Good morning backcountry travelers. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, February 14th 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).
The avalanche danger today is MODERATE on slopes with a shallow snow cover or in steep rocky terrain for deep slab avalanches. There remains a possibility to trigger a deep slab avalanche in these thin snowpack areas. In addition, there is a MODERATE danger for wind slabs on slopes receiving recent wind drifting in the new storm snow.
We received a report yesterday of a skier triggered deep slab avalanche in the Johnson Pass area on Friday, Feb 11, that broke in the loose facets near the ground. The slide was on a northwest facing slope around 36 degrees with the crown estimated at 30 inches. This is the type of avalanche we are most concerned with, one that can be triggered in regions with a shallow snowpack (such as Johnson Pass).
In these shallow areas the slab is often strong enough to allow the weight of a person or snowmachine to travel well onto it before it fails, making it very difficult for escape. Safe travel practices, for example, exposing only one person at a time to a potential hazard, is especially prudent. Also, there are possible trigger points lurking in the deeper snowpacks, such as Turnagain Pass, on the more exposed radical terrain.
The lingering snow showers yesterday added an additional 2-4 inches of light powder to the mountains; this is on top of the 5-8 inches from Friday. Loose snow sluffs and shallow wind slabs were easy to initiate again yesterday and mainly confined to the upper 2-6 inches where density changes in the new snow exist. With the cold temperatures the snow surface should remain loose today but sluffing will likely be less widespread.
Although the winds have been fairly well behaved the past couple days, they did pick up last night from the north and I suspect recent wind slabs to be somewhat sensitive today. Watch for cracks shooting from your sled, board or skis on wind loaded terrain. Also, be wary of any hollow feeling drifts or slabs that have stiffened up over the top of the low density storm snow. Near ridgelines and convex rollovers would be likely spots to trigger a wind slab.
Encyclopedia of avalanche terms.
The snow showers hung on long enough yesterday to lay down a fresh 3-4 inches of low density snow in the Girdwood Valley and Turnagain Pass areas. Overnight, temperatures dropped back into the minus single digits and northerly winds blew 5-10 mph on the ridges, gusting into the mid and upper teens. We should see cold and clear conditions today with temperatures remaining in the single digits. Winds are forecast to pick up from the north, gusting into the 20’s on the ridglines.
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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 FEB 14 2011
…STRONG WIND THROUGH EARLY TUESDAY MORNING FOR FOR WHITTIER AND
.TODAY…SUNNY. AREAS OF BLOWING SNOW…MAINLY NEAR WHITTIER. HIGHS
ZERO TO 15 ABOVE. NORTH TO WEST WINDS 15 TO 30 MPH. NEAR
WHITTIER…SOUTHWEST WINDS 30 TO 45 MPH WITH GUSTS 55 TO 65 MPH. NEAR
SEWARD…NORTH WINDS 15 TO 30 MPH. GUSTS TO 50 MPH.
.TONIGHT…CLEAR. AREAS OF BLOWING SNOW…MAINLY NEAR WHITTIER. LOWS
10 BELOW TO 5 ABOVE…COOLEST INLAND.
NORTH TO WEST WINDS 10 TO 20 MPH. NEAR WHITTIER…SOUTHWEST WINDS 20
TO 45 MPH. HIGHER GUSTS TO 55 MPH IN THE EVENING. NEAR SEWARD…NORTH
WINDS 15 TO 30 MPH WITH GUSTS TO 45 MPH.
.TUESDAY…MOSTLY SUNNY. HIGHS 15 TO 25. NORTH TO WEST WIND 10 TO
20 MPH. NEAR WHITTIER…SOUTHWEST WINDS 25 TO 45 MPH DIMINISHING 15
TO 25 MPH BY NOON. NEAR SEWARD…NORTH WINDS 15 TO 30 MPH WITH GUSTS
TO 45 MPH IN THE MORNING.
TEMPERATURE / PRECIPITATION
SEWARD 13 2 23 / 0 0 0
GIRDWOOD 12 -4 21 / 0 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature -4 F. Westerly wind 10 mph gusting in the upper teens.
-2600′ Seattle Ridge Wx Station-
Temperature -3 F. North wind 5-10 mph gusting into the mid teens.
-1800′ Center Ridge Wx Station-
Temperature 0 F. 4″ of new low density snow.