While we are waiting for the big snow storm that will open all our trails, let’s discuss snow!
This article is about different snow types and how they are formed. There are two variables that determine snow type, temperature and air moisture. Snow comes in five general types: graupel, plates, needles, columns, and dendrites. Each snow type forms in different temperatures and moisture levels.
The Grand Mesa, being roughly 1000 miles from the Pacific Ocean, is most often moisture starved. But when a storm brings sufficient moisture, then snowflake types are a function of temperature. These are good rules of thumb even if they are oversimplified:
- When the Mesa top air temperature is 0 to 10F or perhaps just a bit warmer, big fluffy dendrites are likely. If that temperature zone is saturated and close to the Mesa top, big snow is possible. Dendrite snow has a snow to water ratio of 20:1 or even 30:1. Champagne powder! Downhill skiers love this snow of course.
- When Mesa top temperatures are colder or warmer than that, expect more dense snowfall in the form of plates, columns, and needles. All else considered, Nordic skiers want more dense snow. Snow densities range from 8:1 to 15:1.
- Graupel (soft hail or snow pellets) are formed in mild air temperatures of 15 to 25F and indicates unstable/convective conditions conducive to thunderstorms. Snow densities range from 5:1 to 2:1. Dense!
- Wind and rime icing (when supercooled water droplets freeze onto snowflakes) messes with these rules of thumb, making the snow more dense.
A few other snow facts:
- It is estimated that the GMNC trails average 360 inches of snow a year, but with large year-to-year variation.
- Is it too warm to snow? Snow can fall in temperatures as warm as 37F, even into the low 40s for brief periods, if the near-surface air is quite dry.
- Is it too cold to snow? Very cold air can hold very little water vapor, so it is very hard to produce accumulating snow at around -20F or colder.
- It is possible to get very light snowflakes, called diamond dust, out of a cloud-free but very cold sky. The process of snow forming directly from water vapor is called desublimation.
- Weather nerd further info: -40 is the point where it is too cold for supercooled water to exist (supercooled water vapor will spontaneously turn into crystals even without cloud condensation nuclei). Also, -40 degrees is the same in both C and F scales.
The next article will be an outlook for this winter, or why La Nina gives us hope. In the third article, I will give the weather and waxing nerds some rules of thumb on how to add quality to the forecast for the Mesa top.