Avalanche Forecast
Regions: Mt Hood.
A natural avalanche cycle should occur Monday night through Tuesday morning during peak warming and precipitation. Expect wind loading further downslope than usual due to very strong westerly winds on a variety of aspects. Slabs may fail on weak persistent grain types formed prior to this storm cycle. Travel in avalanche terrain is not recommended Tuesday!
Detailed Forecast
Strong westerly flow will carry another strong frontal system across the Northwest Monday night and Tuesday morning. This will cause strong winds with moderate to heavy snow along the west slopes and a warming trend overnight. The warming trend should contribute to the formation of both new wind slab and new storm slab layers. A sharp cooling trend will take place beginning late Tuesday morning with light to moderate snow showers continuing through the day in continued strong westerly flow. See the NWAC mountain weather forecast for more details on precipitation intensity, precipitation types and temperature trends.
New wind slab is very likely for Mt. Hood on Tuesday. Continued wind transport will deepen these layers mainly on lee north to southeast slopes but wind slab is possible on other aspects due to strong gusts. Also, wind slab may develop below treeline due to the persistence of very strong westerly winds.Â
New storm slab is also very likely Tuesday on any slopes that rapidly accumulate new snow. A change from snow to rain near and below treeline Monday night will also make storm slabs more likely to initiate or cause natural loose wet avalanches in areas lacking a slab structure. Loose wet should only be likely in the morning due to a rapid cool down beginning later Tuesday morning.
A natural avalanche cycle should occur Monday night through Tuesday morning during peak warming and precipitation. Expect wind loading further downslope than usual due to strong westerly winds on a variety of aspects. Slabs may fail on weak persistent grain types formed prior to this storm cycle. Travel in avalanche terrain is not recommended Tuesday!Â
Snowpack Discussion
Weather and Snowpack
The last storm cycle to affect all of the Olympics and Cascades was from Thursday, December 8th through Monday morning, December 12th. About 4 feet of snow were recorded at the NWAC stations in the Mt Hood area.
Another system moved across the Mt Hood area late Wednesday through Thursday morning depositing an additional foot of new snow with moderate southeast winds shifting to the west and decreasing.Â
There has been a lot of snowpack settlement since the last storm cycle ended, allowing this underlying snow to mostly stabilize.
Clear or fair and cold weather has been seen about Thursday at Mt Hood. This should have caused new widespread surface hoar and near surface faceted snow to develop to develop at Mt Hood as in the Cascades. Thin sun crusts have also formed on steeper solar slopes. These layers are expected to act as widespread weak layers or sliding surfaces for the upcoming moderate to heavy snowfall.
Strong westerly winds affected most locations in the Olympics and Cascades including Mt. Hood Monday morning before easing off Monday afternoon. 5-8" of new snow fell at NWAC stations on Mt. Hood with a warming trend through Monday afternoon. Â
Recent Observations
NWAC pro-observer Laura Green was out in the Newton and Clark drainages on Friday a found a mix of surface conditions of recent snow and 3-4 mm surface hoar with a thin sun crust on solar slopes. The upper snow pack on N-NE slopes was right side up with no direct signs of instability.
The Mt Hood Meadows pro-patrol on Sunday reports 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.
No observations were received on Monday.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.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 2
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
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1