Weather Blog

Amid flooding event, Seattle might wonder: 'Where's the rain?'

Amid flooding event, Seattle might wonder: 'Where's the rain?'

Anyone who has lived here for any significant amount of time knows the weather is quite variable around here, but Tuesday might take it to the extreme.

Or at least for anyone who has not spent any significant amount of time in Sequim.

While it will be pouring in the mountains on Tuesday, and reasonably raining just about everywhere else, those in the heart of Seattle and Bremerton might be hardly getting wet at all. In fact, it would not surprise me to see some sunbreaks around the city.

How? We can thank the Olympic Rain Shadow. Upper level winds will be screaming out of the due west on Tuesday and as that wind races up the western slopes of the Olympic Mountains, it'll in essence wring out much of the moisture. Then as that air sinks down the eastern slopes of the mountains, it'll warm and dry, leaving a cone of dryness in its wake.

Models indicate this cone will be right over the Seattle-Bremerton city areas. Here is a forecast chart showing expected 24 hour rain accumulations between 4 a.m. Tuesday and 4 a.m. Wednesday:

(The legend is on the right, divide by 100 to get expected rainfall total in hundredths of an inch. So "512" is 5.12 inches of rain. "32" is 0.32".)

Note that while the mountains are expecting 5 inches of rain or more, parts of Seattle and Bremerton are forecasted by the models to be near zero! ( I wouldn’t expect us to be completely dry, but certainly a lot less than the mountains!).

So if you live in the flood plain but work in Seattle, don't be fooled into thinking the rain storm has or is missing your home.

But look how limited the shadow effects reach -- Tacoma and Everett are expecting 1/3-1/2 inch of rain -- just 30 miles away on either side! (Note also the rain shadowing effects coming off the mountains of Vancouver Island over the Strait of Georgia).

This is how Sequim stays so dry -- normally the upper winds are aligned more southwest-to-northeast so that dry cone is over Sequim, but this time the winds are aligned more to protect Seattle. (This is also a similar windflow to the snow event that happened almost a year ago to the day -- remember that snowstorm that missed Seattle and Bremerton on Feb. 23, 2011? Same shadow - only then it was a "snow" shadow than a "rain" shadow.)

This time it's all rain -- even warm with highs near 60. The strong winds aloft will keep it blustery in the lowlands too so it's not like Seattle will be in a tropical paradise Tuesday -- winds will be gusting 20-35 mph through the day. But it should be relatively dry -- even drier than Sequim!

Tuesday afternoon Update:

Sure enough, the rain shadow is going right according to plan. In the period from midnight to 2 p.m., Seattle had received 0.02" of rain, while Snoqualmie Pass has had 2.76" of rain. Over to the west of Seattle, the rain shadow was even more pronounced with the sun breaking out!

Here is video taken Dr. Dale Ireland's camera in Silverdale -- note the sunbreaks in the afternoon!

And here is the visible satellite showing a break in the clouds over Kitsap County (and Eastern Washington! Major rain shadowing going on there:)