Module 11 | Scenario 3: How Fat Is the Snowpack?

Key Concepts

a. SNOTEL observations

SNOTEL stations collect weather and snowpack observations using a variety of instruments, as depicted in Figure 1. 

Figure 1. SNOTEL station.  Source: NRCS. 

Here we concentrate on the water equivalent in the snowpack (i.e., the amount of water in the snowpack), which is measured by a snow pillow that sits on the ground and can be found in the bottom left of the photo in Figure 1. During the snow-accumulation season, as the snowpack gets deeper, it exerts more weight on the pillow, which can be measured and converted to a water equivalent. The greater the water equivalent, the "fatter" the snowpack from a water resource standpoint. Conversely, decreases in weight indicate a snowpack that is melting and contributing to the runoff. 

SNOTEL observations are available from several sites including those maintained by the NRCS. Here, we use a site operated by the National Weather Service Colorado Basin River Forecast Center, which allows for comparison of current and past years' snowpack water equivalent.  

b. Web access

1. Go to cbrfc.noaa.gov.
2. Click "Show" under "River Conditions" in the right-hand navigation bar. This will turn off the river gauge observations.
3. Click "Snow Conditions," then "Points," and finally "Show" to turn on the SNOTEL sites. If you are taking this class during the summer when many or all stations report no snowpack, you may need to also select "No Data" to see all the stations.
4. Any station can be selected on the map by clicking on it. However, there are scores of them. We will instead focus on three: Snowbird (SBD at 9,177 feet) in Little Cottonwood Canyon, Mill D North (MLD at 8,967 feet) in Big Cottonwood Canyon, and Rocky Basin Settlement (RBS at 8,900 feet) in the Oquirrh Mountains west of the Salt Lake Valley. These sites, which are at nearly the same elevation, are identified on the map in Figure 2, along with several other nearby SNOTEL sites available at the website listed.

Figure 2: Salt Lake area SNOTEL stations.  Source: cbrfc.noaa.gov.

For convenience, here are the direct links to the webpages for the three sites.

• Snowbird
• Mill D North
• Rocky Basin Settlement

c. Interpretation and selecting years

Based on historical and real-time observations, you can decide what year(s) you want plotted, enabling comparisons of the current (if you are taking this during the winter or spring) and past years. See the "previous years" drop down tab above the graph. Figure 3 is an example for Snowbird in which we have plotted the average snowpack water equivalent (black-dashed line) and the values for the year where it reached the highest value on record. Two seasons are tied, 2011 (orange line) and 2005 (red line). Each of these seasons reached a peak of 75 inches compared to an average of 45 inches. Notice how the snowpack gets deeper each year from October 1st (10-01) to sometime in the spring, followed by a rapid decline as the snowpack melts and runs off late spring and early summer.  

Figure 3.  Example SNOTEL graph for Snowbird.  Source: cbrfc.noaa.gov.

On the CBRFC site, you can change the years to plot (including the average, percentile, or median), station to plot, and even select historical years. In the case of the latter,  you can select, for example, "Maximum Peak" under "Historical Years" and it will plot the year that features the largest snowpack water equivalent. If you click "Image" the plot will download to your device and you get a larger graph (very nice). You can also hold down the shift button while you click to select periods of years, including every year in the record.

Figure 4. Guidance on using the CBRFC SNOTEL web site.

One item of note. "Year" here is the water year, which runs from October 1st to September 30th, with the year corresponding to that of September 30th. For example, the 2020 water year is October 1, 2019 to September 30, 2020.