Sunday, February 8, 2015

Milky Rain

The February 6th "Milky Rain"

**** Updated on 9 February with additional information at the end of post ****

A Possible Explanation

A highly unusual "milky rain" occurred over much of eastern Washington and Northeast Oregon on Friday, February 6th. Periods of light rain during the morning and afternoon left cars spotted and smeared with a white or grey residue. 

Picture from a Facebook Friend of the NWS Pendleton OR 
Picture taken at the NWS Spokane office 

Picture taken at the NWS Spokane office

It is not unusual to experience "muddy rain" in the Inland Northwest. During the summer months, dirty brown water marks are frequently deposited on our cars. However, muddy rains rarely occur in the winter. And why the unusual milky white color?

Most plausible explanation: A large dust storm in Northwest Nevada occurred Thursday night into Friday. The dust caused traffic accidents and poor visibility in the Reno area. Winds gusting in excess of 60 mph were reported across the northwest Nevada desert. Here are some peak wind gusts documented by the NWS office in Reno Thursday night into Friday.

     LOCATION                                 REPORT
                JANESVILLE                    62.00 MPH              
                SUSANVILLE  2 NE              66.00 MPH
                ANTELOPE LAKE  5 NNW          70.00 MPH
                PITTVILLE  17 S               73.00 MPH
                HONEY LAKE  15 NE             77.00 MPH
                DOYLE  3 N                    79.00 MPH
                SIERRAVILLE  8 SSE            93.00 MPH

                MONO LAKE  1 NW               63.00 MPH
                CROWLEY LAKE  5 W             76.00 MPH
                COLEVILLE  3 E                82.00 MPH
                BRIDGEPORT  4 WNW             91.00 MPH

                SILVER SPRINGS AIRPORT        62.00 MPH
                SMITH VALLEY                  63.00 MPH
                YERINGTON MUNICIPAL AIR       63.00 MPH
                LOVELOCK DERBY                64.00 MPH
                SWEETWATER SUMMIT             86.00 MPH

                FOX MOUNTAIN  12 WNW          60.00 MPH
                LAKE CITY  3 ESE              70.00 MPH

                SOUTH LAKE TAHOE  3 SSW       64.00 MPH
                RENO  16 SSW                  134 MPH

                RENO  4 SE                    58.00 MPH
                GARDNERVILLE  4 S             59.00 MPH
                MINDEN-TAHOE AIRPORT          64.00 MPH
                COLD SPRINGS VALLEY  2 W      65.00 MPH
                RENO  18 S                    66.00 MPH
                SPOONER SUMMIT  3 E           68.00 MPH
                GARDNERVILLE  5 E             71.00 MPH
                RENO  5 N                     73.00 MPH
                GARDNERVILLE  5 NNW           73.00 MPH
                WASHOE CITY  2 WSW            77.00 MPH
                NEW WASHOE CITY  3 SW         79.00 MPH
                RENO  9 SW                    82.00 MPH
                VIRGINIA CITY  4 NNW          88.00 MPH
                GARDNERVILLE  5 WSW           90.00 MPH
                E GALENA                        109 MPH

Pay particular attention to the reports from Washoe, Humboldt, Pershing, Churchill, and Lyon counties. These generally sparsely populated counties are part of the "desert of Northwest Nevada" and are experiencing a multi-year drought. Numerous reports of blowing dust came from these counties Thursday night into Friday.

Check out some of the pictures from the Reno Gazette-Journal posted in a Saturday story about the storm that pounded the Sierra Mountains with snow and produced strong winds in western Nevada. Note the milky white or grey color of the blowing dust.

 Reno Gazette Journal

Reno Gazette Journal

Reno Gazette Journal

The white colored soil does not appear to be unique to a small area near Reno. Look at this Google Earth Satellite image. Dry lake beds appear bright white in the northwest Nevada desert and throughout the state.

Google Earth Satellite Image

How does dust from as far away as Nevada get to northeast Oregon and eastern Washington? It would take many hours of a prolonged strong south wind to push dust that far. Below are some images from the University of Washington GFS MM5 weather model. These graphics are tough to read. Our apologies. We may be able to update these graphics with some better ones later.

The next two images are 850 millibar model wind and temperature forecasts. This is roughly 4700 feet above sea level. These images show a constant average wind of roughly 40 knots (46 mph) from 10 PM on Thursday to 7 AM on Friday. This is a period of 15 hours of a constant south wind at 4700 feet above sea level.

10 PM on Thursday:  The small arrows on this graph show show south winds of 30-50 knots over the eastern half of Oregon

7 AM on Thursday:  The small arrows on this graph show show south winds of 30-45 knots over the eastern half of Oregon and up to 50 knots in Washington.

A forecast sounding for John Day (central Oregon) at 4 AM from the University of Washington GFS MM5 shows the wind speed even stronger above 850 millibars...up to 60 knots (69 mph) out of the south/southwest.

How long would it take for dust to travel from northwest Nevada to the Inland Northwest?  Gerlach, Nevada is near some of those dry lake beds in Nevada.
  • Spokane to Gerlach:  Distance - 490 miles
    • 490 miles / 40 miles per hour = 12.25 hours
    • 490 miles / 50 miles per hour =  9.8 hours
  • Pasco to Gerlach: Distance - 380 miles
    • 380 miles / 40 miles per hour =  9.5 hours
    • 380 miles / 50 miles per hour =  7.6 hours
So, if dust were to arrive in the Inland Northwest by mid day Friday, we would expect it to originate in Nevada between midnight and 5 AM. 

What time did the strong winds start in Nevada?  The first wind damage reports started to come into the NWS Reno as early as 925 PM on Thursday night and continued through the night. Here is an excerpt from the Local Storm Report issued by the NWS Reno. High wind reports continued into Friday afternoon.

 1107 AM PST SAT FEB 07 2015

 ..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
 ..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....

 0925 PM     NON-TSTM WND GST 5 N RENO                39.61N 119.82W
 02/05/2015  M73.00 MPH       WASHOE             NV   OFFICIAL NWS OBS


 1255 AM     NON-TSTM WND DMG 2 SW SOUTH LAKE TAHOE   38.92N 120.01W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT


 1256 AM     NON-TSTM WND GST 3 SSW SOUTH LAKE TAHOE  38.90N 120.00W
 02/06/2015  M64.00 MPH       EL DORADO          CA   ASOS           

 0431 AM     NON-TSTM WND DMG 2 ENE SOUTH LAKE TAHOE  38.95N 119.95W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT


 0445 AM     NON-TSTM WND DMG 4 SW SOUTH LAKE TAHOE   38.90N 120.04W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT

             6 TREES BLOWN OVER.

 0450 AM     NON-TSTM WND GST 16 SSW RENO             39.32N 119.94W
 02/06/2015  M134 MPH         WASHOE             NV   MESONET        


 0545 AM     NON-TSTM WND GST 5 WSW GARDNERVILLE      38.91N 119.83W
 02/06/2015  M70.00 MPH       DOUGLAS            NV   TRAINED SPOTTER


 0550 AM     NON-TSTM WND GST 9 SW RENO               39.45N 119.94W
 02/06/2015  M82.00 MPH       WASHOE             NV   PARK/FOREST SRVC


Other explanations for the blowing dust have been "floating around". Excuse the pun. Here are a few of them.

Volcanic activity in Russia. Maybe, but concentrations of ash would probably be only trace amounts given the distance required to get here. You would also expect western Washington and western Oregon to have reports of "milky rain" in this scenario.

Ash from burn scars in the Western U.S.  Another maybe. Burn scars are relatively small compared to the Nevada desert, so the source region would be limited. Burn scars in northern California, central Oregon and western Washington have received an abundance of moisture recently. Northwest Nevada has not. Soggy or snow covered ash will not blow around like dry ash or dust.

Observed 60 Day Rainfall from

60 Day Percent of Normal Precipitation

Additional Information on Monday, 9 Feb 2015

Some additional information has come into our office this morning which helps to shed some new light on this event.  First, here's a detailed list of reports received at the NWS Pendleton office:

8 am NWS personnel notice dust hanging on the way to Pasco.  Call from Fossil about the dust hanging looks like fog.
8:18 Report and pic from Umapine
9:18 Report and pic from Milton Freewater
9:46 Pendleton office puts out a post about being aware of the Milky Rain
10:01 Reports from Irrigon
10:04 Report from Dayton
10:09 Report from Tri-Cities
10:12 Report from Pendleton
10:18 Report from Walla Walla
10:19 Report from Helix
10:21 Report from Milton Freewater
10:23 Report from Walla Walla/Irrigon as well
10:24 Report from  Pasco
10:25 Report from Pendleton
10:32 Report and pic from Walla Walla
10:34 Report from Hermiston
10:35 Report from Kennewick… Report and pic from Walla Walla
10:37 Report and pic from Richland
10:43 Report and pic from Kennewick
10:44 Report and pic from Milton Freewater
10:45 Report and pic from Walla Walla
10:52 Report from Richland
11:05 Report and pic from Tri-Cities
11:07 Report and pic from Walla Walla
11:08 Picture from Connell
11:13 Report and pic from Milton Freewater
11:15 in Hermiston
11:21 Pic from Richland
11:22 Report from Tri-Cities
11:26 Report from Spokane
11:27 Report and pic from Kennewick and Finley
11:32 Report from Spokane
11:35 Report from Walla Walla and College Place
11:38 Report from Dayton
11:39 Report from Kennewick
11:45 Report and pic from Irrigon
11:58 Report from Boardman
12:08 Report from Umatilla
12:16 Report from West Pasco
12:33 Report from Hermiston
12:43 Report and pic from Kennewick
12:47 Report from Spokane
12:51 Report from Richland
1:09 Report and pic from  College Place
2:31 Report from Spokane

Here's a map showing the location of all of the reports we received.

There are air quality sensors run by the states of Washington and Oregon.  These sensors measure particulate matter in the air.  Here's the sensor readings from Tri-Cities and from Cheney (southwest of Spokane):

The TPM25 is for very small particulates (e.g. smoke).  There isn't any perceptible difference in these readings at either site (dark green like).  The TPM10 are for larger particulates, typically dust.  At both sites, there was a noticeable increase in PM10 on February 6th.  The PM10 readings started increasing around 7am and peaked midday, before decreasing in the afternoon.  In both cases, the elevated PM10 lasted about 6-8 hours.  This correlates well with the Milky Rain reports.

An additional piece of information is the weather observation at the Pendleton Airport.  At 6am the visibility was reported to be only 4 miles due to Haze, without any rain or fog.  The wind had been blowing from the south for the previous 7 hours, but the visibility didn't decrease until sunrise.  In other words, whatever reduced the visibility was likely not being generated locally.

In yesterday's blog entry (above) it was speculated that the strong winds over northwest Nevada may caused a dust cloud which moved northward into eastern Washington/Oregon, and that dust might have been responsible for the "Milky Rain".  Here's a display of the wind from the Cold Springs, Nevada area:

You can see from the sustained winds (red line) and gusts (green dots) that the wind started blowing around 5am (20-35 mph) and gusted to 62 mph around 7am Friday.  

There is a weather computer program that allows us to enter a source location (e.g. smoke from a fire) and the program will predict where it will go.  So we entered the location north of Reno that was mentioned in the Reno Gazette Journal.  We told the computer to start at 7am February 5th and give us a forecast for each hour through 4pm.  Here's the result of that forecast:

As you can see, this computer forecast model would predict that dust generated just north of Reno would have moved across extreme eastern Oregon and into western Montana.  The forecast model would suggest that the dust would have traveled too far to the east to be observed in central Washington.

But the NWS Pendleton office also received a very valuable weather spotter report from south-central Oregon. They reported blowing dust from the alkali beds near Summer Lake. Here's a couple of pictures of Summer Lake, including one showing the alkali dust blowing:

Summer Lake, Oregon

Blowing Alkali Dust on Summer Lake, Oregon

And here's a view of Summer Lake on satellite:

Summer Lake, Oregon

  There is a weather observation at this location.  Here's the observed wind:

The wind was blowing around 20-30 mph with gusts 35-50 mph on the 5th of February.  Then overnight the wind increased to around 35 mph with gusts 60-70 mph.  These very strong winds lasted about 9 hours, similar to the Milky Rain duration.

So we ran the computer trajectory model from this location for the time of the strongest winds.  Here was the resulting trajectory forecast:

These trajectories start at 10pm on the 5th and continue until 7am on the 6th.  As you can see, the track of dust from this location would move directly over the Tri-Cities and Spokane areas.  Additionally, the timing fits.  The first trajectories arrive in the Pendleton area around sunrise on the 6th. 

So, based on this additional data and analysis, it appears that dust from south-central Oregon near Summer Lake was lofted into the air by strong winds on the night of February 5th.  A trajectory forecast model agrees that dust from this location would have traveled over the Pendleton, Tri-Cities, and Spokane areas on the morning of the 6th.  It is worth noting that a large burn scar from the summer of 2014 is located in central Oregon.  We cannot confirm or rule out that ash from this burn scar may have been a part of the Milky Rain. 

If additional information comes to us, we will update this blog.

Here's some additional pictures from the NWS Pendleton office:


  1. Doesn't anybody have an XRD? If it's playa dust it should be very easy to identify. Send me a sample and I'll tell you what's in it

  2. I've always wanted to go to the Black Rock Desert -- now, it came to me!

  3. This was also seen in Alabama. It appeared on the side of my car that the wind was blowing from. This was Sunday morning, and I showed 2 people in hopes of figuring out what it was. Really strange.