QuestionPredicting valley fog in autumn, what do you actually use?

Every October same story. I drive 2 hours to Tatras for inversion, I stand on ridge at sunrise and there is either nothing or fog so thick I don't see my own boots. Last Saturday was second one.

I check dew point and wind on normal forecast apps, but it works maybe one time from four. I know the rule, clear night + no wind + humid air after rain, but for mountains this is not enough, every valley behaves different.

What do you use? Some special app, webcams, or only experience and luck? I am in Poland but I think principle is same for Peak District or Lakes.

Webcams more than anything. If there's one at the bottom of the valley and one higher up, check both the evening before and again at 5am. In the Peak the Hope Valley inversions are fairly predictable once you've been caught out enough times... which is to say experience and luck, sorry.

Cheers

Ha, the boots thing. Been there on Ben A'an more times than I'd like to admit. There's a UK inversion forecast that a lot of hillwalkers use, works off the temperature at different heights. Not perfect but proper useful. Whether there's anything like it for Poland I've no idea...

Webcams. Nothing else has ever worked for me.

TomekKRK said:

I check dew point and wind on normal forecast apps, but it works maybe one time from four

That's about the hit rate you'd expect, because the surface forecast is the wrong thing to look at. What matters is the temperature profile. If the air at roughly 1,000 to 1,500m is warmer than the valley floor overnight, you have an inversion and the cold, moist air gets trapped underneath it. Most weather models publish a sounding (skew-T) chart for the nearest grid point or upper-air station. It looks like a mess the first time, but once you can read one your hit rate goes up a lot.

My other check is the dew point spread at the valley floor. Under 2°C by midnight, with light wind below the ridgeline, and I set the alarm. Over 4°C and I sleep in. Then I look at the ridge height versus the forecast top of the inversion, because there's nothing worse than hiking up into the fog instead of above it.

We get the same pattern in the Front Range valleys every fall, and I went from roughly one in four to better than one in two once I started doing this.

rjhowell said:

Most weather models publish a sounding (skew-T) chart

This I didn't try. Looked now, there is sounding for Poprad and for Kraków, Poprad is closer to my valleys. Is quite confusing chart, many lines going different directions, but I see the idea, where temperature line goes to the right with height this is the warm layer. I will compare with last Saturday when it failed and see if chart was telling me already. Thank you.

darkslide said:

which is to say experience and luck

Or just go every weekend and accept 1 in 4. Thats what I do in the Cheviots and Ive got about 3 decent inversion shots in 5 bloody years

Update: sounding showed warm layer around 1300m for Saturday night, I went Sunday early and it worked. Sea of fog in valley, only peaks above. Light was not perfect but I am happy. This method is good, now I check it every Friday.