An Analysis of a Mesocyclone–Induced Tornado Occurrence in Northern California

Abstract

Abstract One documented F2 tornado and several other unconfirmed tornadoes were reported in California's Sacramento Valley on 24 September 1986. The synoptic pattern which occurred that day was one long-recognized by California operational meteorologists as being associated with severe weather in the state. The present study documents this event and shows that the parent thunderstorm had supercellular characteristics and that the tornado was mesocyclone-induced. As is the case elsewhere when severe thunderstorms are observed, the mesoscale environment established a focus for late morning and early afternoon deep convection. A quasi-stationary leeside trough acted in concert with local channeling effects to promote the advection of relatively moist air to the northern portions of the Valley. This channeled flow contributed to low-level shear which was much stronger than that evident in the Oakland hodograph and one which was comparable to that found with supercell and mesocyclone development elsewhere in t...