Archived forecast for Friday, March 29, 2024 This is archived in relation to a fatality on 3/29 on or near Cathedral Mountain. The avalanche.ca archives are a bit awkward with flexible regions and the result from clicking on the map can differ from that obtained by the location search. We have tried to get the best result by first using the map and then the location search in that area. We believe the advisory here was in effect for Cathedral Mountain on 3/29. They also date advisories by the ending date so this was listed as 3/30 but expired at 0300 that day. Date Issued: Friday, March 29, 2024 at 03:00 Valid Until: Saturday, March 30, 2024 at 03:00 Prepared by: TH Triggering the Feb 3 persistent weak layer remains the greatest concern. We have not seen any activity on this in the deeper snowpack areas. Use caution in areas with a snowpack depth lower than 200cm on shaded slopes above 2000m where events to the east have occurred. Expect to find developing new slabs with the incoming snow and winds Danger Ratings Friday Alpine: 1 - Low Treeline: 1 - Low Below Treeline: 1 - Low Terrain and Travel Advice Watch for newly formed and reactive wind slabs as you transition into wind affected terrain. Avoid shallow, rocky areas where the snowpack transitions from thick to thin. If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches. Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers. Remote triggering is a concern, watch out for adjacent and overhead slopes. Problems Avalanche Problem 1: Persistent slab What Elevation? - Treeline, Alpine Which Slopes? - North, Northeast, Northwest Chances of Avalanches? - Unlikely - Possible Expected Size? - Large The Feb 3 crust/facet interface is down 70-100 cm. While we have not seen these in deep snowpack areas, there have been several recent skier-triggered slabs in thinner areas east of the divide. All of the recent avalanches that initiate on this layer step or gouge down to the basal facets / ground. Avalanche Problem 2: Wind slab What Elevation? - Treeline, Alpine Which Slopes? - North, Northeast, East, Southeast, south, Southwest, West, Northwest Chances of Avalanches? - Possible Expected Size? - Small On solar slopes expect thin new slabs to be found over sun crusts. On shaded slopes, the new snow buries spotty surface hoar and slabs may also incorporate the 10-30cm of dry snow from the last storm. In either case, check the bond to the old surfaces as these slabs develop into the weekend. Avalanche Summary No new avalanches were observed in this sub-region in the last week, however in thinner snowpack areas east of the divide: There has been four size 2-3 avalanches that have all been remotely or accidentally triggered by skiers. All occurred on northerly aspects between 2000 - 2600m in thin snowpack areas (less than 200cm) with no overlying March 20 crust. These have all initiated on the Feb. 3rd crust/ facet interface and stepped down to basal facets / ground. Snowpack Summary Up to 15cm of storm snow covers sun crusts on solar aspects and up to 30 cm of dry snow on shaded slopes. Below this, the March 20th crust exists everywhere except north aspects above 1800. Our main concern is thin snowpack areas (read: 200cm or less) on northerly aspects where there is no March 20 crust. Here the mid-pack Feb 3 facet / crust layer and the basal facets / depth hoar remain sensitive to triggering. Deeper snowpack areas have fewer concerns. Weather Summary Thursday evening: light snowfall will linger with freezing levels to valley bottom. Light to moderate SW winds at ridgetop. The same light snowfall will continue Friday with freezing levels near 1500m and winds shifting NW. Scattered flurries Saturday. Skies clear and freezing levels rise to 2000m Sunday as winds increase: moderate to strong. Confidence: Moderate, Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast precipitation (either snow or rain) amounts are uncertain.