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Avalanche Forecast

Archived

Mar 1st, 2017–Mar 2nd, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

A strong storm has created very dangerous avalanche conditions. Natural avalanches are likely and human triggered avalanches very likely in terrain near and above treeline where travel in avalanche terrain is not recommended Wednesday. 

Detailed Forecast

Continued very strong winds overnight Tuesday and Wednesday with increasing light to moderate snow overnight and early Wednesday will maintain widespread unstable snow conditions. Natural or triggered avalanches are very likely in exposed terrain near and above treeline. 

 

 

 

Snowpack Discussion

Weather and Snowpack

The most recent warm and wet SW storm arrived on Valentines Day 2/14 and formed the uppermost very strong rain crust in our snowpack. 

About 2 feet of snow accumulated at the NWAC Mt Hood stations from Sunday, 2/19 through Wednesday 2/22. 

Weak weather systems Sunday and again Monday, deposited about another foot of low density snow by Monday evening with light to moderate westerly transport winds near and above treeline

A stronger than forecast storm late Monday through Tuesday deposited an additional 2-2.5 feet of snow by Tuesday evening! The latest heavy snow has arrived with very strong crest level winds with 7300 ft elevation, wind instruments averaging 50+ MPH all day Tuesday with gusts over 100 MPH.   

Recent Observations

Several contacts with the Mt Hood pro patrol through the day Tuesday reported widespread natural and triggered wind and storm slabs Tuesday morning, especially near and above treeline. Avalanches were occurring even on relatively low angled terrain. Over 2 feet of new snow had accumulated by early Tuesday with more snow received through the day. Low visibility limited additional observations, however, by Tuesday afternoon large hard wind slabs were developing above treeline and several sympathetic avalanches were triggered. The recent relatively stable snowpack has quickly become very dangerous avalanche conditions. 

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.