(1/4) Snowy, then rainy weather ahead as cold blast about to end

Travel problems likely starting late Thursday

More very complicated and variable weather ahead tomorrow night into Thursday for the region with vastly differing impacts depending on location.

TONIGHT: Just like the last 24 hours, we’ll have showers of rain or wet snow through tonight. Temperatures could be a degree or two warmer so snow levels are likely to be just above sea level but if heavier precipitation occurs, minor and brief accumulations of wet snow are possible into Wednesday. Also, while temperatures got into the upper 30s to low 40s today, many side streets (particularly nearer the Cascades and Olympics) are still packed with ice and this is not likely to melt much if at all through tonight. Some refreezing of melted ice and snow today is likely. Use caution early.

WEDNESDAY: We’ll turn drier to start Wednesday but still some roads will be icy where they have been. Morning temperatures will be near freezing. By afternoon, a strong warm front will be surging north past Portland and spread precipitation into the area by mid-late afternoon and into the evening. While this warm front will finally mark the end of this long period of wintry weather for the lowlands, the transition period will be a battle between cold air still flowing into Western Washington via the Fraser gap and the much warmer Pacific airmass.

We’ll likely see a northward-moving area of snow or a rain/snow mix even down to sea level as the precipitation moves in with the changeover to all rain occurring several hours after the onset of precipitation in any one location. Temperatures will actually go UP as the period of precipitation continues!

Areas from about Olympia south shouldn’t have any significant accumulation of snow as temperatures will be warmer as the precipitation moves in late in the afternoon. For Tacoma to Seattle to about Everett, I expect a slushy inch or maybe two of wet snow, with precipitation turning over to rain through the evening hours. The fact that we turn to warmer rain as the evening wears on will limit the impact on the roads as brief accumulation of snow should be pretty quickly washed away or melted by the later rain.

North of Everett and near the Cascades, this is going to be a potentially impactful period of snow on Wednesday evening and into Thursday morning. A Winter Storm Watch has been issued. For these locations like our foothill communities including North Bend, Monroe, Arlington and Black Diamond, it will stay colder for longer so we could see two inches or more of snowfall with isolated higher totals. Whatcom and Skagit counties will likely see the most snow, up to six inches.

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THURSDAY: Eventually into Thursday morning, even these snowier spots will see a changeover to rain as the snow level rises to above 1,500 feet, though there could be a period of freezing rain near the Cascades. Our mountain passes will get slammed with another one to three feet of snow, picking up Wednesday evening and continuing into Thursday. A Winter Storm Warning is in effect for the mountains. Expect pass closures at times and avalanche danger will continue to rise.

On Thursday, expect lowland rainfall of 1-2 inches with more in the foothills below the snow line. This, combined with snowmelt will cause some issues with urban and small stream flooding and a Flood Watch has been issued for this.

FRIDAY AND BEYOND: Friday will be rainy and mild with the continued potential for some flooding problems. Also, shallow landslide risk will increase. Over the weekend, however, we’ll dry out with showers tapering off on Saturday and Sunday being partly sunny. Highs will be in the 40s and lows in the 30s. Next week will likely hold some chances for rain and mountain snow but most likely the lowland snow threat next week will be minimal.

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