AM Update: High danger at all elevations. Very large slabs may release naturally from the upper slopes of Mt. Hood. Avoid all terrain where avalanches may start, stop, or run, including open canyon bottoms and valley flats. Large natural and human-triggered avalanches are very likely at all elevations.
Heavy snowfall will push storm slabs near the breaking point. Large natural and human-triggered storm slabs over 1 foot deep were observed early Tuesday morning sliding easily on Monday's Rain crust. Travel in avalanche terrain is not recommended.
(2/14/2021) Large storm slab from the Crystal Backcountry [Photo: Andrew Harrington, Public Observation]
Tuesday we enter day 6 of a prolonged and intense storm and avalanche cycle. Precipitation rates ramped up on Monday and those high rates are forecast to continue into Tuesday. Moderate to strong winds should continue to load lee slopes from the near treeline terrain upwards. With these high snowfall rates and very heavy wind-loading comes the most serious threat of avalanches. With each passing day, wind slabs are growing larger, increasing the risk of very large avalanches running to valley bottoms from above treeline or the upper slopes of Mt. Hood. Avoid all avalanche terrain near and above treeline and large avalanche paths at all elevations where an avalanche can start, run, or stop. This includes valley bottoms where avalanches may reach from above.
(4/10/2019) This very large wind slab avalanche in April 2019 gauged deeply and ran into significantly lower elevation terrain. Note the stunted trees and open terrain in the photo and avoid similar terrain on Monday.
We're becoming increasingly concerned about the threat of larger and more dangerous avalanches as we enter the 6th day of a significant storm cycle on Mt. Hood. Mt. Hood Meadows has picked up 45.5" of snowfall since Thursday morning. Areas on the south side of Mt. Hood received a quasi-breakable freezing rain crust before precipitation switched back to snow by 11 AM on Monday. The snow was very cold and low-density through Saturday morning, but a very rapid warm-up triggered widespread small natural storm slabs on Saturday as denser slabs began building. NWAC professionals observed tree-bomb triggered avalanches at unusually low elevations (5000 ft). A public observation from Bennet Pass documented widespread crowns on steep, convex rollovers. On Sunday, freezing rain created a quarter-inch freezing rain crust on the south side of the mountain. Meanwhile, on the north side of the mountain on a NE aspect at 6000 ft, the freezing rain crust was not present and an observer found reactive snowpack tests on a weak snow interface that pre-dates the storm cycle (2/11). In some areas, the 2/11 interface may involve a thin freezing rain crust. An observation from Newton Canyon found this surface crust even on NE aspects below 6000 ft. Winds in the storm cycle have thus far peaked on Friday with very strong to extreme gusts. Significant wind loading has created the potential for very large avalanches above treeline and above the NWAC forecast bands. Due to poor visibility, we have been lacking observations at higher elevations throughout the last 5 days.
As the snow keeps piling up, the very real threat of Snow Immersion and Suffocation (SIS) increases. If you recreate in forested areas, travel with a partner and maintain visual or audio contact.
The stout mid-January crust is considered the new "ground" with a strong snowpack structure in place below this layer. Weak and faceted snow just above the stout rain crust was responsible for a number of avalanches last week, but no new evidence of avalanches on this interface suggests these facets are gaining strength. This weak layer (which is similar in structure to the fatal avalanche in WA) still exists around Mt Hood and could produce a very large avalanche, but no evidence of recent avalanches on this layer have been reported.
Headed north to recreate? We have a tricky snowpack with persistent slab problems in all forecast zones across the state line. Take the time to read about the different snowpacks that have developed further north and adjust your terrain selection accordingly.
----------------------------------------------------------------
During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.
