Avalanche Forecast

Issued: Jan 6th, 2015 10:00AM

The alpine rating is low, the treeline rating is low, and the below treeline rating is moderate. Known problems include Loose Wet.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Triggered avalanches are unlikely, but areas of shallow wet snow are expected, especially on steeper southerly facing slopes exposed to direct sunshine.

Summary

Detailed Forecast

Another dry, sunny and warm day is expected Wednesday. Freezing levels should again exceed 10,000 feet and along with light winds, causing areas of wet surface snow. Clearing overnight Tuesday should allow for the recent rain soaked upper snow layers to drain further, consolidate and allow for a thin surface crust to form. 

While wet snow avalanches should be unlikely, some shallow surface wet snow may make it possible to initiate a small loose-wet slide on some steep, mostly southerly facing slopes during the warmest part of the day. Watch for areas where surface snow is becoming wet for more than the top few inches.

 

Snowpack Discussion

From 1 to over 3 inches of rain fell over the Cascade east slopes from Sunday night to Monday evening, following about 6-12 inches of snowfall that accumulated prior to the warming. It is difficult to assess just how impactful the warming and rain was along the east slopes, especially in the northern part, where more precipitation fell as snow prior to the full warming Monday. At higher elevations near 7000 feet in the north, there may have only been a light amount of rain that fell before precipitation ended later Monday, however temperatures climbed well above freezing, especially Tuesday. 

No observations were received Monday or Tuesday, however the rain and warming should have caused widespread avalanches involving any recent snow received before the substantial warming arrived Sunday night. The rain reached to near the Cascade crest elevations, thus essentially resetting the snowpack, with the possible exception of the highest terrain in the northeast part.. The rain should have eliminated most, if not all, layers of concern in the upper snowpack, leaving behind wet but draining upper snow layers.

We'll await more detailed impacts of the rain later in the week, as conditions will become more amenable to making observations. 

Problems

Loose Wet

An icon showing 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.

Aspects: South East, South, South West, West.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Jan 7th, 2015 10:00AM