Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Thursday, April 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 increasing to MODERATE overall. This morning, steep slopes facing East, South, and West have a LOW danger, but that will increase quickly with afternoon heating from the sun. There is also a buried layer of surface hoar on North facing slopes that has recently been showing signs of reactivity in stability tests, so elevated caution is recommended on these slopes as well.
Our primary concern is spring-time instabilities. These instabilities manifest themselves in point releases, wet slab avalanches, glide cracks/avalanches, and climax avalanches. This will probably be the name of the game for the rest of our snow season, unless a large amount of new snow falls on this old snow.
Currently, the Southern half of the compass is the most obvious place to find these hazards, and they are most likely to release around noon on East aspects, wrapping clockwise around the compass over to West aspects around 5-8:00pm. Cloudy skies may make this hazard less dramatic, but it is still a heads-up type of situation since UV rays penetrate clouds quite readily. A great way of determining if this instability is rising will be if you start sinking into the snow beyond your ankles. If this is happening as you are climbing a slope, odds are that steep slopes at higher elevations could be close to the point of failure. Moving to harder/cooler snow is a way to abate this hazard.
The secondary concern today is for persistent layers of buried surface hoar being triggered on Northerly aspects. They could possibly break and fail, but may take a very large stress to actually do so. Getting a good idea how deep any potential avalanche would break on these slopes is possible by digging down to the obvious layer in a snow pit, but performing any stability tests may yield inconsistent results. Basing a go or no-go decision on the test results from one snow pit is not advisable.
Glide cracks which look like dark frown marks on slopes are also potentially dangerous, but are easily recognizable when compared to CNFAIC Staff instabilities. Avoid travelling underneath these features, because they may break at any time, and triggering mechanisms are not fully understood right now in the snow science community.
Encyclopedia of avalanche terms.
There is a band of precipitation that is descending upon our advisory area from Prince William Sound. Precipitation may be heavy for a bit in Turnagain Pass, but this depends on how much makes it over Portage Pass and the Spencer Glacier area. Look at the radar for current information on where it is currently located throughout the day.
We may see an increase in winds with the passage of a front today, but they will likely not be able to move any old snow around. Temperatures should be reaching into the upper 30’s again this afternoon, affecting the stability on lower elevation slopes and steep sunny aspects during the afternoon. The precipitation front moving through Prince William Sound may give us snow at upper elevations and rain at lower elevations, but it is forecasted to be a short event with small amounts of total accumulation.
This is my last advisory for the 2010-11 winter season. Have a great summer, and I’ll see you next winter!
Wendy 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 AKDT THU APR 14 2011
.TODAY…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE MORNING…THEN
ISOLATED RAIN AND SNOW SHOWERS IN THE AFTERNOON. HIGHS IN THE UPPER
30S TO UPPER 40S. VARIABLE WIND 10 MPH.
.TONIGHT…PARTLY CLOUDY. LOWS IN THE LOWER 20S TO LOWER 30S.
LIGHT WINDS. NEAR WHITTIER…LIGHT WINDS BECOMING WEST 10 TO
15 MPH AFTER MIDNIGHT.
.FRIDAY…PARTLY CLOUDY. HIGHS IN THE MID 40S TO LOWER 50S. LIGHT
WINDS EXCEPT NORTH 10 MPH NEAR SEWARD.
TEMPERATURE / PRECIPITATION
SEWARD 47 28 49 / 50 0 0
GIRDWOOD 40 24 45 / 30 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
23 degrees. ENE wind 10mph gusting to 15mph.
-2600′ Seattle Ridge Wx Station-
27 degrees. ESE wind 3mph gusting to 6mph.
-1800′ Center Ridge Wx Station-
27 degrees. No new snow.