Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

There should be plenty of wind-affected slopes for you to evaluate on Monday throughout the zone. Ease into terrain slowly as you check the bonding of the recent storm snow and gather information. If you see red-flag signs of instability such as shooting cracks, whumpfing collapses, recent avalanches, or hollow feeling snow, avoid slopes over 35 degrees. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Throughout the zone, strong to extreme winds have transported new snow into Wind Slabs. Slabs will be larger and more widespread as you ascend in elevation and will be most likely on leeward slopes at ridgecrest or near rocky features such as cliffs and gullies. Fresh cornices have also surely been built by the wind and will be sensitive to human triggers, but can be used as a visual clue to help you identify wind-loaded slopes. Other clues such as textured surfaces or smooth pillow-like piles of snow can help you identify wind-loaded slopes to avoid. At lower elevations, Wind Slabs could be complemented by pockets of reactive snow in wind-sheltered areas behaving more like Storm Slabs. Whatever avalanche character you tend to give the new storm snow, avalanches will be more likely on slopes over 35 degrees, near rocks, or on convexities. Uptrack tests or hand pits in non-consequential terrain can help you determine slab potential and some clues to bonding, but you shouldn’t be performing these tests on slopes that may be wind-loaded. A better method is to use test slopes to see how the recent snow has bonded to the previous snow surface and how it is reacting to your weight. If you find a poor bond or suspect wind-loading avoid slopes over 35 degrees.

    (11/27/2020) Active wind loading/blowing snow, rime on trees and cliffs, and snowdrifts are all indicators for Wind Slabs

Avalanche Discussion

NWAC’s weather stations have been spinning all day on Sunday, cranking out huge wind numbers around the zone. Camp Muir takes the cake with 9 hours straight (and counting) of max gusts over 100 mph. During their windiest hour (4:00 pm), we recorded a maximum gust of 143mph, with an average speed of 119mph and a minimum of 98 mph. Those numbers are ridiculous! Although they are the top end of numbers recorded around the zone, they illustrate that this is a windy storm. NWAC stations closer to the crest support this notion, with gusts that approached 100mph and multiple hours with wind speed averages in the 40s and 50s. This storm was definitely more winterlike than springlike, and as the snow continues to pile up, winds should taper, but remain strong into Monday. 

Observations by NWAC forecasters on Sunday indicate that the new snow is not bonding well to the prior snow surface, particularly in areas where a melt-freeze crust existed. This crust varied in thickness but existed in all elevation bands and on most aspects except northerly at upper elevations. This poor bond was due in part to graupel falling near the onset of precipitation and could lead to sensitive conditions on Monday in all areas, not just the ones where the wind has drifted the snow into thicker slabs. Avalanches have the ability to run far and fast on the crust as slabs, loose, or even wet if the sun comes out and destabilizes the newly fallen snow. Wet avalanches may be more likely the further south you go in the zone, where the chance for sun breaks is higher. We expect you will find a mix of wind-stripped surfaces, wind slab, and poorly bonded storm snow on Monday, with all avalanches confined to the new snow above the 3/28 interface.

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.

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