Turnagain Pass

A storm moved through our region yesterday bringing strong Easterly winds and dumping 1-2 feet of new snow across our region. Girdwood was favored with Alyeska reporting 18” at midway and 24” at the top. On the Northside of Turnagain Pass totals were estimated in the 12”-18” and observers reported around 8-10” by 6pm last night at Sunburst. Don’t forget these storm slabs were formed by strong Easterly winds and slabs could be 2-3 feet thick on leeward features in the alpine, especially in Girdwood Valley. This new snow fell on variable surfaces including a slick melt/freeze crust on Southerly aspects and patches of loose faceted snow and crusts on other aspects.  Either way bonding will be poor and triggering a storm slab is likely today. The size of the slab will depend on the size of the terrain. An observer at Tincan reported lots of human triggered storm slabs and loose snow sluffing in the trees throughout the day. Careful snowpack evaluation and caution route finding will be essential. Warming in the afternoon may increase the likelihood for triggering storm slabs. If you see any natural avalanche activity this is a sign to avoid all avalanche terrain and stick to flat mellow terrain well away from the runout zones of larger slopes. 

• Turnagain Pass: 10-18”  (~1.0” SWE)
• Summit Lake: 4-6” (0.3” SWE)
• Girdwood -Alyeska midway: 18” (1.4” SWE) 
• Portage – Bear Valley: 14” (1.3” SWE)

Turnagian Pass Snowstake at the DOT RWIS weather station reported around ~15″ of new snow yesterday.

Observers yesterday on Sunburst reported 9″ of new snow by 6pm. This was quite a bit less than observations from Tincan. 

SPRINGTIME WARMING: Daytime temperatures are expected to increase to the mid 30F’s near ridgetops and low 40F’s near sea level as snow and wind taper off in the afternoon. If the sun appears today or any radiation through cloud cover – this will increase the potential for natural wet-loose avalanches later in the day. Southern aspects will be more likely if the sun come out, but all aspects are suspect if clouds trap the heat. Lower elevations such as Placer Valley and Portage may see more natural activity on lower elevations slopes, especially in channeled terrain. Pay attention to how the snow changes throughout the day. Heavy moist snow and rollerballs will be your first clue the snow is changing. Any natural avalanche activity will be an obvious sign the snowpack is becoming more dangerous and it will be important to adjust your plans. Although it’s not expected, there is potential for a storm related avalanche to trigger a deeper more dangerous avalanche. More on this below.

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. Little is known about how the snowpack is adjusting to its new load, and if one of these older weak layers, facets and buried surface hoar, could wake up today.  This is an additional reason to avoid being on or under any larger slopes. Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges. 

This is a snowpit from yesterday on Sunburst and shows the weak interface between the new snow and old snow as well as several older weak layer buried a few feet below.