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Wednesday, April 8, produced another very weak dust-on-snow event here in Silverton, the second event (D2) of WY 2015.  Strong winds from the SSW and SW were underway at dawn on Wednesday but, as is often the case, dust only became apparent in the air, as reduced visibility, around mid-day.  Farther to the southwest, the USGS webcam at Abajo Peak, in Utah, showed substantial dust in the air by mid-morning, fully obscuring the view of Sleeping Ute Mountain, 55 miles to the southeast of Abajo Peak. 


Scattered clouds developed by mid-afternoon Wednesday and the dust intensified somewhat, still having only comparatively minor effects on long-distance visibility.  A shift to more N'ly winds in the evening resulted in fairly rapid clearing of the air, so visible dust in the air spanned roughly 8 hours.  Skies are 'severe clear' here again this Thursday morning, under light N'ly winds.

Looking south down Silverton’s main Greene Street at Sultan Mountain (13,368’) in the distance, at 5 PM on Wednesday afternoon, April 8.  Dust reduction in visibility was apparent but quite minor when compared to dust storms that completely obscure Sultan Mountain and its forested slopes from this vantage point in front of CSAS’s office.

This D2-WY2015 event fell directly onto the April 1-2 D1 layer still at the snowpack surface - a dust-on-dust-on-snow event.  Layer D1 had become increasingly apparent in recent days, generating the kind of dust-enhanced snow surface roughness observed and documented in prior seasons.  We logged (only) 1 mm of precipitation from 2100-2200 hours Wednesday night so this was another effectively 'dry' dust event, like D1-WY2015 on April 1-2.  

The weather system generating this dust event did produce snow showers farther north, so any dust deposition in those locales was subsequently covered with some amount of new snow, and light snow is ongoing in many locations in the Front Range and northern mountains as of this writing Thursday morning.  We’ve had no reports of dust from other locations, to-date, but our observer network is diminishing as ski areas and other operations shut down.

Additional synoptic-scale weather systems including a closed low over AZ/NM over the weekend, and another system with a significant cold front and strong wind field early next week, are emerging in NWS models for the mid-range period.  The second system may result in additional snowfalls for the central and northern mountains, and both may have the potential to generate additional dust events.

More soon,