Avalanche Forecast

Issued: Feb 11th, 2015 8:52AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

esharp, Avalanche Canada

Northwest Coastal.

Warming and rain will cause an avalanche cycle. There is variability across the region about how high and how much it will rain. Forecast danger ratings are for the worst case scenario where rain falls on previously dry snow.

Summary

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

By the end of Saturday a series of frontal systems will have brought up to 100mm of precipitation on the coast tapering to around 35mm further inland. Unfortunately for the southern half of the region, rising freezing levels will mean that much of this will likely fall as rain.10 to 30mm of precipitation is forecast for Thursday with a freezing level of 2000m. A brief temperature inversion may mean a brief period of freezing rain Thursday morning at lower elevations. Another 10 to 40mm is forecast for Friday as a cold front moves over the region with the freezing level falling to 1500m. The freezing level will continue to drop to 1000m on Saturday when another 5 to 10mm is expected. Winds will remain moderate to strong from the southwest throughout the forecast period.

Avalanche Summary

Warming temperatures, wind, snow and rain will drive a natural avalanche cycle that I expect to last the next couple of days. Avalanche control on Monday produced slab avalanches up to size 3 on virtually all aspects and elevations. It sounds like a lot of these avalanches ran on mid storm instabilities although some larger results observed on South facing slopes released on the late January crust.

Snowpack Summary

I've been unable to access any of the weather stations in the region today so I've had to base this update to the on Wednesday morning's weather forecasts. As freezing levels rise I suspect that the snowpack at lower elevations is being saturated by rain or freezing rain. Above about 1500m up to 20 cm of snow may have fallen on a new layer of surface hoar. Predominantly strong southwest winds will load lee features. What we do know is that the late-January crust is down 60 to 150cm in the south of the region and about half this depth in the north. This crust may also have surface hoar on it. The mid-January rain crust and/or surface hoar layer is down over 160cm in the south and has generally become inactive although it may still be a concern in thinner snowpack areas. The November crust/facet combo near the bottom of the snowpack may still be reactive in the far north of the region

Problems

Storm Slabs

As the freezing level rises rain will fall on previously dry snow above a layer of surface hoar. There is quite a bit of variability across the region as to when and where this will happen, but where it does expect very touch avalanche conditions.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 4

Persistent Slabs

Warming temperatures, snow, and/or rain will stress persistent weak layers lurking in the snowpack at and above treeline. Avalanche control on Monday suggested that these layers still have the potential to produce large and destructive avalanches.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Be aware of the potential for large, deep avalanches due to the presence of buried crusts and/or surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Valid until: Feb 12th, 2015 2:00PM