After a cold and dry March, April is starting us off with a wet sucker punch. Yesterday was the 5th day in a row of elevated avalanche danger due to a series of storm systems moving through. The cycle began with a system bringing snow to sea level (1-3+’ throughout the forecast zone) and this last system (Friday and Saturday) bringing rain to 1,800′. Over the last 24-hours we have picked up ~.4-.7″ of rain below 1,200′ and 4-8″ of new snow above. Today will be a short break between storms before another warm low-pressure moves in tonight – see the satellite image HERE. Although precipitation and temperatures are backing off today, the winds are not, and all of these will ramp back up tomorrow, keeping the snowpack in an unstable state.
RECENT AVALANCHE ACTIVITY:
Significant natural wet slab avalanche activity was seen yesterday as rain fell and saturated the 1-3′ of new snow from last week. Through thick clouds, two large wet slabs were seen at Turnagain Pass, photos below. How many more exist – and just not visible – is a mystery for now. An avalanche professional in the Placer Valley yesterday noted widespread natural wet slab activity occurring in the 1,500′ elevation band. This was along the steep rollovers that line the Valley, such as near Skookum Valley, Spencer Glacier and into Grandview. Wet slabs were also seen in Portage Valley near the Whittier Tunnel entrance – again all releasing near 1,500′.
Dry snow avalanche activity has been prevalent over the last 5 days in the mid and high elevations – though again much is obscured by poor visibility. Debris piles littering the bottom of large and small avalanche paths assures us that widespread naturals have been occurring. If skies part enough today, hopefully we can get a glimpse of the start zones for some of these storm snow avalanches.
Wet slab releasing yesterday on Pete’s South ridge, Southwest aspect ~1,800′ (estimated 12-18″ thick, 300′ wide).
Another wet slab releasing yesterday between 1 and 2pm on Eddies ridge, also a Southwest aspect at 1,500′ (estimated 1-2′ thick and 300′ wide).
Natural wet slabs and wet loose sluffs below 1,800′ are possible today with human triggered slabs and sluffs likely. Once the skies clear and/or temperatures cool enough for the saturated snow in this lower elevation band to begin to freeze up – this issue will get locked into place – but until then, wet avalanches are not manageable and nothing to mess with.
Above 1,500′ where the snow is drier we can expect storm snow instabilities to persist today. These are:
WIND SLABS and CORNICES:
Non-stop Easterly winds will continue to load slopes and build cornices with the new warm, sticky snow. Ridgetop Easterly winds are expected to average 20-35 mph, perfect for keeping the pack unstable. Natural cornice falls are likely and could easily trigger a slab below them.
LOOSE SNOW AVALANCHES:
Sluffs in the dry snow are likely, but much less of an issue compared to the much larger slab avalanche and cornice fall problem.
Debris from the lower slopes of Seattle Ridge – an indication of dry snow avalanches occurring above.
Several old layers of weak snow (near surface facets and surface hoar) sit buried in the snowpack. Avalanches releasing in the storm snow have the potential to ‘step down’ into them. Furthermore, as the new snow piles up and begins to stick to the old snow surface, avalanches breaking into deeper layers are also possible. Both of these situations can create a much larger avalanche – something to keep in mind as the storm cycle continues. Snowpack tests are still showing propagation potential in these layers. The question is how much incremental loading will tip the balance?
Yesterday’s weather consisted of obscured skies, rain to 1,200′ and light snow above. Over the past 24-hours it looks as though Turnagain Pass has picked up another 6″ of new snow above 1,500′ and the Girdwood Valley around 4-6″. Ridgetop winds have been moderate to strong from an Easterly direction, averaging 20-25mph with gusts to 50mph. Temperatures that were warm yesterday (40F up to 1,800′ in places), are on a slight cooling trend as the rain line has dropped overnight to near 500′.
Today, the cooling trend from overnight should swing back the other way with daytime warming – temperatures are expected to be 35-40F at sea level and around 25-30F along the ridgelines. We could see the sun poke out in places but cloudy skies are most likely. Another .1-.3″ of rain may fall below 500′ with 1-3″ of new snow above this. Ridgetop winds are forecast to remain strong, averaging 20-35 mph with gusts into the 50’s from the East.
For tomorrow and early in the week, another low-pressure system is on the way. This storm looks slightly cooler than the last, rain/snow line around 500′ and bringing less moisture but keeping winds strong. Stay tuned as this active pattern continues!
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||36||6||0.6||77|
|Summit Lake (1400′)||36||0||0||30|
|Alyeska Mid (1700′)||32||3||0.42||77|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||27||sensor rimed||sensor rimed||sensor rimed|
|04/21/21||Turnagain||Observation: Sunburst||Schauer/ Behney Forecaster|
|04/19/21||Turnagain||Avalanche: Triangle, Seattle creek||Will Morrison|
|04/18/21||Turnagain||Avalanche: Turnagain Pass Road Obs||Andy Moderow|
|04/18/21||Turnagain||Observation: Seattle Ridge, approximately 300 yards south of the up track||Brent Byrne|
|04/17/21||Turnagain||Avalanche: Road obs||Johnston-Bloom / Moderow Forecaster|
|04/16/21||Turnagain||Avalanche: Seattle Ridge||Wendy Wagner Forecaster|
|04/16/21||Turnagain||Avalanche: Turnagain Pass, non-motorized side seen from Seattle Ridge||CNFAIC Staff Forecaster|
|04/16/21||Turnagain||Observation: Sunburst||Lance breeding|
|04/15/21||Turnagain||Observation: Tincan||Schauer/ Rothman Forecaster|
|04/13/21||Turnagain||Observation: Turnagain Pass Road Obs||A Schauer Forecaster|
Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: firstname.lastname@example.org
|Area||Status||Weather & Riding Conditions|
This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.