SAN FRANCISCO (CBS SF) — There were several reports of rain, thunder and lightning in the North Bay Thursday night as an unstable weather system moved over the Bay Area amid a Red Flag Warning that has fire crews watchful.

The National Weather Service Bay Area Twitter account posted about the lightning and thunder at around 9:20 p.m.

READ MORE: Oakland Ties 2020 Homicide Total in First 9 Months of 2021

The Santa Rosa Fire Department also reported some sprinkles of rain earlier Thursday evening.

The system is expected to bring cool temperatures to the Bay Area this weekend, but has fire officials on edge with concerns that lightning strikes could cause a repeat of last year’s destructive complex fires.

The National Weather Service issued a Red Flag Warning Thursday for the North Bay and East Bay mountains, hills and valleys, in effect from 5 p.m. Thursday through 11 a.m. Friday. The main concern is lightning strikes that could spark additional wildfires in extremely dry vegetation. The warning was an upgrade from a previous Fire Weather Watch.

The wind and lightning strikes are a recipe for disaster, especially with the dry fuels in this area.

Earl Small sat on the porch of his new Santa Rosa home keeping an eye out for lightning and any signs of a fire.

“After waiting four years to get back in our house, it’s nerve-racking,” Small said.

The Santa Rosa fire department has staffed-up its stations although the weather was not expected to be as volatile as the thunderstorms that sparked the LNU Lightning Complex fire last year.

“With how critically dry the fuels are and the erratic winds that are expected with a lot of the fronts as they move through, any strike is going to start a fire. It’s just a matter of how big it’s going to get or how small we can keep it,” said Paul Lowenthal with the Santa Rosa fire department said.

READ MORE: Advocates for Immigrant Rights March From Santa Rosa to Healdsburg

Santa Rosa is working closely with other departments in the North Bay to quickly respond to fires and alert residents about evacuations if necessary. It’s an experience Earl Small hopes he will never have to go through again.

“When you lose everything, you have nothing,” he said.

After years of financial and emotional battles, Small got his house back but not his home.

“Twenty-two years of living in a house, that’s a home. Coming back to a structure that’s a house, people that haven’t been through it and lost everything are never going to understand that,” Small said.

KPIX 5 Weather Center: Current Conditions, Maps, Forecasts For Your Area

More than 600 wildfires were ignited by rare summer thunderstorms across Northern California starting in mid-August of 2020, collectively burning more than 2.5 million acres as the fires stretched into January. At least 23 people died and more than 3,500 buildings were destroyed.

In the Bay Area, the biggest August 2020 fires were the SCU Lightning Complex, the LNU Lightning Complex and the CZU Lightning Complex, which burned nearly 900,000 acres by the middle of September. Further north, the August Complex in Mendocino, Humboldt, Trinity, Tehama, Glenn, Lake and Colusa counties burned more than a million acres and is considered the largest wildfire in California history.

According to the weather service, late-season interactions between tropical moisture and early season troughs, leading to lightning-caused fires are common during the month of September. In Sept. 2009, a lightning event started about 30 small fires in the Bay Area. There were also mid-September lightning events in 2017 and in 2019.

However, what is unusual this year is the extreme dryness and the chance of lightning following days of very hot and dry weather, the weather service said.

“We are at full staffing right now,” says Chelsea Burkett of Cal Fire’s Santa Clara Unit. “We just have a lot of resources out on different incidents in the state of California right now. We’re at where we are able to be.”

Extra equipment is now on standby at the Morgan Hill Headquarters, and other preparations are being made all the way across the hills of the East Bay where fire departments will have extra crews at the ready.

Cal Fire says it’s working with NOAA to track the weather, and if a lightning strike does hit the ground they know where it happened, often within several meters of where it landed. What’s harder to know is whether or not that strike sparked a fire.

“All we can do within our unit is be prepared,” Burkett says. ” And that’s why we have a plan in place so that we can be prepared and send resources as appropriate.”

On Thursday, sub-tropical moisture was over the region as of 10 a.m. with scattered showers moving over the North Bay and several stronger showers over the coastal waters. No lightning was been detected locally as of this morning, but there was a band of lightning west of the Channel Islands in Southern California.

The passing system will result in a gradual cooling trend into late week along with the likely return of a deepening marine layer, with temperatures to be near seasonal averages from Friday into the upcoming weekend with more widespread night/morning low clouds, the weather service said.

MORE NEWS: Pelosi Expects House to Pass Infrastructure Bill This Week

KPIX 5’s Andrea Nakano contributed to this report