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Greetings from Silverton -

Like much of western Colorado, Silverton was under siege from near-continuous SW'ly winds bearing near-continuous dust (and perhaps smoke) for several days starting last weekend, until yesterday afternoon.  The synoptic scale wind field driving this long-duration event has now broken down as the large weather system in the northern Rockies has finally moved eastward, opening the door for more moderate, westerly flow into Colorado.

Although we did see 'clear' skies at dawn on recent mornings here in Silverton, winds rapidly strengthened within an hour or two of sunrise and developing haze was apparent by late morning each day over the weekend and early this week.  Visibilities in Silverton were mildly reduced each day, but first-hand reports from Grand Junction (NWS staff) and images from Glenwood Springs indicated very heavy reduction in visibility on Monday and again yesterday (Tuesday, June 17) along with dust deposition.  (Thanks to Jim Pringle, at NWS, and Jim Pokrandt, at the River District, for these obs).

The Assayii Lake Fire in the Chuska Mountains of western New Mexico has also generated a smoke plume that may have contributed to reduced visibilities in some downwind Colorado locales.  Locally, here in Silverton, the recent winds never delivered the scent of fire during the past weekend or early this week.  There was also no smell of fire in Durango yesterday, as visibilities declined in late morning and early afternoon under strong S and SW winds.  

Images from the USGS Abajo Peak webcam on Friday, June 13 show a major reduction in visibility that afternoon, coinciding with our observations of the D9 dust storm here.  The Assayii Lake fire had not yet 'exploded' into a major fire at that time.  On subsequent days the Abajo Peak camera captured less intense reductions in visibility each day until another major reduction yesterday, Tuesday, June 17.  The strong S'ly winds logged at Abajo Peak may have mixed dust and fire smoke at times.   The USGS Mesa Verde webcam documents the development of either a dust or smoke plume, or a combination of both each day over that period, with sunrise images on the morning of June 17 depicting the red signature of fire smoke.

Farther north and beyond the reach of the fire smoke plume, only minor reductions in visibility were captured at the USGS Island in the Sky webcam over the weekend until a more significant reduction was seen Tuesday, June 17, caused by dust in the air.   

In any case, whether we've been observing just dust, or a combination of dust and smoke, we have observed an unusual and long-running June 'aerosol' event that has deposited small amounts of fresh material onto the remaining snowpack in at least the southwestern and central Colorado mountains.  (Sampling these dust-on-dust events for mass is infeasible).  For the purposes of the CODOS Dust Log, we will let event D9, on June 13, stand on its own.  Then, we will treat the more recent series of more-or-less dusty days up to yesterday, June 17, as a single, long-duration event D10-WY2014.  The wind rose for event D10 spans four days, from June 15 through late afternoon June 18, and shows how sustained, in speed and direction, this wind event was. 

More soon,