Update noon Friday, Aug. 7: The National Weather Service reports nearly 1,000 lightning strikes zapped the greater Bay Area overnight in a fairly uncommon dry thunderstorm system that generated a wildfire warning for a large swath of Central and Northern California.

The majority of the strikes hit the Southern Bay Area between 8 p.m. Thursday and midnight, NWS San Francisco/Monterey Bay Area Forecaster Steve Anderson said.

A California fire weather map on Aug. 7, 2015. (Cal Fire)

A red flag, or fire weather warning, remains in effect for the Sierra Nevada foothills and northeastern California.

Lightning sparked five small fires in Monterey County, Cal Fire spokesman Daniel Berlant said Friday morning. Firefighters were able to contain them overnight, he said.

Cal Fire still reports 22 active wildfires throughout the state. Firefighters slightly advanced containment overnight of the Rocky Fire -- the state's largest fire burning in Lake County, about 100 miles north of San Francisco. The blaze is more than twice the area of San Francisco, and is now 45 percent contained.

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While the lightning threat is currently moving out of California and into Nevada, Cal Fire warns wildfires it may have sparked may be lying in wait. Firefighters are on the lookout for smoldering embers potentially sparked by the thousands of strikes in areas beyond the Bay.

"In the past 24 hours there have been several thousand lightning strikes, especially across the Sierra and Central Coast," Cal Fire reports. "Lightning sparks may smolder for several hours or days before they get enough heat and energy to spread into a wildfire. This means the risk for wildfires continues even after the storms have passed."
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"We are still on high alert," Berlant said.

Original Post Thursday, Aug. 6: The National Weather Service is warning storms carrying the potential for lightning strikes but very little rain will hit large swaths of California Thursday afternoon, compounding the state's wildfire stress.

A red flag warning of "weather events that may result in extreme fire behavior" issued by NWS covers the entire San Francisco Bay Area and a huge swath of Central and Northern California, as well as a southeastern chunk of the state. A slightly less serious fire weather watch is also in effect for northeastern California.

A California fire weather map on Aug. 6, 2015. (Cal Fire)

"During these times extreme caution is urged by all residents, because a simple spark can cause a major wildfire," according to Cal Fire. "The type of weather patterns that can cause a watch or warning include low relative humidity, strong winds, dry fuels, the possibility of dry lightning strikes, or any combination of the above."

The weather could signal a reversal in progress thousands of firefighters have made in recent days containing the Rocky Fire currently burning about 100 miles north of San Francisco. Cal Fire reports the fire has burned nearly 70,000 acres southeast of Clearlake and is currently 40 percent contained.

Cal Fire reports 22 active fires throughout the state. More than 165,000 acres are burning, according to the National Interagency Fire Center.

Forecasters predict the thunderstorm threat will diminish by Friday morning. The red flag warning is in effect until 11 a.m. Friday.

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