Avalanche Forecast
Issued: Jan 16th, 2015 10:12AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Wet Slabs.
NWAC,
Northwest Avalanche Center
Warming and rain affecting any recent storm and wind slab, mainly on lee aspects, especially if overlying a surface hoar layer present in many areas. Watch for unstable slab layers and avoid steep lee slopes that may have received wind transported recent snow, especially steep NW thru NE facing slopes.
Summary
Detailed Forecast
A strong warm front should spread increasing precipitation to the Cascades, spreading from south to north early Saturday with strong winds and substantial warming and freezing levels climbing above 8,000 feet. Freezing levels should remain near the surface in the valleys much of Saturday, causing possible freezing rain.
The rain or heavy wet snow should cause an increasing danger, mainly near and above treeline, in those areas where deeper recent storm snow exists. Where slabs have formed warming and or rain should make wet slab releases possible, while the problem at lower elevations should be confined to loose-wet avalanches.
It should be a good day to let the warming and any rain have its way and wait for the cooling and new snow to follow.
On backcountry travel safety note, watch for terrain hazards (exposed rocks, trees, streams, etc.) at lower elevations and on wind scoured aspects.
Snowpack Discussion
A fast moving front late Thursday, followed by showers Friday has deposited about 4-8 inches of storm snow as of late Friday afternoon.
The latest high pressure was marked by warm temperatures and sunshine in most alpine zones with cooler and sometimes foggy conditions in the valleys and to near treeline along the east slopes. NWAC pro-observer Tom C. Northwest of Blewett Pass Thursday, found widespread surface hoar up to 5mm on most aspects and elevations up to 5400 ft. The non-reactive persistent facet layer found on Jove Peak on Wednesday was also found at 85 cm Thursday, but it also was unreactive to snowpit tests. The stronger crust layers above should be solid enough to support a fairly significant new snow load, so it is unlikely to be a layer involved in future slides, at least in the near term.
Watch and test for the potential of the buried surface hoar layer, where it may have been buried intact by the initial snowfall late Thursday.
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
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 17th, 2015 10:12AM
