Thursday, December 21, 2017

Radar Struggles with Low Density Snow

The total snowfall through 7 am this morning on the Alta-Collins stake sits at 6".  With a snow water content of 0.36", that makes for a water content of 6%.  Perhaps not quite cold smoke, but close to it. 

Alta continues to see some light snow.  This stuff is barely discernible in the radar loop where all one sees are some stronger returns over the high terrain that are ground clutter and some very light returns in a couple of bands that move from east to west across the Wasatch Range, consistent with precipitation in the "wrap around" part of the storm. 

It's very difficult to determine precipitation rates at Alta and in other parts of the Wasatch Range during such conditions using radar.  There are a couple of reasons for this.  First, the precipitation is quite shallow and often the radar beam partially or totally overshoots the precipitation. 

Source: Secrets of the Greatest Snow on Earth
Second, snow scatters a lot less radar energy back to the radar compared to rain.  This is especially true for low density dendritic snow.  As a result, returns are limited and the correlation between the radar reflectivity and snowfall rate can be poor.

Ski Tourers: Note that the Supreme Area at Alta is now closed to uphill traffic.

1 comment:

  1. friends called +- 10 am yesterday from u of u hospital and said plane flew over the downtown sector, moving west to east dumping chem powder gray/white. this plume was by my own eyes only from 1700 so. to 3rd ave.