See the NWAC Spring Schedule 2018 for details on avalanche forecast products for the remainder of the season.
NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.
Throughout the Cascades, the mountain snowpack has transitioned to spring conditions on all but the highest slopes of the volcanoes. You may encounter dry, winter-like snow above 10,000ft. Below 4,000 feet many slopes hold little to no snow.
Expect typical spring conditions with lower avalanche danger early in the morning and elevated danger around the warmest time of the day. Plan to be off of slopes before they are wet and unsupportive. Start your day early and end early. Lower elevation slopes will warm quicker and more significantly than those at higher elevations. Avalanche activity will mostly be limited to loose wet avalanches on steep (40 degrees) slopes.
A slow and drawn out cycle of large wet slab avalanches occurred in the first half of May especially from Steven’s Pass north to the Canadian border on slopes above treeline. Since the last period of cool weather, starting May 16th, observers have reported few of these avalanches. Wet slab avalanches are difficult to predict. They are currently unlikely but not impossible. They could be triggered by rock, ice, or cornice fall and especially during the heat of the day.
Other hazards exist that are typical of spring mountain travel. Most cornices have been trimmed back by either melting or falling earlier in the month. It’s still a good idea to put plenty of distance between your group and any suspect cornices. Glide cracks have opened on many steep rock slabs and glaciated slopes. Crevasse bridges are melting and quickly changing route conditions on glaciated slopes. At low elevations creeks are open and flowing fast.
Observers in the North Cascades, Stevens, Snoqualmie, and the Mt Rainier areas over the past week reported limited new natural avalanche activity. Several small human-triggered loose wet avalanches were reported with daytime warming. The snowpack at lower elevations and on sunny slopes is quickly melting. On Wednesday May 23rd, Forecasters Josh Hirshberg and Dallas Glass were on Mt Rainier. They triggered a very small loose wet avalanches around 8,000 feet. They saw few other signs of avalanche hazard, but did observe fresh serac and rock fall. On May 20th an observer reported a wet slab near Vasiliki Ridge near Washington Pass that may have been triggered by rock fall.
An upper level low pressure system brought somewhat cooler and more showery weather over the area last weekend, however any precipitation received remained as rain. This past week was yet another week of mild temperatures and mostly sunny weather, dotted with some showers and thundershowers Wednesday afternoon. Freezing levels have persisted in the 9000-11000 foot range through the week.
The temperature profile the past two weeks continues to indicate very mild conditions throughout the NWAC network:
Weather Outlook: Friday-Monday
Very similar weather is expected to persist through the Memorial Day weekend over the Pacific Northwest mountains. A weak upper trough should pass the area Friday. No precipitation is expected from this weak feature, however there is a slight chance of a few afternoon showers Friday afternoon. The main affect will be to strengthen the onshore flow and thicken the marine layer clouds at lower elevations. This will mainly affect the lower elevations along the west slopes with morning clouds giving way to afternoon sunshine. Mid and higher elevations should remain mostly fair and mild.
Little change from this pattern is expected Saturday through Monday, with freezing levels slightly warming through the weekend. Expect mostly sunny days and clear nights through Monday. No precipitation is expected through Memorial Day.
Freezing levels should be in the 9000-11,000 ft range Friday and Saturday, rising to 10,000-12,000 ft Sunday and Monday.
USE AT YOUR OWN RISK
This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.
The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.