ZCZC SEASABSEA Å€TTAA00 KSEA 281603 WAZ011-012-ORZ006-291700- BACKCOUNTRY AVALANCHE FORECAST FOR THE WASHINGTON CASCADES, OLYMPICS AND MT HOOD AREA FOREST SERVICE NORTHWEST WEATHER AND AVALANCHE CENTER ISSUED THRU NATIONAL WEATHER SERVICE SEATTLE, WASHINGTON 0800 AM PST SATURDAY December 28, 1996 FOREST SERVICE BACKCOUNTRY AVALANCHE FORECAST FOR THE WASHINGTON CASCADES, OLYMPICS AND MT HOOD AREA FOR SATURDAY AND SUNDAY, DECEMBER 28 AND 29, FOR AVALANCHE TERRAIN BELOW 7000 FEET. THIS FORECAST DOES NOT APPLY TO DEVELOPED SKI AREAS OR HIGHWAYS. ******************************************************************** ZONE AVALANCHE FORECASTS..... OLYMPICS...WASHINGTON CASCADES NEAR AND WEST OF THE CASCADE CREST.... ....................AVALANCHE WARNING..................... High avalanche danger at all elevations slightly decreasing later Saturday morning and early afternoon, but increasing again late Saturday afternoon and night and becoming high at all elevations. Danger further increasing Sunday morning and early afternoon and becoming high to extreme. Danger slightly decreasing later Sunday afternoon and night but remaining high above 4 to 5000 feet and moderate to high below. EAST SLOPES WASHINGTON CASCADES......... ...................AVALANCHE WARNING.................. High avalanche danger above 4000 feet and moderate to high below slightly decreasing later Saturday morning and early afternoon but increasing again later Saturday afternoon and night and becoming high at all elevations. Danger further increasing Sunday morning and early afternoon and becoming high to extreme. Danger generally decreasing later Sunday afternoon and night but remaining high above 5000 feet and moderate to high below. MT HOOD AREA....... ................AVALANCHE WARNING...................... Moderate to high avalanche danger above 5000 feet and moderate below slightly decreasing late Saturday morning and early afternoon, but increasing again later Saturday afternoon and night and becoming high at all elevations. Danger further increasing Sunday morning and early afternoon and becoming high to extreme. Danger generally decreasing later Sunday afternoon and night but remaining high above 5 to 6000 feet and moderate to high below. Please Note: In all areas, back country travel in avalanche terrain is not recommended Saturday and should be avoided Sunday. SNOWPACK ANALYSIS ................. In the Olympics and most of the Washington Cascades except for the extreme south, increasing amounts of new relatively cold, low density snow have accumulated over a variety of weak snow layers over one of several smooth sliding surfaces. Although in areas not receiving wind transport this new snow is extremely light and cohesionless, most areas received strong west winds Friday and this produced increasing areas of large, brittle and unstable wind slabs, especially on northeast through southeast exposures. This new snow, now totaling over 20-30 inches in some areas since early Thursday, was deposited over either hardened wind slabs, refrozen rain or freezing rain crusts or older low density snow. In turn these sliding surfaces lie over significant amounts of lower density snow from earlier this week, with some buried surface hoar as well, especially in the north Cascades and along the Cascade east slopes. Field reports continue to indicate relatively sensitive 1-3 foot soft slab slides releasing from a variety of exposures, with natural, skiier triggered and explosive controlled slides propagating fractures easily, running long distances and entraining considerable amounts of new snow. On northeast through east exposures receiving recent wind transport, larger slide releases of 2 to 4 feet or more are possible, especially above 4 to 5000 feet where stronger winds occurred. In the extreme southern Washington Cascades and Mt Hood area, significant rainfall to 6000 feet Thursday was followed by lowering freezing levels, increasing snow and strong winds Thursday night and Friday. While this helped to slightly decrease the danger at lower elevations through either slide releases, snowpack settlement or refreezing of wet snow, increasing areas of brittle new wind slab have developed over the refreezing and increasingly hard rain crust, producing a moderate to high danger above about 5000 feet, with unstable slabs possible on steeper slopes at lower elevations. SATURDAY....SATURDAY NIGHT...... Light to moderate snow or snow showers should decrease later Saturday morning and early afternoon, along with slowly decreasing winds. This should allow for a slight decrease in the avalanche danger as recent wind slabs and buried weak layers begin to stabilize and settle. However, light to moderate snow, rain or freezing rain should spread northward and increase later Saturday afternoon and night along with rising freezing levels and increasing winds. This should load either existing wind slabs or loose weak surface snow with progressively denser and more unstable new wind slabs. Hence generally increasing danger is expected, with natural or human triggered slab slides increasingly likely overnight, with the greatest danger on west facing slopes near the passes and north to northeast facing slopes at higher elevations. SUNDAY....... Further rising freezing levels, very strong winds, and moderate to heavy rain, snow or freezing rain are expected Sunday morning and early afternoon. This should continue to load or weaken the existing relatively large amounts of recent snow, with extremely unstable and increasingly large wind slabs expected on most aspects and slope angles. Widespread natural or human triggered slides are certain, and large destructive avalanches are possible as slides releasing on weaknesses in the most recently deposited snow may trigger larger avalanches reaching buried weak layers from earlier this month. Back country travel in avalanche terrain should be avoided, and travel confined to relatively flat terrain well away from avalanche path runouts. Decreasing precipitation and gradually lowering freezing levels late Sunday should allow for the high to extreme danger to slowly decrease as loading rates slowly decrease along with some refreezing of wet weak surface snow. However, moderate to heavy showers are still expected and this should help maintain a high danger and mostly unstable snowpack above 4 to 5000 feet. At lower elevations, a moderate to high danger should exist with unstable slabs are probable on steeper terrain, especially from about Stevens Pass northward, where stabilization from the Sunday warming should have been more limited. ******************************************************************** Backcountry travellers should be aware that elevation and geographic distinctions are approximate and 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. ƒ NNNN