The Santa Ana Wildfire Threat Index (SAWTI) categorizes Santa Ana winds in four zones of Southern California based on anticipated fire potential. The index uses a comprehensive, state-of-the-art predictive model that includes dead fuel moisture, live fuel moisture, and the greenness of annual grasses to create a detailed daily assessment of the fuel conditions across Southern California. This information is coupled with calibrated weather model output, such as wind speed and atmospheric moisture, to generate a six-day forecast of Large Fire Potential. The Large Fire Potential output is then compared to climatological data and historical fire occurrence to establish the index rating. This product is produced by the U.S. Forest Service through the Predictive Services program.

Categories in the index are:

• NO RATING: Santa Ana winds are either not expected, or will not contribute to significant fire activity.
• MARGINAL: Upon ignition, fires may grow rapidly.
• MODERATE: Upon ignition, fires will grow rapidly and will be difficult to control.
• HIGH: Upon ignition, fires will grow very rapidly, will burn intensely, and will be very difficult to control.
• EXTREME: Upon ignition, fires will have extreme growth, will burn very intensely, and will be uncontrollable.