Yesterday morning an unexpected sleeper storm was centered over Girdwood and dumped 6-12” of very low-density snow. Snow totals were greater in the alpine. Turnagain Pass received 3” along the road and up to 10” at higher elevations. Winds in the afternoon along ridgetops picked up for a few hours 10-15mph with some gusts in the 20s-40s mph. Triggering an isolated windslab on leeward and cross-loaded features will be possible. Look for smooth or pillow shaped features. Evaluate the snow and terrain as you travel and keep in mind the consequences should even a small rug get pulled out from underneath you.
In areas where winds didn’t change the surface expect new snow to be loose and unconsolidated. Don’t be surprised by ‘sluffing’ and loose snow moving faster than expected.
Low density loose snow was sluffing easily on steeper features yesterday at Tincan. Photo credit: Tully LaBelle-Hamer
There remains some uncertainty around weak snow within older layers of the snowpack. Observations this week have found a facet/crust combo 1-2’ below the surface in the mid-elevations (2000’ – 2700’.) Large collapses “whumpfs” were experienced on Magnum’s NW shoulder on Tuesday and stability tests were quite reactive in this zone. It’s unknown how intact this structure exists into the Alpine. On the Northern end of Turnagain Pass stability tests have been showing a strengthening snowpack at higher elevations. However keep in mind that we’ve seen a lot of snow over the last week and we don’t have a lot of snowpack info. It’s still early season. Areas with a thinner snowpack are more suspect for weaker and unstable snow including the Southern-end of Turnagain Pass, Summit Lake and Girdwood Valley. In general North and East aspects have a tendency to be thinner and there is a zone in the mid-elevations where the snowpack quickly transitions to shallower depths.
Be on the lookout for red flag warnings like ‘whumpfing’, shooting cracks, new avalanche activity or any changes in weather. Keep in mind there is a lot of snow available for transport. Any sign of increased winds could form reactive wind slabs or add stress to a persistent slab.
This is a good example of where the snow quickly transitions shallow and weaker snowpack in the mid elevations. This structure may be more widespread on the Southern end of Turnagain Pass and in Summit Lake.
The first glide cracks of the season were seen on Sunburst SW face under the weather station. A glide crack is the snowpack being pulled by gravity downhill along the ground. They can release at any moment without warning and are usually not associated with human triggers. The best way to manage this hazard is to avoid being on or beneath any slopes with cracks opening up.
Photo taken on Tues December 11, 2018 of new glide cracks on SW face of Sunburst
Yesterday: Snow flurries were the most intense in the morning between 6am to 10am. Turnagain received 3 € of low-density snow along the road and Girdwood 6-10 € at valley bottom. Winds were light with the exception of a few hours along ridgetops where winds increased to 10-15mph with gusts in the 20-40s. Temps at sea level were in the low 20Fs and ridgetops dropped into the single digits.
Today: Temps will be similar with single digits at ridgetops and low-20Fs near sea level. Snow flurries will diminish becoming mostly sunny in the afternoon. Winds are expected to be light (5-10mph) from the West and shift to the East by this evening. Tonight snow flurries will return with a few inches possible overnight.
Tomorrow: An active winter weather pattern will persist tomorrow and into the weekend. A continuation of more snow showers, cool temps and light to moderate winds is expected.
*Seattle Ridge weather station anemometer is rimed and not recording wind data.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||18||4||0.1||33|
|Summit Lake (1400′)||15||3||0.3||10|
|Alyeska Mid (1700′)||17||7||0.11||20|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||14||*N/A||*N/A||*N/A|