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Greetings from Silverton,

Since our last CODOS update on May 9, streamflow at Senator Beck saw a 3 day down-tick (where we saw 1" of additional precipitation), followed by a 5 day up-tick when nicer weather returned.  As I write this Update, snow is lightly falling at Red Mountain Pass and in Silverton the sparse flakes do not accumulate and barely wet the ground.  However, the fresh snow and overcast, cooler temperatures, which is forecasted to intensify and continue the remainder of this week, will again slow snowmelt and consequently reduce streamflows temporarily.  The expected precipitation in northeast quadrant of the state is impressive, but the entire state looks to benefit from additional precipitation over the next few days.  Dry conditions are expected to return on Saturday as a warming trend takes hold for 2-3 days.  And encouragingly, the 1-month forecast calls for an increased chance of above normal precipitation.  SNOTEL data are showing major basins are still staying very near median values.

In the May 9 CODOS Tour Update (http://www.codos.org/#codos), we mentioned that field reports indicated the Grand Junction area experienced a dust event on May 7, remnants of which were observed in the Roaring Fork Valley in the form of dusty cars and other outdoor surfaces.  Field observations on May 9 revealed no additional dust at Senator Beck.  To investigate this dust event further, as well as other potential events from the strong winds out of the south/southwest this past week, we traveled to CODOS sample sites Grande Mesa and Loveland Pass on May 16.        

Although it is difficult to ascertain due to dust from previous events (D1-D4) are on the surface throughout the landscape (which also effects surface roughness a great deal deceasing albedo further), but it is likely that some dust from the May 7 event made it to Grande Mesa.  The telling clue is a CODOS snow pit was dug on May 6 and filled back in leaving cleaner snow on surface before departing site, on May 16 additional dust was observed on this disturbed snow.  Judging by these clues and comparing photos from previous visits, an appreciable amount of dust was not deposited.  The cumulative effect does not change the "average" dust severity classification we have for this site.        

In regards to the question of the extent of the dust event, our observations at Loveland Pass indicate that any additional dust is not discernible.  The landscape looks much the same way as it did on the May 6 CODOS visit.  An ideal candidate site to look for further dust deposition would be McClure Pass, but snow is longer at this site.  However, trajectory wind analysis indicate that this was mostly a localized event. 

There is still a bit of time left in the dust-on-snow season, soil and vegetation indexes show the dust source area is in pre/moderate drought conditions, increasing the likelihood that only the right wind conditions is all that is needed to mobilize dust and transport to Colorado.

Picture of snow surface at Grande Mesa CODOS sample site on May 16.  Clean snow, located 2 cm below snow surface, is shown in the lower left corner.  The dusty and rough surface is seen in the rest of the photo. 

oveland Pass on May 16.  Besides a little bit less snow, the landscape looks very similar as during our May 6 visit.  Compare this photo with the photo in the May 9 CODOS report: http://www.codos.org/codosupdates/may92017

More Soon,

Jeff Derry