Every two months, Ramona Webster makes a donation to Napa’s main blood bank, a suite in a medical building near Queen of the Valley Hospital.

Webster, a dispatcher for a towing company in town, has been a blood donor for five years. “It could possibly save a life or a loved one,” she said this week as she donated a pint of blood to the Blood Centers of the Pacific on Beard Road.

Webster is among the regulars at Blood Centers of the Pacific, a nonprofit organization that distributes blood to 41 Northern California hospitals, including Queen of the Valley, Kaiser Permanente in Vallejo and St. Helena Hospital.

These days, the blood bank is looking for more donors like Webster.

Blood supplies are well below normal this month, in part because the blood bank has not been able to receive its normal shipments of out-of-state blood donations, Blood Centers of the Pacific reported this month. Out-of-state donations make up 20 percent of the San Francisco-based nonprofit organization’s total stock, spokeswoman Lisa Bloch said this week.

The reason: Winter flu and common colds struck would-be donors across the country, forcing the cancellation of numerous blood drives, according to Barb Kain, spokeswoman for United Blood Services, an Arizona sister organization of Blood Centers of the Pacific. Fewer people donate during the holiday season, Kain added.

Systemwide, Blood Centers of the Pacific is short of more than 400 pints of blood, Bloch said. To cope with the shortage, Blood Centers of the Pacific has rationed blood supplies.

Queen of the Valley Hospital, St. Helena Hospital and Kaiser Permanente Vallejo Medical Center have not been affected and surgeries have not been canceled, representatives for the hospitals said this week.

“It’s not an emergency,” Kaiser Permanente spokesman Jim Caroompas said. But “we’re encouraging people to donate because there is obviously a need.”

Queen of the Valley Hospital spokesman Dante Allen noted the hospital also has access to blood banks in Sonoma and Sacramento.

St. Helena Hospital’s spokeswoman, Elizabeth Zima, said the hospital does a lot of minimally invasive surgeries. “We don’t have a huge call for units of blood,” Zima said.

According to Bloch, Queen of the Valley Hospital last year needed 5,860 units of blood and blood components, such as platelets, and St. Helena Hospital required 2,059 units.

Bloch said Napa’s Blood Center of the Pacific collects about 70 blood donations every month. The center receives another 50 to 110 pints of blood monthly from community blood drives.

“That number has decreased slightly over the past several years,” she wrote in an e-mail.