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Jan. 6 weather: 50 avalanches reported

From the Wikimedia Commons, a microscopic image of a rime-covered snow crystal, commonly known as graupel. In some cases, the original shape of the snowflake is no longer visible, but the graupel that fell in Summit County Wednesday morning was only lightly rimed.

It’s a graupel-ly kind of morning in Summit Land, where the CAIC has dropped an avalanche watch, but is still warning of considerable hazards in the backcountry

Graupel piles up on a deck in Frisco. Click on the image for a larger view and look closely to see the stellar shape of the original snow crystals, coated with rime from a bumpy ride through layers of super-cooled water vapor in the atmosphere.

SUMMIT COUNTY — Forecasters with the Colorado Avalanche Information Center dropped an avalanche watch for the north-central mountains as yet another storm fizzled out over the region before dropping the anticipated snowfall.

A-Basin reported .25 inches, with 3 inches at Breckenridge and 2 inches of new snow at Copper.

But don’t let your guard down in the backcountry. The avalanche danger is still rated as considerable near and above treeline on north to south-facing slopes, where triggered releases are still probable in the complex and weak snowpack.

The avalanche center reports about 50 observed slides around the area the last few days, about half of them natural, the rest triggered by control work. Please visit the avalanche center web site for a full forecast and discussion of backcountry conditions. By phone, call the Summit-Vail hotline at (970) 668-0600.

There is still a chance for some light to moderate snow in the area today before some cold Arctic air filters into the area later Wednesday afternoon. Temperatures tonight are forecast to drop well below zero, with highs only in the single digits Thursday, and winds ranging from 15-25 MPH.

The National Weather Service still has a winter weather advisory in effect for the area, with snow showers and 3 to 6 inches of snow on higher west-facing slopes, blowing and drifting snow and wind chill temperatures of 15 to 30 below zero tonight.

Here at the home office of the Summit County Voice, graupel was the word of the morning, as tiny rime-covered snow pellets bounced around on the deck. This form of precipitation is associated with turbulence in the atmosphere. Snowflakes start to fall but are driven back upward to higher altitudes, where they basically get covered with a layer of frost, as super-cooled water droplets condense onto snow flakes. Super-cooled water is water that stays in liquid form even below freezing temperatures.

Graupel sometimes falls during spring and summer thunderstorms, when convection carries the particles of precipitation up and down through the atmosphere. Today’s graupel may be associated with a strong cold front approaching from the north. The cold air is heavy and dense. It slides under the warmer air, lifting the clouds and precipitation as it advances.

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3 Responses

  1. Graupel! I always wondered what it was called.
    Thanks Bob. Your knowledge is unparalleled. Keep up the great work.

    • thanks harold, it was kind of weird to see it in January on a day when it was supposed to be snowing so I thought it would be interesting to explain it. It’s a German word. They and the French have tons of cool descriptive language to describe snow and ice phenomena …

  2. [...] Jan. 6 weather: 50 avalanches reported [...]

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