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Issued
Mon, December 20th, 2010 - 7:00AM
Expires
Tue, December 21st, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, December 20th 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

Today the avalanche hazard remains MODERATE overall. Natural avalanches are unlikely, but small human triggered avalanches are still possible in steep upper elevation windloaded terrain. You may find a few lingering pockets of sensitive windslab at the highest elevations covered up by an inch or two of new snow. Expect some shallow surface sluffing on steep slopes today as well.

AVALANCHE DISCUSSION

We received a report of a skier triggered avalanche yesterday on the back side of Pastoral. While details are limited, it sounds like it was triggered on recently formed windslab from Saturday’s gusty winds. I’m sure some touchy windslab still exists out there today, so be careful in steep committing terrain where even a small slide can take you for a ride.

Our upper snowpack weakened considerably during last week’s cold clear weather. While not a problem right now, it most likely will be in the future. We have numerous persistent weak layers in the top 12 inches but lack a sufficient slab on top to cause avalanches. Sugary facets continue to develop above and below the Thanksgiving Rain Crust (TRC), buried about a foot deep in most places. The past few days we have started to see full fracture propagation above and below the crust in Extended Column Tests…a sign that this layer continues to weaken and will likely become a problem when we get our next big storm. Multiple layers of surface hoar also exist above the TRC, but like I mentioned before, we generally lack a dense slab of snow on top of these layers to cause avalanches. The exception to this will be pockets of windslab up high where dense wind-driven snow is sitting on lighter density snow and buried surface hoar.

Check out an encyclopedia of terms here: www.fsavalanche.org/Encyclopedia.aspx

WEATHER ROUNDUP

A weak surface front dropped an inch of snow last night in Turnagain Pass after seven days of cold clear weather. The inversion eased up a bit yesterday as clouds moved in around noon. Mountain temps warmed up to the mid teens to low 20’s while winds remained light all day. The inversion broke last night with mountain temps now reading 10-12F and sea level temps at 16F. It is currently snowing lightly while ridgetop winds remain light. We may squeeze a few more inches of snow out of this system before it dissipates later today. The northwest winds may increase a bit today while mountain temps will continue to gradually drop.

Jon will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

600 AM AKST MON DEC 20 2010

…STRONG WIND THROUGH TUESDAY NEAR WHITTIER….

.TODAY…SNOW IN THE MORNING…THEN A CHANCE OF SNOW IN THE

AFTERNOON. SNOW ACCUMULATION 1 TO 2 INCHES. HIGHS IN THE MID

TEENS TO LOWER 30S…COOLEST INLAND. NORTH 25 TO 35 MPH NEAR SEWARD.

WEST WIND 45 TO 60 MPH NEAR WHITTIER. NORTHWEST WIND 10 TO 15 MPH

ELSEWHERE.

.TONIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS 5 TO 25

ABOVE…COOLEST INLAND. NORTH 25 TO 35 MPH NEAR SEWARD. WEST WIND 45

TO 60 MPH NEAR WHITTIER. NORTHWEST WIND TO 10 MPH ELSEWHERE.

.TUESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE MID

TEENS TO MID 30S…COOLEST INLAND. NORTH 20 TO 30 MPH NEAR SEWARD.

WEST WIND 40 TO 55 MPH NEAR WHITTIER. LIGHT WINDS ELSEWHERE.

TEMPERATURE / PRECIPITATION

SEWARD 28 21 28 / 100 40 50

GIRDWOOD 22 13 20 / 80 30 20

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded light west winds yesterday averaging 2-10mph and temps ranging from 18F to 23F. The current temp has cooled off to 11F with 5mph winds out of the northwest.

-2600′ Seattle Ridge Wx Station-

recorded mostly light and variable winds yesterday averaging 3-15mph. Temps warmed up from 13F to 20F during the day yesterday. The current temp is 12F with light winds out of the northwest.

-1800′ Center Ridge Wx Station-

recorded 1 inch of new snow last night. Temps yesterday warmed up from 6F to 18F. The current temp is 10F with a total snowpack depth of 52 inches.

Mon, December 20th, 2010
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.