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Avalanche Forecast

Archived

Feb 21st, 2014–Feb 22nd, 2014

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Inland.

The snowpack is in transition now, from storm slab to a persistent slab on a very weak facet/surface hoar/crust layer. Might be time to scale back plans for big lines.Check out the recent Forecasters Blog

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

The last of the Pacific fronts should be gone by mid day today, to be replaced by cold clear weather. Cold weather in the forecast for early next week.Friday night: Freezing at valley bottom, no precipitation in the forecast. Cool dry air moves into the region, ridge top winds, NW up to 40Km/h.Saturday: Freezing level at valley bottom no precipitation, sunny, ridge top winds from the north up to 20 Km/h.Sunday: Freezing level at valley bottom, Cold clear weather, ridge top winds around 15-20 Km/h.Monday: Freezing level at valley bottom, Cold clear weather, ridge top winds around 15-20 Km/h., possibility of a temperature inversion in the Alpine.

Avalanche Summary

A skier controlled size 2 avalanched was reported from The Silvern Lake trail yesterday, 30 slope SE aspect, 35cm fracture line, and we are still hearing reports of whumpfing and wind loaded slopes cracking. Numerous skier remote (up to 50 m away) have been reported in the northern part of the region. I would be highly suspicious of wind loaded slopes at all elevations. Use conservative terrain choices and make observations as you travel. Pay attention to solar radiation.

Snowpack Summary

The region has received between 35-90 cm of new snow, with more snow to the western part of the region, tapering of as you travel further east, now overlying a variety of old surfaces. These buried surfaces consist of weak surface facets, surface hoar (more predominant at tree line and below tree line elevations), a scoured crust, wind pressed snow, or any combination of these left over from earlier weather. Whumpfing, cracking, and reports from the field indicate a very poor bond between the new snow and these old surfaces. Reports from the Hankin area on a NE facing slope 1300m show an ice crust down 50cm with facets above and below. A compression test easy @ 25cm and another down @48cm, sudden collapse ( Thanks BH!) Strong winds and slight warming have added cohesion to the storm slab, and transported some of the new snow into deeper, and more destructive wind slabs on the lee side of ridge tops.The mid and lower snowpack are generally strong and well-settled. Basal facets and depth hoar are likely to exist in some parts of the region, but skier triggering has become unlikely. A wind slab avalanche could step down to these basal facets and produce a large destructive avalanche.

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.