On Convection Bands Within Pacific Coast Storms and Their Relation to Storm Structure

Abstract

Pacific storms entering Southern California have been intensely sampled and subjected to detailed investigation through a storm study program in the Santa Barbara area during the 1960?63 (inclusive) winter storm seasons. One result which has emerged from the analyses of precipitation and upper-air data was the discovery that organized convection bands were a common feature within the main precipitation region. These bands were detected from storm precipitation distributions, which, through quasi-objective methods, have been separated into the following three components: storm mean motion precipitation, orographic precipitation, and convection band precipitation. The typical convection bands appear to be 20 to 40 miles wide, centered some 30 to 60 miles apart, oriented along the upper shear vector (between winds in the convective cloud layers and the adjacent layer above), and moving along a direction of the lower shear vector. There is evidence that the increased convective activity within the bands is associated primarily with the destabilization of the air mass through differential thermal advection.