Wednesday March 7, 2018
Loose Wet, Wind Slab, Storm Slab
Travel & Terrain Advice
Big changes in conditions over this coming forecast period means extra evaluation will be needed by backcountry travelers. Wednesdays warm temps will potentially produce loose wet activity. Avoid exposure above terrain traps as these loose wet sloughs, though small will pack a heavy punch. Thursday the storm arrives with some warm temps and may even begin in some zones as mixed precipitation/rain. This warm new moist snow will have low stability at first and its slab potential will have some force to it even though it is not deep. Avoid exposure above terrain traps and avoid common trigger points like convex rolls, unsupported slopes and zones with weak points. By Friday strong winds from the NW will attempt to relocate the new storm snow from Thursday. The ability of the strong winds to move the new snow will be dependent on the snows moisture content and the temperature. If travelling in the backcountry be on the watch for how much snow is moving and building potential wind slabs on S-E aspects.
No new avalanches during the past forecast period. Ski cutting steep unsupported convex features near ridge line at treeline on NW aspects and below treeline produced only loose surface sloughing of the top 5-7 cm demonstrating good stability.
Wednesdays warm up will most likely see widespread loose wet avalanche activity up to size one on all aspects in the treeline and below treeline elevation bands, especially on solar aspects. These avalanches will likely trigger naturally and are very likely to trigger with human activity.
A 180 degree switch in wind direction after the brunt of Thursday’s storm and snowfall will potentially redistribute snow to S-E aspects in the alpine and treeline. These slab avalanches could be size 1-2 and could possibly trigger naturally and are likely to trigger with human activity.
New snow/mixed precipitation arriving Thursday will increase the chance of storm/wet slab activity. These potential avalanches will be on all aspects and elevations and could possibly be size 1 to 2 in size. Triggering will possibly happen naturally and is likely with human activity.
Very small amounts of new snow (1-2 cm) have fallen during the past forecast period on a very stable snowpack. Some upper snowpack layers present as potential future sliding layers as the next storm system arrives.
|Surface||1-2 cm of new snow preserved on non solar, moist on solar aspects (likely to create a thin crust)|
|Upper||A layer cake of new snow, graupel (only in east and west regions) thin crusts (solar) and buried surface hoar|
|Mid||multiple non reactive crusts and well settled snow|
|Lower||well settled snow.|
The convective activity which resulted in pulses and surges of weather over the previous forecast period eased over the past three days. There were light variable winds and only small amounts new snow fell. Cold temps overnight and warm temps during the day have helped to create stable conditions.
Temps rise as the next storm system arrives bringing moderate amounts of new snow. As the system ends winds fully switch directions and temps drop back to seasonal.
Wednesday - 0 to a trace of new snowfall, light to moderate SE winds, temps -5 to +3, freezing levels 500 m rising up to a significant 1850 m.
Thursday - possible light rain and 4 cm of snow to the north and 10-15 cm of snow/ mixed precipitation to the east and west regions, moderate winds from the SE then a big switch to strong from the NW, temps 0 to -3.5, freezing levels 700 to 1225 m.
Friday - 1-3 cm of new snow, moderate NW to SW winds drop to light S to SE, temps -3 to -7, freezing levels 0 to 1000 m.
Posted on Wednesday March 7, 2018 by Bill Phipps