What was the mysterious dust raining down in eastern Washington?

I love a good weather mystery.

On Friday, I started to get emails and calls about a strange white/gray powder that was being deposited on cars and windows over southeastern Washington and northeastern Oregon.

The picture below is the kind of material we are talking about.    Good for car wash businesses, but roughly a .001 on the meteorological Richter scale.  I put it aside.

The media started having a field day and speculations went wild, many certified by "scientists."

So the possibilities included:

1..   Volcanic dust from Russia
2.     Dust from a Nevada dust storm
3.     Ash from last summer's fires
4.     Dust from the Middle East
5.    Dust from dry lake beds in Oregon

and more.

First, where did folks observe a white/grey powder Friday morning?  Here is a summary produced by the meteorologists at the Spokane office of the National Weather Service.  Southeast Washington and northeast Oregon.

Some of the possibilities were easy to reject.  The dust from the Middle East and volcanic dust from Russian volcanoes didn't make sense, since why would the dust be so localized?   The dust storm in Nevada was promising until I looked at the wind field, which would blow material too far east to reach SE Washington.

Then there was the theory, proposed on the NWS Spokane blog, that the material was blown from the alkali dust field around Summer Lake in southeast Oregon (see red marker on map below for location).

Here is a picture of the lake I found on the web.  And you say a large dusty area on the satellite picture above.

To raise a lot of dust would require strong winds around the dry lake bed.   So I found the winds at the Summer Lake RAWS observing site and plotted them for the Thurs to Saturday period (see below, second panel).    Big winds, gusting to over 65 mph!    More than strong enough to lift loads of dust.

 I wanted to check out the origin of these winds, so I looked at the 18 hr WRF model surface wind gust forecast for 10 PM Thursday night.  If you look closely you will see strong winds (gusts to 55 knots) in the right place--winds associated with strong downslope flow off the Siskiyou/Klamath mountains.

  My final evaluation is to determine the air trajectories that ended up, at say Walla Walla, in the dust zone.  To do so, I ran the NOAA Hysplit trajectory model using the 12-km NWS NAM model for the 3D wind fields.  Lo and behold the air came from EXACTLY the right region...around Summer Lake.

Why is Summer Lake a source of dust this winter and not most winters?  Could it be that this winter has been usually dry and warm?  Here is the percent of average precipitation for the last month.  The summer lake are is has received 25-50% of normal precipitation.

And here is the departure of temperature from normal. Way warm, perhaps 6-9F above normal.   Start with very low precipitation and add much warmer than normal temperatures (which encourages evaporation)--what do you get?  A much drier than normal surface.

Anyway, the NWS Spokane folks deserve credit for suggesting this solution and I basically have just provided a bit of supporting evidence.   There are, of course, some other possibilities, like aliens and chemtrails, but I suspect the Summer Lake  (and similar nearby lake) origin is the right one.

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The Pacific Northwest Weather Workshop

Interested in attending the big local weather workshop of the region?  The Pacific Northwest Weather Workshop will be held in Seattle at the NOAA facility on February 27-28th.   Everyone is invited and the majority of talks are accessible to laypeople.  To attend you have to register or they won't let you in the gate.  There will be a major session on the Oso landslide.  There is a registration fee that covers refreshments and food, and special student pricing.  If interested, check out this website.


Climate Change and the Pacific Northwest

I will be giving a provocative talk on this subject on March 11th at 7:30 PM Kane Hall on the UW campus in Seattle.  Sponsored by local public radio station KPLU, tickets for this event can be secured at this web site.