A new tool is available that predicts the severity of Santa Ana winds in southern California six days in advance. Called the Offshore Flow Severity Index, it combines the relative humidity with the 1:00 p.m. wind speed predicted at the Saugus weather station to rate the events each day on a scale from one to four, with four being the highest. A category four event requires winds in excess of 30 mph with a relative humidity of less than 9%.

The term “offshore” is used because Santa Ana winds usually blow from a high pressure area over the Great Basin to a low pressure area off the southern California coast. These north, northeast, or east winds blow from the land to the ocean, or “offshore”, warming and drying as they move from high elevations to coastal elevations. Many of the larger and most devastating wildfires in southern California have occurred during offshore or Santa Ana wind events.

This forecasting tool will enable wildfire managers to modify their staffing or move fire resources into areas as needed to deal with the potential for large fires.

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UPDATE: October 26, 2011. Access to the site now requires a password, which seems very odd.