Normalcy in Snow Pack

In the seventies, our snow-water records were Jay Penney’s hand-written notes that he brought along while we conducted snow surveys and Phil Farnes’ files in Bozeman.  Now, the records are online, and we don’t even have to do the math.  Still, this last cold snap and snowfall demonstrates why the percentage of normal isn’t a great measurement in early winter.

This two week plot shows Grave Creek nudging normal on February 21 with a couple of inches of precipitation showing up. 

The next chart lets us see that we’ll need 3 inches more of precipitation to bring us up to normal by April 1 – and that’s not an unlikely thing.

As we go through March and April, temperatures begin to make a difference in precipitation and snowpack.  Going back through 2012 to 2022, the April 1 temperatures at Stahl Peak vary considerably:

Date                Year                Temp

April 1             2012                28.9 F
April 1             2013                40.5 F
April 1             2014                26.1 F
April 1             2015                27.9 F
April 1             2016                40.5 F
April 1             2017                31.8 F
April 1             2018                22.5 F
April 1             2019                Not Recorded
April 1             2020                11.8 F
April 1             2021                36.9 F
April 1             2022                29.1 F

We could calculate standard deviation . . . and even go back to 1989 for temperature data on the site – but the most significant data is that snow melts when the temperature is over 32 degrees Fahrenheit.  Three of the ten recorded years show melting snow, and seven do not.  Here, we can see the maximum and minimum temperatures that have been recorded this year (for those who notice, the hydrologic year begins on October 1).

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