Snow profile at Swamp Angel Study Plot, Wednesday April 16. The D3 dust layer is seen just below the D4 dust layer. Approximately 2" of SWE (as clean snow) overlies D4 at this site.
Greetings from Silverton on Wednesday afternoon, April 16, 2014. Streamflow surging late last week at virtually all of the gauges that CODOS monitors was clearly related to the series of sunny days, the widespread emergence of dust layer D4 at the snowpack surface (possibly merging with D3), and very warm temperatures.
Then, last weekend's winter storm produced snowfalls of varying depths around the state but were generally sufficient to bury layer D4 and restore high snow albedo to most snowcovered terrain (the exception being the very lowest snowcover, where the storm may have produced mixed rain/snow precipitation). Streamflow surges have reversed over the weekend and early this week, statewide, to varying degrees.
Here in the southwestern corner of the San Juans, last weekend's Storm #22 deposited over a foot of clean snow containing over an inch of water content at Senator Beck Basin; D4 remains buried beneath some 2" of SWE and has not made a significant re-appearance at Red Mountain Pass, as of this writing (as seen in the snow profile performed this morning at Swamp Angel Study Plot). However just to our south Storm #22 produced much less snow and dust layer D4 has widely re-emerged at Molas Pass, even at higher elevations. This re-emergence of layer D4 at higher elevations, merged with layers D3 and D2 at the lowest snowcovered elevations, may be unique to this locale but, where deposited, D4 may be re-emerging at the lowest snowcovered elevations throughout the Colorado mountains.
As of this afternoon, the National Weather Service does not anticipate new snow accumulations this evening and tonight to exceed more than a 1-3" at most mountain passes. Then, showery weather may result in only very minor additional precipitation (perhaps even some rain at lower elevations) along with partly sunny/mostly cloudy skies over the coming several days until a perhaps significant weather system arrives Tues/Weds.
Given that scant additional precipitation in coming days, and some periods of some sun, the ablation of last weekend's new snow overlying dust layer D4 may outpace any new snow accumulations. On 'solar' aspects (E-S-W), that ablation may be sufficient to enable layer D4 to re-emerge extensively in the higher subalpine and alpine terrain. Streamflows may once again respond to that reduction in snow albedo with another surge, 'ratcheting' upward. In some locales, however, the Storm #22 layer may persist in sufficient depth to prevent D4 from re-emerging before next Tues/Weds.
NWS discussions of the approaching cold front and weather on next Tues/Weds are not yet detailed enough to anticipate the precipitation amounts associated with that system, but increasing winds do appear likely. Should that system dig deeply enough into the Great Basin and generate a strong SW'ly wind field over the Colorado Plateau, another dust-on-snow event may ensue.
More soon,
Chris