A Red Flag Warning is in effect for most of Los Angeles and Ventura counties through 8 p.m. Saturday, with Santa Ana winds expected to raise the risk of rapidly spreading fires.

The National Weather Service forecasts northeast to east winds of 20 to 40 mph, with gusts that could reach 50 to 70 mph. The strongest winds are expected from Thursday afternoon through Friday afternoon. Winds may strengthen before dawn, peak in mid-morning and ease somewhat later in the day.

Heat will add to the danger. Friday temperatures in coastal and valley areas are forecast to reach the upper 80s and 90s, with some places possibly hitting 100 degrees. Forecasters say the combination of heat and wind could help a fire spread if one starts. Residents are urged to take extreme care with anything that could spark a wildfire.