A North Pacific storm that’s drawing moisture from the subtropics could drop 1.5 inches to 2.5 inches of rain at the coast and 3 inches or more inland Friday and Saturday across San Diego County, largely bringing fire season to an end, the National Weather Service said.

The system could also produce lightning in many areas, including Mission Valley, where San Diego State University’s football team will host Boise State at Snapdragon Stadium on Saturday starting at 7:30 p.m.

“This system is volatile … there’s very high uncertainty” about what will happen, weather service forecaster Dave Munyan said Wednesday afternoon.

The weather service added that “roads may become impassable due to flooding or flood damage. Heavy rain on wildfire burn scars have an increased risk of flash flooding along with mud and debris flows.”

The energy from the subtropics will come in the form of an atmospheric river that will hit the northern half of California especially hard, delivering lots of water to the region’s large reservoirs.

The weaker tail of the river will pass through San Diego County, soaking chaparral in the backcountry and causing the risk of wildfires to plummet, forecasters said. That same area received a modest amount of rain in October, which is unusual.

The region often gets little or no rain in the fall, raising the risk of wildfire from the mountains to the sea. Forecasters are especially pleased the rain is coming now, before the onset of dry Santa Ana winds, which rapidly spread fire.

The winds typically peak in December and January. But they can arrive earlier. On Oct. 23, 2003, the so-called Cedar fire erupted in eastern San Diego County, killing 15 people, destroying or damaging 2,820 buildings, and burning more than 280,000 acres of land.

This week’s projected rainfall — which could change — indicates that San Diego will get 1.5 to 2 inches of precipitation, roughly the same as El Cajon. Mira Mesa could get 2 to 2.5 inches, and Julian would receive 3 to 4 inches.

Forecasters say a second, weaker storm could move into San Diego County sometime on Monday.