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Issued
Tue, December 28th, 2010 - 7:00AM
Expires
Wed, December 29th, 2010 - 7:00AM
Forecaster
Jon Gellings
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, December 28th 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 is LOW, with pockets of MODERATE. Natural avalanches and human triggered avalanches are unlikely throughout our general advisory area, while small human triggered avalanches are possible in steep upper elevation windloaded terrain. Be on the lookout for pockets of sensitive wind slab in isolated areas at upper elevations. Currently, a 964mb Low pressure system is moving toward us, which will increase the avalanche danger tomorrow.

AVALANCHE DISCUSSION

We are about to receive a potentially significant amount of new snow overnight, which might be pleasing to hear, but is going to throw a wrench into our snowpack stability assessments. We still have layers of facets and surface hoar which are buried in the snowpack, and they do not look like they are leaving anytime soon. Do not forget about them, because they will not disappear even if you think they did.

The layer of facets growing underneath the Thanksgiving Rain Crust (TRC) has been recently noted as being the most unstable layer in our area. Recent tests on Tincan and Eddies revealed that this layer is exhibiting signs of moderate to high strength, with fairly low energy and non-planar breaks. Once we get a large stress added to this snow, I would expect failures within this layer throughout our advisory area. It is currently unclear just how big of a punch this storm will bring to us, but our alertness should be elevated until we find out.

In steeper, more exposed slopes at higher elevations, the TRC has been observed much closer to the surface than in most CNFAIC Staff areas. We got a report yesterday of shooting cracks at the East end of Center Ridge, where one of these snow pillows was recently deposited and was showing increased energy. Recent human triggered avalanche activity points out that these areas have been showing increased activity over CNFAIC Staff areas as well.

A significant recent avalanche report from Goat Couloir on upper Crow Creek Rd tells of how a backcountry skier was briefly caught before they were able to control the fall and ski to the flank of the avalanche. From this vantage point, they were able to watch while the avalanche debris cascaded down the rest of the slope. This area has terrain steeper than 50 degrees at an elevation of around 6000 ft a.s.l. Utilize safe travel procedures whenever you are out in the backcountry, but more cautious and conservative decision making in committing terrain like this is essential.

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

WEATHER ROUNDUP

Temperatures at different elevations seem fairly similar, with fairly light winds. It should warm up a little bit with the approach of our storm over night. There is a little bit of precipitation currently showing up on the Middleton Island radar, but more should follow with this new storm. Tomorrow will be the first snowstorm with a larger amount of measurable precipitation since our Blizzard warning on December 3.

I 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

500 AM AKST TUE DEC 28 2010

.TODAY…PARTLY CLOUDY WITH ISOLATED SNOW SHOWERS THIS MORNING. HIGHS

IN THE LOWER TEENS TO LOWER 30S…COOLEST INLAND. NEAR SEWARD…NORTH

WINDS 15 MPH WITH LOCAL GUSTS TO 25 MPH THIS MORNING. NEAR

WHITTIER…SOUTHWEST WINDS 15 MPH WITH LOCAL GUSTS TO 35 MPH THIS

MORNING. LIGHT WINDS ELSEWHERE.

.TONIGHT…INCREASING CLOUDS WITH SNOW LIKELY AFTER MIDNIGHT. SNOW

ACCUMULATION 1 TO 3 INCHES. LOWS ZERO TO 10 ABOVE EXCEPT IN THE MID

20S NEAR SEWARD AND WHITTIER. VARIABLE WIND TO 10 MPH. NEAR SEWARD…

NORTH WIND 10 MPH.

.WEDNESDAY…SNOW LIKELY. SNOW ACCUMULATION 1 TO 4 INCHES. HIGHS IN

THE MID TEENS TO LOWER 30S…COOLEST INLAND. VARIABLE WIND TO 10 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 25 22 28 / 20 60 70

GIRDWOOD 16 9 26 / 0 70 70

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded wind speeds yesterday from 10-22mph, and temps from 18F to 20F. The current temp is 18F with 3mph winds out of the northeast.

-2600′ Seattle Ridge Wx Station-

recorded mostly light southeast winds yesterday averaging 1-7mph, while temps ranged from 20F to 23F during the day. The current temp is 19F with calm winds.

-1800′ Center Ridge Wx Station-

recorded 1″ settlement in the past 24hrs. Temps yesterday ranged from 19F to 26F. The current temp is 19F with a total snowpack depth of 52 inches.

Tue, December 28th, 2010
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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. Dangerous avalanche conditions. 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.