Avalanche Forecast
Regions: Cascades - South East.
Yet another storm will impact the Cascades on Thursday with increasing rain and snow, wind and rising snow levels beginning in the afternoon and continuing Thursday night. Travel in avalanche terrain is not recommended on Thursday due to the increasing hazard in the afternoon.
Detailed Forecast
A weak low pressure system should produce up to 6 inches of snow for the east slopes of the Cascades Wednesday afternoon and night. Â
However the main event will be the storm system forecast Thursday afternoon through Friday morning. Â A low pressure system tracking north across Washington State will bring increasing precipitation first for the southeast and central-east Cascades Thursday afternoon and then to the northeast Cascades Thursday night. This will be accompanied by a warming trend most pronounced in the southeast and central-east Cascades and a shot of strong W-SW winds Thursday evening through Friday morning.
Less precipitation, warming, and wind is forecast for the northeast Cascades through the daylight hours than for areas further south hence the slightly lower avalanche danger.Â
All of these weather factors will stress the upper snowpack still struggling to settle and stabilize. The warming trend and increasing snowfall will increase the likelihood of new storm slab layers.
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.
The persistent slab problem has returned to the Northeast zone forecast due to recent avalanches and some reactive tests on the Valentine's Day or 2/17 crust. Avalanches down to these depths 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 freezing rain crust exists throughout the Washington Pass and Harts Pass areas.
Strong southwest flow carried a strong front across the Northwest on Friday evening March 3rd. 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. A region wide avalanche cycle was seen late Friday 3/3 and Saturday 3/4.
NWAC and NRCS Snotel stations reported 6-12 inches of snow from the weather system Tuesday and Tuesday night.Â
Recent Observations
North
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 3/5Â 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 3/6 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 was down 125 cm in this location and not reactive.
The NCH were out on Tuesday 3/7 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 crust was not found.
On Wednesday, the NCMG on Delancey Ridge observed crowns from recent natural storm slabs about 20-30 cm deep on S-SW aspects near and above 5500 feet. In a test pit on a SE aspect at about 5400 feet, the 2/17 melt freeze crust gave hard but sudden planar results in compression tests failing on facets above the crust.Â
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 of 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: Likely
Expected Size: 1 - 1