Avalanche Forecast
Regions: Mt Hood.
Pay attention to changing weather and avalanche conditions late in the day! New wind slab may develop near and above treeline by early Monday evening and should be particularly sensitive on lee slopes with an underlying crust. The avalanche danger will ramp up quickly Monday evening, so plan accordingly for deteriorating conditions. The surface crust formed last week is hard enough to present an out-of-control fall danger.
Detailed Forecast
After a benign start to Monday, an incoming frontal system will spread light rain and snow south, reaching Mt. Hood late in the day on Monday. Above treeline winds will quickly ramp up in the afternoon. Expect stormy conditions Monday night with increasing avalanche danger. Pay attention to changing weather and avalanche conditions late in the day!
Fresh wind slab may develop by late Monday afternoon or early Monday evening near and above treeline. Wind slab will likely be the most sensitive in areas where it poorly bonds to an underlying crust.  Â
The surface crust formed last week is hard enough to present an out-of-control fall danger.Â
Â
Â
Â
Snowpack Discussion
Weather and Snowpack
Strong westerly flow directed two Pacific frontal systems into the PNW Sunday night and again Monday night (12/18-12/19)Â with generally 3Â inches of water accumulating at NWAC stations at Mt Hood through early Tuesday morning.
Unfortunately, much of the heavy precipitation fell in liquid form with rain likely reaching up to at least 7000 feet late Monday night and Tuesday morning.Â
A sharp cooling trend followed mid-day Tuesday with about 2 inches of snow in post-frontal showers.  A strengthening rain crust was noted near and below treeline by late in the day Tuesday with the arrival of colder air. Â
Another front crossed the Northwest on Thursday followed by an upper trough on Friday. This produced about 5 inches of snow at NWAC stations on Mt Hood.Â
NW winds near and above treeline were moderate at Mt. Hood Friday night through mid-day Saturday.  Christmas Day was partly to mostly sunny with light winds and cold temperatures. Â
Recent Observations
Reports from the Mt Hood Meadows pro-patrol Wednesday reported a significantly different snowpack following rain, avalanches and cooling. A stout surface crust was found on all elevations up to at least 7200 feet. On exposed terrain, the crust was very supportable while in treed terrain the crust ranged from breakable to supportable.
The Meadows patrol checked in early Sunday morning to report NW winds had scoured windward aspects near and above treeline exposing the thick crust on many aspects. The crust was slick enough that Santa had trouble landing his sled on any slope steeper than 20 degrees.
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1