Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 19th 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).
Today the avalanche hazard will remain MODERATE overall. Natural avalanches are unlikely, but small human triggered avalanches are possible in steep upper elevation windloaded terrain. Strong winds were observed yesterday pluming snow off isolated peaks and ridgetops in Turnagain Pass. The primary concern today is triggering newly formed windslab near ridgetops.
Our last reported human triggered avalanche was one week ago when a skier triggered a small windslab about 6 inches deep in the Magnum/Cornbiscuit area. We saw a bit more snow moving around at the highest elevations yesterday, so I’m sure some touchy windslab exists out there today. Be especially careful in steep committing terrain where even a small slide can take you for a ride.
Our upper snowpack continues to weaken due to this cold clear weather. While not a problem right now, it 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. Several groups reported full fracture propagation either above or below the crust in their Extended Column Tests the past few days…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 obviously be pockets of windslab up high where a dense slab of 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
It has been 7 days since our last snowfall in Turnagain Pass. Clear and cold has been the name of the game this past week. La Nina is in full force. We had about a 20-25 degree temperature inversion yesterday with sea level temps bottoming out at -8F in Portage and ridgetop temps hitting the low 20’s. Winds were mostly light yesterday, averaging 5-10mph out of the west, but snow plumes were observed on isolated peaks. The inversion continues this morning with temps similar to yesterday. Skies are currently clear, and winds are averaging 5-10mph out of the northwest. Look for clouds to move in later today and maybe a trace of snow this evening. Ridgetop winds should remain on the light side as well.
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-
500 AM AKST SUN DEC 19 2010
…STRONG WIND THROUGH THIS AFTERNOON NEAR WHITTIER…
.TODAY…MOSTLY SUNNY IN THE MORNING THEN BECOMING PARTLY CLOUDY.
HIGHS IN THE MID TEENS TO LOWER 30S…COOLEST INLAND.
NEAR WHITTIER…WEST WIND GUSTING TO 60 MPH DIMINISHING TO 45 MPH IN
THE AFTERNOON. NEAR SEWARD…NORTH WIND 30 MPH DECREASING TO 15 MPH
IN THE AFTERNOON. NORTHWEST WIND TO 10 MPH ELSEWHERE.
.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS
5 BELOW TO 10 ABOVE EXCEPT IN THE LOWER 20S NEAR SEWARD AND
WHITTIER. NORTHWEST WIND TO 10 MPH EXCEPT WEST WIND 15 TO 25 MPH NEAR
.MONDAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE
20S. NORTHWEST WIND 10 TO 15 MPH EXCEPT WEST 20 TO 35 MPH NEAR
TEMPERATURE / PRECIPITATION
SEWARD 28 20 28 / 0 40 40
GIRDWOOD 19 11 25 / 0 40 40
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light northwest winds yesterday averaging 5-12mph with gusts to 24 and temps dropping from 20F to 14F. The current temp has warmed up to 20F with 10mph winds out of the northwest.
-2600′ Seattle Ridge Wx Station-
recorded light westerly winds yesterday averaging 5-10mph with gusts to 20 and temps fluctuating from 11F to 19F yesterday. The current temp is 17F with light winds out of the west.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 7 days. Temps yesterday ranged from 3F to 7F. The current temp is 6F with a total snowpack depth of 53 inches.