Avalanche Forecast
Regions: Cascades - North East.
Deep storm snow and recent, fresh wind slabs should maintain dangerous avalanche conditions, especially above treeline. Avoid steep slopes recently loaded with wind transported snow. Conservative decision-making remains essential.
Detailed Forecast
Deep storm snow and large wind slabs will require extra time to stabilize. This is a time to plan travel on lower angled terrain well away from avalanche paths or run out zones. Avoid large steep open slopes or terrain of consequence.
Light to moderate snow showers at cool temperatures are expected overnight and Monday. Winds should be moderate, but strong enough to easily transport loose surface snow, building some fresh wind slabs on lee exposed slopes.
Generally light accumulations of new snow are expected and with cold temperatures and light to moderate winds this should maintain the current level of avalanche danger. Cold temperatures may help maintain older wind slab layers near and above treeline.
Dangerous avalanche conditions should persist near and above treeline Monday. Cautious terrain selection and conservative decision-making remain essential.Â
Cornices won't be listed as an avalanche problem in this area, but avoid travel on ridges, where recent cornices may have formed and avoid steep slopes below cornices, that may fail at any time.
Snowpack Discussion
Weather and Snowpack
The most recent wet warm storm arrived on Valentines Day 2/14 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. As of Sunday, March 5th, the Valentives Day rain crust ranges from about 20 inches below the surface in the Harts Pass area and in the Washingrton Pass zone, about 2.5-3 feet and is more reactive in this area.
Strong southwest flow carried a strong front across the Northwest on Friday evening. Along the Cascade east slopes this caused strong southwest alpine winds and heavier moist or denser new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft.
A widespread natural avalanche cycle occurred during the storm late Friday with many avalanches up to size 3 observed.Â
Recent Observations
North
AÂ report from the NC Heli Guides indicates a cycle of natural and ski triggered wind slab avalanches during the wind event on Tuesday and Wednesday 2/28-3/1. About 50-80 cm of storm snow was found with a good bond to the Valentine's Day crust. About 20-30 cm of recent snow was covering about 10 cm of wind slab in some areas.
A party of four skiing at Washington Pass near the highway hairpin on the east side of the pass was hit by a natural cornice released avalanche on Tuesday afternoon. Four people were caught and carried up to 1000 ft downslope. Fortunately, there were no fatalities and no full burials but there were apparently some injuries. The release occurred on a very steep slope at the top of a northeast facing bowl at about 6600 ft.
Windy conditions prevented the North Cascades Heli Guides from flying on Wednesday.
Another recent and large cornice failure was observed by the NCH on Thursday in the Cutthroat drainage. Plenty of other unreleased large cornices were noted.
A NC Mountain Guides 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, 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 a weak interface above 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, in the Cedar Ck drainage, east of Washington Pass.
The many recent natural avalanches that occurred late Friday also appear to be mostly on this same interface just above the V-Day's crust.
There is ample weak surface snow available for transport and caution is urged with the expected increase in alpine winds over the next few days. Â
Central
Numerous avalanche involvements occurred Saturday, March 4th 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. It's possible this avalanche involved multiple burials but this information is likely to change as we investigate the accident. Check the NWAC observations page for more details  Â
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: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2