SAN DIEGO - Heavy rainfall and flash flooding possible Monday afternoon through Tuesday afternoon for the mountains, lower deserts and valleys, according to the National Weather Service.
The heavy rain and thunderstorms likely to drench parts of San Diego County Monday will bring increased humidity and heighten the risk for dangerous flash flooding in some areas.
A NWS flash flood watch for the valleys, mountains and deserts took effect at 11 a.m. and was expected to be extended until Tuesday afternoon.
Although the coast was not included under the watch, forecasters said showers, thunderstorms and humidity are likely this afternoon as temperatures push into the low 80s.
Forecasters predicted rainfall in excess of an inch in the deserts and the inland valleys, and more than two inches in the mountains. The heaviest rain is likely this evening into Tuesday morning as low pressure combines with an approaching plume of deep moisture, increasing the possibility of flash flooding.
"Areas most affected will be the mountains, low deserts, the San Diego County valleys and the Inland Empire,'' according to the weather service. "However, heavy rain is possible for all other areas as well. The risk of flash flooding will diminish as the upper low moves off to the northeast Tuesday evening into Wednesday morning.''
Locales in and below recently burned areas will be particularly susceptible to heavy runoff and debris flows should strong thunderstorms develop nearby. Forecasters advised residents with outdoor plans or who live near a flood-prone area to "be alert to rapidly changing weather conditions.''
Forecasters said drier conditions would prevail later this week as high pressure builds over the southwest.