Southern California’s extended heat wave continues Sunday with another Flex Alert and a chance of thunderstorms across the mountains, deserts and some valley locations.

The seemingly endless heat wave is likely to continue through Wednesday of next week, and possibly longer, according to the National Weather Service.

Excessive heat warnings are in place for parts of San Diego, Los Angeles, Ventura, Orange, Riverside and San Bernardino counties.

Forecasters are calling for well above average temperatures in all areas:

  • Coasts: 80-95 degrees
  • Valleys: 100-113 degrees
  • Mountains: Up to 105 degrees
  • Deserts: 105-113 degrees

Residents are urged to wear lightweight and light colored clothing, stay hydrated and avoid outdoor activity during the heat of the day.

In order to reduce the energy strain on the power grid, California Independent System Operator (ISO) has issued a Flex Alert for the fifth consecutive day.

Consumers are urged to conserve energy between 4 p.m. and 9 p.m. by setting thermostats to 78 degrees or higher, avoid using major appliances and turning off all unnecessary lights.

Cal ISO says that consumer response to the Flex Alerts has been helping to ease strained conditions on the power grid.

The National Weather Service is alerting some Southland residents about a chance of rain.

There is a threat of monsoonal thunderstorms Sunday across the mountains, deserts and portions of the valleys.

Heavy downpours could strike quickly with localized flooding, strong winds, hail and frequent lightning possible.

A flash flood warning was in place for parts of the San Bernardino County Mountains, including Lake Arrowhead, Running Springs and Rimforest from 2 p.m. to 5 p.m. Sunday, according to the National Weather Service.