Wednesday, May 16, 2012

Galena Summit Snowpack

The Galena Summit SNOTEL is arguably one of the best indicators of the Salmon River's high elevation snowpack.  Having been through the mid and low elevations of the Upper Salmon River last week, we can attest that there isn't enough snow left in those locations to add to the streamflow.  The bulk of the streamflow right now is coming from the high elevation snowpack runoff.  As soon as this snowpack is depleted, the river flows will begin to recede.  The year we are having right now would tend to suggest an impending peak in the streamflow, perhaps as early as this week but almost certainly before the end of May.  Note in the Galena Summit data below the snowpack has lost 50% of both its water content and its snow depth during the past week alone!

In our 30+ years of watching how snow melts and how that melt pattern contributes to stream flow, we have developed a theory that the peak flow actually occurs BEFORE the end of the snow melt.  It has something to do with the density of the snowpack and the momentum generated by the sheer volume of the water coming out of the snow.  Generally, our theory concludes that the last 20% of the snowpack will come off rather slowly unless it affected by a rainstorm.  At the current rate of loss of both snow and water, the next half of the snowpack should be gone within 3-5 days.  By that time, the snowpack will be down to the about 20% of its starting depth and flows should begin to taper off.

If I had to take a Unscientific Wild Anatomy Guess, I'd tend to think the peak flow of the Upper Salmon will occur on May 20--right in time for the solar eclipse.  (This is barring an unusual rainstorm on the remainder of the snowpack.)  Whatever the date of peak flow may be this year, I can virtually guarantee you it will take place prior to May 31.

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