East slopes WA Cascades - north of Stevens Pass

Issued: 7:07 AM Sunday, April 20, 2014
by Garth Ferber

Please note that regularly scheduled mountain weather and avalanche forecasts for the past winter season have ended.  However weather and snow conditions will continue to be monitored at the Northwest Avalanche Center with the information that remains available.  Additional forecasts or special statements will be issued according to the criteria and schedule given here.

Forecast updated 7 am Sunday.

A continuing mix of spring and winter avalanche conditions should be seen on Sunday.

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Avalanche Concerns

Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

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Wind Slabi

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

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Storm Slabsi

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

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Snowpack Analysis:

A warm front caused snow and warming on Wednesday. This was followed by a cold front with you guessed it snow and cooling on Thursday. By Friday morning 48 hour snowfall at NWAC sites at Hurricane, east of the crest and Mt Hood above about 5000 feet was light to about 6 inches.  

Small shallow wind and storm slab may have formed Wednesday and Thursday but reports are getting few and far between.

NWAC observer Tom Curtis was at Smithbrook east of Stevens Pass on Friday and reported fairly deep wet surface conditions but no current avalanches. The Mt Hood Meadows ski patrol reported minor ski triggered wet loose avalanches on Friday.

A general profile of surface layers on non-solar slopes in this area Saturday morning above about 5000 feet should be up to a few  inches of snow from Thursday generally bonded to a crust from about Wednesday night over wetter snow from Wednesday.

Much less snow and consequently much less avalanche activity has been seen below about 4-5000 feet in all areas the past couple days.

Another front crossed the Olympics midday and is crossing the Cascades this afternoon. A short wave should rapidly follow the front across the Northwest this afternoon and evening. Showers should decrease tonight and end Sunday morning. This should generally cause southwest winds and light amounts to a few inches of new snow above in the ATL zones with cooler temperatures and lower snow levels by Sunday morning.

Detailed Forecast for Sunday:

A short wave ridge, weak surface high pressure and drier air mass is indicated to move to the Northwest on Sunday. In the Olympics and at Mt Hood clouds in the morning should decrease by afternoon. Mostly sunny weather should be seen east of the crest. Temperatures and freezing levels should rise a fair amount by Sunday afternoon.

Natural or triggered wet loose avalanches seem possible and more extensive than other concerns on Sunday. The late April sun can be counted on to act on new snow deeper that a couple inches on any steep solar slope. This will be mainly in the ATL and NTL zones. Watch for surface wet snow deeper than a few inches, pinwheels or roller balls which usually precede larger wet loose avalanches.

Small new areas of wind slab from Saturday also seem possible on lee slopes. This will mainly be on north to southeast slopes in the ATL zone. Watch for signs of firmer wind transported snow or cracking snow.

Small areas of new shallow storm slab will be possible in the ATL zone as well but this should be very limited to areas that receive at least a few inches of new snow.