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Colorado Dust-on-Snow (CODOS)
With direct funding support from stakeholders, CODOS monitors the presence/absence of dust layers at 11 mountain pass locations throughout Colorado.

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     CODOS 2012 Updates > March 7

March 7, 2012: Verification of D4

Greetings from Silverton on Wednesday, a blustery March 7th -

This morning I verified that we have received our 4th dust-on-snow deposition of the season at Senator Beck Basin - event D4-WY2012, as predicted by the National Weather Service's Grand Junction forecasters.  This event is likely to have impacted other Colorado mountain ranges besides the western San Juan Mountains.  Large amounts of dust were clearly visible in the USGS Abajo Peak webcam images on Tuesday (yesterday) afternoon but only very weak hints of dust were visible in the sky here in Silverton by sunset Tuesday (the 6th).  The bulk of this D4 event arrived here overnight but, given the observations of blowing dust in the source area on Tuesday afternoon, we will log this event as commencing on March 6th. 

As of this writing, fierce SW'ly winds and sporadic snow showers are continuing at Senator Beck Basin.  USGS and UDOT webcams also show rain and snow showers underway in the Colorado Plateau, so dust emission may have been largely curtailed from most Plateau source areas.  We will determine, after the storm, whether additional dust was deposited with this additional snow here at Senator Beck Basin.

Last Sunday afternoon (March 4th) we had an unusual deposition of valley pollution here in the western San Juan Mountains.  This haze-on-snow event was, by all reckoning, very localized and, although this sort of snowpack contamination may be more common in other areas, like the Wasatch Range of Utah, this was the first event of the kind that I've observed here.  The National Weather Service was monitoring a strong and persistent inversion over the Grand and Uncompahgre valleys, at 700 mb (about mountain-top elevation).  As often occurs, that inversion had trapped considerable local 'smog' underneath (or the West Slope's version of smog) until, on Sunday, N'ly flow pushed that dirty air south and eventually up the Uncompahgre watershed, against Red Mountain Pass, the Sneffels Range, and other local terrain, and clearing the air farther north.  In effect, the dirty air had sloshed to the southern edge of the containing basin.   

Although this haze was enough to reduce visibility along the Hwy 550 corridor over Red Mountain Pass, the view north from Ridgway of the Grand Mesa, over 50 miles away, was crystal clear and no blowing dust was observed in the valley or, according to the NWS, in Grand Junction.  No deposition was visible at the snow surface at Red Mountain Pass on Sunday afternoon, perhaps because most of the aerosol particles were too fine to fall out of the haze and, instead, remained suspended.  By Tuesday morning it finally became apparent that some very minor deposition of the haze had occurred, perhaps as a result of simple collision of this dirty air with the terrain.  However, because there was no corresponding dust event at the ground in the Grand Valley (which had recently received rain and snow), this event has not been logged as dust-on-snow.  Further, the effects are thought to have been very local, perhaps including the Grand Mesa.  D4 dust fell directly onto the same surface as that 'haze-on-snow' and vastly exceeds the mass of dark material that Sunday's haze deposited. 

Any reports you may, have from your locales, of last night's D4 event, or of the recent haze 'storm', are appreciated in advance.  

More soon,
Chris

Chris Landry, Executive Director
clandry@snowstudies.org
Center for Snow and Avalanche Studies
PO Box 190, Silverton, CO 81433 USA
(970) 387-5080
www.snowstudies.org