Seattle Will Tie the Record for Driest May, While Nevada and Northern CA Aew Wet

Here is a meteorological quiz.  In May, where should you go for dry conditions with lots of sun?

1.   Western Washington State
2.    Eastern Washington State
3.    Northern California
4.    Nevada
5.   All but western Washington

This year the correct choice would be (1) Western Washington State!

It is increasingly possible that this extraordinarily dry May will tie the record for lowest May precipitation total ever observed at Seattle Tacoma Airport.  The record low amount is .12 inches for the month.  And that is exactly what we have right now.

The expected rain for the last week of the month in Seattle.  Zero. 

Here is the cumulative total precipitation predicted from 5 AM this morning through the end of the month. Western Washington gets a few sprinkles, while really heavy (and unusual) precipitation is found from northern CA, Nevada, southern/eastern Oregon, into Idaho, and Montana?  Want a suntan?  Western Washington is the place!

Below is the difference from normal precipitation over the last 2 weeks for the western US.   Western WA and NW Oregon are several inches below normal, but head east in to the desert areas and precipitation is well above normal.

A more deceptive (but fun!) way to look at precipitation is the percentage of normal precipitation for the past two weeks.  Parts of western Washington are enjoying less than 5% of normal, while sections of the Sierra Nevada mountains and Nevada have had 400% of normal or more.  Arizona has been very dry.

So what is been going on to give this strange precipitation pattern?  I can tell you, by showing the upper level (500-hPa) weather map for today at 8 PM. 

A ridge of high pressure is over Washington, but it is undercut by a trough moving into California.  This kind of configuration has been occurring on and off for several weeks, bringing clouds and showers (lots of thunderstorms) to northern CA and the western interior.

And did I mention lightning?  Let me show you an AMAZING image--the lightning strikes over the Northwest for the 24 h ending 1 AM Thursday.  Mama Mia..that is a lot of lightning.... and notice how it totally avoids the lowlands of  western WA and Oregon.

So if you want to get wet, head to California and Nevada.  Like dry conditions?  Western Washington is the place to be.