Turnagain Pass

Skies cleared just enough yesterday to see some of the aftermath of Wednesday’s storm. It was no surprise to see many small to very large slabs in the region. The largest avalanches seen so far in Turnagain Pass were in the upper Pete’s drainage (released during the storm) and one reported late in the day yesterday on the NW shoulder of Magnum that sent debris between Magnum and Sunburst and possibly triggered other slabs (no photos). This avalanche on Magnum is thought to have occurred during the hot evening hours due to sunshine. We will try to get a look at it today; big thanks to Amanda for sending us that info. Other areas with big slabs were in Portage and Placer valleys. Otherwise, many of your garden variety storm snow avalanches were seen, some photos below. Note: many areas remain a mystery.

Mid-slope storm slabs on the northern face of Sunburst. Likely released at the tail end of Wednesday’s storm. Photo from day after on 3.23.23 by Travis Smith. 

Large slab on corner of Portage and Placer Valleys. 3.23.23

Moist to wet loose snow avalanches in the afternoon due to solar warming yesterday, Thursday, 3.23.23. This is south facing terrain across from Silvertip on the south side of Turnagain Pass.

After all that snow fell from the 8 day storm cycle, it looks like the northwest outflow winds will follow up today. We are expecting ridgetops to see winds in the 20-30mph range with stronger gusts. As is often the case, Turnagain Pass (especially the non-motorized east side) can be somewhat sheltered. The non-motorized side can see southerly winds below 3,500′ in these events interestingly enough. That’s because the terrain forces the wind back around to Turnagain Arm. The strongest northwest winds however should be in the usual areas like Crow Pass, Portage Valley and down to Summit Lake and Lost Lake.

With so much loose snow on the surface, wind slabs should form quickly and may release on their own. Watch for pluming in the mountains from the road and avoiding any area seeing active wind loading is a good idea. Because there is also a less likely but more concerning issue deeper in the snowpack, under all the storm snow (see Problem 2 below), we are advising folks to stick to mellow terrain. This would be slopes 30 degrees or less and staying out from under large steep slopes.

Final snowfall totals from March 15 (after the 2 week dry spell in early March) until the end of the storm cycles on March 22nd, were 70-100″ of snowfall depending on what side of the Pass (more on the north end, less on the south end). Wow! The Turnagain Pass SNOTEL station reported 7.8″ of SWE (water weight). This is a lot of load for those old early March surfaces. As we’ve been talking about, those were sun crusts on solar aspects and facets with wind hardened snow on shady aspects. We have some evidence that those old surfaces are not completely bonding like we want them to; both at the mid elevations as well as the higher elevations. This is concerning.

The big question is how likely is it really that a person, a wind slab, or solar loading (daytime heating by the sun), can trigger a huge avalanche, 3-6+ feet deep, that breaks on those old early March surfaces. We know this happened at Summit Lake last Monday where only 2′ of storm snow fell. We are also keen to know what that reported NW shoulder of Magnum looks like as we know from a photo there was no avalanche there as of 1pm yesterday. This would mean that the slope was so close to failure that it only took some warming by the sun to trigger it – scary. Because we still have very limited information and a high degree of uncertainty we continue to recommend playing it safe and avoiding large terrain and steep slopes.