High-Inversion Fog Episodes in Central California

The meteorological conditions associated with the high-inversion fog episode on 23–28 December 1978 near Chico, California, are described. In general, the meteorological conditions throughout the fog and inversion layers were characterized by wind speeds ≤3.5 m s−1, wind speed shear <1.0 m s−1 (100 m)−1, and wind directional shear of 10–20°(100 m)−1. Diurnal temperature variations at the earth's surface were 2°C or less. The fog layer had a near moist adiabatic lapse rate and a maximum height of 530 m. Pilot reports of the fog top (inversion base) suggest slight spatial and temporal variations in the fog-layer thickness during the 6-day episode. The inversion above the fog was moderately stable with low relative humidity and a thickness ranging from 200 to 1000 m. These meteorological conditions also were typical of other high-inversion episodes from 1954–80 in the Central Valley.