Avalanche Forecast

Issued: Apr 23rd, 2013 4:00PM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs, Loose Wet and Cornices.

rupert wedgwood, Parks Canada

Jasper.

The melt freeze crust is lowering the avalanche danger during the morning and early afternoon. Once thawed the danger will increase both rapidly and dramatically. Avoid being on or below steep sun exposed slopes by mid afternoon. Monitor the crust.

Summary

Weather Forecast

The cold Northerly air mass which has blanketed the area during the past week will be pushed out by a warmer moister Westerly flow over the next 24hrs. Winds at ridge tops will increase into the strong range. Cloudy skies will releasing precipitation in the form of light rain at lower elevations and snow flurries near treeline and the alpine.

Snowpack Summary

A spring temperature crust up to 15cm thick can be found near the top of the snowpack. This crust has been found as high as 2600m in the Icefields area. In places it is buried under several inches of new snow. Wind slabs can be found at upper elevations on most aspects due to varied wind direction patterns. Cornices are large and ready to drop.

Avalanche Summary

The avalanche danger will increase during the day particularly at lower elevations if it rains. Strong Westerly ridge top winds will add to the thin wind slabs on easterly facing slopes as well as building cornices. Pay close attention if the sun comes out as this will dramatically and rapidly increase the avalanche danger on solar facing slopes.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Thursday

Problems

Wind Slabs

Isolated pockets of wind slab can be found on lee aspects in exposed alpine terrain near ridge crests. Expect to encounter this condition on NW and SW aspects due to variable wind directions over the past week.

Be cautious as you transition into wind affected terrain.Be careful with wind loaded pockets

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Loose Wet

Cool temperatures and limited direct solar radiations will preserve the melt freeze crust in most locations until mid afternoon. Once gone the avalanche danger will increase rapidly.

Start and finish early before the surface crusts melt.Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Cornices

It is that time in the spring when warmer daytime temperatures combined with milder overnight temperatures will make cornices more susceptible to collapsing. They seem larger this year and may still trigger deep instabilities on north aspects.

Do not travel on slopes that are exposed to cornices overhead.Stay well back from cornices.

Aspects: North, North East, East, South East, South.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Apr 24th, 2013 4:00PM