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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, March 11th, 2009 - 7:00AM
Expires
Thu, March 12th, 2009 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, March 11, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area(Turnagain Pass is the core advisory area). Local variations always occur. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.

MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS

-General Weather Observations-

A trace to 0.1 inches of precip in past 24 hours for Summit, Grandview, Turnagain Pass, Portage, and Girdwood. Winds have been light to moderate. Temps are warmer at all weather stations from Summit Lake to Turnagain Arm by 1-5 degrees. Portage is above freezing. The NOAA models are forecasting .25-.5 inches of precip for the Kenai Mountains today

The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass

Has a temp of 26 degrees (3 degrees warmer than yesterday). 0.1 inches new water and a trace to 1 inch of new snow. Total snowpack depth is 68″.

The Sunburst weather station at 3800 feet in Turnagain Pass

Is recording a temp of 20 degrees (3 degrees warmer than yesterday). Winds have been light to moderate averaging 6-16 mph out of the E, with moderate gusts up to 24mph.

-Surface Analysis Maps-

Between 3am and 9pm yesterday….Show a couple of weak storms fizzling out. There is a 1016mb low to our southeast. Maybe that is what will bring the forecasted precip?

-Radar/Satellite-

The radar over Prince William Sound shows moderate precip with patches of green moving slowly. If that hung around all day, I could see us getting some precip today. Cook Inlet has a little less but similar precip.

AVALANCHE HAZARDS

Primary avalanche concerns

-Below 3000 feet. The “Janurary Hurricane” rain crust buried under 1-4 feet of surface snow. There is a layer of weak sugary faceted snow on top and below this hard rain crust. We are finding DECREASING stability in spots on top of this crust. This weak layer is still showing signs of life, and probably will become very dangerous if it gets any sort of rapid load, especially rain.

-Sea-level to ridgetops up to at least 3800 feet (Probably higher). The “glazed donut” freezing rain crust that formed 3/5/09 has been observed in Girdwood, Turnagain Pass and Summit Lake. It was everywhere on all aspects and could become a bad weak layer if it gets buried under slaby snow.

AVALANCHES AND SNOWPACK

Bottom Line

Elevated Caution is advised today because we have a deep weak layer showing signs of decreasing stability and the “glazed donut” freezing rain crust that might become a problem after it gets buried, and the weather forecast below is calling for new precip and warm temps up to the lower 40’s.

Discussion

The weather does not sound like its going to pack a huge punch today, but that is what we need to watch out for. Our snowpack has not had a major load for a while, and we have been watching sugary facets grow in our intermountain style snowpack. Last week, I was thinking that the January Hurricane rain crust needed a large trigger like a major storm to trigger it, but it is also showing some signs of being reactive to human triggers.

We got a report of frequent collapsing between 1200-1800 feet on Pete’s South at the southern end of Turnagain Pass. This party investigated these shooting cracks that propogated up to 70 feet long. They dug in the snow, and found that these cracks were failing on top of the Janurary Hurricane layer (see photo gallery).

Lisa has been digging pits every Monday for the past couple weeks at a study plot on Tincan. She has been finding decreasing stability with here shovel compression tests on top of the Janurary Hurrican rain crust. The facets on top of that crust have become more sugary.

Yesterday, we dug a pit in an area on Main Bowl where I’ve been digging all season. I was suprised to see and feel how much the facets developed since my last pit at this location on 2/19/2009. The facets I’ve been seeing all over the place are mixed forms (rounds going to facets). They are still very sugary, but they are not completely square. They still have some rounded edges that allow these sugary facets to stick together fairly well. I was able to pull out entire isolated columns of these sugary facets and hand the column to my buddy without them falling apart.

I think we are going to see big avalanches after the next big storm (if that every happens). As far as human-triggers today. I’d say its less likely, but the snowpack is not improving. I keep saying to myself that this year’s snowpack is wierd. Personally I’m not into skiing big lines right now. I think we should treat this snowpack differently than what we’ve seen in the past couple years.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT WED MAR 11 2009

.TODAY…SNOW LIKELY. SNOW ACCUMULATION UP TO 2 INCHES.

HIGHS IN THE LOWER 30S TO LOWER 40S. EAST WIND TO 15 MPH.

.TONIGHT…SNOW LIKELY…ESPECIALLY ALONG THE COAST. SNOW

ACCUMULATION UP TO 2 INCHES. LOWS AROUND 30. LIGHT WINDS.

.THURSDAY…CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE 30S.

NORTH TO WEST WIND 10 TO 25 MPH.

.THURSDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS.

LOWS IN THE LOWER 20S TO LOWER 30S. NORTH TO WEST WIND

10 TO 25 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 36 30 37 / 60 40 40

GIRDWOOD 36 30 36 / 80 40 40

This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Thursday, March 12th. Thanks and have a great day.

Wed, March 11th, 2009
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
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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.