Avalanche Forecast

Issued: Apr 25th, 2015 11:00AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Don't underestimate the effects of the strong April sun, which can make avalanches touchy Sunday, especially in areas of heavier storm snowfall.

Summary

Detailed Forecast

High pressure should begin building into the Pacific Northwest Sunday, causing clearing and slow warming. Temperatures should be cool early Sunday with only a moderate rise in freezing levels by afternoon. This should allow for recent snow over the past few days to settle. 

The main avalanche problems Sunday should shift from any recent storm or wind slab to mainly loose wet avalanches on slopes receiving sunshine and during the afternoon in areas with sufficient snow cover for avalanches. 

Watch for wet surface snow that gets deeper than a few inches, pinwheels or initial small natural avalanches from rocks or cliffs that are signs to shift to lower angle slopes.

Cornices won't be listed as an avalanche problem, but avoid slopes below cornices and areas on the ridge where it may be difficult to know if a cornice is present.

Remember that this forecast applies to elevations up to the Cascade crest and does not apply to higher elevations on the volcanoes where conditions at this time of year are often more dangerous.

The mid and lower snowpack is most areas should consist of stable, rounded grains and crust from warm periods this winter. Many areas at low elevations east of the crest do not have enough snow to cause an avalanche danger.

The work of the 3 NWAC forecasters is transitioning to other essential parts of the program before the NWAC closes for the summer.

 

Snowpack Discussion

After a cool, snowy start in early April, mid April provided about a week of warm dry weather. This caused loose wet snow avalanches and consolidation. Layers from early April have stabilized, making any avalanche activity confined to new snow received over the past few days.

A cold front moved across the Northwest on Thursday. The front was followed by a low pressure system, south to southwest winds and a cool unstable air mass that caused snow showers at low freezing levels Friday and Saturday. Storm snow amounts are likely to be variable under the showery recent weather pattern. The greatest recent snow has been over the volcanoes with only very light amounts of a few inches recorded at NWAC sites along the east slopes.

 

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Apr 26th, 2015 11:00AM