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Avalanche Forecast

Archived

Jan 4th, 2017–Jan 5th, 2017

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

Regions

Mt Hood.

Strong E-NE winds Tuesday night and Wednesday have loaded unusual aspects and built wind slab in all elevation bands on Mt. Hood. Allow fresh wind slabs time to stabilize and avoid terrain where even a small slab avalanche could have unintended consequences. 

Detailed Forecast

Temperatures will remain cold Thursday at Mt. Hood but E-NE winds should quickly subside through the morning hours and be accompanied by mostly sunny skies.

Strong E-NE winds Tuesday night and Wednesday have loaded unusual aspects and built wind slab in all elevation bands on Mt. Hood. 

Allow fresh wind slabs time to stabilize and avoid terrain where even a small slab avalanche could have unintended consequences. Remember to watch for firmer wind transported snow on all slope aspects or cross loaded slopes especially in areas with varied terrain and modified wind directions.  

Snowpack Discussion

Weather and Snowpack

A low pressure system moved south over western Washington on Saturday night followed by cold Arctic air. NWAC stations at Mt Hood had SW winds Saturday and 5 inches of snowfall by Sunday morning.

An unusual moist reverse orographic east flow caused snow mainly in the central to south Cascades Sunday afternoon and night. NWAC stations at Mt Hood had a shift to NE winds and another 10-12 inches of snow on Monday morning and further cooling as the Arctic air mass further moved into the Northwest.

Strong E-NE winds likely ravaged the snow surface on Mt. Hood Tuesday night and Wednesday. Winds near treeline regularly gusted into the 50s and 60s while the upper stations at Meadows and Timberline had multiple gusts to 100 mph. Winds were still strong but starting to moderate Wednesday afternoon. 

Recent Observations

The Mt Hood Meadows pro-patrol on Monday reported that the recent wind shift was moving snow to S-W slopes. On avalanche control on Monday morning sensitive 4-6 inch storm slabs were released by skis on most test slopes. Deeper storm slab to about 2 feet was expected in loaded areas which could release to the Solstice crust. The shift to NE winds as also building new local soft 8-24 inch wind slab on S-W slopes.

NWAC pro-observer Laura Green was on E-NE slopes on Elk Mountain on Monday and found minor wind transport in the above tree in the 4200-5400 foot range but no signs of instability.

Laura was at the Mt Hood Meadows Ski Area on Tuesday and also found minor wind transport in the above tree line. 

No reports were received on Wednesday and fierce winds that kept the ski areas from running most of their lifts also likely prevented anyone from venturing into the near or above treeline on Mt. Hood. 

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.