Yesterday an impressive Northwest outflow wind event impacted our region. Starting around noon numerous large natural avalanches released in Summit Lake on East and Southeast aspects along the road corridor on Fresno Peak, Colorado Peak, and Summit Peak. This includes a close call by a group (myself included) on Fresno Ridge who turned around due building winds and rapid loading. Just after our descent a large natural avalanche ran adjacent to the route we had descended. This avalanche had a powerful powder blast that blew over some of our tracks. See the report HERE for details.
In some parts of our region winds were much stronger and more sustained than forecasted. Mile 43 along the Alaska Railroad reported average speeds in the 40s and gusts in the 60-80s mph. In Summit Lake wind speeds were likely gusting into the 50s mph and higher at times, but was not accurately captured by MP 45 weather station. In Turnagain Pass the winds were milder, Seattle Ridge weather station and Sunburst averaged 15mph with gusts in the 20-30s mph. Blowing snow was observed throughout this area, but not nearly as much as in Summit Lake. Several fresh natural wind slabs were observed on the SE aspect of Seattle Ridge near the motorized lot. By comparison these avalanches were much smaller in size and only ran a few hundred yards.
Today Northwest winds will start to diminish this morning and become light by the afternoon. Natural avalanche activity is becoming less likely as winds decrease, but human triggered avalanches will be a concern on aspects that received significant loading. East and Southeast aspects are the most suspect, but cross loading may exist on all aspects. Be suspect of smooth supportable surfaces or pillowed snow on steep or unsupported terrain. These slab may have formed on weak faceted snow buried last weekend (2/16) and may initiate easily with the weight of a person or snowmachine. Shooting cracks will be an obvious clue wind slabs are touchy. Wind slabs could be small and isolated or large enough to bury a person if one releases in an older mid-pack layer. More on this below.
*Although there is not much loose snow available at this point, solar radiation may warm up Southerly aspects when winds calm down. Roller balls and small wet loose point releases are possible on steep Southerly aspects near rocks.
This photo above illustrates the difference between the large avalanches that released naturally in Summit Lake yesterday compared to the photo below of the avalanche activity on Seattle Ridge in Turnagain Pass. These two pictures are a good example of how different the snowpack and weather can be from one part of our zone to another. Also note the ski tracks on looker left. Our group feels lucky we chose to descend when we did.
These 3 wind slabs were the only recent avalanches observed yesterday in Turnagain Pass where winds were much milder than Summit Lake.
In the periphery zones of Summit Lake and Johnson Pass an overall poor snowpack structure exists. Yesterday’s natural avalanche cycle in Summit Lake was clear evidence that these older layers are still reactive to additional loading. In Turnagain Pass, where the snowpack is deeper and less loading occurred, the balance was not tipped as of mid-day. However… a layer of widespread buried surface hoar is lurking 1.5’-3’ below the surface across the region. Stability tests over the last 10 days have not been very reactive and the last human triggered avalanche on this layer was over two weeks ago in Turnagain. With that said, some uncertainty exists due to yesterday’s loading event. It is good to keep in mind triggering an avalanche today could be larger than expected on slopes that have recently been loaded. Northwest winds this morning may still be actively loading leeward aspects. Triggering a deeper more dangerous avalanche is more likely in and around Summit Lake where the snowpack has proven itself guilty. Conservative decision making and cautious route selection is recommended. Be on the lookout for obvious clues like whumpfing, shooting cracks and recent avalanches.
Rapid loading due to strong winds overloaded an old weak snowpack and caused avalanche activity to run farther and faster than expected in Summit Lake yesterday. This powder blast from the second avalanche crossed over the terrain we descended. For the full report click HERE.
Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. New glide cracks are opening up around our region and the most recent glide crack to avalanche was a few days ago on the south side of Goat mountain in Girdwood Valley on Tuesday. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.
Yesterday: Skies were overcast becoming mostly sunny by the late afternoon. Moderate to strong Northwest winds were observed across the region. Most of the local ridgetop weather stations recorded average speeds around 15mph with gusts in the 30s mph, but in some areas winds were more sustained and much stronger. Temperatures average in the 20s F. At sea level temps reached a high of 30 F and upper elevations temps dipped to low-teens F overnight.
Today: Clear skies and sun will dominate as high pressure settles in over most of Southcentral, Alaska today. Gusty Northwest winds will quiet down by early this afternoon to 5-15mph. Temperatures will be in the teens F at ridgetops and low-mid 20s F at lower elevations. Valley fog is likely. Expect inverted temperatures wherever fog develops.
Tomorrow: Sunny clear skies will persist through the weekend and into next week. Expect inverted temperatures with ridgetops averaging in the 20s F. Valley bottoms will be in the low teens F to single digits F. Daily temperatures swings with solar warming and warmer air aloft may allow ridge tops to reach warmer than normal temperatures for this time of year. Valley fog is possible and will keep temps in the teens F in the lower elevations. Winds will be light to calm.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||25||0||0||62|
|Summit Lake (1400′)||25||0||0||31|
|Alyeska Mid (1700′)||23||0||.01||57|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||21||NW||11||33|