Turnagain Pass

Over the last 3 days we’ve seen three significant storms impact our forecast zone bringing heavy rain and snow and hurricane force winds. The third storm is upon us and expected to pass over by late morning. Strong Easterly ridgetop winds averaging 50-70mph with gusts in the 100’s mph will decrease to 15-20mph by early afternoon. An estimated 10-15” of new snow has fallen in the alpine in Turnagain Pass overnight and a few more inches possible this morning. Girdwood has seen double them amount of snow than Turnagain Pass and triple in Portage Valley. See storm totals below.

Large natural avalanches are expected this morning until winds and precipitation decrease. In the afternoon as the weather mellows out human triggered avalanches will be likely in avalanche terrain and will be large enough to bury or kill a person. These storm slabs are expected to be large and could easily connect an entire slope. Storm snow this week has fallen on very weak snow surfaces (widespread buried surface hoar)  and any slope that hasn’t already naturally avalanched will be extremely suspect. Very few natural avalanches were seen yesterday in Turnagain, and don’t forget this poor structure is prevalent across our forecast zone.

Another factor to keep in mind is that precipitation totals across the region have varied significantly over the last three days. The heart of our forecast zone in Turnagain Pass has seen less snow than Girdwood Valley, but observations yesterday did confirm slab depths in the alpine were over a foot. Today we estimate closer to 2’ with the additional 0.7” SWE and strong winds overnight. If you do venture into Turnagain Pass as the weather improves today careful snowpack and terrain evaluation coupled with conservative decision-making are essential. Unlike the last few weeks our current snowpack structure is primed for remotely triggered avalanches. Avoiding runout zones of smaller features is very important.

 Storm totals Tues 6am – Fri 6am: Snow Water Equivalent (SWE) and estimated storm totals

• Turnagain Pass – SNOTEL (1800’): 1.2” SWE, 12”–25” new snow above 2500’
• Girdwood – Alyeska Midway (1700’): 2.7” SWE, 3-5’ new snow above 2500’
• Portage – Bear Valley Tunnel (100’): 7.0” SWE, 7-10’+ above 2500’

Storm slabs in the alpine may release naturally while winds are strong this morning and likely trigger wet loose snow in the mid to lower elevations. Seattle Ridge and Sunburst are good example of where this occurred yesterday in Turnagain Pass. In Portage and Girdwood where precipitation amounts have been higher the last few days, storm slab are expected to be large and run father distances in steep channeled terrain. Avoiding all runout zones is recommended today.

Wet debris at the bottom of a North chute on Sunburst occurred yesterday 1/24/19.

South of Turnagain – Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas.  Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as a facet/crust combination in the bottom of the snowpack. New snow overnight (0.5” SWE), strong winds over the last three days and warming temperatures have added additional stress to the snowpack. A recent natural avalanche that in the alpine that entrained wet snow in the mid elevations was observed yesterday. Rain/snow line was around 2000’. Overnight an additional 5” of new snow may have fallen in the upper elevations and this may also be adding additional stress to older layers in this zone. The possibility of triggering a slab deeper in the snowpack is the primary concern in this area, but finding a newly formed storm slab could be consequential in a terrain trap or step down to an older layer. Look for signs of instability, avoid wind-loaded terrain and evaluate new snow as you travel.