ZCZC SEASABSEA Å€TTAA00 KSEA 231812 WAZ011-012-ORZ006-241700- 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 9 am pst MONDAY DECEMBER 23, 1996 FOREST SERVICE BACKCOUNTRY AVALANCHE FORECAST FOR THE WASHINGTON CASCADES, OLYMPICS AND MT HOOD AREA FOR MONDAY AND TUESDAY DECEMBER 23 AND 24 FOR AVALANCHE TERRAIN BELOW 7000 FEET. THIS FORECAST DOES NOT APPLY TO DEVELOPED SKI AREAS OR HIGHWAYS. ******************************************************************** ZONE AVALANCHE FORECASTS..... WASHINGTON CASCADES NEAR AND WEST OF THE CREST... OLYMPICS....... MT HOOD AREA........ ........AVALANCHE WARNING................. High avalanche danger above 4000 feet and moderate to high below Monday, gradually increasing later Monday and Monday night. Avalanche danger continuing to increase early Tuesday becoming high below 7000 feet. Significantly increasing danger late Tuesday in the south and Tuesday night in the north becoming high to extreme, with natural avalanches imminent and some possibly large destructive slides possible. CASCADE EAST SLOPES... Moderate to high avalanche danger above 5000 feet Monday through early Tuesday. Avalanche danger significantly increasing during the day Tuesday becoming high below 7000 feet through Tuesday night, with natural avalanches becoming increasingly likely later Tuesday and Tuesday night. SNOWPACK ANALYSIS.......... Moderate new snow amounts were received in most areas with 24 hour new snow amounts between 6 to 10 inches near or west of the Cascade crest and 2 to 4 inches over the east slopes. This continued the moderate to heavy snow that has fallen over the past four days where between 20 to 35 inches have accumulated over the west slopes and 10 to 20 inches over the east slopes. All the recent snow overlies a strong crust formed during the warm period early last week. And in many areas the snow is weakly bonded to the crust, especially in the central Washington Cascades, near and west of the crest. The weak layers at the crust include surface hoar or needles or graupel snow which fell late Thursday. Within the recent snow other weak layers of low density snow, graupel or needles exist. Some periods of strong winds during snowfall have also created some sensitive and highly unstable wind slabs, with many skier triggered 1 to 2 foot slides being reported, releasing down to the crust formed early this week. However, weaknesses in the underlying new snow are inconsistent in many areas, with field reports indicating that snowpack stability varies over short distances. Backcountry travellers should use extreme caution and it is advised that travel should be confined to relatively shallow angled slopes away from open slopes, gullies or chutes. Slightly less danger exists over the east slopes where less recent snow has been received, however, in areas receiving wind deposited snow, triggered avalanches remain likely on steep open slopes, mainly north through east facing at higher elevations. MONDAY... Periods of moderate snow showers and strong ridgetop winds should continue to build unstable wind slab over a variety of weak layers within the recent snow. This should maintain mostly unstable wind slab with some natural or triggered slab avalanches likely, especially at higher elevations receiving wind deposited snow. Some slides may reach the crust formed early this week, now buried 2 to 4 feet in most west slope areas and up to 2 feet along the east slopes. Slightly warmer temperatures along with continued snowfall later Monday should produce more cohesive and unstable slabs above the lower density snow which accumulated earlier. This should also lead to a greater avalanche danger. TUESDAY.......... Heavy snow and very strong winds at rising freezing levels should lead to a significantly increasing avalanche danger, especially late Tuesday as snow changes to rain at lower elevations and spreads northward, eventually reaching higher elevations, mainly in the south. The dense heavy snow or rain later Tuesday should cause widespread natural avalanches with some potentially large and destructive slides possible, especially from the central Washington Cascade west slopes southward, where rain is most likely. Slides may reach 4 to 6 feet in some areas and backcountry travel in avalanche terrain should be avoided. ******************************************************************** 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