Friday February 7, 2020
Loose Wet, Wind Slab, Storm Slab
Travel & Terrain Advice
Avoid open terrain after the new snow arrives Friday afternoon into Saturday, especially windloaded slopes on the SE to NE. Give the snowpack and aggressive terrain time to heal after the big snow and wind event. Temps will play a role in converting new snow into a wet snow avalanche problem at lower elevations (Friday with possible rain and via a solar heating influence Sunday).
No new avalanche activity has been reported over the past two days.
Dangerous warming of the upper snowpack is possible twice during the next three day forecast period. Once midday Friday as precip falling at the beginning of the big storm may fall as rain at lower elevations and secondly in the afternoon Sunday as temps climb and the freezing level goes up to approximately 1800 m. During these warm periods the upper snowpack might lose strength and result in loose wet avalanches up to size 1.5. Friday this will be confined to the below treeline elevation band on all aspects and Sunday we will see this mainly on solar aspects in the below treeline and up into the treeline zones. Triggering of these loose wet pushy slides will be likely to possible so during these times it would be smart to avoid exposure to terrain traps (like being above cliffs, depressions, gulleys or bands of trees) that increase the potential depth of burial and the chances of serious trauma.
Strong winds during the storm from the SW and then from the NW after the storm will transport a significant amount of snow to lees and result in wind slab development. These wind slabs will create avalanche danger in the alpine and treeline zones. We can expect these slabs will have a very likely to likely triggering sensitivity and will result in avalanches from size 1 to 2.5.
Significant snowfall Friday afternoon into Saturday morning will result in potential for storm slab avalanche activity. We can expect this problem will be present on all aspects and elevations, with triggering likely to possible and avalanche sizes of 1 up to 2.
A few centimeters of new snow fell Thursday onto a thin crust. The crust was formed by the cooling of the moist surfaces left behind after Wednesday’s light rain, freezing rain and moist snowfall. This thin crust caps 6-30cm of snow (location dependent) over the thick rain crust that formed after the big rain event last Friday.
|Surface||a few cm of new snow over a thin crust|
|Upper||moist snow bonding well to the thick rain crust created by last fridays rain event with some weak snow below|
|Mid||a bunch of well settled moist snow, sitting on a very thick crust|
|Lower||well settled snow underlying the very thick crust|
Warm temps Wednesday saw light rain and freezing rain at lower elevations and some damp new snow higher up. Cooling Thursday created a crust on most surfaces that was then buried by light new snowfall.
A significant storm is set to rolling Friday afternoon in to Saturday morning with a good dump of snow and high winds. Then a clearing after will cool things off Saturday prior to a slight warm up Sunday.
Friday - 15 to 36 cm of new snow (higher amounts to the west Strathcona, moderate amounts to the north Cain, and lower numbers to the East Washington. Winds will be strong from the SW during the storm. Temps 1 to -3. Freezing levels 600 to 1500 m.
Saturday - The precip will taper off in the morning. The strong winds will switch direction from the SW to from the NW. Temps will drop to -1 to -8. Freezing levels will be 100 to 800 m.
Sunday - No new precip. Winds will drop to moderate NW. Temp will rise to 0 to +2. Freezing levels will be 900 to 1800 m.
Posted on Friday February 7, 2020 by Bill Phipps