It’s a simple equation: new snow falling on a slippery surface + wind loading = easily triggered avalanches.
Heads up for anyone headed out today. Storm snow avalanches are expected to be easily triggered. These will be in the form of wind slabs on wind loaded slopes, storm slabs in areas out of the wind, cornice falls and new snow sluffs. The size of the avalanche will depend on the amount of new snow and wind loading. In the Girdwood Valley slabs could be up to 3′ thick on wind loaded slopes. In the Turnagain Pass area, slabs could be up to 2′ thick. Come tomorrow, add another 10-20″ to the thickness of these slabs.
Although hidden from view, under the storm snow is the old surface, which is a combination of sun and wind crusts, facets and surface hoar. Not only will this old surface inhibit bonding with the new snow, it may also allow slabs to propagate wider than expected. Remotely triggered avalanches are also possible, meaning triggering a slide from the ridge or the bottom of a slope. With another round of snow and wind slated to hit later today, pushing the danger to HIGH, now is the time for us to keep out of avalanche terrain and let the mountains do their thing.
Estimated storm totals (mid-upper elevations) beginning Thursday ending Saturday 6am:
Rain has been falling below 1,000′ and expected to continue today. This whas saturated the low elevations and wet sluffs will be possible.
Storm slab avalanche in the Tincan Trees from yesterday. Roughly 6 more inches of snow has fallen with more on the way, which will create much larger slabs for today. Photo: Allen Dahl.
The photo above shows the 6-8″ of new snow from yesterday sliding easily on the old sun crust that was the surface a few days ago. (Photo: Allen Dahl)
Yesterday: Light to heavy snowfall was over the region as the second storm front passed through. Rain fell up to 500′ and in some areas up to 1,000′. Snowfall amounts across the region varied greatly from only a trace in the Summit Lake area to over 2 feet in the upper Girdwood and Portage Valleys. Turnagain Pass has seen around a foot of new snow. Ridgetop winds over the past 24-hours have been blowing 20-30mph from the east with stronger gusts. Temperatures have been steady in the low to mid 20’sF along ridgelines and in the mid 30’sF near sea level.
Today: A brief break between storms is expected this morning with the third wave of precipitation moving in midday and peaking late tonight. An additional 3-6″ of snow is expected to fall today with 10-14″ tonight. The snow/rain line should creep up to 1,500′ in areas and therefore, rain will be falling at the low elevations. Ridgetop winds are forecast to remain easterly in the 20-30mph range with gusts up to 50mph. Temperatures may reach the upper 40F at sea level, 32 at the mid elevations and the mid 20’sF along ridgelines.
Tomorrow: Stormy weather will continue Sunday and into Monday with an additional 6-12″ of snow at the mid and upper elevations. Cooler air looks to be entrained on Monday, which will lower the rain line and snow could fall near sea level. Another small break in storms may occur Tuesday before another round of precipitation hits. Stay tuned!
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||31||10||0.8||63|
|Summit Lake (1400′)||33||trace||0||26|
|Alyeska Mid (1700′)||30||14||1.05||67|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||27||SE||14||27|