Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, 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).
Since February 25, Turnagain Pass has received 5.5 feet of snow and 7 inches of water with even more at the higher elevations. It has pretty much snowed nine out of the last ten days! The pass picked up 1 inch of snow yesterday while ridgetop winds were light and variable. Temperatures took a serious nose dive in the last 24 hours and currently range from -2F at 3800 feet to 15F at sea level. As of 4am this morning, skies are mostly cloudy with ridgetop winds averaging 15 mph out of the west gusting to 27mph. Today is the calm before the next major storm rolls in tonight. Expect clearing skies later today, winter-like temperatures from zero to ten degrees, and light to moderate southerly winds averaging 10-20mph.
Today the avalanche danger is rated MODERATE. Natural avalanches are unlikely, but human-triggered avalanches will be possible on windloaded slopes steeper than 35 degrees. Our main concern today is sensitive windslab above treeline where the snowpack is more wind-affected from Friday’s big storm. Windslabs 6-18 inches thick were reactive to human triggers on steep test slopes yesterday.
Jon and I toured up Tincan yesterday and found no signs of instability on the non-wind-affected snow below treeline. Above treeline, the snowpack varied from powder to soft windslab to completely supportable hardslab. The windslabs we intentionally triggered on small test slopes failed on the softer snow underneath and generally did not propagate very far. The harder windslabs were more reactive than the soft slabs, fracturing up to 10 feet wide on small rollovers approaching 40 degrees.
Most of these windslabs are small and manageable slabs that will fracture right under your skis, board, or sled. Ski cuts are very effective with the softer slabs if you know how to do them safely. The main hazard would be unexpectedly triggering one above steep complex terrain. Harder, drum-like windslabs also exist, especially at the higher elevations above 2500 feet. These are the ones to look out for because they could fracture unexpectedly above you.
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 MAR 7 2010
…BLIZZARD WATCH IN EFFECT FROM LATE TONIGHT THROUGH MONDAY
AFTERNOON THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…
.TODAY…NUMEROUS SNOW SHOWERS IN THE MORNING NORTH OF MOOSE
PASS…THEN BECOMING PARTLY SUNNY. ADDITIONAL SNOW ACCUMULATION UP TO
2 INCHES. HIGHS IN THE LOWER TO MID 20S. NORTH TO WEST WIND 10 TO
15 MPH BECOMING VARIABLE IN THE AFTERNOON. THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…WEST WIND 15 TO 25 MPH SHIFTING TO THE
EAST 10 TO 20 MPH IN THE AFTERNOON.
.TONIGHT…SNOW DEVELOPING IN THE EVENING. SNOW AND BLOWING SNOW
POSSIBLY REDUCING VISIBILITY TO ONE QUARTER MILE OR LESS AFTER
MIDNIGHT THROUGH PORTAGE VALLEY AND TURNAGAIN ARM. SNOW ACCUMULATION
3 TO 8 INCHES. TEMPERATURES STEADY IN THE LOWER TO MID 20S. NORTH TO
EAST WIND 10 TO 15 MPH INCREASING TO 15 TO 30 MPH AFTER MIDNIGHT.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 15 TO 30 MPH
INCREASING TO 30 TO 45 MPH TOWARD MORNING.
.MONDAY…SNOW AND BLOWING SNOW POSSIBLY REDUCING VISIBILITY TO ONE
QUARTER MILE OR LESS THROUGH PORTAGE VALLEY AND TURNAGAIN ARM. SNOW
MIXING WITH RAIN AT SEA LEVEL IN THE AFTERNOON. SNOW ACCUMULATION 4
TO 8 INCHES. HIGHS IN THE 30S. NORTH TO EAST WIND 20 TO 35 MPH EXCEPT
EAST 50 TO 65 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
TEMPERATURE / PRECIPITATION
SEWARD 24 24 35 / 0 100 100
GIRDWOOD 22 22 33 / 70 80 70
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded calm to light winds yesterday averaging 0-15mph. The current temp is -2F (17 degrees colder than yesterday) with light winds averaging 15mph out of the west.
-2600′ Seattle Ridge Wx Station-
is not working.
-1800′ Center Ridge Wx Station-
recorded 1 inch of new snow in the last 24 hours. The current temp is 6F (15 degrees colder than yesterday) with a total snowpack depth of 125 inches (5 inches of settlement in the last 24 hours/11 inches of settlement in the last 42 hours).