The first occurred late Tuesday when strong south winds produced a plume that extended from the Sevier Lake Bed to the Salt Lake Valley.
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| Satellite image source: College of DuPage |
Dust in the eastern Salt Lake Valley and Wasatch Mountains was thickest just ahead of, during, and immediately following the cold frontal passage. The post frontal dust may have originated to the west. In any event, the visibility at the Salt Lake airport dropped to 1/4 mile and PM2.5 concentrations reached 149 ug/m3, higher than achieved during wintertime inversions the past two years. Nasty stuff. The dust was followed by a relatively small storm on Tuesday night, but with a bit of wind to blow the snow around, plenty of dust-covered chocolate snow remained unburied at Alta on Wednesday.
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| Photo courtesy Will Farr |
Then we had a weaker dust event on Friday. One could see the degraded visibility in the afternoon before the precipitation picked up.
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| Dust in the air on Friday afternoon |
The weak Friday event was followed by a more substantial storm Friday night though Saturday night, with more than an inch of SWE at Alta Collins.
As a result, the dust layers formed by the Tuesday and Friday events are buried, but one needs only whip out the snow shovel to find them lurking 8 inches below the surface.
What will happen as the snow starts to melt is it will percolate through the snowpack, passing through the dust layer. Eventually, the dust will reach and remain on the snow surface, forming snirt (part snow, part dirt). Dust is darker than snow and, as a result, it absorbs more energy from the sun than pristine snow. This leads to a more rapid snowmelt and an earlier loss of snowcover in the spring or early summer (depending on elevation). The bottom line is that dust is a "Korn Killer." Spring skiing would be better without it.
Dust-on-snow is a wild-card in our consideration of water resources in the mountain west. It is such a complex issue, and anecdoteal evidence suggests it has occured more in the last decade or so than in the past; would you care to make a statement about what is causing these events, and do you think there is any hope for policy addressing it?
ReplyDeleteBecause of a lack of good dust data going back for many decades, this is a difficult question to answer definitively. Lake cores from the Uinta Mountains and in Colorado clearly show a massive increase in dust deposition ~1870AD, almost certainly related to land surface disturbance owing to western migration. In Steenburgh et al. (2012), we examined dust reports at the Salt Lake Airport since 1930 and found a long-term decline in frequency, but also an uptick since about 2000. We didn't put a lot of faith in these trends given the variations in reporting approaches.
DeleteMy usual summary of this information is that dust has been playing a role in the western US hydrologic system for many decades, but there are large variations from year to year and from decade to decade in it's importance. Further, those variations are likely to vary from location to location.
Jim