Turnagain Pass Avalanche Forecast

Finally, after an 11 day stretch of benign weather a storm is headed into the region. Ridgetop winds began picking up around 4am and snowfall should begin around 6am. The avalanche danger will rise through the day relative to the amount of new snow and wind. Turnagain Pass could see up to 18″ of snow by 6pm. Other areas could see more or less depending on where the storm favors. Ridgetop winds however should be widespread through the region blowing 45-55mph with gusts into the 70’s and 80’s mph.

If the storm verifies, we can expect a variety of storm snow avalanches to start occurring through the day. The first is storm slabs that form on slopes out of the wind. These are composed of the new snow and release when the new snow hasn’t bonded yet with the older snow surface. Second are wind slabs that develop on wind loaded slopes. These could be up to 2′ deep due to the strength of the winds. Third are loose snow avalanches that are common during storms in steep terrain. And last are fresh cornices. Chunks of cornices are likely to break off and could trigger avalanches below. Hence, we are expecting a HIGH avalanche danger by sunset.

For those headed out today, paying close attention to the changing weather will be key. Areas seeing less snowfall could still be quite dangerous due to the strong winds. If you are getting out early, know the danger will be rising rapidly. This new snow should be very light and with snow falling all the way to sea level, avalanches could be seen even in the lower elevations. Additionally, powder clouds and debris could run further than expected.

A quote from our friends at the National Weather Service this morning:
“There is quite a bit of uncertainty in snow amounts in the Portage and Turnagain Pass areas, where high snow ratios could bring up to 2 ft for Turnagain Pass and 3 ft for Portage Valley of snow through Monday morning.”

Snowfall amounts from 6am this morning through 6am Monday. Graphic by the NWS that can be found on their Avalanche Weather Guidance page HERE. 

Today’s new snow and wind will be a good test for the layer of buried surface hoar that we’ve been worried about for the last two weeks. This layer was 2-3′ deep but should be 3-4′ deep after today. After being very reactive 2 weeks ago, it was healing and not showing signs of reactivity the past several days. We will be trying to assess if any storm snow avalanches will step down and cause this layer to fail. If that happens, a much larger avalanche would result.

We are still tracking the Thanksgiving facet/crust combo at the base of the snowpack. Even with 1-1.5″ of water weight with today’s storm, it’s unlikely this is enough load to reactivate this very deep layer. This is something we are watching for in the future if we get into a more potent storm series.