For anyone that was out yesterday, you may have noticed that the several inches of fluffy low-density snow greatly improved the surface conditions. Despite the good news, warmer temperatures have set in along with heavier and denser snowfall. The National Weather Service has continued their Winter Weather Advisory and is expecting an additional 7-10″ of snow today. This has set the stage for touchy new snow avalanche issues. The old hard surface will provide a slick bed surface and yesterday’s low-density snow will make it tough for the new heavier snow to stick right away. This type of storm, which begins cold and ends warm, is what we call in the avalanche world an ‘upside-down’ storm.
If the forecast verifies and we really do see 7-10″ of new snow we can expect:
All this said, the size of these avalanches is directly related to the amount of new snow. With somewhere between 10-18″ of storm snow total by this afternoon, wind slabs should be in the 1-2′ range and storm slabs in the 8-16″ range.
Storm Totals at mid-elevations as of 6am Sunday morning:
Turnagain Pass: 4-6″
Girdwood Valley: 7-10″
Summit Lake: 4-6″
Bear Valley (Whittier Tunnel): 7-10″
Moose Pass: 3-4″
Seward (Exit Glacier): 4-6″
The load of the new snow today will again add stress to underlying weak layers. As we have been hammering home, roughly 1-3′ below the snow surface sits a layer of buried surface hoar and in some areas facets in Turnagain Pass proper. Periphery zones such as Summit Lake and Johnson Pass harbor a weaker snowpack with a variety of weak layers. Although these layera have not been reactive lately, additional load may start to tip the balance. It is good to keep in mind that avalanches occurring today have the ability to step down and trigger a larger more dangerous slide. This is a more likely case for the Summit Lake and central Kenai mountains.
Glide avalanches may be on the move again with the warm up seen over the past two days. Many cracks are present on heavily traveled slopes. The best way to manage this problem is to identify and avoid traveling directly below them.
Yesterday: Overcast skies and light snowfall covered the region. Roughly 4-6″ of low-density snow has fallen over the past 24-hours at most mid-elevations with the exception of Girdwood Valley that recorded up to 8″. Ridgetop winds have been 15-25mph with gusts in the 40’s from the east. Temperatures remained in the teens to 20F yesterday along ridgelines before warming up overnight to the mid 20’sF and the low 30’sF at sea level.
Today: Moderate to heavy snowfall adding 7 to 10″ is expected over the course of the day with an additional 2-4″ overnight. Warm air is streaming in and pushing the rain/snow line up to ~500′. Ridgetop winds are rising and forecast to average in the 40-50’s mph from the east. Temperatures will sit in the mid 30’sF at sea level and in the mid 20’s F above treeline.
Tomorrow: Another frontal system moves in on President’s Day, which will continue our active weather pattern into the work week. Right now models are showing a cooling trend with this next system and snow to sea level.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||26||4-6||0.3||61|
|Summit Lake (1400′)||25||4-6||0.3||27|
|Alyeska Mid (1700′)||25||8||0.6||54|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||22||SE||15||36|