Just enough cold air will remain in place for locally heavy, accumulating snow to fall along the Interstate 5 corridor in Washington into Monday.
At the very least, a few wet snowflakes will mix in down to sea level.
Temperatures at or just above the freezing mark during much of the storm will cause rain to mix in at times elsewhere in the I-5 corridor.
However, even where a combination of rain and snow occur, roads will become slippery, especially on bridges and overpasses.
"Around Seattle, 1 to 3 inches of snow is likely with the greatest amounts over the hilly areas," according to AccuWeather Meteorologist Evan Duffey.
"For locations above 500 feet or so, and especially south of Seattle, toward Tacoma and Olympia, Washington, 3 to 6 inches of snow is likely," Duffey said.
A heavier amount of snow can fall along the western base of the Cascades.
Farther south, it will take a bit longer for snow to reach northwestern Oregon.
"The Portland, Oregon, area will likely get some snow from the storm late Sunday night into Monday morning with 1 to 2 inches possible, but more over the higher elevations surrounding the city," Duffey said.
The snow will be wet, slushy and difficult to remove.
Wet snow can cling to trees, causing limbs to sag and possibly break. Sporadic power outages can occur as a result.
Temperatures will rise enough during Monday midday and afternoon to allow any precipitation that falls to take the form of rain. The accumulated wet snow will melt as a result.
Another bout of snow and a wintry mix are likely in the Seattle and Portland areas for a time Tuesday night.