Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 24th, 2019–Dec 25th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

.

Happy Holidays! If you find an area that has the combination of a thick recent slab and presence of weak older snow below it, you can trigger a deep and dangerous avalanche. Be most cautious above 6,000ft, and on steep slopes that face the north half of the compass. 

Discussion

Happy Holidays from all of us at NWAC! The recent atmospheric river event left 3ft of settled storm snow on the ground in many places near the crest, while the Wenatchee Mountains east of Blewett Pass received less than 1ft of new snow. Observers at Holden Village and in the Icicle Creek drainage reported a cycle of large, natural avalanches on the 20th and 21st. These avalanches were easily big enough kill a person (up to size D2.5). Some broke widely across the terrain, ran on weak old facets, and may have been triggered remotely. On the 23rd, Mission Ridge Ski Patrol got results with explosive work below the Microwave Tower. The slab was observed to have failed on a layer of facets over a crust, which coincides with the same layer of concern we have closer to the crest. Watch this video I put together from my field day in the Icicle drainage on the 23rd for more info.

A sometimes breakable, sometimes supportable, but now frozen melt freeze crust can be found up to mid 5,000ft throughout much of the zone, making travel difficult at these lower elevations. 

Crown of an explosive triggered slide at Mission Ridge. NW at 6,700ft on December 23,2019. Jacob Peterson photo.

Snowpack Discussion

New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.

 

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.