Avalanche Forecast
Regions: Mt Hood.
Newly forming wind transported snow is the primary concern by later Thursday as the front arrives. Watch for new firm snow layers forming over an existing hard rain crust. Avoid steep slopes receiving new wind deposits.
Detailed Forecast
A weak front will move across the Cascades Thursday, depositing generally light amounts of new snow, but arrive with a period of moderate ridge top winds. This may build some new shallow slab layers on some lee slopes at higher elevations near ridges.
Fresh wind slab should be the primary problem Thursday as older layers have either released or now have a solid crust. Â Â
Snowpack Discussion
Weather and Snowpack
Clear and cold weather from Wednesday, December 14th to Friday, December 17th allowed widespread surface hoar and near surface faceted snow to develop in the Cascades and Mt. Hood. Thin sun crusts formed on steeper solar slopes during sunny periods.
However, persistent weak layers likely have not survived in the Mt. Hood zone due to the copious water amounts received over this latest storm cycle. Strong westerly flow directed two Pacific frontal systems into the PNW Sunday night and again Monday night with generally 3Â inches of water accumulating at Mt. Hood NWAC stations through early Tuesday morning.
Unfortunately, much of the heavy precipitation fell in liquid form with rain likely reaching up to about 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
Cold and clear weather overnight Tuesday and early Wednesday helped strengthen surface or near surface crusts up to at least 7000 ft.
Recent Observations
The Mt Hood Meadows pro-patrol on Sunday reported fairly widespread surface hoar and near surface faceted snow up to about 7300 feet. Calm winds have allowed it to develop or grow the past couple days.
Avalanche control observations were limited Tuesday morning and the below treeline snowpack appeared to be handling the heavy rain remarkably well with little natural or human avalanche activity observed. However, by late Tuesday afternoon and after some partial clearing, debris from a very large wind slab avalanche was observed above treeline on a ENE aspect at 7500 feet in the Mt. Hood Meadows ski area. This R4.5 - D3 avalanche likely occurred Monday night and cleared out two start zones running roughly 1500 feet vertical. From a distance, the crown was estimated to be several feet thick!Â
Reports from the Mt Hood Meadows patrol Wendsday, reported a significantly different snowpack following the 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.Â
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, South, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1