April 16, 2003 SOUTH COAST REGION WEATHER: Unsettled spring weather continues to cause mostly cloudy conditions with flurries at higher elevations and rain showers below treeline. Snowfall amounts of up to 50cm have been reported in alpine areas over the past week. Winds have been light to moderate from the southwest and freezing levels have been near treeline elevations. Friday may see a bit more sun but then the cloud returns Saturday. SNOWPACK: The new snow and winds continue to form areas of windslab on upper elevation lee slopes. Usually these slabs warm and begin to bond with 24 hours of forming, just in time for the wind to slab up the next snowfall. High freezing levels and solar radiation cause wet snow on all slopes to mountaintop except for north aspects, which remain dry above 2000m. Whether the wet snow surface recovers overnight and forms crusts depends on weather conditions ^Ö the temperature of the airmass and the amount of cloud cover. AVALANCHES: Numerous loose wet snow avalanches on south and west aspects, generally size 1 to 2 with one size 3 reported. On Tuesday a skier on a steep NW aspect at 2200m triggered a 30cm thick size 2 windslab. FORECAST OF AVALANCHE DANGER UP TO FRIDAY EVENING (APRIL 18) ALPINE - Moderate, deteriorating with warm daytime temperatures TREELINE - Moderate, deteriorating with warm daytime temperatures BELOW TREELINE - Moderate, deteriorating with warm daytime temperatures TRAVEL ADVISORY: Overnight crust formation varies from day to day and with local weather conditions. If a crust holds the weight of a walker it signals reasonable stability but the crusts can break down very quickly when the sun pokes out: keep this in mind Friday. Cornices are also large and fragile, give them a wide berth. NORTH COLUMBIA REGION WEATHER: 10-30 cm of snow at higher elevations, rain showers at lower elevations and light southwest winds are the result of a stagnant low pressure system over central BC. Freezing levels have been variable but average around 2200m in the afternoons. There is still no end in sight to this weather pattern! Expect more of the same through the long weekend. SNOWPACK: Windslabs formed in the new snow can be expected on upper elevation lee slopes. Although these slabs begin bonding well within a day or so of forming, new ones take their place with continued snow. Cornices are large and susceptible to failure with warm temperatures. Wet snow can be found most afternoons on all slopes except north aspects above 2200m. Some nights the wet snow cools enough to form crusts, some nights not. Some days remain cool enough at and above treeline that crusts remain strong throughout the afternoon. It all depends on present weather conditions. Below 1700m the snowpack is wet and weak to ground. AVALANCHES: Numerous wet loose snow slides on southerly aspects, to size 2. A size 2.5 cornice fall in the Cariboos and a size 2.5 temperature triggered slab 40cm deep in the Selkirks occurred on Monday. FORECAST OF AVALANCHE DANGER UP TO FRIDAY EVENING (APRIL 18) ALPINE - Moderate, deteriorating with warm daytime temperatures TREELINE - Moderate, deteriorating with warm daytime temperatures BELOW TREELINE - Moderate, deteriorating with warm daytime temperatures TRAVEL ADVISORY: Conditions will vary from valley to valley depending on snowfall amounts, how much overnight cooling occurs and how much sun is seen over the day. Keep track of the weather in your area. The November facets still linger near the ground and remain a significant weak layer. A relatively small surface snow avalanche could still trigger this deep weakness, causing a large avalanche running to valley bottom. SOUTH COLUMBIA REGION WEATHER: A lingering low centered over the Cariboo-Chilcotin gave us snowfalls of 10-35cm at higher elevations with mixed rain and snow below treeline. Winds were light to moderate from the southwest. Freezing levels fluctuated but averaged around 2200m in the afternoons. No change is expected through the weekend. SNOWPACK: On north aspects above 2200m dry snow can be expected and windslabs in the new snow can be found in lee areas. Cornices are large. On sunny aspects above 2200m wet snow can be found to mountaintop with resulting surface instabilities in the afternoons and crust formation with overnight cooling. The strength of these crusts varies from day to day and depends upon weather conditions at the time. Below treeline all slopes are wet, with the entire snowpack becoming wet and weak below 1700m. Little overnight crust recovery occurs at these lowest elevations. AVALANCHES: Numerous loose wet snow avalanches in the afternoons, size 1-2. On Tuesday, several natural and skier controlled windslabs were reported in alpine areas of the Monashees, size 1-2, 25-60cm thick. FORECAST OF AVALANCHE DANGER UP TO FRIDAY EVENING (APRIL 18) ALPINE - Moderate, deteriorating with warm daytime temperatures TREELINE - Moderate, deteriorating with warm daytime temperatures BELOW TREELINE - Moderate, deteriorating with warm daytime temperatures TRAVEL ADVISORY: The windslabs will vary from area to area, depending on how much snow the convective flurries give us. The same holds true for afternoon instabilities; a hole in the clouds allowing the sun to poke through will cause rapid deterioration of crusts. And let^Òs not forget the November facets buried near the ground. They remain a suspect layer until the snow melts this year, continue to use caution especially on steep unsupported terrain. KOOTENAY BOUNDARY REGION WEATHER: Up to 20 cm of snow was reported at higher elevations (mixed rain and snow below treeline) with continued unsettled spring weather. Freezing levels were around treeline with minimal overnight cooling. Southerly winds were light. Not much is expected to change as the pattern changes from a stationary low over central BC to a southwest flow in this region. SNOWPACK: Generally a wet springtime snowpack with dry snow found only on the highest elevation north aspects. On northerly alpine slopes expect areas of soft windslab that settle quickly only to be replaced with new slabs with continued snowfalls. Elsewhere, wet instabilities occur with daytime warming but a series of crusts deeper in the snowpack continue to provide enough strength to keep avalanches confined to surface layers for now. A layer of concern remains 60-80cm down where a wet and weak layer around an old crust is less supportive than the rest of the snowpack. Watch for this layer to fail as a slab with continued warming and if a large enough load is applied in the form of a large wet surface avalanche or a cornice fall. AVALANCHES: Small size loose wet snow avalanches. FORECAST OF AVALANCHE DANGER UP TO FRIDAY EVENING (APRIL 18) ALPINE - Moderate, deteriorating with warm daytime temperatures TREELINE - Moderate, deteriorating with warm daytime temperatures BELOW TREELINE - Moderate, deteriorating with warm daytime temperatures TRAVEL ADVISORY: In this winter of lingering weak layers we can^Òt forget what may lie deeper in the snowpack. There have been few observations made in this region over the past few weeks so we need to make some ourselves. If you are on alpine north aspects, dig down and test for the February 15 surface hoar layer and then probe for the November facets. Beware of cornices that may fall and apply a large load to the slope. SOUTH ROCKIES REGION WEATHER: The low centred over BC has given the South Rockies up to 20cm of snow at and above treeline the past few days, mixed rain and snow at lower elevations. Winds have been light in Fernie and moderate on the Alberta side; afternoon freezing levels have been rising to treeline. Little overnight cooling has taken place. Expect more sun and rising freezing levels as we approach the weekend, especially on the Alberta side. SNOWPACK: A wet springtime snowpack on all but the highest north aspects is now overlain by the most recent snowfalls. Expect some soft windslabs in alpine lee areas. Although these stabilize quickly with the warm temperatures, continued snowfalls create new slabs daily. Wet surface snow instabilities can be expected as the day warms and some nights are not even cool enough to create crusts that significantly increase stability. The warm temperatures are especially a concern in the shallower Alberta snowpack, which has become weaker than that in the Fernie area. Although all areas have a series of crusts buried deeper in the snowpack that provide some support, the entire snowpack is slowly breaking down with the continued warm temperatures. We have to keep in mind the deeper weaknesses from earlier in the winter, especially the November facets that lie at the very base of the snowpack. AVALANCHES: Size 1-2 loose wet snow avalanches at treeline elevations. FORECAST OF AVALANCHE DANGER UP TO FRIDAY EVENING (APRIL 18) ALPINE - Moderate, deteriorating with warm daytime temperatures TREELINE - Moderate, deteriorating with warm daytime temperatures BELOW TREELINE - Moderate, deteriorating with warm daytime temperatures TRAVEL ADVISORY: Although avalanche activity has been minimal, expect that to change if the sun starts coming out and causing intense radiation and raising freezing levels. Larger wet surface avalanches will begin occurring, cornices will fall off, and lingering instabilities will wake up. Expect avalanche danger to go to High and some larger slab avalanches to run if the weather forecast holds true.