Two storms expected to douse the Bay Area this week with a healthy amount of rain could impact the annual Bay to Breakers event Sunday in what forecasters are calling an unusual spring weather pattern.

The coming cold front likely will produce a cool, gray blanket of clouds and precipitation as early as Tuesday, with up to an inch of rain by Friday for all parts of the region, according to the National Weather Service.

The series of storms is unusual because spring cold fronts typically break up and scatter moisture in particular areas, said Carolina Walbrun, a National Weather Service meteorologist.

“It’s holding together fairly well and it’s going to spread rain across the whole region,” she said.

A deep marine layer and cooler temperatures are expected to develop Tuesday, and light rain will start around nightfall, officials said. The brunt of the storm should trudge into San Francisco, the East Bay and South Bay by Wednesday.

Dry weather will prevail Thursday and Friday morning, before a second cold front moves through the area midday Saturday, bringing additional moisture ahead of Bay to Breakers on Sunday.

As for whether San Francisco’s quintessential foot race and street party will be rained out? Forecasters can’t rule it out yet.

“We’re a little too far to really get dialed in on the timing, (and) I would say there’s a good chance of lingering light showers around start time as people are gathering in the streets,” said Steve Anderson, a National Weather Service meteorologist.

Another system is expected to arrive early next week, bringing a third shot of cold temps and moisture.

“The storm door’s back open,” Anderson said.

A string of heavy winter storms pummeled the North Bay and flooded parts of Sonoma County, but the coming storms are expected to produce a uniform amount of rainfall over the entire region, Walbrun said.

“It’s more than what we’re typically used to for this time (of year), but not unheard of or unprecendented,” she said.

San Francisco has received 23.78 inches of rain since the water year began Oct. 1, according to the National Weather Service. Officials said the coming storms bode well for the state, which recently emerged from an eight-year drought.

“If you can catch any of the rain and use it for your gardening, that’s always a positive,” Walbrun said.

Santa Rosa has received 43.63 inches of rain, Oakland has received 19 inches of rain and San Jose has received 15.02 inches of rain since the water year began, according to the National Weather Service.

Gwendolyn Wu is a San Francisco Chronicle staff writer. Email: gwendolyn.wu@sfchronicle.com Twitter: @gwendolynawu