Quick report
- Red Flags
- Wind Loading, Rapid Warming, Poor Snowpack Structure
- Red Flags Comment
- <p>Rapidly warming snowpack at low elevations, especially below about 7,000' Some wind drifting along the upper ridges.</p>
Here's an overview of the snowpack at various elevations in Big Cottonwood Canyon and some of the things to watch out for when traveling in the backcountry. Remember, you can experience wet avalanche problems even in the foothills and off your roof as the snow suddenly warms.
Snowpack
- Instability Comment
- <p>The main concern today was wet sluffs at lower elevations. Why? For the past two weeks, we've had a very stong temperature inversion in Salt Lake City, with very cold air trapped in the valley along with all our car exhaust. The today "overrunning" warm, moist air arrived with rain at elevations below about 7,500' and a couple inches of snow above. The rain in the valley instantly froze on contact (freezing rain) which cause havoc on the roadways and turned the sidewalks into skating rinks. </p> <p>Rain falling on the previously-cold, dry snowpack came as quite a shock to the snowpack and it caused quite a few wet and damp sluffs on steep terrain. The previous snowpack at lower and mid elevations was mostly loose, weak, faceted snow with giant surface hoar crystals on top. As it has become damp and wet, it created some very interesting looking crystals in various stages of being destroyed by the warm rain. The lower elevations were most affected by this because in a temperature inversion, the lower you go, the colder it is, so when the warm rain arrived the lowest elevation snow experienced the most rapid change. Just like people, snow does not like rapid change. (To experience this, jump into a cold shower.) So watch out for terrain traps like gullies and steep slopes especially at low elevations. This includes the foothill trails and roofs of houses.</p> <p>Up along the ridge tops, the moderately strong southwest ridgetop winds have been drifting snow onto downwind terrain and we got quite a few reports of fresh wind slabs in the upper terrain. Wet slides down low, wind slabs up high. Sheesh, if it ain't one thing, it's the other.</p>
What a yucky day. With steady drizzle below 7,000' it made all the snow surfaces damp to wet with rollerballs and wet sluffs on steep terrain. When you got above about 8,000' there was about 2 inches of dense new snow. Along the ridges there was some moderate southwest ridgetop winds blowing snow into drifts.