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Issued
Fri, February 19th, 2010 - 7:00AM
Expires
Sat, February 20th, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday, February 19th at 7 am. 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).

WEATHER ROUNDUP

AnCNFAIC Staff wave of wind and rain is currently moving through the area. This round of wetness has the snowline pushed way up to 3200 ft. Very strong easterly winds are again present with gusts over 90 at Turnagain ridgetop elevations. The radar shows heavy precipitation moving into our area. The models indicate this weather will move through the area by this afternoon. The jet stream continues to bump into the panhandle and Olympic ridge and turn north right at us. This strong south to north flow is responsible for our warm wet weather. This jet stream pattern is expected to break up next week.

AVALANCHE DISCUSSION

Today’s avalanche danger is HIGH due to the heavy precipitation and wind that is being forecasted by the National Weather Service. This means we have very dangerous avalanche conditions and travel in avalanche terrain is not recommended. Natural avalanches likely and human triggered avalanches very likely.

Yesterday, we saw more natural and human triggered avalanches from Girdwood to Summit Lake. DOT, AK Rail Road, and Alyeska Ski Patrol crews reported significant avalanche activity. Avalanches covered the Seward Highway and the AKRR.

I think we probably reached the apex of the storm and avalanche cycle yesterday morning; however, very strong winds and additional rain and snow are assaulting the mountains again today. With weather like this starting zones reload very quickly. In addition, we are seeing rain pushing back up in elevation. This will add additional stress to the snowpack.

As we look into the weekend and see the weather letting up, we need to keep ourselves in check. This is the exact setup we had two years ago when we had a fatal avalanche in Seattle Creek, followed by a very large storm, followed by anCNFAIC Staff large human triggered avalanche on Sunburst that buried a skier for 15-20 minutes. The Sunburst avalanche happened with the same type of weak layers present and the same 5-10 feet of new storm snow.

We already have one avalanche recovery effort still underway. Don’t charge the backcounty this weekend. Give the mountains and your mCNFAIC Staff a break from the stress.

There are two main weak layers in our snowpack:

1.A thin breakable melt-freeze crust with surface hoar on top of it. We have seen this weak layer up to 3000′ on multiple aspects on both sides of highway at Turnagain Pass. This weak layer is generally buried 4-6 feet deep. Surface hoar has been observed on top of this layer in several pits, as recently as Sunday 2/15/2010. This surface hoar has not been seen in all pits, and these feathery crystals get smaller as you gain elevation, but you have to give a weak layer like this lots of respect. This combination of surface hoar on top of a crust is historically responsible for the majority of avalanche surprises and fatalities.

2.The Jan 7 rain crust is generally buried 6-8 feet deep. This particular weak layer has been reactive to explosive triggers and most likely has been naturally triggered during our current avalanche cycle. This persistent weak layer has been showing significant signs of instability since its formation last month. This weak layer is widespread on all aspects up to 3000 feet.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST FRI FEB 19 2010

…URBAN AND SMALL STREAM FLOOD ADVISORY REMAINS IN EFFECT THROUGH

1000 AM AKST THIS MORNING…

…STRONG WIND THROUGH THIS AFTERNOON THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…

.TODAY…RAIN. HIGHS IN THE 40S. EAST WIND 10 TO 15 MPH EXCEPT EAST

35 TO 50 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.TONIGHT…RAIN LIKELY IN THE EVENING…THEN A CHANCE OF RAIN AND

SNOW AFTER MIDNIGHT. LOWS IN THE UPPER 20S TO MID 30S. EAST WIND 10

TO 15 MPH EXCEPT EAST 15 TO 30 MPH THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM.

.SATURDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN. HIGHS

IN THE MID 30S TO LOWER 40S. VARIABLE WIND 10 MPH EXCEPT EAST

10 TO 20 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.SATURDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN.

LOWS IN THE MID 20S TO MID 30S. VARIABLE WIND 10 MPH.

.SUNDAY…SNOW AND RAIN LIKELY. HIGHS IN THE MID 30S TO LOWER

40S. VARIABLE WIND 10 MPH.

.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN.

LOWS IN THE 20S.

.MONDAY…PARTLY CLOUDY. HIGHS 35 TO 45.

TEMPERATURE / PRECIPITATION

SEWARD 44 32 40 / 100 70 50

GIRDWOOD 43 32 41 / 60 40 40

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 27 degrees F

Winds: very string to extreme with easterly averages in the 30’s and gusts over 90 mph.

2600′-Seattle Ridge Wx Station

Broken. We will fix as soon as possible.

1800′-Center Ridge Wx Station

Current Temp: 35 (5 degree warmer than yesterday)

Precip: .5 inches of water and approx. 6 inches of new snow. Total snowpack depth is 109 inches.

Thanks for checking today’s avalanche advisory. I will post again tomorrow morning February 20th by 0700.

Fri, February 19th, 2010
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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.