The National Weather Service issued a flood warning for the Napa River at St. Helena Monday afternoon.

The river was expected to "briefly" reach flood stage of 13 feet by Monday evening, according to the weather service. A flood warning means that flooding is either occurring or is imminent. The flood warning is expected to last until noon today.

On Monday afternoon, the weather service Web site predicted that "a powerful Pacific storm will impact northern and central California through this evening, bringing periods of heavy rain across the North Bay, based on current rainfall projections, the upper Napa River is forecast to rise rapidly this afternoon and may briefly reach flood stage tonight."

Flooding was not expected to occur in the city of Napa, but sandbags were being distributed at Napa High's Memorial Stadium on Menlo Avenue as a precautionary measure, said Craig Smith, executive director of Downtown Merchants Association.

"The next thing that happens is that if there is a flood warning, we will start calling businesses and we'll let them know that," he said. "One of the things we will try and do is give them information."

According to the California Highway Patrol, no roads were closed in Napa County due to flooding. But in Sonoma County, Highway 121 at Schellville was closed due to flooding around 3 p.m. In nearby Solano County, pre-emptive flood measures including sandbagging and automated telephone calls warning residents of possible floods.

Napa, where the scars created by the New Year's Eve flood have only started to heal, was not affected by flooding Monday afternoon. About 1.56 inches fell on Napa as of Monday afternoon. Heavy rain is forecast through today.