Avalanche Forecast
Regions: Cascades - East.
There has been a lot of snow the past few days and you may not be able to use the backcountry in your usual manner. Your usual slopes and routes may not be safe from avalanches. Plan to stay on low angle slopes away from avalanche terrain. Careful snowpack evaluation and cautious routefinding will be essential on Wednesday.
Detailed Forecast
Strong southwest flow carried a front across the Northwest on Tuesday. This should bring another 5-10 in of snow to most of the Cascade east slopes by Wednesday morning with SW-W alpine winds and warming temperatures. Warming temperatures favor denser surface layers and the formation of wind and storm slab avalanches.
There has been a lot of snow the past few days and along the Cascade east slopes you may not be able to use the backcountry in your usual manner. Your usual slopes and routes may not be safe from avalanches. Plan to stay on low angle slopes away from avalanche terrain. There is more uncertainty than usual due to lack of backcountry field reports and the new snowfall. Avalanches may be larger and run farther than usual.
Wind slab should be watched for on all aspects but should be found mainly on NW to SE aspects due to recent SW to W winds. Watch for firmer wind transported snow on varied aspects especially in areas of complex terrain.
Most areas will have seen rapidly accumulating snowfall by Wednesday. Previous storm slab may not have stabilized. The warming trend will increase the likelihood of new storm slab layers.
The persistent slab problem has returned to the Northeast zone forecast due to recent avalanches and some reactive tests on the Valentine's Day crust in this area. We may have had enough snow for avalanches to step to or run on the Valentine's Day crust in other areas. Such avalanches would be large and very dangerous.
Cornices won't be listed as an avalanche problem but avoid travel on ridges near where cornices may have formed and avoid steep slopes below cornices that may fail at any time.
Snowpack Discussion
Weather and Snowpack
The most recent warm, wet storm arrived on Valentines Day and formed the uppermost strong rain crust in our snowpack in the Central East and Southeast Cascades while a thinner but prominent rain crust exists throughout the Washington Pass and Harts Pass areas.
Strong southwest flow carried a strong front across the Northwest on Friday evening. Along the Cascade east slopes this caused strong southwest alpine winds, heavy, moist, dense new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft.
Most NWAC stations and NRCS stations along the Cascade east slopes have had about 4-18 in snow in the past 5Â days.
A region wide avalanche cycle was seen late Friday and Saturday, with some more avalanches on Sunday.
Recent Observations
North
A NCMGÂ report for Friday for the Delancey area indicates heavy snow in the near and below treeline and 35-60 cm of storm snow on the Valentine's Day crust. Moderate planar shears were found in recent storm snow layers. New storm slabs were forming and ski tests were producing storm slab and loose dry releases. Whumpfing and cracking was seen above 6600 ft.
There was a skier triggered storm slab avalanche involvement Saturday in the Cedar Creek drainage resulting in a full burial and beacon recovery. The full details are not known at this time, but the party member is expected to be fine, another fortunate outcome. Investigations on scene Sunday indicate that this slide released on the Valentine's crust buried nearly 3 feet in this area. The avalanche was triggered well below ridgeline, at about 6600 feet on a north aspect.
NWAC observer Jeff Ward was in the Willow and Cedar drainages on Sunday and found reactive tests on the Valentine's Day at 85 cm. Whoomping was experienced while traveling on an up track. Numerous avalanches up to size 3 were noted on all aspects near and above treeline from Friday night. He also reported that the Valentine's Day crust was found 50 cm down at Hart's Pass.
Jeff was out again on Monday in the Cutthroat drainage and found a generally right side up snowpack with no significant results from ski tests. The thinner crust from 2/17 was spotty and generally not an issue. The Valentine's Day crust here at 125 cm was not reactive so note the varying results on this layer in different areas.
The NCHG were out on Tuesday in the Silver Star drainage and reported that on a NE slope at 7000 feet ski tests only gave small loose dry avalanches. On a north slope at 6300 feet the Valentine's Day layer was not found so there is spatial variability in the presence of this layer.
Central
There were numerous avalanche involvements Saturday 3/4 in this zone. We do not have adequate information at this time, other than to say, there was a fatality to a snowmobiler in the Gallagher Head Lake area, north of the Salmon La Sac area where 2 snowmobilers were buried by an avalanche. This avalanche may have released on the Valentine's Day crust. This information may change as we investigate the accident. Check the NWAC Observations page for more details.
South
No recent observations.Â
Avalanche Problems
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 1