Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, February 28th 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 4-6 inches of new snow fell last night in Turnagain Pass, bringing our snowfall total for the last 3 days to around 12 inches of snow and 0.7 inches of water. Skies were mostly cloudy yesterday with a few sun breaks, ridgetop winds averaged 10-20mph out of the east and southeast with gusts to 35mph, and mountain temperatures ranged from the mid teens to upper 20’s. As of 4am this morning, winds continue to average 10-20mph out of the east while temperatures have warmed up by about nine degrees to the low 20’s. It is currently snowing in Girdwood with about 7 inches of new snow that fell last night. A large low pressure system and its associated front will move through our area today and tonight bringing an additional 9-14 inches of snow to the higher elevations. Look for rain to develop below 800 feet later today as temperatures continue to rise. Easterly ridgetop winds will average 10-25mph today while mountain temperatures will warm up to the mid 20’s to low 30’s.
The avalanche hazard has increased since yesterday. Today the avalanche danger is rated CONSIDERABLE on all windloaded slopes steeper than 35 degrees. All CNFAIC Staff slopes have a MODERATE danger. We now have up to a foot of new snow on top of a slick crust and winds strong enough to transport this snow to leeward aspects. Wind slabs 1-2 feet thick near ridgetops will be sensitive to human triggers. As temperatures warm up and the snow continues to fall today, an increasingly top-heavy slab will form on top of the crust creating unstable conditions. Large sluffs are likely on steep non-windaffected slopes over 40 degrees and have the potential to run long distances. Human-triggered avalanches will be likely today on steep windloaded slopes with natural avalanches possible on any actively loading slopes. Rain on new snow will also cause almost instant natural avalanching, so be careful on lower elevation slopes later in the day.
Avalanche activity the last few days has been limited to sluffing on steep slopes and small windslabs near the ridgetops. I expect more action today as additional snow, wind, and warming temperatures create an upside-down 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 slab avalanches and sluffs today.
Jon and I toured up Lipps yesterday specifically looking for old buried surface hoar layers and the Jan. 7 rain crust. We easily found both at 2300 and 2800 feet on southwest aspects, but neither was reactive in our isolated column stability tests. The Jan. 7 crust was anywhere from 3 to 6 feet deep, and the buried surface hoar layer was consistently 6 inches above the crust. Both layers were smCNFAIC Staffed by extremely dense storm snow from the Feb. 9-19 storm. I think it’s going to take one heck of a storm to reactivate these layers at this point. At the least we’ll see them again in the spring when the snowpack goes isCNFAIC Staffmal.
Numerous glide cracks formed this past week at the mid elevations, so keep an eye out for these gaping crevasse-like features that will swallow humans and sleds. As always, stay out from under them in case they decide to avalanche.
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 FEB 28 2010
.TODAY…SNOW BECOMING RAIN AND SNOW IN THE AFTERNOON. SNOW
ACCUMULATION 2 TO 5 INCHES. HIGHS IN THE UPPER 20S TO MID 30S.
VARIABLE WIND 10 MPH.
.TONIGHT…SNOW. SNOW ACCUMULATION 3 TO 6 INCHES. LOWS IN THE MID
20S TO LOWER 30S. EAST WIND 10 TO 20 MPH.
.MONDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE
AFTERNOON. SNOW ACCUMULATION 1 TO 3 INCHES OVER THE HIGHER
ELEVATIONS. HIGHS IN THE 30S. EAST WIND 10 TO 15 MPH EXCEPT EAST 25
TO 40 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.MONDAY NIGHT…SNOW AND RAIN. LOWS IN THE UPPER 20S TO MID 30S.
VARIABLE WIND 10 MPH EXCEPT EAST 10 TO 25 MPH THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM.
.TUESDAY…RAIN. HIGHS IN THE MID 30S TO LOWER 40S. SOUTHEAST WIND 10
TO 20 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 29 29 36 / 80 80 80
GIRDWOOD 29 29 37 / 80 80 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light to moderate easterly winds yesterday averaging 10-20mph with gusts to 35mph. The current temp is 19F (8 degrees warmer than yesterday) with winds averaging 17mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded light to moderate southeasterly winds yesterday averaging 10-20mph with gusts to 31mph. Winds are currently averaging 8mph out of the southeast this morning.
-1800′ Center Ridge Wx Station-
recorded 4 inches of new snow and 0.2 inches of water in the last 24 hours. The current temp is 23F (9 degrees warmer than yesterday) with a total snowpack depth of 92 inches.