Avalanche Forecast
Regions: Mt Hood.
The avalanche danger at Mt Hood will go up another notch on Monday. Careful snowpack evaluation and cautious routefinding will be essential at Mt Hood on Monday.
Detailed Forecast
Weakening low pressure systems will pass near Cape Flattery on Sunday and near Astoria on Monday. This will generally cause a trend of increasing alpine winds and increasing snow especially in the south Cascades and Mt Hood by Monday. Temperatures should not change greatly through Monday. Expect up to about 10-20 inches of snow Sunday and Monday with possibly the most at Mt Hood.
This will cause the avalanche danger at Mt Hood to go up another notch on Monday.
The size and extent of wind slab should increase at Mt Hood on Monday. Watch for firmer wind transported snow on potential lee slopes. Significant winds lately and on Monday will have been mostly south to southwest so north to southeast aspects will be indicated but keep an eye on all aspects.
The size and extent of storm slab should also increase at Mt Hood on Monday. Storm slab is most likely in areas that receive more than a few inches of rapidly accumulating snowfall.
Loose wet avalanches will not be indicated as an avalanche problem but watch for loose wet surface snow if you find yourself on solar slopes during cloud or sun breaks.
Snowpack Discussion
Weather and Snowpack
Hopefully the last atmospheric river of the season arrived on Valentines Day 2/14 causing heavy rain, avalanches, crusts and consolidation through Thursday including at Mt Hood. About 5-8 inches of snow was seen at Mt Hood at the tail end of the storm.
A short period of fair weather on Friday 2/17 caused another surface crust at Mt Hood.
Some snow was seen with light winds on Saturday. NWAC stations at Mt Hood had about 4 inches ending Sunday morning.
Temperatures haven't changed much on Friday to Sunday
Recent Observations
A backcountry report from NWAC pro-observer Laura Green from the White River drainage on Friday indicated a mix of surface conditions. Below treeline she found plenty of roller balls. Near and above treeline she found a firm rain crust near and above treeline with varying amounts of recent snow above depending upon wind exposure. Isolated wind slabs had formed on the leeward terrain below ridges, with one natural wind slab at about 7700 feet on an ESE facing wind loaded slope. Elsewhere she found firm conditions on an exposed hard rain crust.
Laura was out again on Sunday at Bennett Pass up to about 6000 feet and found recent snow well bonded to the 2/17 crust and observed no signs of avalanches.
The Mt Hood Meadows pro-patrol on Sunday found N-E slopes up to about 6600 feet a bit loaded with 8-10 inches of wind transported snow on the 2/17 crust but no significant wind slab.
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, Treeline.
Likelihood: 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: Likely
Expected Size: 1 - 1