Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, December 13th 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 still possible in steep upper elevation windloaded terrain where multiple layers of buried surface hoar exist in the upper 12 inches of the snowpack. The primary concern today is triggering a slide on one of these layers, especially if buried under newly formed windslab. If and when the north winds pick up, wind driven snow will further stress the buried surface hoar layers and increase the avalanche danger on leeward aspects.
We received a report of a small skier triggered avalanche somewhere in the Magnum/Cornbiscuit area. The windslab was only 6 inches deep, but it entrained quite a bit of snow on the way down. I’m not sure if it ran on one of the many layers of buried surface hoar that formed the past two weeks, but I can only assume. The surface hoar layers formed from the valley bottoms to the ridgetops nearly everywhere in Turnagain Pass and were covered up by small incremental amounts of snow this past week. For the most part the deepest layer a few inches above Thanksgiving crust has lost a lot of its reactivity, and the newer layers in non wind-affected terrain are simply not buried deep enough yet to be a problem. If the winds pick up, remember that surface hoar tends to survive down off of windswept ridgelines in more protected areas, so be prepared for buried pockets midslope and always have an escape route.
As far as the Thanksgiving Rain Crust (TRC), we continue to receive varying observations. It’s buried anywhere from 4 inches to 1.5 feet deep. Some folks are reporting collapsing of the snowpack under the crust where facets are starting to develop while CNFAIC Staff folks are reporting no failures above or below the crust in their snowpit stability tests. No avalanches have run on this layer yet as far as we know. At this point, I think it’s going to take a much bigger snow load before we see any action on or below the crust.
If you were lucky enough to get above the thick fog in Turnagain Pass yesterday, you were treated to a beautiful sunny day. Winds were light out of the northwest yesterday while mountain temperatures dropped into the single digits and low teens. A slight inversion exists this morning with ridgetop temps in the low teens and sea level temps in the single digits. Skies are clear as of 4am, and winds remain light out of the north. Expect fog down low this morning giving way to high clouds this afternoon from a weak low pressure in the gulf. Winds should remain on the light side except near Whittier where west winds will average 20-40mph.
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-
500 AM AKST MON DEC 13 2010
…STRONG WIND THROUGH WEDNESDAY NEAR WHITTIER…
.TODAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY CLOUDY.
PATCHY MORNING FOG INLAND. HIGHS IN THE LOWER TEENS TO MID
20S…COOLEST INLAND. LIGHT WINDS EXCEPT NORTH 10 TO 25 MPH NEAR
SEWARD. NEAR WHITTIER…WEST WIND 20 TO 40 MPH WITH GUSTS TO 60 MPH.
.TONIGHT…CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS ZERO TO
10 ABOVE EXCEPT IN THE LOWER 20S NEAR SEWARD AND WHITTIER.
VARIABLE WIND 10 MPH EXCEPT NORTH 10 TO 25 MPH NEAR SEWARD. NEAR
WHITTIER…WEST WIND 30 TO 45 MPH.
.TUESDAY…NUMEROUS SNOW SHOWERS IN THE MORNING…THEN PARTLY
CLOUDY IN THE AFTERNOON. LITTLE OR NO SNOW ACCUMULATION. HIGHS
10 TO 20 ABOVE…COOLEST INLAND. VARIABLE WIND 10 MPH EXCEPT NORTH 25
TO 40 MPH NEAR SEWARD. NEAR WHITTIER…WEST WIND 40 TO 60 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 26 21 21 / 0 40 40
GIRDWOOD 13 9 11 / 0 60 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light northwest winds yesterday averaging 4-8mph and temps dropping from 20F to 12F. The current temp is 15F with light winds out of the northwest.
-2600′ Seattle Ridge Wx Station-
recorded light north winds yesterday averaging 3-5mph temps dropping from 20F to 6F yesterday. The current temp is 8F with light winds out of the northeast.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. Temps yesterday dropped from 16F to 3F. The current temp is 7F with a total snowpack depth of 54 inches.