Avalanche Forecast

Very large avalanches may release from the upper elevations of Mt. Hood. Avoid large avalanche paths were avalanches may come down from the upper elevations of Mt. Hood. Check a map to ensure flat slopes are not connected to larger terrain before crossing open areas.

A relative break in the intense weather will not allow sufficient time for a variety of avalanche problems to heal. Dangerous avalanche conditions exist near and above treeline on Saturday.

Large Wind Slabs formed Wednesday afternoon through Friday during periods of heavy precipitation, strong winds, and warming temperatures. These slabs will continue to be reactive near and above treeline on Thursday. Avoid wind-loaded aspects steeper than 35 degrees. You are most likely to trigger a Wind Slab on NW through SE aspects below cornices, on convex roll overs, or on cross-loaded features.

You can trigger a storm slab as well from the top of the below treeline band upward on Saturday. These formed during periods of heavy precipitation Wednesday thorough Friday. A warming trend on Friday created unstable snow as denser snow sits on top of lower density layers within the 20-24" of recent snow that sits on a crust. You are most likely to trigger storm slabs on unsupported slopes, near convex rollovers, and in very steep terrain.

At lower elevations, rain on Friday created wet surface snow conditions. If you see new rollerballs, fan shaped avalanche debris, or experience periods of intense rain, stay off of slopes greater than 35 degrees. Loose wet avalanches can entrain additional snow allowing them to grow large. Use caution if you travel in areas where loose wet avalanches may carry you into or off of terrain with higher consequences.

Watch for other spring hazards such as recent cornices along ridges, open glide cracks and opening creeks.

In general 20-24 inches of new snow fell in the Mt Hood area stations Wednesday afternoon through Friday afternoon, but new snow distribution varied by a factor of 2 due to wind transport. Moderate to strong south to west winds increased to strong on Friday at upper elevations and easily transported the new snow, forming new wind slabs near and above treeline on a variety of aspects and these are likely to be large. On the upper mountain at Mt. Hood, Wind Slabs are likely to be very large. The heavy snowfall rates on Friday also created storm slabs with heavier, denser snow on top of lower density layers.. This most recent round of precipitation fell on a new melt-freeze crust (4/11) formed during warm weather earlier this week. Observations demonstrate the new crust is strong and supportable. The snowpack now consists of a slab (wind or storm) on top of lower density snow, sitting on an older crust. That is a prime recipe for dangerous avalanche conditions in the upper snowpack.

Reports indicate that the snowpack consist of various layers of melt –freeze crusts, refrozen snow, and strong rounds. This has resulted in a generally strong snowpack without any significant layers of concern.

Observations

On Friday, Pro Observer Laura Green traveled in the Newton/Clark drainage between 4500 and 5900 ft. She avoided higher elevation or larger avalanche terrain due to strong winds, heavy snowfall and poor visibility. With warming temperatures during the day, snow surfaces were moist to wet. On a NNE aspect at 5600' she observed up to 2' of upside down snow on top of lower resistance wet snow layers. Although she didn't find a particularly cohesive slab in the location tested, she suspected they exist higher up.

On Friday, Mt. Hood pro patrol reported reactive 6-18" explosive triggered slabs with limited visibility up high. Snow was falling at the base, but it was very heavy and wet.

On Thursday, Mt Hood Meadows ski patrol reported wind slabs ranging from 8 to 12 inches (20-30cm). Wind and storm slabs were reactive during avalanche control work Thursday morning. The most recent melt-freeze crust was reported as strong and supportable.