• Two years, two of the wettest rainy seasons ever

    By: KIRO 7 Chief Meteorologist Morgan Palmer


    A remarkably wet February and March across much of Western Washington is bringing the "rainy season" 2016-2017 very close to the wettest on record -- from just one year ago.

    The six-month period from October through March is undoubtedly the "rainy season" for Seattle and Western Washington.  

    On average, Seattle receives 75 percent of its yearly rainfall during this time.

    But the last two rainy seasons truly knocked it out of the park.  Happy ducks and geese.  Moss-covered sidewalks and roofs.  And very long, grumpy faces of many of the humans of the Pacific Northwest.

    More rain this "rainy season" than in a typical year in Seattle

    As of Thursday night, Seattle has tallied 37.83 inches since the rainy season began Oct. 1.

    The average yearly rainfall at Sea-Tac Airport -- also referred to as "normal rainfall" for Seattle -- is 37.49 inches.

    While having more rain in this rainy season span than a normal year is impressive, it has now happened a total of ten other times in the last 122 years since records started being kept for the city during 1894.

    Back-to-back extremely wet "rainy seasons"

    The aforementioned 37.83 inches now ranks the (very) Emerald City at the No. 9 position for the "rainiest rainy season of all-time" in Seattle. 

    But still, we're still 5.50 inches below the Oct. 2015-Mar. 2016 record total of 43.33 inches.  Could we get there?  With more rain in the forecast, it's possible!

    Now this gets fun (for this math geek). 

    If you add together the past two rainy seasons, they beat out the combined rainy seasons of Oct.-Mar. 1949-51, the previous leader!



    2015-16 & 2016-17:  81.16 inches
    1949-50 & 1950-51:  80.47 inches

    Truly astounding!

    Interestingly, looking at the graph of "rainy season" rainfall since the 1890s, the 1950s through the early 1970s trended up a bit for rainfall during this time of year compared to other eras, and temperatures were overall a bit cooler (quite cold in the late 40s and 50s).

    Could these past two years be the start of a wetter trend during fall and winter seasons?  Well, two years certainly does not make a trend, and the winter of 2014-15 was rather dry, especially when it comes to snowpack.

    But meteorologists are always looking for trends!  We shall see what occurs next winter, especially if we flip to an often-drier El Nino pattern, which looks more probable than a return to La Nina (though no guarantee.)

    How did this happen and what does it mean for the summer?

    Throughout rainy winter seasons, the overall mean (average) storm track is closer to the Pacific Northwest.  We often see this in La Nina winters, though we can and often do get above-normal precipitation even in so-called "neutral" years.  

    This rainy season, we had rather persistent upper-level low pressure over or near the Pacific Northwest, which helped to bring more precipitation, especially after the first of the year.

    What does it mean for the upcoming summer?

    Pretty much nothing, except that our excellent mountain snowpack will prevent us from having significant water shortages even if the summer is drier than normal (a distinct possibility.)

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    The present outlook is for a better chance than normal for generally warmer and drier conditions in the Pacific Northwest during the upcoming summer months, though this is absolutely not a guarantee.

    A lot of people (myself included) wouldn't mind that after this winter that seemingly wouldn't end!


    Follow me on Twitter, Facebook and Instagram!  I'm @MorganKIRO7 on all three.  

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