Cloud in the valleys below Monte Generoso, and Rigi Kulm inside it

At 13:46 CET this afternoon the camera on Monte Generoso was looking down on cloud. The Capolago camera sits on the Ticino ridge the rack railway climbs, 1,704 m by the railway's own reckoning, and the frame it served showed white packed into the valleys below, dark ridges standing out of it, and a second flat deck of grey overhead. The camera was between the two. We re-fetch that frame every 10 minutes, measured from our own fetch record on 2026-11-06.

A hundred and thirty kilometres north, over the Alps, the Rigi Kulm camera was inside the weather instead of above it. Same afternoon. Wet tarmac, a furled parasol, benches nobody was sitting on, and the Bahnhöfli sign that reads 1605 m in the frame going soft at the edges. We re-fetch that one every two and a half minutes, which is fast enough to watch the cloud thin and close again.

Low cloud in a cold valley has a top, and that top has a height. A camera is either under it or over it, and the pairs worth knowing are the ones that sit either side.

The north side of the Alps today

The Swiss Mittelland spent today under a lid. The 12:50 UTC METAR from Bern reported overcast at 900 ft above the field with the temperature at 8 and the dew point at 6. Zurich was at 6,000 m visibility by then, having sat at 4,500 m in mist with a broken deck at 1,000 ft an hour and a half earlier.

You can see all of that without reading a single code group.

Chasseral, on the Jura ridge above Nods, was a white rectangle this afternoon. The corner of the hotel roof in the bottom right of the frame is the only thing in it, and even that is going. The Chaumont camera above Neuchâtel still had the lake, grey and textured and perfectly flat, with the far shore gone and the sky and the water meeting in the same shade. Down on the plain, the Hitzkirch camera burns its readings into the corner of every frame: 06.11.2026, 14:10 CET, 5 °C, 1.6 km/h WNW. It is pointed southwest at Titlis, which was not there.

Then there is Napf, the hill above Trub, which at 13:57:33 had clear air at the camera, picnic benches, a bit of lawn, and the murk starting a few ridges out. Napf is the one I would open first on a clear cold morning after rain. We re-fetch it every 10 minutes, so it is a camera to check twice rather than to sit in front of.

The honest limit on all of these is the dark. Valley fog does its best work between about 02:00 and sunrise, and a webcam looking at an unlit hillside at 04:00 gives you a black square.

Under the same cloud in Italy

Today was wet rather than the cold clear setup that makes the best valley fog, and the Po frames show it. The Milano ovest camera at Baggio stamps its own height into the frame, 148 m above sea level, and at 14:00:51 it had autumn trees in the foreground, a purple-grey wash behind them, and the towers of the Milan skyline as faint grey shapes you would miss if you did not know where they were. Malpensa was reporting 4,000 m visibility in light rain and mist ten minutes before that frame. Linate had 8,000 m, with the temperature 11 and the dew point 10.

That one degree of spread is the number to watch.

Torino San Raffaele, on the hills east of the city, gives the widest view of the lot: a long panorama where the plain simply stops being a plain and becomes a flat grey band. Turin's airport was reporting broken cloud at 1,200 ft. And a hundred and fifty kilometres east, the Ponte Po camera at San Benedetto Po was having a perfectly ordinary Friday, timestamp 06/11/2026 14:11, lorries going both ways, visibility down the carriageway for a kilometre at least. Fog in this valley is local, and three hundred kilometres is more than enough to be out of it.

The spread, and where it is not fog

The arithmetic a pilot does is the arithmetic worth doing here. Air that is cooled to its dew point gives you cloud, so a small gap between temperature and dew point means the valley is close to the edge.

The Istanbul Bosphorus panorama is the clean counter-example. Like Hitzkirch, it burns its readings into the frame, and at 16:10:24 local it read 11.8 °C, 63%, 1020.7 hPa, 7.0 kt from the north-east. Out at Istanbul Airport, the 12:50 UTC observation put the temperature at 11 and the dew point at 1. Ten degrees of spread, and the frame is exactly what you would expect: sun on the bridge towers, fair-weather cumulus, traffic stacked on the approach, the strait a hard blue. The Bosphorus does get its mornings, but it needs a different setup than today's, and we only re-fetch it once an hour, so it is one to check rather than to watch.

San Francisco is the honest disappointment of the list. The Golden Gate camera was still dark when I looked, and the airport was reporting ten statute miles and clear sky at 12:56 UTC with a temperature of 12 and a dew point of 10. Two degrees of spread and no fog at all, which is the correction the arithmetic needs. A narrow gap tells you the air is close to the edge, not that it will get there. The park service puts the Golden Gate's fog season in summer, predominating in most coastal parts of the park by July. November is the wrong month to go looking for it there.

The season that starts this month

California's fog is in the Central Valley instead, and it is just getting going. The National Weather Service describes tule fog as forming on many nights from late October through February, when a cool moist layer off the Pacific sits under clear skies with light winds.

It had already started this morning. Fresno reported 5 statute miles in mist at 12:53 UTC with the remark that visibility to the east-southeast was down to 2, and Bakersfield had 6 miles in mist at 12:54 with 10 over 8 on the thermometers. The Caltrans camera at SR 168 and Herndon Avenue is a video stream rather than a still, so it is the one to leave running as the sun comes up and the fog either lifts or does not.

What I am going to do with this is keep a short list. Generoso and Napf above, Rigi and Chasseral in it, Hitzkirch and Baggio underneath, and check the pairs each morning this month to find out which cameras sit nearest the top of the deck on a given day.

The question I cannot answer yet from the frames alone is how high the top actually was. Those two cloud bases, 900 ft at Bern and 1,200 ft at Turin, were measured at airports, and the cameras that matter sit on ridges nowhere near one. Short of a camera that can see its own cloud base, I think the answer is a pair of cameras at known heights on the same hillside, one in and one out. We do not have a pair like that yet, and I would like to find one.