Avalanche Forecast
Issued: Mar 26th, 2016 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
A mix of likely dangerous winter and spring avalanche conditions is likely along the west slopes on Sunday. The sun is getting much stronger and new snow may be very reactive to solar effects. The greatest danger should be in the afternoon and to the end of the daylight hours.
Summary
Detailed Forecast
Southwest flow should carry an energetic front and shortwave to the Northwest Saturday evening and night. Moderate west flow should carry a 2nd short wave, an upper low and a cool unstable air mass to the Northwest Sunday. This should cause southwest to west winds, rain or snow changing to snow showers and lowering snow levels on Sunday. Snow and snow showers should cause up to 6-12 inches of snow by the end of the daylight hours on Sunday with the most on the volcanoes and in the central Cascades in likely convergence. There is a chance of thunderstorms in the forecast along the west slopes Sunday afternoon and evening.
A mix of likely dangerous winter and spring avalanche conditions is likely along the west slopes on Sunday. The sun is getting much stronger and new snow may be very reactive to solar effects. The greatest danger should be in the afternoon to the end of the daylight hours.
New wind slab of a foot or more is likely on lee slopes mainly in the near and above treeline on Sunday. This is most likely on north to east slopes but possible on other aspects. Watch cracking and firmer or chalky wind transported snow. Snow pits may not be helpful due to variability in the snowpack.
New storm slab layers will be likely in areas where there is rapidly accumulating snow for more than a few hours. Warming daytime temperatures may contribute to upside down layers and instability. Pay special attention to slope convexities where storm slab is mostly likely to be triggered.
Loose wet avalanches may be possible on steep solar slopes on Sunday. Don't overstay your welcome if you start seeing pinwheels or small initial natural loose wet avalanches. Be aware of terrain traps where even a small loose avalanche could have unintended consequences if you venture out on Sunday.
Cornices have grown large recently. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.
Although not listed as an avalanche problem, large powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.
Snowpack Discussion
Weather and Snowpack
Snow accumulations Wednesday to Friday following the last front varied based on elevation, with only a few inches below 4000 feet and 6-21 inches above. The most snow was received at the NWAC Baker and Paradise stations. The new snow since Monday is generally well-bonded to a moist crust buried March 22nd.
Frequent March storms have built large cornices along ridges in many areas.
The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
Snoqualmie Pass avalanche professionals reported loose wet avalanches triggered by light rain running far on Wednesday in paths below treeline. Glide avalanches releasing to the ground off of rock surfaces were also reported near the same Snoqualmie Pass paths Thursday morning.
NWAC pro-observer Dallas Glass was in Kendall Peak area of Snoqualmie Pass Thursday and found small but sensitive wind slabs near treeline. Dallas also found loose snow concerns transitioning to shallow storm slab problem by mid-day with settlement and daytime warming.
The Mt. Baker pro-patrol reported only scattered and small soft storm slabs in area Thursday morning. Stevens Pass pro-patrol reported strong west winds had redistributed the new snow, but that the new wind slab was stubborn and generally nonreactive to ski cuts.
On Friday, Baker pro-patrol reported natural slab activity above treeline on Mt. Shuskan but only small loose wet releases in area and a generally right side up upper snowpack. A professional guide observation from the Snoqualmie Pass area Friday morning indicated generally well layered and bonded storm snow with increasing potential for loose wet avalanches by late morning.
NWAC pro-observer Lee Lazzara was out near Mt Baker on Friday and generally found 50 cm of storm snow on a rain crust from 3/21. He saw numerous loose wet avalanches on various aspects and despite warm temperatures some ski triggered loose dry avalanches were still seen on steep north slopes.
Further south Dallas Glass was out again near Paradise on Friday and found 60 cm of settled, bonded storm snow. He witnessed large rollerballs to 3 feet in diameter - watch out for those! Several small natural and ski triggered loose wet avalanches were seen on east to south facing slopes. There was significant wind redistribution of snow in the above and near treeline wind possible wind slab to 15 inches deep on north to southeast slopes.
Problems
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: Alpine, Treeline.
Likelihood
Expected Size
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.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 27th, 2016 11:00AM
