At issue is why did the water content of the snow increase overnight? Looking at the hourly data from Alta-Collins suggests that the density of the freshly fallen snow increased after about 0700 (12 AM MST) when precipitation rates increased dramatically with >0.1" of SWE falling each hour through 1100 UTC (4 AM MST). During this period, the snow interval increased 7 inches, with .67" of snow-water equivalent, which is a water content of about 10% compared with the 4% that was falling yesterday.
Yesterdays snow was produced by a very shallow orographic cloud. Snowflake images from Alta show aggregates of nice dendritic (tree or fern like) snowflakes with plenty of pores that are full of air rather than water. In other words, low density snow.
|Snowflake images courtesy University of Utah, Alta Ski|
Area, and the Center for Snow Science at Alta
The radar reflectivities broadened and intensified overnight, so the storm dynamics did change from the localized orographic storm that was present yesterday.
On the other hand, it is impossible to say from this data alone that this resulted in a major change in the snow growth processes. We also know that the winds were quite strong, so this could also have played a role.
What is needed are good observations of snow crystals. Perhaps Alta will post up some images of the crystals last night or some of our readers can provide their perspectives from the field. Help us understand this mystery!