Friday, February 25, 2011

Wasatch Mountain Microscale Snowfall Insanity

I love days like today when I can just look out the window in amazement at how the Wasatch Mountains can create an intense snowstorm that pummels Alta and environs but does very little elsewhere.

For most of the day today, it has been snowing in an area confined to the region immediately downstream of the Wasatch from about Provo Canyon to Big Cottonwood Canyon.  Radar echos do not begin over the initial westward slope of the Wasatch, but somewhat downstream.  This is evident in the radar image below and also longer loops covering the afternoon (loops not shown).

Visually, this is what it looks like from the Avenues.  There is an incredible, shallow, cumuliform cloud banked up over Lone Peak.  This is the so-called Lone Peak cap cloud that appears frequently in southwesterly flow, but isn't always associated with heavy snowfall.  

Note that it is not snowing at all at the mouth of Little Cottonwood Canyon, Big Cottonwood Canyon, or along the base of the Wasatch Mountains.  Based on the radar, it has also snowed little in Mill Creek Canyon.  

Within the shallow orographic cloud, it has been snowing all day.  Precipitation began to become localized and the Lone Peak cap cloud emerged from the broader cloud deck at around 8 am this morning.  Since then it has snowed about 6 inches at the Alta-Collins snow stake, with about .24 inches of water.  That's cold smoke at 4% water content and reports are that the skiing today was fantastic. 

All in all, this is a remarkable storm.  The dynamics of the event, especially the shallow convective dynamics, microphysical processes, and local forcing, are worthy of further investigation.  

1 comment:

  1. One of the things that I found odd today (Friday) was the variability in wind speed. I made it to Solitude from about 1:30 - 4:00 and was surprised that not only were the mountain anemometers not showing particuraly high wind speeds, but there really was not much wind around Solitude.

    Having said that on the way up the Canyon we encountered 2 areas of complete white out from what I assume were gusts. We also heard howling winds from the lift out in SIlver Fork. Snow could also be seen blowing off various ridges along the length of the Canyon.

    Finally, on the way down and out, there was no wind at road level until we were hit with a huge wind way down low between the power line couloirs and the pump station. It was really odd and unusual.

    A most unusual day - but hey - it was unusual in Seattle and SFO as well ...