So Much Snow, So Little Water

It was wonderful to see the white stuff return to the valley and the Wasatch Front this weekend.  Everybody got some.  Here are some of the bigger totals as reported to the National Weather Service (water equivalent in parentheses).

Bountiful Bench (through 5 PM Saturday): 13.5" (0.87")
Bountiful (5 PM Saturday): 10.8" (not reported)
Cottonwood Heights (7 AM Sunday): 17.5" (1.64")
Holladay (7 AM Sunday): 15.5" (0.91")
Summit Park (12 PM Sunday): 20" (not reported)
Alta Collins (4 PM Sunday): 23" (1.16")
Canyons 8800 ft (3 PM Sunday): 20" (0.90")

It was a complicated storm featuring a frontal phase Friday night, a period Saturday and Saturday evening with strong enhancement along the benches, and a period Saturday night when the Little Cottonwood magic kicked in. 

There are, however, a couple of key observations to be made.  The first is that the water-equivalents were largest along the east bench of the Salt Lake Valley, not in the highest elevations of the Wasatch Mountains.  Alta-Collins, Snowbird, and Alta-Guard were the three wettest sites, each coming in just over an inch of water.  In contrast, two sites in Cottonwood Heights reported over 1.5 inches of water. 

A big reason for this is the first two storm phases, which featured strong frontal forcing and then a period with weak low-level northwesterly flow in the Salt Lake Valley, but light flow aloft with strongly stable conditions.  One can't always assume the climatological increase of precipitation (water equivalent) with elevation, and Friday night and Saturday provided a good example of that. 

The second key observation is that this storm really didn't add much to the snowpack.  The 23 inches of snow that fell at Alta-Collins sounds like a lot, but it had an average water content of only 5%.  The 10 inches that fell Saturday night had a water content of only 3%. 

So much snow, so little water!

Basically, the storm put smiles on skiers faces, but water managers still have heartburn.  The Snowbird SNOTEL snowpack water equivalent didn't go up as much as one might expect from the precipitation gauge observations (this is not uncommon), but even if one jacks up the snowpack water equivalent to account for this, we're still losing ground to average.  At the end of December, we were 6.1" below average snowpack water equivalent.  Today, even with the weekend snow, we're 9.1" of water below average. 

Source: NWS

This time of year, we should be adding about 1.5 inches of water to the upper-elevation snowpack in Little Cottonwood Canyon every week.  In the first 3 weeks of January, we added about 1 inch per week.   We're still losing ground. 

This trend looks to continue for the next week.  Other than some snow showers today, our next change of a storm is in the Thursday-Friday time range.  The downscaled NAEFS ensemble generates anywhere from about 0.25 to 0.9" of water with that storm at Alta Collins.  Some members produce a bit more after that event, but not much.  Only one NAEFS member reaches the coveted 1.5" water mark for the week.   

The end of January roughly marks the midpoint of the winter snow accumulation season at upper elevations.  At Snowbird, for example, the snowpack water equivalent averages 22.1" on February 1, roughly half the average peak of 44 inches on April 27.  With 9.9" currently on the ground, we look to be about 50% of average at the end of the month, with somewhere between 10 and 11.5 inches of snowpack water equivalent.  

We need a real storm cycle and we need it now.