Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, March 1st 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).
AnCNFAIC Staff 8 inches of new snow fell in the last 24 hours in Turnagain Pass, bringing our snowfall total for the last 4 days to around 18-20 inches of snow and 1.3 inches of water. Yesterday ridgetop winds averaged 10-20mph out of the east, and mountain temperatures ranged from the low to upper 20’s. Since 6pm last night, ridgetop winds on Sunburst have averaged 25-40mph out of the east with gusts to 57. Winds on Seattle Ridge were a bit lighter, averaging 20-30mph out of the southeast. It started raining at sea level around midnight last night as temperatures shot up to 37F. As of 4am this morning, ridgetop winds continue to average 20-40mph out of the east while temperatures range from 37F@sea level to 31F@1800′ to 24F@3800′. A complex low pressure system in the gulf along with southeasterly flow will bring an additional 2-4 inches of snow to the higher elevations and rain below 1000 feet today. Look for strong to gale force easterly winds today averaging 25-40mph and mountain temperatures in the mid 20’s to mid 30’s.
Today the avalanche danger is rated CONSIDERABLE on all windloaded slopes steeper than 35 degrees. This means that dangerous avalanche conditions exist, and conservative decision-making is essential to staying out of trouble. Twenty inches of snow on top of a slick crust, and winds strong enough to transport this snow to leeward aspects, means that human-triggered avalanches are likely on steep wind-loaded slopes. Natural avalanches are certainly possible on any actively loading slopes over 35 degrees. Rain on new snow will also cause almost instant natural avalanching, so be careful on lower elevation slopes if the rainline creeps higher today.
Avalanche activity this past week has been limited to sluffing on steep slopes and small windslabs near the ridgetops. I expect way more action today as additional snow, much stronger winds, and warmer temperatures create an upside-down cohesive slab on an extremely slick crust. This crust formed during the powerful Feb. 9-19 storm that pummeled our area with rain, high winds, and heavy dense snow at the higher elevations. The snow is like concrete underneath all this fluff and thus provides an excellent sliding surface for soft slab avalanches today. Matt and I toured up to treeline on Tincan yesterday and found that the foot of new snow was not cohesive enough yet to propagate a fracture. We did, however, easily trigger loose snow sluffs on slopes approaching 40 degrees. We did not get high enough to test the wind-affected slopes where I suspect we could have triggered soft windslabs.
Matt 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 MAR 1 2010
…STRONG WIND TUESDAY MORNING THROUGH TUESDAY EVENING THROUGH
PORTAGE VALLEY AND ALONG TURNAGAIN ARM…
.TODAY…SNOW AND RAIN. SNOW ACCUMULATION UP TO 4 INCHES OVER HIGHER
ELEVATIONS. HIGHS IN THE MID 30S TO LOWER 40S. NORTH TO EAST WIND 10
TO 20 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 20 TO
35 MPH DIMINISHING TO 10 TO 20 MPH.
.TONIGHT…RAIN AND SNOW. SNOW ACCUMULATION UP TO 3 INCHES OVER THE
HIGHER ELEVATIONS. LOWS IN THE UPPER 20S TO MID 30S. NORTH TO EAST
WIND 10 TO 20 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST
WIND 10 TO 15 MPH INCREASING TO 20 TO 35 MPH AFTER MIDNIGHT.
.TUESDAY…SNOW AND RAIN. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS
IN THE 30S. EAST WIND 35 TO 50 MPH THROUGH PORTAGE VALLEY AND
TEMPERATURE / PRECIPITATION
SEWARD 38 33 38 / 100 100 80
GIRDWOOD 37 30 38 / 90 70 70
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light to moderate easterly winds yesterday averaging 10-20mph with gusts to 34mph. The current temp is 24F (5 degrees warmer than yesterday) with strong winds averaging 38mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded light easterly winds yesterday averaging 5-10mph. Winds are currently moderate averaging 20mph out of the southeast.
-1800′ Center Ridge Wx Station-
recorded 8 inches of new snow and 0.6 inches of water in the last 24 hours. The current temp is 31F (9 degrees warmer than yesterday) with a total snowpack depth of 100 inches.