The various places where mist appears, the thickness of the vapour and the time of day can all be brought to bear for weather forecasting:
Mist on the hills, weather spills; Mist in the howes [hollows], weather grows (traditional).
Thick rouk [mist] in the morning, thairafter warme and fair (Andrew Hay The Diary of Andrew Hay of Craignethan 1659).
I minded an old saying of Tam Todd's, “Rouk’s snaw’s wraith,” and I looked for a wild storm with gladness (John Buchan John Burnet of Barns 1898).