Sunday, November 23, 2014

Natural Snowmaking Today

It doesn’t need a reason to snow in Little Cottonwood Canyon; it needs a reason to stop.” 
- Alta Meteorologist Mike Kok

The natural advantages of upper Little Cottonwood Canyon and the high terrain surrounding the Cottonwoods are on display today.  It doesn't look like much, but notice the weak radar reflectivities that have been lingering in the central Wasatch this afternoon.  Alta and upper Little Cottonwood Canyon identified with a red box.

Those weak radar returns have been producing about an inch an hour of low-density fluff at the Alta-Collins site this afternoon.  

Most of that snow growth is probably occurring at very low levels, some of it below the radar beam.  This is often a problem in shallow orographic storms, as illustrated conceptually in the figure below from my book Secrets of the Greatest Snow on Earth.

Source: Secrets of the Greatest Snow on Earth
If you look carefully at the radar loop above, you can see another area of light but persistent radar returns in the mountains southeast of north Salt Lake and Bountiful.  Here and in the Cottonwoods further south, the northwesterly flow is encountering pronounced concavities in the terrain thanks to the Avenues foothills and the Traverse Range, respectively, which extend westward from the main body of the Wasatch.  Coincidence?  I think not.  

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