Sunday, February 20, 2011

Anatomy of a Faceshot

Ryan Murphy, 13, gets the goods today at Solitude
Sure, it's Presidents Weekend, traffic stunk because the canyons were closed at times, and it was packed at the ski areas.  But, you have to admit, the snow today was sublime.  In fact, it was one of the better faceshot days I've had this year.  My cheeks are still burning!   The Greatest Snow on Earth is back after a month of unusually high water content snow in Utah.

Erik Steenburgh, 12, sampling the Greatest Snow on Earth.
Yes, his Dad is raising him right.

It takes special snow to make great face shots.  Yes, you need deep powder, but it also has to be light and dry so that it easily waffles up in your face when you make a turn or pop off a mogul or jump.  For faceshots, you need dendrites stacked deep.

Dendrites are are snowflakes with lots of tree like branches.  The stellar dendrite serves as the official logo for Alta, and the unofficial ice crystal of Utah.

Examples of stellar dendrites from, the
ultimate web site for snow-crystal geeks like me.

Other dendrite types recognized by scientists include spatial dendrites, fernlike stellar dendrites, and radiating dendrites.  Check them out on

The significance of dendrites for skiing is that they have lots of pores, cavities, and gaps that are filled with air instead of ice.  When dendrites are stacked deep, you have a snowfall that has a very low water content and snowflakes and snowflake fragments that are easily lofted for faceshots.

The snow that fell overnight and this morning was full of dendrites or fragments of dendrites.  The fragments come from snowflake collisions, which cause mechanical fracturing.

Dendrite potpourri at Solitude this afternoon
Severe fracturing of dendrites can result in snow densification, as occurs when a wind slab is produced by strong winds, but last night and today the wind was fairly light, so that even the fractured dendrites were just fine for bone dry powder.

These dendrite fragments ski just fine thank you.

Dendrites form only under very special conditions.  In particular, temperatures where the snowflakes are forming must be between -12 and -18C.  You also need the relative humidity to be just right.  The upper-air sounding from KSLC this morning shows that temperatures at and above the elevation of the upper Cottonwoods lied in this magic temperature range.

The bottom line is that we were in the dendritic sweet spot.  Wasn't that just grand!  


  1. Hooray for dendrites! Perhaps instead of designating a state gun, we should instead the time making dendrites our official state snowflake! Thanks for the great blog Jim! While I was on maternity leave your blog was my main way of keeping up on the weather!

  2. I saw some riming on a few flakes late in the day at Snowbird when the upper mountain was in cloud. Some of the dendrites were 4-5 mm. They were very nice.