March 19, 2003 SOUTH COAST REGION WEATHER: New snow since Monday totalled only 8cm. Daytime highs have reached -1 at treeline while the alpine remains seasonably cool. The minimum temperature at Cayoosh Pass was ^Ö6 deg C overnight. The weather forecast calls for 20 cm of new snow Wednesday night, with a brief clearing followed by some more light snow on Friday. Temperatures will begin to cool off slightly during the later part of the week. SNOWPACK: Wet surface layers have formed a melt-freeze crust below treeline and above 1000m elev. Although many slide paths cleaned themselves out last Thursday, pockets of thick windslab remain. The interface below is a weak layer of small surface hoar at some sites and facets at all sites. Old shears within the slab have strengthened but storm snow instabilities will likely develop by Thursday. Shallow snowpack sites can be expected to be weaker. Cornices have grown quickly and are very fragile. AVALANCHES: Explosive control triggered slabs and cornice failures to size 2.0 in previously unreleased rocky terrain Monday mid day. Naturally triggered activity has slowed. FORECAST OF AVALANCHE DANGER UP TO Friday EVENING (Mar 21st) ALPINE ^Ö Considerable TREELINE ^Ö Considerable BELOW TREELINE ^Ö Moderate TRAVEL ADVISORY: The new snow has improved the skiing but masks the clues. Small slabs failing in the new snow have the potential to trigger deeper instabilities. The sun is in full spring intensity. Cornices pose a threat to terrain below. Sunny aspects will weaken during the afternoons. NORTH COLUMBIA REGION WEATHER: Convective snow showers continue to add light snow amounts from this unstable air mass. Temperatures in the alpine have remained cool while below treeline is now getting a good freeze at night. Moderate SW winds have moved the new snow around. The cool showery pattern will persist through Friday with more organized snow during a weakening cold front Thursday. SNOWPACK: A crust has formed at mid and lower elevations due to overnight cooling of the moist surface layers. A variety of easy shears exist in storm snow layers, especially under wind slabs near ridgelines. The mid February surface hoar persists as a weak layer under a 90cm hard slab and fails easily in snowpack tests. Cornices have grown rapidly to a delicate balance. Wind slabs have been less reactive at treeline and alpine but with such variability not much trust exists in steep terrain. AVALANCHES: Avalanche activity has dropped dramatically since the chaos of last week. No natural releases were reported. FORECAST OF AVALANCHE DANGER UP TO Friday EVENING (Mar 21st) ALPINE ^Ö Considerable with areas of High TREELINE ^ÖConsiderable with areas of High BELOW TREELINE ^Ö Moderate TRAVEL ADVISORY: Numerous shears compound the danger as a storm snow avalanche can still easily step down into deeper instabilities. Deep slab potential remains a sleeping giant waiting for a trigger in big alpine terrain. Watch for the crust breaking down in warmer afternoon temperatures at lower elevations. Remember most accidents happen during times of Considerable Danger following a big storm. SOUTH COLUMBIA REGION WEATHER: Little change has occurred as the cool unstable air mass drops light amounts of new snow over the region. Temperatures remain cool in the alpine with moderate SW winds. Afternoons warm to near freezing at treeline. The cool showery pattern will persist as a weakening cold front moves through. Little change is expected through Friday. Freezing levels should fluctuate daily between 1300 and 1600m SNOWPACK: A surface crust formed overnight in the moist layers as temperatures fell around treeline. Moist snow is found down 20-60cm from valley bottom to 2000m elevation. A hard slab up to 150 cm thick sits on the old mid February surface hoar and facet layer. These weaknesses will persist, especially at shallow snowpack sites in the Purcells. Cornices have grown quickly and will remain fragile. AVALANCHES: The rate of activity has slowed but large triggers were still releasing slabs over 100 cm thick on buried surface hoar. Solar triggered size 2.0 slabs were observed Tuesday afternoon. A naturally triggered size 4.0 ran full path to the valley in the Monashees on Monday. FORECAST OF AVALANCHE DANGER UP TO Friday EVENING (Mar 21st) ALPINE ^Ö Considerable, areas of High TREELINE ^Ö Considerable, areas of High BELOW TREELINE ^ÖConsiderable TRAVEL ADVISORY: Keep the goals conservative while you step out into the backcountry again. Deep slab potential remains waiting for the right trigger in the alpine. Confidence in this recently loaded snowpack is low due to high variability. KOOTENAY BOUNDARY REGION WEATHER: The snow showers have added 15cm to the snowpack. Moderate winds have accompanied the new snow. Temperatures have remained cool in the alpine while treeline and below warms daily to near or above freezing. The cool unstable airmass will persist through Friday with a weakening cold front enhancing the flurries Thursday morning. Freezing levels will be around 1800-2000m and a bit lower at night. SNOWPACK: Cooler temperatures and settlement have strengthened the shears in the storm snow. A crust has formed in the old moist snow surface. The snowpack is still showing signs instability at the old weak layers of surface hoar and facets that formed mid February. The hard slab over this weakness is 70-100cm thick. The surface layers will warm and weaken the crust on sunny aspects as the day warms. Cornices are large and easily triggered. AVALANCHES: Sluffs were triggered by warming on solar aspects during the afternoons. Slab avalanches to size 2.0 were observed just north of the area from large triggers. FORECAST OF AVALANCHE DANGER UP TO Friday EVENING (Mar 21st) ALPINE - Considerable TREELINE - Considerable BELOW TREELINE ^ÖModerate, Considerable in the afternoon. TRAVEL ADVISORY: While the storm snow is stronger now, the weak surface hoar buried below is not. Numerous shears in the upper snowpack reduce confidence as their failure could trigger deep weaknesses. Give cornices a wide berth. SOUTH ROCKIES REGION WEATHER: Days remain warm but temperatures were dipping below freezing overnight by mid week. Snow flurries have added some new snow load. Little change in the weather is forecast. Snow flurries should continue through Friday with mild temperatures as freezing level hovers at 1800m, lowering at night. SNOWPACK: A crust has formed at the surface from overnight cooling, but this slowly deteriorates on south aspects in the afternoon sun. At alpine sites, hard slabs over weak early season facet and surface hoar layers remain a real danger, especially near the Continental Divide. Cornices have grown large in the past week. AVALANCHES: Sunny aspects are releasing loose sluffs to size 1.0 in the afternoons. Cornices are very easily triggered. One cornice triggered size 2.5 stepped down to the November crust near Fernie Tuesday. A large explosive charge near Pincher Creek released a size 3.0 in previously skied terrain Sunday. FORECAST OF AVALANCHE DANGER UP TO Friday EVENING (Mar 21st) ALPINE ^Ö Considerable, High in the afternoon TREELINE ^Ö Considerable, High in the afternoon BELOW TREELINE ^ÖConsiderable TRAVEL ADVISORY: Ensure cornice fall or avalanches running full path do not threaten your route. The isothermal snowpack below treeline will make travel miserable where a crust has not formed. Don^Òt be caught out by a crust that is strong in the morning turning to mush in the afternoon, making travel much slower on your return.