LFM Forecast Variables Related to Santa Ana Wind Occurrences

William T. Sommers Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley, CA 94701

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Abstract

Surface weather conditions in the southern California mountains during Santa Ana occurrences are related to LFM forecast variables. The strong downslope winds and low relative humidities during Santa Ana conditions pose a serious fire problem. Synoptic conditions leading to Santa Anas should incorporate subsidence and flow perpendicular to the local mountains, at mid-tropospheric levels, on the windward side of the mountains.

Twelve hour LFM 500 mb forecasts of height, wind and omega, in relation to Santa Ana wind occurrence, were examined for 16 cases. A case study illustrates the typical synoptic-scale transition to subsiding, northerly flow that leads to Santa Ana occurrence. A graphic summary shows how the relative strength of the 16 cases was related to LFM v wind component and omega forecasts.

Abstract

Surface weather conditions in the southern California mountains during Santa Ana occurrences are related to LFM forecast variables. The strong downslope winds and low relative humidities during Santa Ana conditions pose a serious fire problem. Synoptic conditions leading to Santa Anas should incorporate subsidence and flow perpendicular to the local mountains, at mid-tropospheric levels, on the windward side of the mountains.

Twelve hour LFM 500 mb forecasts of height, wind and omega, in relation to Santa Ana wind occurrence, were examined for 16 cases. A case study illustrates the typical synoptic-scale transition to subsiding, northerly flow that leads to Santa Ana occurrence. A graphic summary shows how the relative strength of the 16 cases was related to LFM v wind component and omega forecasts.

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