Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, February 9th 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 remains at CONSIDERABLE today. A few inches of new snow and strong easterly winds at higher elevations 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 yesterday could break and step down to previously buried weak layers. Triggering these deep slab avalanches from thin spots in rocky terrain, or areas with a shallow snowpack, is likely.
New wind slabs have formed on leeward slopes in wind affected terrain throughout our advisory area. Shooting cracks on test slopes have shown propagation, and broke down to our newly buried layer of surface hoar.
Triggering one of these avalanches on capable slopes (30+ degrees) could create a much larger avalanche by stepping down to CNFAIC Staff weak layers buried several feet deeper.
Over the past three days, we have heard/felt large collapses (which created “whoomph” sounds), heard of two human triggered avalanches, and saw one new natural avalanche. This information, coupled with increased stress on an already sensitive snowpack, warrants increased 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). Many recent avalanches have failed in these facets, and slid on the TRC.
Our previous weather events have left us with a classic slab avalanche recipe in many areas. Our 2010-11 snowpack setup is comprised of a growing 3-5+’ 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 slide. This image shows an example of the situation we are dealing with:
Our snowpack depth is below average for this time of the year, and is constructed with a variety of weak layers. This deep slab setup has been recently reactive in two different types of areas. One area is in rocky terrain in upper elevations, where variably thin spots exist and a person could collapse a buried weak layer, triggering an avalanche. The CNFAIC Staff is in different 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 through Johnson Pass and the Summit Lake Area, as well as north through the Girdwood Valley area.
Avalanches in these areas could potentially break in steeper terrain above a traveler, 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
Winds several hours ago were sustained above 50mph, with gusts over 70mph, and are currently blowing between 20-40mph. The temperature is forecasted to be similar to yesterday. There has been only a very small amount of new snow at the Center Ridge SNOTEL site, with more likely at higher elevations. Radar images show a large amount of precipitation in Prince William Sound, but it is mainly flowing northeast toward Cordova and Valdez.
Kevin 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 WED FEB 9 2011
.TODAY…RAIN AND SNOW. SNOW ACCUMULATION UP TO 2 INCHES…MAINLY
AT HIGHER ELEVATIONS. HIGHS IN THE 30S. VARIABLE WIND TO 10 MPH.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…SOUTHEAST WIND
15 TO 30 MPH DECREASING TO 15 MPH OR LESS IN THE AFTERNOON.
.TONIGHT…CLOUDY WITH SCATTERED RAIN AND SNOW SHOWERS…MAINLY
ALONG THE SOUND. LOWS IN THE UPPER 20S TO MID 30S. LIGHT WINDS.
.THURSDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS. HIGHS
IN THE LOWER TO MID 30S. VARIABLE WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 36 31 35 / 90 30 20
GIRDWOOD 37 31 36 / 100 60 20
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station- Temperature 22F degrees. Winds are blowing strongly from the ENE, gusting to 36mph as of 4am.
-2600′ Seattle Ridge Wx Station- Temperature 26F degrees. Winds are blowing strongly from the SE, gusting to 43mph currently.
-1800′ Center Ridge Wx Station- Temperature 32F degrees. 1-2” new snow. Current snow depth 83 inches.