Avalanche Forecast
Regions: Mt Hood.
Rapidly changing weather and snow conditions are expected on Sunday at Mt Hood. Back country travel is not recommended in avalanche terrain near and above treeline by Sunday afternoon.
Detailed Forecast
A deep low pressure system should move over about Cape Flattery and across south Vancouver Island Sunday morning and afternoon. This should bring stormy weather and heavy snow to Mt Hood Sunday. This is a little faster than previously expected. A vigorous, strong front should rapidly cross the area and cause rapidly shifting winds Sunday.
The main avalanche problem Sunday should be increasing strong winds and increasing moderate to heavy snow rapidly transporting recent or new snow and building new wind slab on lee slopes. This is very likely to be northwest to southeast slopes. New storm slab should also be likely where there is rapidly accumulating new snowfall.
The pattern makes for a tricky forecast Sunday. Dangerous avalanche conditions are expected to develop Sunday afternoon. Back country travel is not recommended in the near and above treeline by Sunday afternoon at Mt Hood.
Snowpack Discussion
Weather and Snowpack
The nonstop active weather pattern continues to push a storm system through the PNW almost every day or two resulting in fluctuating snow levels and periods of very strong winds (100+ mph gusts have been seen at the Mt Hood Meadows Cascade Express station over the last 2 weeks).
A last storm arrived Wednesday bringing heavy snowfall/rain at rising temperatures and very strong S-SW ridge top winds. About 2 inches of water and 8 inches of snow was seen the the NWAC stations at Mt Hood Meadows and Timberline for the 2 days ending Thursday morning with much of the water in liquid form.Â
A front on Saturday is causing west-southwest winds and there should be up to a few inches of new snow at Mt Hood by Sunday morning. Â
The mid and lower snow pack at Mt Hood should be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
On Wednesday morning, new extensive wind slabs were forming on lee slopes near and above treeline. Explosive control performed by Mt. Hood Meadows pro-patrol Wednesday produced widespread slab releases on wind loaded N-NE facing terrain with crown depths of 2 feet common. Storm slabs Wednesday morning changed to loose-wet avalanches by midday as temperatures rose and snow changed to rain below treeline.Â
On Thursday, NWAC pro-observer Laura Green toured in the Mitchell and Heather drainages and found evidence of rain up to at least 6600 feet. Thin wind pockets were observed on lee slopes above treeline. A supportable rain crust did not make for good skiing, but on the plus side no avalanche problems were noted. Runnels were observed below 6000'.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.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 1