Thursday, April 17, 2014

Altitude and the Timing of Snowmelt

Altitude strongly affects the timing of peak snowpack [snow water equivalent (SWE)] and melt throughout the central Wasatch.  Here's how things are progressing this year.

The lowest SNOTEL station in the Wasatch Mountains is Ben Lomond Trail in the northern Wasatch (6000 ft).  This is a remarkably snowy location for its elevation.  On average, Ben Lomond Trail reaches a peak SWE of almost 20 inches in late March.  This year, however, the peak of about 16 inches occurred in early march, afterwhich the snowpack clung to life until early April when it began to melt rapidly.  More than half of the peak SWE is already gone as of today.

Source: CBRFC
In the central Wasatch Mountains, Parley's summit is the lowest SNOTEL (7500 ft).  Here, the average peak SWE of about 15" occurs somewhere in mid-March to April 1st (more data is needed for a smoother curve!).  This year, Parley's has behaved a bit like a low-elevation station that experiences mid-season thaws.  Note that there was a snowpack peak in mid March, followed by one in early April, both fairly close to the climatological peak.  Since that peak in early April, they've lost nearly half of the snowpack.  

Source: CBRFC
The fact that Ben Lomond Trail, which is 1500 ft lower, has a deeper snowpack than Parley's Summit, illustrates just how wet and snowy the Ogden Valley is.  What a great low-altitude snow climate!

Moving higher we find the Mill-D North SNOTEL in Big Cottonwood Canyon (8960 ft).  Here the climatological snowpack peak of about 24 inches is in early April, and this year was pretty much right on the nubbin for SWE and timing (despite a late start).  We've also seen a small (~15%) loss of snowpack in the past two weeks.  

Source: CBRFC
Similarly, the Brighton (8750 ft) and Thaynes Canyon (9200 ft) SNOTESL have peaked and are on the decline.  Barring a big storm, this is the beginning of the end of the snowpack at this elevation.

Finally, we have Snowbird, the highest SNOTEL in the central Wasatch (9640 ft).  Ah, it's good to be high and on a north facing aspect.  Here, the peak snowpack occurs climatologically in very late April.  This year, we haven't come close to that peak, and we're just starting to get the snowpack ripe enough (i.e., warmed up to the melting point through its entire depth) to start losing snow.

Source: CBRFC
Snowbird may not have peaked yet.  If we can get a late season storm, we might see it go up a bit more.


  1. Gotta love snotel.

    One oddity I noticed is the Snowbird snotel SWE peaks around 42 inches late April, which is more than cumulative precipitation at that time, about 41 inches. Is this possible, or is it measurement error?

  2. Interesting. There are a few possibilities here:

    1. These are two separate measurements. PREC comes from a precipitation gauge that is known to have "undercatch" issues (meaning it doesn't measure all of the precipitation that falls). SWE is measured by a pillow underneath the snowpack. Given that most of the precipitation that falls during this period at this elevation falls as snow, there's the possibility that undercatch is biasing PREC low.

    2. Snow creep or wind transport could contribute to a high bias in the SWE measurement of snow on the ground.

    3. For the climate stats, SWE is the median and PREC is the average. Different stats. However, the fact that this years SWE was behind this years PREC until March, and then it overtook it, suggests to me that some aspect of how the two measurements are made is contributing to this odd behavior.