SAN FRANCISCO (CBS SF) – Seasonal temperatures and a chance of showers Thursday won’t necessarily mean relief for tired firefighters as the chance of thunderstorms looms overnight.

The National Weather Service has issued a red flag warning for the San Francisco Bay Area from 5:00 pm. Thursday to 11 a.m. Friday, with thunderstorms expected to produce significant lightning activity.

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Light coastal clouds and fog are expected to give way to highs in the upper 60’s at the coast, with inland highs topping out above 90 degrees in the warmest locations.

Subtropical moisture moving in will bring back clouds in the evening and the thunder risk lasting into Friday morning.

“The best chance for thunderstorms is in the mountains,” said KPIX Weather Anchor Roberta Gonzales. “I would keep it at chance of thunderstorms this evening and overnight. Any local rain will be less than .05 of an inch.”

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The fire-dampening benefits of any rain may be offset by the potential for lighting.

“Fire risk heightens due to the possibility of dry lightning,” said Gonzales. “This is bad news for firefighters.”

The forecast led the National Weather Service to issue a Red Flag Fire warning

“Lightning from high based thunderstorms will lead to an increased risk of fire starts – especially given dry fuels. Isolated downbursts may also cause erratic winds near existing fires,” the NWS said via a press release.

Last week, Gov. Jerry Brown was forced to declare a state of emergency throughout California as wildfires rage in the parched state.

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At times this month, crews have been forced to battle some 20 active wildfires at a time, including the massive Rocky Fire in Lower Lake, which has scorched more than 100 square acres and forced 12,000 from their home.