Wednesday April 18, 2018
Cornice Fall, Loose Wet, Wind Slab
Travel & Terrain Advice
Cornices will become weak when temperatures warm and the sun is radiating.
Identify and seek terrain options when entering areas with recent wind loading (North aspects).
Caution on South aspects when the temperature warms and solar radiation begins to rapidly effect the slope.
Numerous loose wet avalanches all aspects and elevation from the alpine to below tree line with a few gaining enough mass to be large in size (2).
One wind slab on north aspects below 1500 meters on thin steep rocky terrain approx crown of 40 cm small in size (1).
Cornice tabs are dropping and a few failures were noted at treeline on north aspects and one initiated a small loose wet avalanche.
Very large cornices exist with new tabs formed during the last snow fall, these features have been reacting naturally and will continue to persist and be hazardous during the remainder of the spring season. Found on north aspects in both the alpine and at tree line. Expect these frail hazardous features to be sensitive to human triggering. If trigger these features could when failing and falling onto the slopes below, then trigger either a wind slab or loose wet avalanche. Expect if triggered these avalanches to be large in size and in isolated terrain very large all with the potential to bury injure or kill a mountain traveler.
Forecast daytime warming and especially solar effect specific to southern aspects will decompose the upper snow pack and contribute to the formation of loose wet avalanches. Expect to find these avalanches at all elevations and especially treeline and below and be very touchy to human triggering. If triggered these hazardous avalanches will initially start as small but will gain mass and become large, size 2 and in big and exposed terrain features have the ability to become very large.
Past strong winds and snowfall have on northern aspects at ridge top and specific terrain features created wind slab. Expect to find these wind slabs in the alpine and at tree line and to be stubborn to light triggers but in isolated areas expect wind slabs to be touchy and deep between 50 and 100 cm in depth. If triggered these avalanches will be large in size up to or exceeding size 2 and have the ability to bury injure or kill a mountain traveler.
The upper surface snow received significant solar effect and warming creating a wide spread melt freeze crust that is present on all aspects and all elevations. Recent snow fall and wind loading has deposited a variety of new snow depths on primarily north aspects. In the alpine and at tree line on ridge tops and lee features have very large cornices with weakening tabs that will present problems as the spring weather cycle begins. The upper snow pack is moist to wet and in large open areas lee depositing exceeds 100 cm. The march 22 melt freeze crust is now buried down over 150 cm and shows little in the way of reaction and at this time could be considered dormant. The lower snow pack is well settled and dense
|Surface||5 to 10 cm thick melt freeze crust|
|Upper||moist to wet|
|Mid||march 22 melt freeze crust can be found down 150 to 200 cm|
|Lower||well settled and dense|
Moderate to heavy snow fall with strong southerly winds, followed by warming temperatures, clear sky and sunshine. On Monday night freezing levels dropped to 400 meters and alpine temperatures hovered around minus 5.
A stable weather system with some daytime convective alpine snow showers. Mostly clear conditions and overnight cooling, beginning Friday a change to a southwesterly flow will deliver to the forecast area light to moderate amounts of precipitation and south west wind.
Wednesday no new snowfall temp -2 to 3, winds light south east, freezing level to 1200 m.
Thursday no new snowfall temps -2 rising to 6, winds light south east, freezing level to 1500 m.
Friday 5 to 10 cm of snowfall temps 0 to +3 winds light to moderate south west , freezing level to 1300 m.
Posted on Wednesday April 18, 2018 by Jesse Percival