March 22, 2001 NOTICE OF UNUSUAL AVALANCHE CONDITIONS: Valid until further notice. This season avalanche professionals between the Inner Coast Mountains and the Rocky Mountains have observed snowpacks that are unusually weak. The combination of below normal snow depth and low temperatures has produced layers of facetted grains and surface hoar with a low strength. These types of weak layers can persist for a long time, and the avalanche danger will increase with every load of new snow onto this weak base. The present snowpack is less stable than in most other years and remarkably different from the snowpack at the same time last winter. Back country users will have to pay much attention to snowpack structure and strength during this winter. SOUTH COAST REGION WEATHER: Although the general trend in the weather this week was toward warm conditions, some weak disturbances tracked through early in the week, leaving behind up to 30cm of storm snow in the mountains. By Thursday, a ridge of high pressure was firmly established over the coast, bringing on serious warming, sun filled days, and a general feeling that spring was on the doorstep. The weather forecast calls for the ridge to slip eastward, maintaining warm weather but allowing a gradual decay to scattered flurries by Monday. SNOWPACK: The new snow formed a wind slab in exposed areas, but the sustained warm weather of the last few weeks has begun to seriously affect the mid and lower layers. Solar aspects have the storm snow sitting on a sun crust, and the interface shows a weak bond during afternoon heating. Surface hoar layers in the upper metre of the snowpack are showing easy shears in some snowpack tests, and of even more importance, shallow snowpack areas now exhibit deteriorating strength in the layers found above the November facet weakness. AVALANCHES: Storm snow naturals to size 2 continued to be observed on Thursday. Occasional larger avalanches to size 3.5 were observed stepping down to buried surface hoar layers 60-120cm down, and even worse, stepping to the November facet layer found near the base of the snowpack. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Mar 26th) ALPINE - Considerable TREELINE - Considerable BELOW TREELINE ^Ö Considerable with afternoon heating TRAVEL ADVISORY: Solar heating will be a significant factor this weekend. Watch for overnight temperatures which stay near or above zero, signaling rapid strength deterioration. Cornice fall is likely to occur right now, and cornice drops triggering deep instabilities, even the November facet weakness, have recently been reported from this region. NORTH COLUMBIA REGION WEATHER: This week brought generally warm weather, with daytime highs well above zero even up on the glaciers. Despite this, some cloud slipped through early in the week, leaving up to 15cm of storm snow behind. By Thursday, a ridge of high pressure had filled the skies with brilliant sunshine, and the call of returning songbirds announced that spring was upon us. The weather forecast calls for a gradual deterioration, with a chance of showers by Monday as the ridge slides eastward into Alberta. SNOWPACK: The region is still feeling the effects of the rapid loading event last week, and the upper metre of the snowpack continues to settle into a more cohesive slab under the bright sun. A surface hoar layer buried the end of February lies just under this, and persists as a common failure plane. Midpack layers are loosing strength due to all the warm weather, and the November Facet layer is awakening from its bed down near the base. AVALANCHES: Frequent naturals and human triggered events to size 3.5, failing in the storm snow, the buried surface hoar beneath, and occasionally stepping to the November facets. The intense solar radiation will sustain this potential. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Mar 26th) ALPINE ^Ö High in the afternoons TREELINE ^Ö High in the afternoons BELOW TREELINE - Considerable TRAVEL ADVISORY: A snowmobiler lost his life on Wednesday in an avalanche near McBride, and several incidents have been reported recently. Solar radiation has begun to seriously erode our alpine snowpack. Below it all waits the mother of all layers, the November facets, which is showing strong signs of coming to life. SOUTH COLUMBIA REGION WEATHER: The South Columbias continued to hold under a general warming trend, with daytime highs well above zero each afternoon. Periods of cloud occurred early in the week, but resulted in only light snowfalls. A ridge of high pressure was over the region by Thursday, bringing strong solar radiation from clear blue skies. The weather forecast calls for the ridge to slip east into Alberta by Monday, bringing cloudy periods and a chance of showers. SNOWPACK: The storm snow from last week is settling and improving in strength. In many areas thicker windslabs from last week continue to fail on the surface hoar layer found down about 70cm. The November facets sit at the bottom of the snowpack, and it is becoming evident that the strength in the layers above is being eroded by the sustained warm conditions. AVALANCHES: Frequent storm snow activity to size 2.5 earlier in the week, tapering off to occasional by Thursday. Explosive testing of fat wind loaded pockets in the alpine produced failures to ground on the November facets. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Mar 26th) ALPINE ^Ö Moderate, Considerable in the afternoons TREELINE ^Ö Moderate, Considerable in the afternoons BELOW TREELINE - Moderate TRAVEL ADVISORY: Keep an eye on snowpack temperatures. Overnight lows remaining near or above zero will signal poor temperature recovery in the snowpack, allowing snowpack strength to deteriorate more rapidly. The November facets are not yet fully awake, but showing signs of coming to life under the influence of the approach of spring. ROCKIES REGION WEATHER: Considerable variation in weather occurred in the region, with the remnants of a storm continuing to affect the northern part of the region, while more stable weather was observed in the south. The weather forecast calls for generally cloudy condition to persist, with a chance of light snows near the continental divide. SNOWPACK: Although the recent storm snow is bonded well in southern regions, significant weakness continues to be found just under the layer further north, particularly in the Columbia Icefields area. The midpack layers continue to isolate the significant weakness at the base of the snowpack in all but shallow snowpack areas. Concern is mounting that as spring approaches, the November facet layer near the base of the snowpack will produce significant avalanche activity as solar heating takes the strength out of the midpack. AVALANCHES: Large, widely propagating naturals are being reported near Parker^Òs Ridge and the Columbia Icefields. Less frequent and smaller activity is being reported further south, with very little by the time you near the US border. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Mar 26th) ALPINE ^Ö Considerable, High in the north TREELINE ^Ö Considerable, High in the north BELOW TREELINE - Moderate TRAVEL ADVISORY: This may be one of the last opportunities to take part in a Recreational Avalanche Course over the coming long weekend. Check out the list of providers at www.avalanche.ca for a course near you.