it’s as if we were in a different world, because of course geographically we are.

Fog and frost in the south

It’s the coldest morning that we’ve had in our part of Devon in this recent ‘cold’ spell, on a night when it stayed cloud clear and the wind at last died out for a change. It looks like a layer of SC has saved stations north of London from also fogging out, which may stations south of the M4 seemed to have done this morning.

Forget this cold spell – the next one might be better

For the snow lovers amongst us, especially down here in the south, I think this short one day ‘cold’ spell will certainly a big disappointment. Even if we do get some wet snow accumulations today or overnight, it’ll very soon be gone. There are changes ahead though, and towards Wednesday of next week (if the latest NWP is to be believed) we could see the start of a cold spell that lasts a lot longer, take a look at the latest T+186 from the GFS (fig 1).

Figure 1 – Courtesy of NetWeather

An anticyclonic easterly with a cold pool edging westward across the British Isles, it’s not particularly deep cold air, or well-connected connected cold air, but it’s cold air nonetheless, and for once the Southwest of the country looks at risk from snow. Of course as usual, it’s not long before the anticyclone over eastern Europe declines and slips southeastward, but the good news in the later frames of the GFS (fig 2) is that pressure builds to the northwest of the British Isles and extends the cold spell to at least five days, which is nothing short of miraculous in a British winter. Admittedly this is high pressure, so snowfall might be in short supply away from windward coasts, but there could be a good deal of frost and fog, spells of which seem to have been a recurring feature since November.

Figure 2 – Courtesy of NetWeather

Of course, as I’ve warned before on this blog, this is all science fiction, and may not happen. But I think a change to a more blocked anticyclonic type, and which has been anticipated since before Christmas, may well happen this time round.

 

Foggy France

Still foggy over much of France this morning, the only difference is that temperatures are well below freezing so much of the fog is freezing, in fact at Trappes they’re reporting snow with 1 cm of snow lying at 09 UTC. Still foggy down here in Devon on the last day of what’s been quite a foggy last month of the year.

Lost in France

There seems to have been a surfeit of fog across the southeast of the UK today. It may have been patchy (I do hate the phrase) here in the UK, but the patch was somewhat larger over France, and I’m sure that some of our Gallic neighbours across the channel did get lost in it. It was interesting to see how the fog was slowly being blown out into the Wash and the North Sea by a light southwesterly flows as the day progressed.