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Greetings from Silverton,

Starting Sunday evening (February 18) a disturbance entered Colorado bringing snow and sustained high winds that continued through late Monday (February 19) evening.  Average wind speeds out of the southwest were 35.8 mph with gusts up to 83 mph.  Gusts from 50-70 mph were the norm.  With the snow blowing sideways we still managed to observe 6.3" (16.1 cm) of snow accumulation and 0.6" (15 mm) of water.  Not surprisingly we observed our first significant dust storm this winter season.  This dust event (D2) is the second event of the season with D1 located at the very base of the snowpack and is very faint.  D2 was a wet event (deposited with precipitation) which is diffuse in approximately 6-8 cm of snow which fell at the onset of Winter Storm #7. The dust is barely visible in pit walls but was highly visible on the surface before it was fully buried. As the new snow continues to settle this layer should become more evident in snow pit walls. Because this event is more than a meter from the ground in the snowpack, we expect this event to have hydrologic consequences once exposed in the spring.

Starting in March the CODOS team will begin state-wide sampling tours, at which time we will ascertain the full severity and spatial extent of this event, which is likely widespread with locales like Aspen Mountain reporting dust arriving on this storm front.  Winter storm opportunities also mean dust opportunities, and the very low storm count this season in the San Juan Mountains (currently 7 storms with 14 being the average) is one of the reasons we have not received a notable dust event so far this season.  ENSO forecasts indicate that La Nina conditions are expected to decay rapidly and transition to neutral conditions during spring.  Overall however, the 90-day outlook still calls for increased chance of higher than average temperatures and decreased chance of average precipitation, with the low precipitation forecast consistent with lingering impacts of La Nina.   

Our biggest dust-on-snow months are April, March, and May (in that order).  As we head into spring, D2’s effect on the already low snowpack and the interplay of new snow and dust accumulation will have decisive effects on timing/rate/amount of snowmelt runoff.  New dust deposition remaining mostly covered with new snow accumulation will be very important in minimizing the impacts of dust until the latter part of spring and the normal snowmelt timeframe - not to mention added SWE.  The month of May has been cooler than normal for the last four years and largely wetter than normal. Hopefully that will be the case again this year.  Below is the windrose plot for the duration of dust event D2.         

Jeff Derry