Tale of Two Radars: Rainshadow and Windward Enhancement

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 Dog Alert!  See Message at the Bottom---Particularly If You Live in Mountlake Terrace.

With weather radars on both sides of the Olympics now, we can do something we have never done before:  examine simultaneously both the enhancement of precipitation on the windward side of the mountains and rain shadowing on the other.

Here is the storm-total precipitation from the new Langley Hill radar for the past two days.

I know it is hard to see the geography well.... but if you examine this closely you see values of over 2.5 inches on the southwest side of the Olympic, with lighter amounts offshore.  This is a good example of orographic enhancement, with the showers coming off the Pacific being enhanced from uplift on the western and southwestern slopes of the mountains as the air is forced to rise by the terrain.  The sharp cut-off of precipitation over the mountains is not real...it is due to mountain blockage effects.

What about the other side?   Here is the view from the Camano Island radar:

A complex pattern, but with a big hole of light precipitation to the northeast of the Olympics--this is the rainshadow, which extended from the north Sound to Bellingham. Rainshadows are caused by air descending and warming down mountain slopes on the lee side of a barrier.  The rainshadow was shifted away from Sequim and Victoria because the coastal winds have been more west-southwest than southwest or south-southwest.  And you will notice the precipitation really picked up over the western slopes of the Cascades as the air was forced to rise again--some amounts exceeded four inches.   Now these values are not well-calibrated, but the qualitative picture is certainly realistic.

For comparison, take a look at the visible satellite image this morning at 10:45 AM.  You can see the convective showers approaching the coast, the enhancement on the windward (western) side of the mountains, and if you look carefully you can spot some rainshadowing (really cloudshadowing here!) over northeastern Puget Sound.  Of course, the big kahuna rainshadow is to the east of the Cascades, where you could have escaped all the showers today.   And then air rises over the western side of the Rockies and clouds return from Spokane westward. 

At the UW we have software that combines the National Weather Service and Canadian radars--here is a view at 4:20 PM:

Really nice.  You can see the showers offshore, how they become more intense over land, how they die just east of the Cascade crest, are absent over eastern Washington, and start again...in a wimpy way... over Idaho.  And I haven't even mentioned the blustery winds of 20-35 mph all around the region today.

You got to love the weather around here...lots of variability!  Don't you feel sorry for people back east where the weather is so uniform and boring?

My Dog (see picture to the right) was seen today (10/12) near the intersection of 236th St SW and Cedar Way.  If you see her please call immediately (206 719 5603) 
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