Monday, June 9, 2014

The Insidious Loss of Snow during the Past Month

Albion Basin and Greeley Hill, 8 June 2014
Loss of snowpack in May and June is pretty much the way things work in Utah, but this year, the decline has been remarkably steady and consistent.

On May 11th, the snow depth at Alta-Collins sat very near its maximum for the year at just under 120 inches.  At that time, the snowpack was fairly consolidated and ripened, meaning it has warmed to 0ÂșC throughout its depth, so additional energy input from above freezing temperatures and solar radiation would result in snowmelt.  

Source: MesoWest
Indeed, it was just a couple of days later that temperatures popped up to near or above average and, despite some ups and downs, they have stayed there for nearly a full month.  

Source: NWS
Indeed, since May 15, there hasn't been a single day at Alta with a below average maximum temperature and only one day with a below average minimum temperature (and that was only by a degree).  We've also had little in the way of cloud cover during this period, and most of the energy that melts snow comes from the sun.  Basically, if you want to melt snow in Utah, it's best to have above average temperatures, lots of sunny days, and dirty, dusty snow.  We have all in spades this year.  

This has led to a non-stop decline in snow depth at Alta–Collins.  If you look carefully at the graphs above, you can also see that the rate of snow depth decline increased around May 25th, which is also when there was somewhat of a step up in the temperatures (especially the maximum temperatures).  Since that day, we've been losing about 2.8 inches of snow a day.

On May 19th, I guestimated Alta-Collins would lose all its snow around June 27th.  That's still looking like a decent guess, although the current melt rate would bring an end to snow cover at that location at around June 25th.  

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