Regions
Northwest Coastal.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Synopsis: Friday looks cool and dry, and then a series of weak systems should deliver small amounts of precipitation through the weekend. There's potential for significant precipitation, extreme winds and freezing levels in excess of 2000m beginning Sunday night.Friday: Freezing Level: 700 - 1100m Precipitation: Trace; Wind: Treeline: Light, SW | Ridgetop: Moderate, SWSaturday: Freezing Level: 900m - 1300m; Precipitation: 1:10mm - 1:15cm; Wind: Treeline: Moderate, S/SW | Ridgetop: Strong, SWSunday: Freezing Level: 1000m - 1200m; Precipitation: Trace; Wind: Treeline: Moderate, SW | Ridgetop: Strong, W/SW
Avalanche Summary
No new avalanche activity to report from Wednesday. I suspect that activity ramped up Thursday, look for details in tomorrow's discussion.On Tuesday there was one report of a remotely triggered size 2 wind slab avalanche on a NE facing aspect at 1500m. This location had previously slid on the early February crust/facet/surface hoar combo. Isolated loose wet avalanches to size 1.5 were also reported from steep southerly terrain.On Monday a large rock fall event initiated a size 3.5 avalanche that failed on the early February persistent weak layer. Several smaller loose snow avalanches to size 2 were running in the recent storm snow on steep solar aspects too.
Snowpack Summary
The storm has produced 15 - 25cm of new snow as of Thursday afternoon. This snow rests on surface hoar, small grained facets and melt freeze crusts.Previous to Thursday's snow, it was starting to feel like spring in the NW. Valley temps have been creeping into the double digits during the day, and there are reports of the top 15 cm of the snowpack regularly becoming moist with daytime heating.Prior to the snowfall Thursday, the last significant shot of snow was on March 27th, another 10 - 15 fell on March 30th. This old storm snow rests on top of a haggard old surface composed of old wind slab, melt freeze crust, and faceted old snow. I suspect the ongoing melt freeze cycles have largely healed any instabilities associated with this interface.The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm, and I suspect it's gone mostly dormant for now.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.