Avalanche Forecast
Issued: Mar 14th, 2015 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
It's a tricky forecast but in general expect increasing avalanche danger with elevation. A mix of storm and loose wet avalanche problems are likely Sunday.
Summary
Detailed Forecast
Sunday should be another stormy day as a low pressure system lifts precipitation north across the Cascades with snow levels in the morning starting lower than they have been in a long time and then slowly rising through the day.
The avalanche danger will be directly tied to the snow level, with increasing storm related avalanche danger with elevation. An afternoon increase in temperatures should also make loose wet avalanches involving morning snowfall possible. An easterly component should help enhance precipitation along the east slopes Sunday. W through E aspects (clockwise) should become loaded near and above treeline.
It's a tricky forecast but in general expect increasing avalanche danger with elevation and remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). Significant new snowfall was received near and above these elevations on Saturday near the Cascade crest.
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The latest installment of warm and dry weather occurred from early March through midweek leading to more snowpack consolidation and a scarcity of avalanche activity. The North Cascade Mountain Guides were in the Harts Pass and Washington Pass area last weekend. They reported some cool varied surface snow on north slopes, corn snow on south slopes, and no stability concerns. The snow study plot on a north aspect at 6600 feet above Varden Creek measured a snow depth of nearly two and a half meters.
NWAC observer Jeff Ward was in the Hart's Pass area of the northeast Cascades Friday and reported isolated and very small wind slab not bonding well to the underlying crust above 6500 ft.
On Saturday, the most significant weather system this month brought new precipitation with snow level mainly between 6000-7000 feet. 24 hr water accumulations at NWAC stations east of the crest were up to 1.0 inches ending 4 pm Saturday, with much lower totals in the Blewett-Mission Ridge area. The Hart's Pass snotel picked up a few inches of new snow before temperatures settled in the mid 30s during the afternoon.
There have not been any reports of significant avalanches in the Cascades for many days. There was nearly no snowfall January to so far in March near and below treeline. The snowpack at low elevations remains meager to non-existent.
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: All elevations.
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.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Mar 15th, 2015 11:00AM
