Greetings from Silverton-
Our third dust-on-snow event of WY 2015 did pan out, as was speculated upon yesterday, with the heaviest deposition of the season at Senator Beck Basin. Timing of this event was a bit slower than anticipated. Somewhat surprisingly, visibility from Silverton was still virtually undiminished at around 6 PM on Wednesday, April 14, even under strong SW’ly winds.
However, overnight winds increased and a significant dust deposition, D3-WY2015, fell almost entirely during darkness, along with a trace of new snow (a nominally ‘wet’ event). Winds remained high at dawn, and a very light haze was still visible. Winds then began a westward shift and skies were notably clear and clean by late morning. Overall, this dust event spanned approximately 16 hours, mostly overnight.
Samples of this D3 deposition were collected today at the Swamp Angel Study Plot at Senator Beck Basin. A “concentrated” sample capturing as much dust as possible in a large carboy was collected in a small depression where new snow containing dust had drifted.
CSAS’s “mass loading” sample capturing the dust covering a carefully sampled area of 0.5 m2 was collected closer to the SASP instrument array, on a planar surface that had been pre-scraped clean of the prior (merged) D1 and D2 dust layers on Wednesday morning, hours before the D3 event. Even though a thin layer of clean snow overlay the D3 dust, solar energy was rapidly heating the dust and melting that clean snow.
Although not equivalent to the larger dust-on-snow events in our period of record, this D3 event is nonetheless sufficient to quickly result in reduced snow albedo and increased snowmelt rates at Senator Beck Basin and likely throughout the western San Juan Mountains, so long as the dust is exposed or near (within inches of) the snowpack surface. Starting tomorrow, Thursday, April 16, the CODOS team will begin a two-day circuit covering the Grand Mesa, Park Cone, Spring Creek Pass, and Wolf Creek Pass sites (the McClure Pass site is now snow free), verifying the presence or absence of dust-on-snow in those snowpacks. Our remaining Front Range and northern sites will be visited after the major winter storm expected by NWS later this week has finished. Any old or new dust at those sites is likely to be substantially buried during that storm, delaying the dust’s effect on snow albedo.