Expect storm slabs in terrain 35 degrees and steeper today, the bigger the slope the more potential hazard. Look for signs of instability. Slabs maybe quite soft and manageable but it will be important to ease into terrain and use small test slopes to get a sense of reactivity and depth. Yesterday’s storm brought periods of heavy snow to the advisory area with observers reporting snowfall at an inch an hour in the afternoon. Storm totals were in the 6″ to 1′ foot range favoring Girdwood Valley. Expect deeper snow in the upper elevation terrain. Observers on Tincan and Notch Mountain reported cracking and reactive shallow storm slabs in the afternoon. The storm snow was a bit more cohesive yesterday than the snow that fell prior. Today this instability may settle fairly quickly but should be approached with caution. Easterly winds gusting into the 30s yesterday may have also increased slab depth and slab cohesion, especially in the Alpine.
Loose snow avalanches: In areas where the snow does not act as a slab the sluffs may be quite large and pushy in steep terrain. These could knock you off your feet and carry you. Choose terrain carefully.
Storm slab on Notch Mountain, 12-16-18. Photo: Andy Moderow
Slab depth in the mid-afternoon (snow continued through the night). Notch Mountain, 12-16-18. Photo: Andy Moderow
We are tracking buried layers of facets and crusts that sit 1-3′ under the snow surface. These layers are more prevalent in the mid-elevations (2000’ – 2700’). Snow pit data and a lack of avalanche activity has been pointing to an unlikely chance for an avalanche releasing deeper in the pack. However, observers yesterday on Sunburst were able to get propagation on weak snow near the ground at 2100′. Additional snow load especially in the Summit area could start to tip the balance. Evaluate the snowpack and terrain as you travel. The thinner the snowpack the more suspect it is. Observers keep finding spots that whumpf on facet/crust combinations reminding us not to forget about this potential avalanche hazard.
Glide cracks are beginning to open up in many places, including Sunburst’s SW face under the weather station, SW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and there was one glide avalanche in the Johnson Pass area. These cracks can release at any moment. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks.
Yesterday: Skies were obscured and it snowed throughout the day with periods of heavy snow in the afternoon and into the night. Temperatures were in the 20Fs. Winds were easterly 5-15 mph with gusts into the 30s.
Today: Mostly cloudy skies and snow showers are forecast for the day. Winds will be SE 5-15mph with gusts into the 20s. Temperatures will be in the 20Fs to low 30Fs depending on elevation.
Tomorrow: Skies will be mostly cloudy with a chance for snow, light winds and temperatures in the 20Fs. Tomorrow afternoon there is an increased chance of snow into Wednesday as a small low circulates in the Gulf. The pattern continues to be active into the weekend.
*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||23||6||0.3||37|
|Summit Lake (1400′)||20||6||0.4||17|
|Alyeska Mid (1700′)||20||10||1.01||29|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||24||*no data||*no data||*no data|