Saturday, May 7, 2011

Spring Skiing, Snow, and Runoff

With beaucoup snow in the mountains, I took my son out for his first ski tour this morning and was quite pleased to hear him say that he had a lot of fun going up.  He even had a decent Euro-style look going with the Italia hat.

We opted to skin up Collins Gulch and ski the groomers where the snowpack was well consolidated and where we could follow routes that avoid avalanche concerns.  The skiing was remarkably good as we descended shortly after 11 am and he commented it was one of his best runs of the year.  I suspect some of his perspective stems from earning his turns, which always makes the skiing better, but the corn was indeed quite good.

Debris piles from recent avalanches on the north side of Little Cottonwood are very impressive, with a couple running to the road.  There is a pile at the bottom of Tanners Gulch from a slide last weekend that sticks up very dramatically above the scrub oak.  It's going to be there a very long time.  

Snowpack snow-water equivalent (SWE) at the Snowbird SNOTEL station presently sits at 77.2 inches, which is 199% of average and the highest observed at the site since installation in 1990. 

If you have a careful eye, however, you will notice that the Snowpack SWE has increased over the past few days despite no precipitation being observed.  SNOTEL stations measure SWE using a snow pillow that measures the weight of the snowpack.

Craters Meadow SNOTEL photo showing a typical SNOTEL
site configuration.  Source: NRCS.
Thus, some other process besides precipitation may be altering the weight of the snowpack.  This could be snowpack creep or perhaps horizontal transport of meltwater in the snowpack.  Any other ideas out there?

The flow in Little Cottonwood Creek this morning was rather unimpressive.  Observations provided by the Colorado Basin River Forecast Center show normal river conditions for Mill, Big Cottonwood, and Little Cottonwood Creeks.  This contrasts, however, with the flows along several rivers to the north that are now above flood stage.  

River Conditions 3 PM MST 7 May 2011.
The rivers above flood stage drain basins with widespread low-elevation snowpacks that are well above average in depth, have ripened (i.e., warmed to the melting point), and are melting in earnest.  Runoff in the Cottonwoods depends more on high-elevation snow that has not yet warmed to the melting point through depth.  Hence, increased runoff in the Cottonwoods is still to come.

3:23 PM MST Update:

The CBRFC river condition graphic above suggests several rivers above flood stage (red dots), but inspection of the hydrographs suggests most are not presently above flood stage, but are predicted to be in the near future.  Consult the National Weather Service web site for the latest information. 

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