Rain, wind and snow in forecast

Impacts possible from multiple weather issues

Rain, wind and snow in forecast
Friday December 20 was the wettest day in Seattle in the past 10 years, and the most rain recorded for Dec. 20 since record-keeping at Seattle-Tacoma International Airport began in 1945. (KIRO 7/KIRO 7)

Friday will be a really active day with heavy rain and wind, and the possibility for flooding.

Rain and flooding

We had some good rain Thursday night and the snow levels in the mountains are going way up above 7-8,000 feet. This will mean it’s all rain at the passes with lowland rain accumulating to a half-inch or more by Friday afternoon. This could cause some localized urban flooding or some standing water.

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The Friday morning commute was wet, but as the atmospheric river pushes north, we’ll see more of a showery nature to the rain around by afternoon -- meaning some breaks in the action. That’s good news to mitigate the flood potential.

Friday evening through Saturday, the wet and windy atmospheric river moves south once again, drenching the lowlands with 1-3 inches of rain over a little more than 24 hour period with 5-8 inches in the mountains. This will force rivers to rise to minor or moderate flood stage to start the weekend, with rivers running high or in flood into Sunday. There is a slim chance for major flooding but it looks like Friday's relative "break" in the rain will keep flooding from getting too much out of hand.

Away from the rivers, we could see some serious traffic issues Friday evening into Friday night as the amount of rain falling might exceed the capacity for drainage on roads and streets.

Wind

It will be getting increasingly breezy around by early Friday afternoon and winds at the coast and from about the Everett area north will gust over 35 mph along the water. From Western Snohomish County north and to the Coast and the Hood Canal, we have High Wind Warnings in effect. Gusts there could be around 50 mph, but possibly closer to 60 mph north late Friday. We also have Wind Advisories for the rest of Snohomish County south. Elsewhere, winds will be in the 25-35 mph for gusts (isolated to 40-45 mph) Friday afternoon through Friday evening.

On Saturday morning, as a cold front moves through, there will be "burst" of westerly winds that could cause some issues along the Strait, Admiralty Inley, Whidbey/Camano Island and some coastal locations of Skagit and Snohomish counties. This will bear watching for Saturday morning as previous setups like this have caused damaging winds (60mph or greater) in those most prone locations to westerly, down-Strait winds, like western Whidbey.

Winds will die down Saturday afternoon but remain blustery into Saturday night.

Snow

Biggest thing working against significant snow late Saturday through Sunday is the fact the ground will be unusually warm for this time of year, even as temperatures drop Saturday afternoon and evening.

Snow levels will be below 1,000 feet by mid-late afternoon on Saturday. While precipitation for most areas will be rain (and intensity and coverage will be diminishing), the westerly winds could cause a Puget Sound Convergence Zone to develop. This will probably be (if it develops) in the usual spots from north King into Snohomish counties, possibly as far south as Seattle. If precipitation is heavy enough, some wet snow could make it to the surface and accumulate, though likely only briefly on roads because of the warm ground. Details to come on this wrinkle to Saturday afternoon and evening, but it’s something we’ll be watching for.

On Sunday, it'll be cold enough for snow from 500 feet elevation down to sea level the whole day. However, moisture looks to be pretty limited. Still, rain/snow showers will probably dot the landscape with minor, spotty accumulations possible, though ground temperature still will work against significant widespread issues on the roads. Locally heavy showers, though, could cause brief problems.

We look to dry out Sunday night and Monday so it doesn't look like a big issue to start the work and school week.

We will NOT flash freeze the moisture anywhere in the lowlands. Temperatures will remain above freezing through Monday, with the exception of the far north (Bellingham area) where we could see some patchy ice issues.

More moisture arriving Tuesday could hold a better chance of some minor snow accumulations before we quickly warm up into mid-week. More to come.