Avalanche Forecast

Issued: Mar 18th, 2019 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Loose Wet, Persistent Slabs and Deep Persistent Slabs.

stephen holeczi, Parks Canada

Little Yoho.

http://www.pc.gc.ca/apps/scond/Cond_E.asp?oID=34810&oPark=100092 Its time to step way back in terms of terrain choices and exposure, and let this spring cycle clean up the mountains. AM danger will be lower, but be out of all avalanche terrain by the time the day heats up as the change will happen quick.

Summary

Weather Forecast

A decent freeze tomorrow AM but again temperatures will spike rapidly with valley bottom highs in the 10-15C range, and 3000m temperatures approaching 0C. Skies will be very clear and winds mainly calm. This heat peaks on Wednesday but stays warm until next weekend.

Snowpack Summary

Sun crusts or moist snow on solar aspects and moist snow at lower elevations. 15-50 cm of snow has accumulated since March 7. This sits over a mix of facets, sun crust and wind slabs above treeline, and over 30-50 cm of weak facets elsewhere. While a supportive mid-pack exists in thicker areas, weak facets to the ground are seen in many thin areas.

Avalanche Summary

A widespread spring avalanche cycle has started, with the bulk occurring on solar aspects. Avalanche size ranged from size 1-3. Most slides have been within the surface snow (March 7 interface) with some stepping down a bit deeper; however, we have seen only a few avalanche step down to the basal layers.

Confidence

Problems

Loose Wet

Rapidly warming daytime temperatures and high solar inputs are causing loose wet avalanches to start by mid morning. Some of these are running long distances or triggering slabs along the way. Avoid exposure to these slopes when they heat up.

If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.Use extra caution on slopes if the snow is moist or wet.

Aspects: East, South East, South, South West, West.

Elevations: All elevations.

Likelihood

Very Likely - Certain

Expected Size

1 - 2.5

Persistent Slabs

10-50 cm of snow since March 7 has formed slabs above treeline due to winds and warm temperatures and sits over a variety of weaker surfaces. Natural and skier triggering of this recent snow has occurred in the last several days on all aspects.

Watch for surface cracking and stiffer surface layers of snow.Use conservative route selection, stick to moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

We are starting to see places where avalanches are failing on the basal weaknesses and scrubbing to ground. This is mostly occurring with large triggers in thin rocky areas but we expect this type of avalanche activity to increase with more heat.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.Be aware of the potential for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 3.5

Valid until: Mar 19th, 2019 4:00PM