A reinforcing shot of cold, dry Canadian air is surging south out of interior British Columbia into eastern Washington, Idaho, and Montana. The airmass is very dense and that will mean a pressure gradient between high pressure east of the Cascades and lower pressures west tonight through Tuesday. This air will be "squeezed" through the gaps in the Cascades creating some gusty conditions for foothill communities tonight into Tuesday morning. A Wind Advisory is in effect for these foothills and spots nearer the mountains in King, Pierce and Snohomish counties tonight through Tuesday noon.
The strongest wind gusts will be in the Enumclaw and North Bend areas where peak gusts could exceed 45mph. These locations are the typical "Cascade gap" or "Cascadia Winds" regions but we haven't had a really windy time in these spots for a while, so there could be some branches or trees down with the strongest winds overnight and Tuesday morning.
Winds could gust over 35mph in other areas of the Eastside like Issaquah as well as in a band in south King County westward out of the mountains to about Sea-Tac Airport. This is also a favored area for stronger winds in a situation like this. Elsewhere, wind gusts of 15-25mph can be expected.
Despite the cold temperatures, fog and/or frost will be very isolated to only those most-sheltered locations where there is no wind.
Winds will let up a bit after late morning with a nice, crisp day expected with highs in the upper 40s to around 50. This will be the coldest day for most locations since March 12, the last day of the epic 40-day stretch of cold (and sometimes snowy) weather early this year.
Wednesday morning will be very cold with lows near freezing in Seattle but a lot of upper teens and low 20s in the South Sound. This will be the coldest time of this long period of dry weather.
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