Avalanche Forecast

A temporary break in the active weather pattern should be seen during the daylight hours on Tuesday. While it won't be particularly warm, sun or solar effects should be seen especially in the south Cascades and east of the crest.

New snow can be particularly sensitive after spring storms due to sun or solar effects and warm daytime temperatures! And there has been a lot of new snow 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 should rapidly active avalanche problems and result in a dramatic increase in avalanche danger.

Deep storm slab may linger in areas that had rapidly accumulating new snow on Monday.

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 Tuesday.

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.

Heads up because another strong system will move across the Northwest Tuesday night and Wednesday. This should mean a greatly increased avalanche danger in most areas of the Olympics, Washington Cascades and Mt Hood on Wednesday. Another special avalanche statement is likely for Wednesday.

The active weather pattern continues in late April 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. 

Friday was a warm day with most NWAC stations in the Olympics and Cascades reaching into the 40s and 50s. Breezy E-SE winds were seen in the Passes and in the southwest Cascades including Mt. Rainier and Crystal. This will have formed surface crusts on many slopes.

A renewed active weather pattern Saturday brought periods of light rain and snow showers through the day, with a slow cooling trend. These were mainly rain showers below about 5500 feet.   

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

A weak surface low pressure system is moving east along the Washington - Oregon border on Monday. An upper shortwave trough will follow and move to the east over the Northwest on Monday afternoon. Further new denser spring snow is expected above about 5000 feet on Monday on the volcanoes south of Mt Rainier and especially at Mt Hood.

Recent observations

The Chinook Pass DOT crew on Thursday reported loose wet avalanches becoming increasingly sensitive during sunbreaks below 5000 feet with ski cuts and explosives, with larger slides gouging down to older wet snow. A 12-16 inch wind slab was triggered below the ridge crest with explosives.

NWAC observer Lee Lazzara was out on Friday in the Baker backcountry on Ptarmigan Ridge. Lee observed numerous loose wet slides on all aspects near and below treeline. Anatural 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. 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.