Turnagain Pass Avalanche Forecast

After a two week dry spell, a pattern shift is here bringing a few inches of snowfall today and possibly heavier snowfall on Friday. As the graphic below from the National Weather Service suggests, varying degrees of snow is expected (3-6″ ish) in general with the highest amounts in Portage and Placer Valleys (6-10″). Ridgetop winds have already ramped up overnight and are blowing in the 15-25mph range with stronger gusts from the east.

Avalanche danger will depend on 1) how much new snow falls and 2) how strong the wind blows. With such meager snow amounts, the most likely avalanche type will be wind slabs where winds are blowing the new snow, and possibly some old soft snow, into slabs. These are likely to be on the smaller side, maybe up to a foot thick. The old snow surfaces were a mix of sun crusts on aspects facing ESE through WSW and soft old faceted snow and harder wind affected snow on shadier aspects. Wind slabs forming on either one of these surfaces should be touchy, even if they are smaller, the sun crust especially. Watch for stiffer wind deposited snow and shooting cracks. Wind slabs should be easy to identify if we look for them.

Sluffs in the new snow should be easy to trigger on steep slopes with over 4″ of new snow. These could run further than expected if a sun crust is underneath.

If a zone sees snowfall in the 6-10″ range, such as forecast for Portage Valley or Placer, then shallow storm slabs may form in areas out of the winds. This means triggering a slab avalanche composed of the storm snow is possible.

Travel Advice:  Paying attention to new snow amounts and wind loading will be key. Many areas may not see enough snow/wind to even elevate the danger. For example, if only 2-3″ of new snow falls with no wind loading, the danger will remain LOW.

Snowfall totals through today. There is high uncertainty, but it looks promising for a little refresh. Graphic courtesy of NWS Anchorage. 03.14.2023

Southerly slopes, and a few east and west aspects too, sport a sun crust of varying thicknesses. This will provide a slick surface for the new snow to fall on. 3.14.23.

Example of a low angle northerly facing slope with soft old faceted snow. This was an old wind crust that has been slowly weakening (faceting) with the cold temps over the past week. 3.14.23.

We are still concerned about a layer of weak facets buried about a foot deep in the southern edge of our forecast area. This layer is most problematic in a small area between Pete’s North and Johnson Pass, The layer was the culprit in a wide propagating skier-triggered avalanche last Monday (3/6). These stubborn persistent weak layers can be difficult to predict and there could still be a chance a person could trigger another slab, as occurred just over a week ago. Extra caution is recommended in this area.