Purcells

There is uncertainty with precipitation amounts Wednesday night through Thursday. This forecast is based on the upper end of estimates.

Moderate - Intensity of incoming weather systems is uncertain on Thursday

WEDNESDAY NIGHT: Snow, accumulation 10-15 cm / Moderate southwest wind / Alpine temperature -7 C THURSDAY: Snow, accumulation 10-20 cm / Moderate to strong southwest wind / Alpine temperature -3 C / Freezing level 1300 mFRIDAY: Flurries, accumulation 5-10 cm / Moderate to strong south wind / Alpine temperature -7 C SATURDAY: Isolated flurries / Light to moderate west wind / Alpine temperature -6

Expect to see avalanche activity increase on Thursday as a storm passes through the region Wednesday night through Thursday.Reports from Sunday show a few very large (size 2.5 and size 3) deep persistent slabs running during the last storm. These occurred in alpine terrain and are suspected to have failed on deep weak layers formed early in the season. A convincing pattern of deep persistent slab activity has yet to emerge, but these events highlight lingering hazards in thin or variable snowpack areas in the alpine.

An additional 10-15 cm of new snow falling Wednesday night will add to last weekend's storm snow totals of 20-30 cm.A weak layer that formed during the dry spell in early December is now 80 to 110 cm deep. The layer is composed of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects). Another similar weak layer is buried 90 to 150 cm deep. Finally, the base of the snowpack has weak faceted layers at alpine and treeline elevations. These basal weak layers have been producing large avalanches as recently as December 31st. Human triggering any of these layers is most likely on slopes that didn't previously avalanche and on slopes that have variable snowpack depth (such as rocky alpine features).