A storm system that moved across Western Washington Sunday afternoon was expected to bring an overnight mix of rain and snow, with accumulations of a half-inch possible, mostly from the Everett area north, said the National Weather Service.

In the Seattle area, where slightly warmer temperatures are expected, the snow isn’t likely to stick or accumulate, said NWS meteorologist Carly Kovacik.

The precipitation was expected to start after midnight Sunday, with a snow-rain mix most likely in the early morning hours before dawn. “We’re looking at mostly just a quick shot,” she said. Bellingham and parts of Whatcom County might see as much as an inch of snow on the ground — at least briefly.

Shortly after daybreak Monday, snow levels across the region will rise quickly, erasing any further chance of lowland snow. “We’re not expecting any road impacts,” Kovacik said. “If there are any accumulations, it would be mostly on grassy areas or elevated surfaces.”

Snoqualmie and Stevens passes should get about half an inch of snow overnight Sunday, with little impact on travel. But snowfall will intensify Monday morning though midafternoon with an additional three inches likely at Stevens Pass and up to two inches at Snoqualmie Pass, Kovacik said. “With those amounts folks can expect some wintry driving conditions.”

The chances of significant mountain snow will increase through the week, as one system after another sweeps through, separated by occasional short breaks. The storm queued up for Tuesday night and Wednesday looks cold enough to deliver a sizable dump in the Cascades, Kovacik said. Another system looming for Saturday also could be a major snow-producer.

It’s not clear yet whether the snow will be sufficient to allow Stevens Pass ski area or the Summit at Snoqualmie to open. The latter’s website projects a Dec. 17 opening.

“I would say overall it’s going to be a good week for ski areas,” Kovacik said, “At least in terms of getting some of that snowpack back that we lost through November.