This could be a dry winter, but that doesn’t mean a stealth storm couldn’t clobber Napa, causing flooding.

That’s the word from the National Weather Service, which looked into its crystal ball and saw classic La Niña weather conditions for the next three months.

Typically, a La Niña winter means lower than normal rainfall for Napa, while an El Niño year means more, said Bob Benjamin, a forecaster with the National Weather Service.

The reality can be quite different, Benjamin said. Because Napa is close to the middle of the state, wine country can be caught up by the pattern affecting either end of California, he said.

Even if this winter proves drier than normal, there can be periods of heavy rain capable of triggering flooding, Benjamin said. A series of water-rich tropical storms — the feared “Pineapple Express” — can strike anytime, he said.

“It’s the storm that causes the flood, not the winter,” Graham Wadsworth, a city engineer, told the City Council earlier this month.

The Public Works Department has been clearing drains, tuning up pump generators and working hard to keep leaves out of storm drains, Bob Quinn, the city’s streets division supervisor, said.

“We’re as prepared as we can be,” said Quinn, who reported hiring a fourth street sweeper to pick up autumn leaves.

The city is prepared to rent a long-reach excavator if it appears that Napa Creek will go over its banks at Behrens Street, Wadsworth said. This machine would be used to remove logs and other debris that can clog the bridge.

In a small flood, removing a clog can make a difference, Wadsworth said. In a major flood like the one on New Year’s Eve 2005, water will be leaving the creek at many locations, he said.

The Napa Creek flood of 2005 was triggered when 9.5 inches fell in 24 hours on Mount Veeder, Wadsworth said.

It was one of the heaviest deluges in city records, topped by 15.3 inches that fell atop Atlas Peak over 24 hours in 1986, leading to the major river flooding, he said.

The Napa River flood control project, which is about half finished, is providing some flood relief along the river from downtown to below the city limits, Wadsworth said.

New bridges and flood terraces allow water to move faster, with less backup, he said.

Wadsworth knows what a perfect rain year would look like. “We’re crossing our fingers we have no flooding this winter, but enough water to fill the reservoirs,” he said.

A La Niña winter would tend to produce a lot of snow in the northern Sierra mountains, but not as much in the south, Benjamin said. Napa County communities receive water from the Sierra snowpack as well as from local reservoirs.