By Reginald Stanley. Posted July 11, 2019, 8:42 PM.

Interrupting what has so far been a rather mild summer, a strong high pressure ridge over the Four Corners region is turning up the heat for Southern California late this week well into the middle of the following week.

High temperatures in the triple-digits are expected to be widespread inland from Friday through at least Monday, before the ridge breaks down around the middle of the week. The National Weather Service has issued a Heat Advisory for western Riverside County and southwestern San Bernardino County from 10 AM Friday through 8 PM Monday, during which days high temperatures are expected to peak. The heat will be even more pronounced in the low desert, where the National Weather Service has issued an Excessive Heat Warning for the same time period. The affected low desert region includes the cities of Palm Springs, Indio, Borrego Springs, and El Centro.

Monsoonal moisture is also expected to enter the region Friday and Saturday, however it will be confined mostly to the mountains. Thunderstorm chances in and near these areas will be greatest during the afternoon. The high pressure ridge is forecast to weaken mid-week, with temperatures returning to seasonal averages.