Avalanche and Weather Summary
Valid Saturday, November 18th - Sunday, November 19th
Winds in the past 24 hours have moved significant amounts of recent and easily transportable storm snow. Wind effects near ridgelines in the Washington Cascades and wind slabs near Mt. Hood will be difficult to manage until they stabilize. Travel near ridge-crests should be undertaken with caution elsewhere. Overall, chances of triggering avalanches exist in new storm snow and wind-loaded terrain, particularly above 4000 ft where snow depths have increased markedly during the first half of this month. Remember that closed ski areas without avalanche mitigation are equivalent to backcountry terrain early in the season!
Welcome to an early start to winter here in the Pacific Northwest! The snowpack is rapidly deepening above about 4000 feet, with snow levels coming down during the past four days.
Snowfall totals the past four days range from:
- Hurricane Ridge: 3-4'
- Washington Cascade West Slopes (except 5' at Mt. Baker): 1.5-3.5'
- Washington Cascade East Slopes: 1-2'
- Mt. Hood: 2-3'
NWAC pro observers began to make observations today.
Lee Lazzara was in the Bagley Lakes area near Mt. Baker and observed evidence of a few large soft slab avalanches overnight associated with recent storm snow on a variety of specific terrain features - north to east aspects. His test slopes produced cracking and small pockets released on steeper terrain (wind-loading), up to 60 cm deep. Wind loaded areas were touchy. Good coverage, excellent ski quality (14” new). His primary concerns were snow and wind loading during the past 24 hours on a subtle new/old interface.
Jeremy Allyn traveled into ridge-line terrain in the Crystal Backcountry today. Ridge-top winds up to 35-40 mph produced significant snow transport and rapidly decreased stability during the late morning hours, giving touchy (isolated specific to ridge) small 6-8” SS/WS on most aspects. He ski triggered numerous small Storm/Wind slabs near ridge-crest running up to 100 ft. A couple hundred feet below ridge the snow was generally unconsolidated without significant layering.
Ski Area Reports
Mt. Hood Meadows reports widespread wind effects due to today's winds. Small N-E test slopes produced easily triggered (touchy) 6-8” windslab/storm slab. Propagation spanned the entire test features in the near and below treeline terrain. The patrol assumes it would be easy for human to trigger size small-to-large avalanches on bigger terrain. Surface snow density has increased to four finger hardness, with fist density snow underneath.
Decreasing winds Friday night and slightly warming temperatures Saturday should enable recent storm slab and wind slab to partly stabilize. Wind effects and small areas of wind slabs should be most likely near ridge-crests in the Washington Cascades. Wind effects and wind slab will be more extensive in all the elevation bands on Mt. Hood. Careful snowpack evaluation and cautious route-finding will be essential in these areas. Use extra caution when you encounter signs of wind-transported snow from the last 24-48 hours near ridge-crests in the Washington Cascades, with more widespread slab danger necessitating extra caution near large terrain features at Mt. Hood.
Increasing winds, increasing rain or snow, and warming will lead to an increasing avalanche danger on Sunday. Watch for the development of new, denser storm and wind slab layers. New slab development will probably progress from the Olympics and N. Cascades to the S. Cascades and Mt. Hood during the day on Sunday. Possible loose wet conditions may develop at low elevations in the South Cascades and Mt. Hood. Changing conditions expected Sunday increase the likelihood of natural and triggered avalanches and will require a more conservative mindset and tour plan.
See Forest's excellent blog post when thinking about traveling in avalanche terrain earlier in the season.
Winter 2017-18 Forecast Schedule
Daily Mountain Weather Forecasts, issued once a day in the afternoon, began Monday, Nov 13th.
The next Avalanche and Weather Summary will be issued:
Monday, November 20th
The first Avalanche Forecast will be issued Tuesday, November 21st @ 6 PM, valid for Wednesday November 22nd. The full winter forecast schedule will follow through mid-April.