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Issued
Mon, March 7th, 2011 - 7:00AM
Expires
Tue, March 8th, 2011 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Good morning backcountry travelers. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, March 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

The avalanche danger is generally LOW. There remain pockets of MODERATE danger for an avalanche to break into deeper weak layers creating a potentially unmanageable slide. These spotty trigger points are most likely associated with lingering hard wind slabs and can be found on steep wind loaded slopes with rollovers, rocky features and gullies. There are also pockets of MODERATE for sluffs initiated by direct sun on southern aspects.

AVALANCHE DISCUSSION

It was fairly quiet in the backcounty this weekend despite the warm temperatures, light wind and mostly sunny skies. It seems navigating the mixed bag of facets, crusts and wind slabs, all coming in a variety of thicknesses, have not been the highest on the priority list. Of note, and to add to the surface conditions, I did notice a thin sun crust over soft snow on a few south aspects where winds were calm yesterday.

A report came in from mid elevations in the Girdwood valley where enough warming initiated sluffing on south aspects with some sluffs propagating into small slabs. Calm winds and direct sun with the warming temperatures may increase this today. Watch for dampening of the surface and any rollerballs, especially under rocks or trees.

Today, the main concern is triggering a slab avalanche that fails in the weak sugary snow near the ground. These are most likely to be found in shallow wind loaded terrain where an older lingering wind slab can step down to the deeper weak faceted snow beneath. In this case a large avalanche may be triggered similar to many of the natural avalanches seen during the wind event over the last week of February. A look yesterday at a 3-4 foot deep snowpack in a NE starting zone ~3800′ confirmed this concern showing extremely poor structure in shallow areas.

Smooth snow surfaces are clues to where wind slabs are present. These are most suspect for triggering on slopes that rollover or are unsupported (meaning no compressional support below, such as a slope above cliffs) along with shallow rocky areas and steep cross loaded gullies. As time goes on with no added precipitation these slabs are becoming more difficult to trigger. However, with the recent warm up in temperatures to around 30 degrees I did notice the old drifts becoming slightly more sensitive yesterday. This may again be the case today.

WEATHER ROUNDUP

Temperatures felt down right balmy yesterday anywhere out of the breeze. We hit the mid to upper 20’s at 3500′ and the upper 30’s at 1000′. Winds remained light with gusts in the 20’s from an easterly direction. Overnight temperatures remained in the 20’s at all stations above 300′ with a very strong but shallow inversion below 300′. Today expect sunny skies and temperatures in the upper 20’s and 30’s with light easterly winds. This persistent high pressure over the state looks like it is locked in place for now. The groomers are nice.

For kicks, some snowfall numbers:

We have had only 16-20” of new snow in the Turnagain Pass area in the past 4 weeks (since Feb. 4th, first day after the early February rain/snow event). No new snow is in the forecast, yet.

Center Ridge SNOTEL site:

November – 123“

December – 29“

January – 63”

February – 31”

To date, total snowfall is 246” which has settled to a snow depth of 81”. SNOTEL’s do not track accumulated snowfall but we can compare current SWE (Snow Water Equivalent) and snow depth to the long term average. SWE is roughly 68% of average while snow depth roughly 83%.

ANNOUNCEMENTS An APU student is conducting a survey on backcountry skiing group dynamics. Click on the link to participate in research on avalanche safety. Click here to take survey

The Forest Service is installing winter use bridges across Granite creek in Turnagain Pass. Be aware of an ice road from the Lyon creek bridge south towards Johnson Pass on the West side of the highway. Heavy equipment will also be used in the area.

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

500 AM AKST MON MAR 7 2011

.TODAY…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS SOUTH OF MOOSE

PASS. ELSEWHERE…MOSTLY SUNNY. HIGHS IN THE MID 30S TO LOWER 40S.

VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 10 TO 15 MPH.

.TONIGHT…PARTLY CLOUDY. LOWS 10 TO 25 ABOVE…COOLEST INLAND.

LIGHT WINDS EXCEPT NORTH 10 TO 15 MPH NEAR SEWARD.

.TUESDAY…MOSTLY SUNNY. HIGHS IN THE LOWER TO MID 30S. LIGHT

WINDS EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.

.TUESDAY NIGHT…CLEAR. LOWS 5 TO 25 ABOVE…COOLEST INLAND.

LIGHT WINDS EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.

.WEDNESDAY…SUNNY. HIGHS IN THE LOWER TO MID 30S. LIGHT WINDS

EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 38 24 35 / 20 0 0

GIRDWOOD 35 20 33 / 0 0 0

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

Temperature 22 degrees. NE wind around 10mph gusting into the 20’s.

-2600′ Seattle Ridge Wx Station-

Temperature 27 degrees. SE wind around 10mph gusting into the 20’s.

-1800′ Center Ridge Wx Station-

Temperature 29 degrees. No new snow.

Mon, March 7th, 2011
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.