---------- Forwarded message ---------- Date: Thu, 25 Feb 1999 19:36:28 -0800 From: Evan Manners Reply-To: bulletin@listserv.islandnet.com February 25, 1999 AVALANCHE BULLETIN SOUTH COAST REGION WEATHER: The Pacific weather machine. A deep depression centered in the Gulf of Alaska continues to spin off a repeated series of major frontal systems one after another. The most resent southwesterly system has been driven by the jet stream in an arc from the California coast up into southern BC and across into Alberta. Warm temperatures associated with the SW flow and strong winds affected most areas of southern BC last night, while moderate locally heavy rain, and snow at higher elevations occurred in many areas. Further strong systems are expected over the next period. SNOWPACK: Storm snow instabilities continue to be the major concern, with initially poor bonding of newer snow layers to one another, as well as to the older surface. Whistler areas report up to 40cm of new snowfall in higher areas in the last 24 hrs. Warming temperatures and strong winds have contributed to major wind-slab development throughout all areas at treeline and above. Easy shears are being observed in the new snow interfaces. Freezing levels have risen to approximately 1000m, but some cooling is forecast to occur behind the passage of this latest front. Rain at lower elevations is rapidly warming up the snowpack. AVALANCHES: Widespread natural activity. Reports of several human triggered releases up to size 2.0, 20-60cm deep fractures, in the Whistler-Blackcomb areas. Duffy Lake road and east side of Coast Range reports of size 3.0's, one fracture-line 3meters deep. Coquilhalla area wet naturals to size 2.0. DANGER: Above Treeline: HIGH (decreasing with less precipitation and forecast cooling) Below Treeline: CONSIDERABLE (HIGH below the freezing level) TRAVEL ADVISORY: It's obviously a very unstable period. Travel in avalanche terrain should be avoided. Reports from avalanche control operations are that slabs are running easy and fast in the higher elevations. At lower elevations, caution concerning the higher freezing levels, especially in rain soaked snowpack areas should be closely considered. NORTH COLUMBIA REGION WEATHER: This region is experiencing similar conditions to the coast. The resent SW flow is bringing precipitation, strong winds and warmer temperatures further northward. Breaks between systems may occur, but will be followed by continuing westerly frontal systems over the next several days. Moderate snowfall is forecast for this region through Thursday, lighter Friday. A partial sunny break Saturday will be followed shortly by the next system. SNOWPACK: Reports Wednesday of up to 65cm of storm snow in many areas. Continued snowfall last night, and rain at lower elevations has added considerable load to previous new snow layer instabilities. Shears down on the old snow interface, especially on previously sun crusted aspects is showing slow bonding. Wind action at higher elevations has built deeper wind-slabs in lee areas. Stellar and surface hoar weaknesses are showing up at various levels in the storm snow accumulations. There is a wide distribution in snowfall amounts across the region. Warmer temps at lower elevations are causing increased weakening of the upper snowpack. AVALANCHES: Widespread activity. Size 1.0-3.0 natural, explosive and human triggered activity, both above and below treeline. Rogers Pass A-C operations report 24 naturals adjacent to highway. DANGER: Above Treeline: HIGH (decreasing with less precipitation and forecast cooling) Below Treeline: CONSIDERABLE (HIGH below the freezing level) TRAVEL ADVISORY: This is a period for very cautious route selection. The higher freezing levels can significantly affect stability at lower elevations even in denser forest. SOUTH COLUMBIA REGION WEATHER: The old subtropical SW'ly rides again. The jet stream veered northward once again bringing a stream of moist air and strong winds too much of the region. Southern and eastern areas of BC appear hardest hit by the resent warm frontal system. The freezing level in the Southern Kootenay area early this AM was at around 1500m, compared to 1000m at Whistler. Rain through much of the night and moderate snowfall above the freezing level has added considerable loading to the snowpack. Forecast precip for the region is for light through today and tomorrow, winds remaining SW and W, with the freezing level forecast to fall to 1100m this afternoon. SNOWPACK: Storm snow accumulations over the last 4-5 days range from 40-100cm. Some locations in the West Kootenays, especially around the Nakusp and Meadow Creek areas, are reporting easy and reactive shears on the surface hoar buried around February 16th , now buried up to 1 meter down in places. Several new snow instabilities exist above this interface, and many releases are occurring initially in the new snow layers. Rapid warming of the snowpack has also occurred. AVALANCHES: Widespread in many areas. Many natural and human triggered releases, size 0.5-2.5, occurring in the new snow down to 70cm. Remote human triggering of some of these from a distance. Poor visibility in many areas has impeded observation above treeline. Loose wet releases occurring at lower elevations. DANGER: Above Treeline: HIGH (decreasing with less precipitation, and forecast cooling) Below Treeline: HIGH (decreasing with cooler temperatures and lower freezing levels) TRAVEL ADVISORY: Good time to stay well away from most moderate and steeper terrain. The snow stability may improve quickly after the warmer snowpack temps which promote crystal bonding processes, are followed afterwards by cooler temperatures. But it will take time for the cooling to take place. Backcountry travelers must monitor temperatures closely during these transitional periods. ROCKIES REGIONS WEATHER: The current series of Pacific systems crossing BC will continue to move through to Alberta. Southern Rockies regions will experience the warmest temperatures from the SW flow, but generally warm temps will affect all the Rockies region. Strong winds continue to accompany these aggressive Pacific systems. Precipitation amounts will lighten up towards the weekend, but a new system is expected through by Sunday again. Freezing levels are expected to drop today and tomorrow. SNOWPACK: In the Rockies for a rare change this season, most instability concerns remain in the new and storm snow layers. Wind-slabs in higher areas continue to be developed in lee deposition zones, and shear failures are often on the old smoother wind-slab surfaces. Bonding has been slow often in gaining strength on these old surfaces. In the Central Rockies, Lake Louise to Jasper, new snowfall amounts are 15-30cm. In the south around Fernie storm snow accumulations are 40-60cm with active shears in the new snow interfaces. Snow profile tests show easy shears within the new snow layers and some moderate to hard shears down lower in the older snowpack in areas. AVALANCHES: Many wind-slab occurrences size 1-2.0, natural, human and explosive triggered. Most activity noted on east and north aspects. Kananaskis area reported a natural size 2.0 cornice release at 2600m on a north aspect, which produced a 40cm deep fracture, and ran far. DANGER: Above Treeline: CONSIDERABLE (HIGH in southern areas, decreasing if cooler) Below Treeline: MODERATE (Higher in the south where freezing levels are high) TRAVEL ADVISORY: Backcountry travelers must keep observant. Wind-loading and new slab development is the most serious current hazard. Warmer temperatures are also a significant change. -------------------------------------------------------------------- The message above was sent via the bulletin@listserv.islandnet.com list. Send an e-mail with the subject "help" to bulletin-request@listserv.islandnet.com for more information. --------------------------------------------------------------------