Finally, Some Real Precipitation for the Pacific Northwest

One thing that really stands out this winter has been the lack of heavy rain over western Washington, particularly since the start of the new year.   One hardly needed an umbrella for the past few months.

To illustrate, below is a plot of the daily precipitation over the past six months at SeaTac.  A handful of wet days (up to 1-1.5 inches) in December and then the spigot turned off in 2023,  with the wettest days only hitting around 0.5 inches.   I have cycled to work pretty much every day.


The central issue is that there has been a lack of warm, wet atmospheric river events moving into the Northwest.  Instead, the moisture plumes have gone into California.   Interestingly,  during this winter San Francisco has received Seattle's normal rainfall and vice-versa (see below).
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A big change in all this will occur over this weekend.  A strong atmospheric river of substantial moisture will be directed into the Northwest on Sunday and Monday (see the forecast of atmospheric moisture below for 11 AM Sunday).

This moisture plume will be backed by strong winds from the southwest, resulting in moderate to strong levels of moisture flux (moisture times winds), which is a measure of how much water vapor is being pushed against our regional terrain (see below).


As you can imagine, the impact of all this incoming moisture will be substantial precipitation over the region, as shown by the predicted totals through 5 PM Monday (see below).  3-7 inches in the mountains and a substantial band over southern Puget Sound.


As shown by a close-up view of the predicted precipitation, there will be a profound rainshadow northeast of the Olympics, with Sequim, Port Angeles, and Victoria being relatively dry.  SeaTac Airport will be wet.  Very wet.


This event will bring substantial warming aloft and by the end of Sunday, the snow level will rise to at least 6500 ft.    The mountains will be challenging, first heavy snow followed by heavy rain.  Rivers will rise rapidly around the region.

Time to find your umbrella!




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