Alaska Airlines is adding an extra daily flight to Seattle over the holidays, another temporary boost in operations from the Charles M. Schulz-Sonoma County Airport in order to capture an expected increase in demand.

Two daily nonstop flights will operate to Seattle from Dec. 17 to Jan. 3, an airport spokeswoman said this week.

Alaska previously added an extra flight to Seattle for part of the summer and switched to an extra fourth flight to Los Angeles during September and October.

In November, the company operated three flights to Los Angeles, one more than last year, an Alaska spokeswoman said.

As a result, the number of flights increased 18.9 percent last month, and the number of passengers rose 19.7 percent, according to the airport.

As of November, the airline has boosted the number of flights to and from Santa Rosa by 7.3 percent, the airport reported. Ridership has grown even more, increasing to 9 percent during the same period.

Alaska, the airport’s sole commercial carrier, offers daily flights from Santa Rosa to San Diego, Los Angeles, Portland and Seattle. The company last month announced plans to begin daily service in March to Orange County.

Alaska began service in Sonoma County in 2007. Ridership has risen steadily each year since 2009.

The county last year completed a $55 million runway expansion project that allows larger planes to land at the airport. Since then, airport officials have talked to various airlines about new service from Santa Rosa to Denver, Salt Lake City, Las Vegas and Phoenix.

You can reach Staff Writer Robert Digitale at 521-5285 or robert.digitale@pressdemocrat.com. On Twitter @rdigit