Tuesday will be marked with the rainy and windy portion of our weather program as a potent warm front sweeps through the area. Expect increasing rain through the day, becoming moderate to heavy by the evening into the Tuesday night hours. Forecast models indicate the lowlands could see anywhere from roughly 0.67-2.00 inches of rain, while 3-5" totals are likely in the Olympics and North Cascade mountains. (Lesser amounts of about 1-2 inches of rain equivalent are expected in central and southern Cascades).
The heavy rains have prompted Flood Watches to be issued for all rivers that flow off the Olympic Mountains and Cascade-fed rivers in Snohomish County (mainly the Stillaguamish). The Watch is in effect from 10 a.m. Tuesday through Wednesday afternoon. Any flooding that does occur is expected to be minor.
But what's a January storm without some wind as well? Southerly winds will increase Tuesday afternoon and evening as the warm front passes and a moderately strong low pressure center makes landfall in northern Vancouver Island. Gusts to 50 mph are likely along much of the area, including the Seattle-Tacoma Metro area, the coast, Hood Canal and Northwest Interior. A Wind Advisory is in effect there through 4 a.m. Wednesday.
If you're trying to drive over the mountains, it'll be quite tricky as snow levels will vary quite a bit Tuesday. Snow levels are low enough to begin Tuesday that it'll be snow at Stevens Pass and points north. Stevens Pass could receive up to 6-12 inches of snow during the day and a Winter Weather Advisory is in effect through 3 p.m.
Snow levels will eventually rise to 4,500 feet Tuesday evening, switching Stevens Pass to a slushy rain but higher elevations will get as much as 10-18 inches of additional snow late Tuesday evening into Wednesday morning. On the other hand, it's just rain at Snoqualmie Pass as snow levels will gradually rise to 6,000 feet in the Central Cascades and remain above pass level until Wednesday afternoon, meaning rain across much of I-90 until then.
Snow levels to take a plunge
Rain tapers to showers Wednesday but cooler air from the Gulf of Alaska will begin its march into Western Washington. By Wednesday night into Thursday morning, snow levels are expected to drop to around 400-500 feet.
We won't have a whole lot of moisture left by then, but what few isolated showers are around could bring a dusting to an inch of wet snow to the lowlands, especially on the hilltops. Those would be rather random in location but one spot where snow has a bit better of a chance would be in the usual Puget Sound Convergence Zone locations of southern Snohomish County and northern King County -- especially those areas above 300 feet close to the I-5/I-405 corridor (Alderwood, Harbour Pointe, south Everett, Shoreline, Mountlake Terrace, Canyon Park, Mill Creek) and points east.
Depending on where the zone forms, how strong it gets, and how long it lasts, those areas could see 1-2" of snow by Thursday morning.
The rest of Thursday will feature a chilly day with limited showers and highs struggling to get beyond the upper 30s.
Friday is looking dry with highs around 40, and then another round of showers are expected Saturday and Saturday night with snow levels remaining in that 400-500 foot range for the possibility of more rain/snow mix or wet snow showers.
We dry out for Sunday and long range models suggest we could stay in a fairly dry pattern through next week. Good thing our weather bingo cards come with a free space!