Turnagain Pass
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Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, March 29th 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).
WEATHER ROUNDUP
About 2-6 inches of new snow fell in the last 24 hours in Turnagain Pass. Yesterday saw scattered snow showers, a few sunny breaks, and gusty east winds. Mountain temperatures warmed up to the mid 20’s to upper 30’s while ridgetop winds averaged 20-30mph in the afternoon. As of 4 am this morning, ridgetop winds are averaging 5-10mph out of the north and northeast while temperatures range from 33F@sealevel to 29F@1800′ to 22F@3800′. It is currently snowing/raining at sea level in Girdwood. Shortwaves spinning off the low in the gulf will continue to bring pulses of rain and snow today with sunny breaks in between. We could get an additional 2-5 inches of new snow. Mountain temperatures will warm up to the mid to upper 20’s at the higher elevations and push 40 degrees at the mid elevations while ridgetop winds should remain on the light to moderate side out of the east.
AVALANCHE DISCUSSION
The avalanche danger remains CONSIDERABLE today on all slopes steeper than 35 degrees. This means that human-triggered avalanches are likely on steep slopes while natural avalanches are possible. Saturday’s 1-2 feet of heavy wet snow continues to settle rapidly into a dense slab. It fell on a variety of weak layers including a slick sun crust on southerly aspects, cold powdery snow on higher elevation north aspects, and a recently formed layer of surface hoar on all aspects up to 4000 feet. You may find a few fresh windslabs near the ridgetops as well from yesterday’s new snow and strong easterly winds. The wet snow avalanche danger will also be on the rise today if the sun breaks through the clouds. We will likely see the new snow slide easily on steep southerly aspects. If the sun is out for an extended period, natural wet sluffs may gouge into the snowpack and trigger slab avalanches on deeper buried weak layers.
A few sunny breaks yesterday quickly turned the southerly slopes to mush. We saw some small wet snow sluffs on Sunnyside below sun-warmed rock outcrops. Jon noticed a recent natural avalanche on the south face of Sunburst yesterday that broke 60 feet wide, ran downslope a bit, then fractured an additional 60 feet to one side. He also spotted a recent natural in Todd’s Run on the north side of Tincan that ran 1000 feet. Matt and I toured up Tincan yesterday and thankfully did not have to break trail through the 1-2 feet of mashed potatoes. We intentionally triggered an avalanche on a 40 degree test slope at 2000 feet on a west aspect (see photo below). It fractured 30 to 40 feet wide, broke 2 to 2.5 feet deep, and ran 150 feet on the melt-freeze crust that formed March 18. We also got 15 ft. long shooting cracks on steep rollovers breaking down to a sun crust. Matt found a layer of buried surface hoar on a windloaded west aspect at 2500 feet 2.5 feet down. It failed twice on the backcut during compression tests producing clean and fast Q1 shears. Although it took slopes pushing 40 degrees to fracture, we both agreed that we would not feel safe skiing big open steep slopes in the lesser 35 degree range. This thick slab of snow is still actively settling right now, so I would stay off the big slopes and manage my terrain carefully today.
Of equal concern today are the multiple buried weak layers in the top 2 to 4 feet of the snowpack that formed during the last few weeks. New snow avalanches triggered today could step down to these deeper layers. These weak layers include numerous sun crusts on SE-S-SW aspects, a 1-inch thick melt-freeze crust below 2000 feet on all aspects, large developed facets on shallow north aspects above 3000 feet, and 3 separate scattered layers of buried surface hoar on multiple aspects. Some of these layers were responsible for five skier-triggered avalanches this past Thursday and Friday:
– North aspect of Granddaddy Chute (Bertha Creek drainage), 2.5 feet deep, 150-200 feet wide.
-Taylor Pass between Sunburst and Magnum, windloaded north aspect, triggered while skinning, 3400 feet elevation, 80-90 feet wide, 1.5-2 feet deep, ran 300 feet on layer of buried surface hoar.
-South face of Sunburst at highest point, triggered while skiing on convex rollover, 6-9 inch deep crown face, ran 3/4 of the way to the bottom, happened at 12:30pm.
– North face of Sunburst near the top of Elevator Shaft. The skier triggered it on his third jump turn from the top. It broke 2-3 feet deep and ran 1000 feet.
-South face of A1 in the Upper Girdwood Valley between 4000 and 5000 feet. No information reported on this slide.
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-
INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS
500 AM AKDT MON MAR 29 2010
.TODAY…SNOW…MIXED WITH RAIN AT SEA LEVEL IN THE MORNING. THEN
NUMEROUS RAIN AND SNOW SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION UP
TO 3 INCHES. HIGHS IN THE UPPER 30S. VARIABLE WIND 10 MPH EXCEPT
NORTH 15 TO 25 MPH NEAR SEWARD.
.TONIGHT…RAIN AND SNOW SHOWERS…MAINLY ALONG THE COAST. LITTLE OR
NO SNOW ACCUMULATION. LOWS IN THE UPPER 20S TO MID 30S. NORTHEAST
WIND 10 TO 15 MPH.
.TUESDAY…SNOW AND RAIN LIKELY. LITTLE OR NO SNOW ACCUMULATION.
HIGHS AROUND 40. VARIABLE WIND 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 43 29 43 / 100 80 60
GIRDWOOD 43 31 42 / 80 50 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded moderate winds yesterday afternoon averaging 20-25mph out of the east with gusts to 37mph. The current temp is 22F (1 degree warmer than this time yesterday) with winds averaging 10mph out of the northeast.
-2600′ Seattle Ridge Wx Station-
recorded moderate to strong winds yesterday afternoon averaging 20-30mph out of the southeast with gusts to 46mph. The current temp is 25F (1 degree warmer than this time yesterday) with winds averaging 5mph out of the north.
-1800′ Center Ridge Wx Station-
recorded 0 inches of new snow and 0.5 inches of water in the last 24 hours. The current temp is 29F (1 degree warmer than this time yesterday) with a total snowpack depth of 139 inches (3+ inches of settlement in the last 24 hours). I’m guessing there’s at least 5 inches of new snow, but the snowpack is settling much faster so it’s difficult to get an exact number.
