A complicated and dynamic weather set-up exists for Western Washington over the next few days, with warmer-than-normal temperatures and some very sporadic sunshine this afternoon… collapsing to a breezy, colder and wet period to start the work week.

Showers will pick up along the coast this afternoon through evening, spreading into the area ahead of the cold front Sunday night and early Monday.  

Forecast models continue to push the front’s arrival earlier and earlier, making the rainfall forecast the heaviest through the morning commute on Monday around the urban corridor.   There is no threat of lowland snowfall for the early Monday morning commute.

The main batch of rainfall will arrive at the coast by 2 a.m. and in the central Sound at 6 a.m.  

Cold air following quickly behind that frontal rain band will lower snow levels to the point that a showers could put down some wet snow on Monday morning.

Forecast models are not in agreement about the depth of the cold air and if a mix or change-over to snow would even occur on Monday morning at all.  

However, one computer model from the University of Washington does suggest that several inches of snow could fall before the noon hour in the Puget Sound lowlands, mainly from east and north of Seattle north through Snohomish County.

The main variable will be how fast cold air can build into the region behind the front.  

It does not take just some cold air, but below-freezing air with significant depth.  Higher elevations above 500 feet will have the best chance of more significant accumulations in any event.

Other forecast models available on Sunday suggest that cold air will not be able to build with enough depth to "catch up" with the heavier frontal precipitation.

If snow does fall in the lowlands Monday morning, warm pavement will keep many roads free of major travel issues, but drivers should be aware of changing weather conditions.

Convergence zone snow likely

By afternoon, a Puget Sound convergence zone will develop across the central or north Sound regions, producing several inches of quick-hitting snow in isolated areas mainly from north King County through Snohomish and Skagit counties.

This has the potential to be much like last Thursday morning with some spots seeing a few inches of snow, and as is characteristic with convergence zone events, other areas within a few miles receiving nothing at all.

Convergence zone rain and snow will persist into Monday evening and possibly even into Tuesday morning before tapering.

More mountain snow

A Winter Storm Warning is in effect for the Cascades from late tonight through Monday night.  Eight to 18 inches of snow will fall through the ski resorts and the passes, and travel will be difficult.

Stay tuned to KIRO 7 Eyewitness News tonight at 5, 5:30, 6 and 11 p.m. for the latest on this developing situation.  Also, join me for a live weather online webchat at KIROTV.com at 1 p.m. Monday, or earlier if conditions warrant.