Rain, thunderstorms possible for SD County

Posted at 1:56 PM, Sep 21, 2015
and last updated 2015-09-21 16:56:59-04

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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 National Weather Service flash flood watch for the valleys, mountains and deserts is scheduled to take effect at 11 a.m. and extend until Tuesday afternoon.

Although the coast was not included under the watch, forecasters said showers, thunderstorms and humidity are likely Monday afternoon as temperatures push into the low 80s.

10News meteorologist Megan Parry says: "Monday's highs will top out 4 to 9 degrees above average from the coast to the valleys, but it's still 10 to 15 degrees cooler than yesterday. Sunday was hot, record-breaking hot, in fact, for the following cities: Escondido 100 (old record 97, El Cajon 105 (94 old record), Ramona 102 (old record 98) and Vista 98 (old record 97)."

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 Monday 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.