Friday, August 22, 2014

Thunderstorms and Flooding in Northeast Washington

This is turning out to be the summer of thunderstorms in parts of eastern Washington and yesterday was no different.  Strong thunderstorms hit Okanogan County, including much of the area of the Carleton fire, resulting in mudslides and flooding.  At least ten homes were destroyed and both SR 20 and 153 were closed (see pics from Methow Valley News and Wenatchee World).



Take a look at the "storm total" of the precipitation from Thursday to Friday morning based on the Spokane National Weather Service radar:  1-1.5 inches fell, with most of that happening within an hour or so.



The thunderstorm tops were so tall (about 35,000 ft) that they were picked up by the Camano Island radar (see image at 5:08 PM yesterday).

As an aside, I should note that radar coverage is very poor over the eastern slopes of the Cascades, with the radar beams from the Seattle, Spokane, and Pendleton radars being quite high (about 6000 ft!) by the time they get to say Wenatchee.   Thus, shallow rain can be missed by these radars. The solution to this problem would be to secure smaller, gap-filler radars.   Folks in Wenatchee, Ellensburg, and Yakima might lobby for decent coverage.

The heavy precipitation caused some of the rivers to rise very fast;  here is an example of the river stage of the Methow River near Pateros.  Nice spike from a passing thunderstorm.


Why the thunderstorms?  Same old story...a weak upper trough moved through when potentially unstable air was over Washington (see upper level map for 5 PM Thursday below)

Let me give you an idea about how unusual things have been.  Here is the departure from normal of precipitation over the last month.  Except for the Olympic Peninsula, it has been wetter than normal and MUCH wetter than normal over the Cascades and eastern slopes of the Cascades.

 Want to be impressed?  Here is the percentage of normal for the same period. Much of eastern Washington has received 300+% of normal (but keep in mind that normal is modest this time of the year).

 It looks like things will dry out this weekend as the trough moves eastward.  Nice weekend.

1 comment:

Buddy said...

Terrific thunderstorms in Yakima Co. today. While valley locations were spared, great day of chasing coming across several flash floods.

It'd be interesting to know the volume of water that fell out of the sky today on this ordinarily dry area. Radar coverage is actually pretty good here but agree with the area in north central WA.