Avalanche Forecast
Issued: Feb 1st, 2016 10:35AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly N-SE facing slopes. Watch for signs of cracking or firmer wind transported snow. Snow pits will still be worthwhile to determine if persistent weak layers from January 3rd and 11th are still present or reactive in your area.
Summary
Detailed Forecast
A day of light winds, some sun and cool temperatures should be seen along the east slopes on Tuesday.
This weather should bring a further gradually decreasing avalanche danger.
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly N-SE facing slopes. Watch for signs of cracking or firmer wind transported snow.
Also watch for lingering storm slab in areas that had rapidly accumulating snowfall.
Snow pits will still be worthwhile to determine if persistent weak layers from January 3rd and 11th are still present or reactive in your area.
The weather should stay cool tomorrow but expect sun along the east slopes. Loose wet avalanches also won't be listed as a problem but if solar effects or sun are significant watch for wet snow deeper than a few inches and pinwheels or small natural loose wet avalanches that usually precede larger loose wet avalanches on solar slopes.
New surface hoar will need to be watched if it gets buried by future snowfall.
?Continue to evaluate snow and terrain carefully on Tuesday.
Snowpack Discussion
Weather and Snowpack
Two fair weather periods earlier this month allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on Jan 3rd and 11th throughout the Cascades.
A warm front about January 21st caused up to about a foot of snow in the northeast zone. Freezing rain or rain created a crust in the central east and southeast zones.
Another wet warm front was seen last Wednesday-Thursday. This brought up to another 1.5 feet of snow in the northeast zone and probably created another crust in the central and southeast zones.
A strong occluded front with strong winds crossed the Northwest on Friday. NWAC stations along the east slopes had about 4-14 inches of new snow by Saturday morning. Cool weather and some sun has been seen along the east slopes Sunday and Monday.
Some areas have reported a strong bond of the new snow to the crust and some a poor bond depending on if the new snow arrived after cooling began. Sensitive storm layers have also been reported within the storm snow which will take a bit of time to gradually stabilize.
Recent Observations
The January 3rd and 11th layers were reactive with widespread triggering during the warm fronts. The latest observations indicate that these layers have gradually become unreactive and persistent slab will be removed from the east slopes as an avalanche problem. We will need to watch closely to continue to be sure these layers have been put to rest.
NWAC pro-observer Tom Curtis was at Blewett Pass on Saturday and found remnants of the January 3rd and 11th layers but they were not reactive.
The January 3rd and 11th layers were seen at 60 cm and 50 cm in a test pit reported via the NWAC Observations page for Saturday for the Clara Lake area. The January 11th layer gave no result and the January 3rd layer gave a hard test for propagation.
A report on Turn All Year for the Clara Lake area indicated that the January 3rd and 11th layers are no longer reactive there. Extensive new surface hoar was noted.
The North Cascades Mountain Guides were on Driveway Butte near Mazama on Sunday and also found the January 3rd layer there unreactive.
NWAC pro-observer Jeff Ward was in the Chumstick Mountain area today. The January 3rd and 11th layers were found at about 75-85 cm and 70-80 cm and gave hard or no results in tests. Jeff noted isolated, stubborn to release small wind slab near ridges and new widespread surface hoar.
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.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Valid until: Feb 2nd, 2016 10:35AM
