All the snow coupled with this--Backcountry Avalanche Forecast
WA Cascades near and west of crest - north of Stevens Pass
Northwest Weather and Avalanche Center Seattle Washington
1339 PM PST Mon Nov 21 2011
This forecast applies to back country avalanche terrain below 7000 feet and does not apply to developed ski areas or highways.
...CORRECTED ZONE
Forecast
...AVALANCHE WARNING MONDAY AFTERNOON THROUGH TUESDAY NIGHT...
Monday and Monday night: High avalanche danger above 4000 feet and considerable below and increasing. Greatest danger expected on north through east facing terrain. Significantly increasing avalanche danger Monday night becoming high below 7000 feet. Very dangerous avalanche conditions developing Monday night with natural avalanches likely.
Tuesday and Tuesday night: Avalanche danger becoming extreme above 5000 feet and high below. Natural avalanches are certain with large to very large avalanches in many areas. Avoid all avalanche terrain.
Snowpack Analysis
Recent weather: A series of storms from November 11-15 deposited 1-3 ft. of low density snow. A strong storm with warming last Wednesday caused widespread avalanches and allowed a crust to form in many areas. Colder storms since Wednesday have deposited an additional 1-2 feet of weak low density snow. Some clearing and lighter winds allowed surface hoar to form in many areas as of Sunday morning. The most recent storm Monday morning has come with warming and very strong winds.
Snowpack concerns: The current snowpack structure consists of a variety of potentially significant layers. Prior to the latest frontal passage, there were many reports of fantastic low density surface snow conditions over firmer old slabs or a crust layer along with reports of widespread surface hoar. Both the low density surface snow and/or existing surface hoar have now likely been buried by denser surface layers. These denser and potentially unstable layers now cover a variety of weak snow structures.
The main present avalanche concern has now shifted to newly formed slab layers over weaker snow, surface hoar, old slab layers and possibly a weak rain crust/facet combination formed last Wednesday in many areas below mainly 6000 ft.
This snowpack structure is primed for some rather large and very dangerous avalanches when loaded with additional snow and rain expected beginning tonight and lasting into Tuesday.
Detailed Forecasts
Monday
Continued strong winds and additional light to moderate snowfall is expected Monday afternoon at further slowly rising freezing levels. This weather should further build unstable layers on all aspects, but especially lee slopes, mainly north through northeast facing terrain at higher elevations. Very strong winds and heavy precipitation late Monday and Monday night should cause very dangerous avalanche conditions to develop as deeper unstable layers form over weaker snow or a variety of buried weak layers. Travel in avalanche terrain should be avoided by Monday night.
Tuesday
Very strong winds further warming and very heavy precipitation is expected with snow changing to rain in many areas. This should cause widespread and potentially large and very dangerous avalanche releases on many slopes, especially above 5000 feet where a deeper early season snowpack exists. Avoid all avalanche terrain above 5000 feet Tuesday and Tuesday night.
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Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone between dangers exists. Remember there are avalanche safe areas in the mountains during all levels of avalanche danger. Contact local authorities in your area of interest for further information.
NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at
www.nwac.us.
Kramer/Northwest Weather and Avalanche Center Seattle Washington
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Danger Scale Legend
= Extreme avalanche danger
= High avalanche danger
= Considerable avalanche danger
= Moderate avalanche danger
= Low avalanche danger
Warning = Extreme or high avalanche danger occurring or expected to occur within 12 hours: at or below 4000 feet in the Olympics and/or WA Cascades; at or below 5000 feet in the Mt. Hood Area.
Watch = Warning conditions expected within 12-48 hours.
Special Conditions = Unusual conditions meriting special attention that do not meet Watch or Warning criteria.
Click here for complete definitions of the avalanche danger scale.
BE SAFE OUT THERE
