Avalanche Forecast

An initial front will move mainly across the south part of Washington and Oregon on Tuesday afternoon. A second front, propelled by a strong westerly jet, will follow a similar route on Tuesday night and Wednesday.

New snow can be particularly sensitive after spring storms due to sun or solar effects and warmer daytime temperatures. There has been a lot of recent snow more on the way Wednesday in the south Cascades and especially at Mt Hood.

Large or very large loose wet avalanches are very likely due to the heavy new snow and sun or solar effects. Sun or solar effects can rapidly active avalanche problems and result in a dramatic increase in avalanche danger.

Deep storm slab may linger in areas that have recently had rapidly accumulating new snow.

In the near and above treeline large areas of deep wind slab may linger on lee aspects.

Travel in avalanche terrain is not recommended in the south Cascades and especially at Mt Hood on Wednesday.

Cornices are still large so give them a wide safety margin. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

Avoid unsupported slopes with overhanging blocks of snow and smooth rock underneath. Glide avalanches are difficult to predict and can release at any time, not just during the heat of the day.

As of Tuesday afternoon, cool weather with orographic showers, low snow levels for this time of year, and convergence zone effects looks likely for Thursday.

The active weather pattern continues in the Pacific Northwest.

Last week from Monday 4/17 to Thursday 4/20 Mt. Baker picked up about 3 inches of water equivalent (WE) while other areas along the west slopes picked up 1 - 1.5 inches of WE. Much or all of this fell as snow above 5000 feet in the north and 5500-6000 feet in the central and south Washington Cascades. Natural loose wet avalanches likely occurred throughout this period as the snow-line oscillated or on solar aspects at lower elevations during sunbreaks. 

It continued to snow on Sunday and Sunday night. Areas near and above treeline on the volcanoes had about 3-6 inches of new snow on Monday morning with the most at Mt Hood.

A weak surface low pressure system moved east along the Washington - Oregon border followed by an upper shortwave on Monday. NWAC stations at Mt Hood had 8-12 inches of new snow with little in the Olympics and Washington Cascades.

Recent observations

NWAC observer Lee Lazzara was out on Friday 4/21 in the Baker backcountry on Ptarmigan Ridge. Lee observed numerous loose wet slides on all aspects near and below treeline. A natural cornice fall along Ptarmigan Ridge ripped out a D2.5 wind slab on a north aspect (see photo below, thanks Lee!), and other natural cornice fall was noted as well. Note the massive cornices in the photo! 

Photo by Lee Lazzara, 4-21-17.

Laura Green checked in from the Mt. Hood Meadows pro-patrol Friday 4/21. During morning avalanche control work with explosives, stubborn wind slabs were not widespread, but propagating well on lee NE - ESE aspects between 6600 and 7800 feet. Crowns were up to 2 feet deep. Recent and natural wind slab avalanches had occurred in White River Canyon on similar aspects and elevations.

The Chinook Pass DOT crew reported widespread, sensitive size 1-2 loose wet avalanches on all slopes steeper than about 30 degrees by ski tests on Monday that were largest below 55500 feet.