This series of storms continues to build storm slabs and overload the weak layer of surface hoar and near surface facets that formed last week. Yesterday folks continued to trigger small avalanches in the Tincan Trees and observed signs of instability including whumpfing, cracking and hand pits failing on isolation. There was low visibility which made it difficult to see into the alpine but strong winds were rapidly loading leeward slopes. Sunburst saw gusts as high as 102 mph. Temperatures rose and the snow became more and more upside down. Since the storms started on Saturday, Center Ridge Snotel has received 1.8″ of water and mid-elevation stations in Girdwood received 2.4″ of water. This translates to 15-30″ of total snow since Saturday up high. Unfortunately at lower elevations some of this precipitation came as rain overnight as temperatures rose and rain fell to as high as 2300′. Today the recipe for avalanches is pretty simple. Weak snow has been overloaded by heavy snow, wind loading or rain. Slabs in upper elevation terrain could be 2-4 feet thick. Travel in avalanche terrain (on slopes steeper than 30 degrees) is not recommended. Runout zones should also be avoided due to the potential for natural avalanches and as always steer clear of terrain traps. Even a small avalanche in the wrong spot could be very hazardous.
Screen shot of Sunburst Weather Station this am. Note the wind profile since Saturday = rapid loading!
Layer of surface hoar that is buried below the storm snow. This is the weak layer of concern.
Slopes triggered by skiers and boarders on Sunday were reloaded on Monday.
Rain fell overnight to as high as 2300′. It is adding weight to the already stressed snowpack and breaking bonds between snow grains. Water saturating new snow could cause natural wet loose or wet slab avalanches. Triggering wet avalanches in the treeline elevation band is also likely today in steep terrain. This is another reason travel in avalanche terrain is not recommended today.
In the alpine, above 3,000’, rapidly loading slopes may awaken a large and dangerous deep slab avalanche. At these elevations, a hard slab, 3-5+ feet thick, is sitting on top of weak sugary snow (basal facets) near the ground. As new snow increases the load over this snowpack structure during the current storms, there will be the potential for large natural avalanches. Between storms, human triggered deep slab avalanches will be possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as breaks between storms may allow for travel to the Alpine.
Yesterday there were light rain and snow showers in the morning and the next storm system picked up mid-day with low visibility, gusty winds, and heavier snowfall and rain. Approximately 10-15″ of additional new snow fell in the upper elevations of Girdwood Valley and the Turnagain Pass area. 24-hour totals are below in the table. Lesser snow amounts were seen on the South end of Turnagain Pass and in the Summit Lake area. Ridgetop winds were Easterly averaging 35-45mph with gusts to 102mph. Temperatures were in the mid 20Fs at treeline and rose to mid 30Fs at 1,000′. Overnight rain fell to as high as 2300′.
Today, rain and snow showers continue with another 5-10″ of snow or .35 inches of rain possible. Rain/snow line is forecasted to be around 2300′ today. Precipitation will taper off overnight. Temperatures start warm today in the upper 30Fs above 1000′ and 40Fs at sea level. They will cool down this evening into the 20Fs. This will bring the rain/snow line down, with snow showers possible overnight. Winds will be easterly 20-30 mph, gusting into the 50s. Winds speeds will decrease in the afternoon.
Wednesday into Friday looks to be a break in the storms with a chance of some sunshine, lighter winds and temperatures in the 20s. Stay tuned for the next storm details, as there is still a fair bit of uncertainty about what the weekend will bring.
*Seattle Ridge is anemometer is rimed and under reporting.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||34||9||.8||48|
|Summit Lake (1400′)||33||1||.2||14|
|Alyeska Mid (1700′)||32||6||1.35||41|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||28||*n/a||*n/a||*n/a|
|12/10/19||Turnagain||Avalanche: Tincan and Sunburst from the air||CNFAIC Staff|
|12/10/19||Turnagain||Observation: Tincan||Nancy Pfeiffer|
|12/08/19||Turnagain||Avalanche: Tincan||Ryan Van Luit Forecaster|
|12/06/19||Turnagain||Avalanche: Sunburst||Billy Finley|
|12/04/19||Turnagain||Observation: Sunburst||A.Johnston-Bloom/ W.Wagner/ R.Van Luit Forecaster|
|12/03/19||Turnagain||Observation: Hippy Bowl||Nick Langowski|
|12/01/19||Turnagain||Observation: Tincan, All elevations||Eric Roberts|
|12/01/19||Turnagain||Observation: Tincan||Andy Moderow|
|11/30/19||Turnagain||Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge||Eric Roberts|
|11/29/19||Turnagain||Observation: Sunburst Ob #2||Aleph Johnston-Bloom 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: email@example.com
|Area||Status||Weather & Riding Conditions|
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