LAKE COUNTY, Calif. – With forecasters predicting that a prolonged heatwave is about to hit the western United States, Lake County and much of Northern California is under an excessive heat warning for Friday and Saturday, when temperatures across the region will surpass the century mark.

The National Weather Service issued the excessive heat watch which is in effect from noon on Friday to 7 p.m. Saturday.

At the same time, the California Independent System Operator has issued a statewide Flex Alert, which is a call for voluntary electricity conservation, from 3 to 10 p.m. on Friday in response to the forecast for near-record or record-breaking heat – up to 10 to 20 degrees above normal in some areas.

The National Weather Service’s excessive heat warning predicts “dangerously hot conditions” with afternoon temperatures between 100 and 110 degrees.

The forecast said that Friday and Saturday “will likely be only the first two days of an extended heatwave that may last for much of the next week.”

There’s a potential for some minor cooling on Sunday, but forecasters said county residents can expect prolonged above-average temperatures for several days.

The specific Lake County forecast predicts daytime temperatures of up to 104 degrees on Friday and 103 degrees on Saturday.

Sunday is expected to see temperatures around 100 degrees, with the heatwave continuing through next week, when temperatures are forecast to reach 106 degrees on Tuesday and 105 degrees on Wednesday, particularly in the Clearlake area and the south county near Middletown.

Nighttime temperatures over the coming week also will be well above normal, with forecasters predicting temperatures could rise into the low 70s.

Officials are also raising concerns about the potential for fire danger, as the high nighttime temperatures limit the window for relief, which is why the National Weather Service said it issued the excessive heat warning for much of Mendocino and Lake counties.

The long-term forecast also reported that the remnants of a tropical system will arrive in the region on Friday and Saturday, “presenting an opportunity for some isolated showers and thunderstorms across interior areas both afternoons.”

Forecasters said it is possible that a few thunderstorms may develop as early as Friday afternoon, and as late as Sunday afternoon as well.

“The biggest impact of these storms, should they develop, will be the potential for new wildfire starts due to lightning,” the forecast said.

Email Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it. . Follow her on Twitter, @ERLarson, or Lake County News, @LakeCoNews.