Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Mar 27th, 2017–Mar 28th, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Fresh wind slabs and cornices will be the main problem Monday. Loose-wet avalanches will become likely on steeper sun exposed slopes during extended sun breaks Monday. Keep terrain selection simple and conservative. Cornices have recently proven dangerous and unpredictable and capable of triggering very large avalanches. 

Detailed Forecast

Rain and snow late Sunday should change to showers with cooling overnight. Showers and moderate ridgetop winds should persist early Monday before tapering late Monday. This should maintain unstable wind slabs on lee slopes below ridges, in exposed terrain near and especially above treeline. 

Recent winds have been mostly SE-S-SW, so firmer wind slab should be found mainly on NW-N-SE slopes near and above treeline. However, due to terrain effects, wind slabs may have formed on a variety of aspects 

Recent cornices are very large. Make sure to avoid areas on ridges where there may be an overhanging cornice as well as travel on steep slopes below cornices! Natural cornice releases and resulting slab avalanches are unpredictable. See a blog post regarding cornices here.

Snowpack Discussion

Weather and Snowpack

The first week or so of March was very cool and snowy.  NWAC stations at Mt Hood piled up about 6-7 ft of snow.

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately, these systems delivered far more rain than snow. At least two regional avalanche cycles occurred during the stretch. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. 

This past week has also been active weather-wise, but water amounts/snowfall totals have been slightly lower relative to the extreme wetness of the past few weeks. Since Thursday, 3/23, Mt. Hood stations have picked up 20 inches of snow and climbing.

A strong front Sunday, continues to deposit snow as of Sunday evening, with 8 inches of snow since Sunday morning. Winds above treeline have been moderate to strong, from the SE-SW.  

Recent Observations

The Meadows patrol was unable to reach terrain above treeline Saturday due to winds and poor visibility. Near treeline, a few triggered wind slabs were able to be released with skis, but were only 1-2 inches deep. Large cornice releases at higher elevations may have released avalanches on the slopes below, but this was unconfirmed due to visibility. Below treeline, shallow surface snow was producing rollerballs and small loose-wet slides Saturday afternoon during extended sun breaks.   

On Monday an initial report from the Meadows patrol indicated touchy size 1-2 wind slab on NE aspects near and above treeline. The avalanche forecast for the near treeline for Mt Hood has been updated on Monday due to this information.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the 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. 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.