On the Accuracy of Interpolated LFM Forecasts and Their Use in Predicting Surface Conditions in Mountainous Terrain

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  • 1 Pacific Southwest Forest and Range Experiment Station, Forest Service, U. S. Department of Agriculture, Riverside, Calif. 92507
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Abstract

Limited-area Fine Mesh (LFM) forecasts were interpolated and compared with surface observations in the southern California mountains and on-site soundings.

Descriptive case studies show that during sea-breeze type of flow, when synoptic-scale forcing is weak, surface flow in mountain canyons can be uncoupled from free atmosphere flow and totally driven by local diurnal forcing mechanisms, while ridgeline sites conform to free atmosphere conditions. During Santa Ana flow, when synoptic-scale forcing is vigorous, surface flow in canyons and on ridges shows only kinematic adjustment of the synoptic-scale flow.

Root-mean-square difference comparisons of interpolated 12 and 24 h LFM 850, 700 and 500 mb forecasts of height, temperature, dew point and wind with on-site sounding data are presented.

Abstract

Limited-area Fine Mesh (LFM) forecasts were interpolated and compared with surface observations in the southern California mountains and on-site soundings.

Descriptive case studies show that during sea-breeze type of flow, when synoptic-scale forcing is weak, surface flow in mountain canyons can be uncoupled from free atmosphere flow and totally driven by local diurnal forcing mechanisms, while ridgeline sites conform to free atmosphere conditions. During Santa Ana flow, when synoptic-scale forcing is vigorous, surface flow in canyons and on ridges shows only kinematic adjustment of the synoptic-scale flow.

Root-mean-square difference comparisons of interpolated 12 and 24 h LFM 850, 700 and 500 mb forecasts of height, temperature, dew point and wind with on-site sounding data are presented.

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