The first heat wave of the year continues to hit our desert areas hard in San Diego County Thursday with an excessive heat warning in place. Southwestern U.S. Experts say a "heat dome" across the Southwestern United States is the source of the sweltering temperatures. “This is the first time we’ve seen it so far this year so it’s more or less our first heat wave,” said Stefanie Sullivan, Lead Meteorologist at National Weather Service San Diego. Day two of this heat wave brought scorching temperatures well over 100 degrees in places like Ocotillo Wells and Borrego Springs. “Across pretty much all of the Southwest we have this high-pressure area, and that’s what’s bringing our heat,” said Sullivan. MORE: https://www.cbs8.com/article/weather/severe-weather/whats-a-heat-dome/509-10af9c79-abbb-4689-87ca-7045b7599768