Inversions when the mountain is warmer than the valley
A temperature inversion happens when warm air sits over cold air — the opposite of the normal pattern. On Monte Sano they're common at night when valley air pools and chills below the plateau. This page catalogs every hour the plateau average exceeded downtown by ≥ the threshold.
About inversions on Monte Sano
Inversions develop on clear, calm nights when air at the valley floor radiates heat to space and cools faster than the air above it. The plateau, sitting in the freer-flowing air aloft, stays warmer. This is what makes the bias-correction project useful — every regional forecast assumes a standard lapse rate and gets these nights wrong.
Plateau average = mean of the 5 canonical ridge stations (KALHUNTS130, 179, 560, 555, 264). Valley = Downtown (KALHUNTS129).