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Issued
Tue, February 7th, 2012 - 7:00AM
Expires
Wed, February 8th, 2012 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

Good morning. This is Graham Predeger with the Chugach National Forest Avalanche Information Center on Tuesday, February 7th at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

BOTTOM LINE

Lower elevation slopes experiencing less wind effect continue to settle out today with these warm ambient temperatures and increased solar influence. The danger is MODERATE on these slopes, where we can expect to see small moist avalanches releasing naturally today in specific areas around rock bands and trees where solar input is magnified. At mid and upper elevations, the avalanche danger is CONSIDERABLE due to stiff, reactive wind slabs that may be very LARGE AND UNMANAGEABLE.

AVALANCHE DISCUSSION

There has been a significant natural avalanche cycle within the forecast zone over the last 2 days and at least one snowmachiner triggered avalanche on the backside of Seattle Ridge yesterday. Details are limited, but it is believed to be about a 3′ deep wind slab that propagated at least 100′ on a mid-elevation slope.

The primary concern in the backcountry today comes in the form of these stiff, wind slabs at mid and upper elevations. The low-density loose snow that we have all been enjoying for the last several weeks was transformed this weekend (Sunday) into fresh, tender wind slabs at mid and upper elevations. These can be especially dangerous in the backcountry as slopes are accessed from the bottom, luring skiers and snowmachiners onto a slab where a failure has the potential to propagate above you and your party. Pay particular attention to the changes in surface conditions today as you ascend. You will likely find moist, loose snow at lower elevations; a nasty breakable crust at mid elevations changing to wind slab in the likely areas such as below steep rollovers and under ridges. Shooting cracks or collapsing (whumpfing) observed is a tell tale sign that you have found these tender wind slabs.

Lower elevation slopes experienced significant settlement yesterday. Roller balls were also quite prevalent. Indicative of warming surface conditions these form on steep terrain due to high (above freezing) ambient temperatures and/ or solar influence. My guess is that both of these drivers were in play yesterday (and will be again today) on sun-affected slopes. These have the potential to entrain a significant amount of HEAVY and WET surface snow that can step down into deeper layers. Below the top 4-6″ of moist surface snow, you will find our dry low-density powder from just a few days ago.

MOUNTAIN WEATHER

Yesterday felt a lot like springtime in the backcountry. Partly cloudy skies and temperatures in the mid 30’s at 1800 feet made for gloppy surface conditions. Winds continued from the east, though scaled way back from the gale force experienced on Sunday.

Today we can expect sunny skies and spring like temperatures again. Ridge top winds will continue from the east in the range of 7-20mph. Temperatures look to be warmer today than yesterday topping out at around 38 degrees at 1000 feet. Couple this with direct sun and you will want to put a fresh coat of wax on your skins before leaving the parking lot today. Solar influence will begin to be a bigger player in our forecasts over the coming weeks and months as the trajectory of the sun changes heading into spring.

CNFAIC Weather Page and the NWS forecast

Kevin will issue the next advisory Wednesday morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.

Tue, February 7th, 2012
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.