California faces "critical" wildfire risk on Thanksgiving

Details: Red flag warnings are in effect for about 18 million people. The peak winds are expected Wednesday night through Thanksgiving Day.

• Forecasters measure the intensity of Santa Ana events by the difference in air pressure between Los Angeles International Airport along the coast, and an obscure tower of weather instruments well inland, located in the tiny Mojave Desert community of Daggett.
• The greater the forecast pressure difference, the stronger that dry, downslope winds are likely to howl through canyons and mountain passes, blowing from high pressure inland toward lower pressure closer to the coast.

Threat level: The forecasted pressure difference during this upcoming event puts it on the higher end of the scale.

• Peak winds may reach 70 miles per hour at the same time relative humidity plunges into the single digits. Southern California Edison is notifying residents it may cut power to about 150,000 customers in advance of the winds to prevent wildfire ignitions.
• The National Weather Service is warning residents and visitors who may be in the area for Thanksgiving to have a plan to evacuate on short notice: "Any new fire starts can spread rapidly!"