Avalanche Forecast
Regions: Cascades - North West.
The storm snow is still stabilizing and may continue to be reactive to human triggers on Saturday. Be leery of large convex slopes and terrain features greater than 35 degrees where you are most likely to trigger an avalanche. Carefully assess the upper snowpack and ease into terrain slowly.
Discussion
The recent storm favored the West North zone which received almost 2ft of new snow since Thursday night, while zones to the south and east only picked up only a few inches. On Friday, Mt. Baker Pro Patrol reported several natural and triggered avalanches to size D2 (large) failing 4-8in deep within the recent storm snow. Loose dry avalanches were also a player on Friday and ran impressively far and fast. Winds were strong and gusty at the onset of precipitation Thursday night, but tapered off dramatically during the storm, leaving new snow relatively undisturbed. Expect cool temperatures (1500ft snow levels) with a few more inches of snow and light southerly winds Saturday, and skies to remain cloudy throughout the day.
Snowpack Discussion
March 5, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
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Ridgetop wind transport near Washington Pass. 3/4/20 Photo: Josh Hirshberg
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The beginning of March brought the first spring-like weather to the region. The days are getting longer and the sun (when it shines) has a noticeable effect on the snow. Alternating sun breaks and snowstorms is the theme of the week and the avalanche danger fluctuated just as fast as the weather. The southern zones and the east slopes have seen periods of light snowfall and significant sunshine while the northern zones and west slopes have had significant snowfall and occasional sun breaks. Above freezing temperatures were common at lower elevations throughout the region.Â
Last week in review: Temperatures were above freezing at most trailhead locations and concerns about the previous week’s buried surface hoar and weak layers were fading. Saturday temperatures plummeted as strong winds and new snow built wind slabs in most areas and drove the avalanche danger to considerable in almost every zone. Sunday’s calm weather and clearing in most areas helped stabilize wind slabs, but our attention turned to the strength of the sun and daytime warming. Lingering wind slabs and loose wet avalanches were forecast in every zone. For the remainder of the week, the avalanche problems in every zone were confined to the recent snow and each brief storm cycle had us thinking about wind slabs at upper elevations and loose wet avalanches from daytime warming and sunshine.
Spring isn’t actually here -- another round of cold temps and snow showers are on the way this weekend, but this past week’s oscillating weather is a good reminder to begin to shift our mindset. The sun is gaining strength, the days are getting longer, and we begin daylight savings this week. Even a brief period of sunshine can dramatically alter fresh, new snow. Check the mountain weather and avalanche forecasts for the most up to date info, enjoy the backcountry and let us know what you see out there!
--Peter Moore
Wet loose avalanche debris near Snow Lake. 3/5/20 Photo: Dallas Glass
Fresh cornice development from strong winds in the Stevens Pass backcountry. 3/4/20 Photo: Tom Whipple
Avalanche Problems
Storm Slabs
The snow from the Thursday/Friday storm still needs time to settle and stabilize. You can trigger slab avalanches within recent snow in terrain 35 degrees and steeper. Be especially leery of unsupported slopes and rollovers at upper elevations. Keep loose dry avalanches in mind as well. These sluffs could knock you off your feet and carry you into trees and rocks, or even trigger slab avalanches as they run downslope. Gather information as you travel by digging with your hand and using small slopes to test the upper snowpack. Seek out supported slopes, and dial back your terrain choices to more conservative options if you see signs of unstable snow like recent avalanches, shooting cracks, or whumphing collapses.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1