Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, February 8th 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 is increasing to CONSIDERABLE for today. If the forecast becomes verified, then several inches of new snow and strong easterly winds will have created dangerous avalanche conditions. Shallow areas of the snowpack are suspect for deep slab avalanches. Areas of sensitive wind slabs created last night and today could break and step down to our previously buried weak layers. Triggering these deep slab avalanches from thin spots in rocky terrain, or areas with a shallow snowpack, is likely.
There was one reported snowboarder triggered avalanche in our advisory area yesterday. This was on a south facing slope around 3400′ on Magnum, and is estimated at 150-200′ wide, 600-800′ long, and 2-3′ deep in most areas; up to 5′ deep in some areas.
Over the past two days, we have heard/felt large collapses (which created “whoomph” sounds), heard of two new human triggered avalanches, and saw one new natural avalanche (Glide Avalanche photo in gallery). This information, coupled with increasing stress on an already sensitive snowpack, warrants increasing caution while travelling on or around slopes steeper than 30 degrees. The weak layers of greatest concern are the faceted snow grains from cold, High Pressure weather events during December, and buried up to several feet deep on top of the Thanksgiving Rain Crust (TRC).
Our previous weather events have left us with a classic slab avalanche recipe in many areas. Our 2010-11 mixing bowl consists of a growing 2-4+’ hard slab, layered above 6” – 2′ of weak faceted snow. If you load all of this on top of a good sliding surface (TRC) in suitable terrain, the potential avalanche is ready to go. This image shows an example of the situation we are dealing with:
Our snow cover this year is showing below average depth, and is comprised of a variety of weak layers. This setup has shown us two different areas to trigger our current deep slab so far. One is in the upper elevation rocky terrain, where variably thin spots exist and a person could collapse a buried weak layer and trigger an avalanche. The CNFAIC Staff is in regions where the overall snow depths are shallow. Remotely triggering an avalanche from above, from the side, or from below, is LIKELY and more widespread (Johnson Pass and south through Summit Lake and north through the Girdwood Valley area). Avalanches in these areas could potentially break large with high consequences, so avoiding terrain closely connected to slopes above 30 degrees is recommended. Encyclopedia of avalanche terms.
The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it! Click here to take survey or cut and paste the address directly: https://www.surveymonkey.com/s/THWXVCD
The weather is changing from clear yesterday, to stormy today. Easterly winds are increasing, and temperatures are forecasted to increase as well. There is a large amount of precipitation being aimed toward us from Prince William Sound, but it is currently being absorbed by the glacial buffer.
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 TUE FEB 8 2011
…STRONG WIND THROUGH LATE THIS EVENING THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…
.TODAY…SNOW…BECOMING MIXED WITH RAIN ALONG THE COAST. SNOW
ACCUMULATION 4 TO 8 INCHES. HIGHS IN THE 30S. NORTH TO EAST WIND
10 TO 25 MPH WITH GUSTS TO 35 MPH NEAR WHITTIER IN THE AFTERNOON.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 30 TO 45 MPH
INCREASING TO 45 TO 60 MPH IN THE AFTERNOON.
.TONIGHT…RAIN AND SNOW BECOMING ALL RAIN NEAR SEA LEVEL.
ADDITIONAL SNOW ACCUMULATION 2 TO 4 INCHES THROUGH TURNAGAIN
PASS. LOWS IN THE LOWER TO MID 30S. NORTH TO EAST 10 TO 25 MPH
WITH GUSTS TO 35 MPH NEAR WHITTIER…DECREASING TO 15 MPH OR LESS
AFTER MIDNIGHT. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST
WIND 40 TO 55 MPH DECREASING TO 25 TO 40 MPH AFTER MIDNIGHT.
.WEDNESDAY…RAIN. HIGHS IN THE MID 30S TO LOWER 40S. SOUTH
TO EAST WIND 5 TO 20 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 38 34 39 / 100 100 80
GIRDWOOD 35 34 38 / 100 90 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station- Temperature 17F degrees. Winds are blowing strongly from the ENE, gusting to 47mph currently.
-2600′ Seattle Ridge Wx Station- Temperature 21F degrees. Winds are blowing strongly from the SE, gusting to 55mph currently.
-1800′ Center Ridge Wx Station- Temperature 28F degrees. No new snow. Current snow depth 83 inches.