Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, December 14 at 7 am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (advisory does not apply to highways, railroads, or operating ski areas).
All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow.
After 12 days of stubborn high pressure and no snow, the weather is finally changing. Yesterday ridgetop winds were light and variable except on Seattle Ridge where they averaged 10-15 mph out of the southeast. The inversion finally broke, and mountain temperatures above 3000 feet cooled off by about 10 degrees (to the upper teens) while sea level temperatures warmed up by about 10 degrees (to the low 20’s).
As of 4 am this morning, ridgetop winds are light out of the southeast with gusts in the teens to low 20’s. No snow fell last night unfortunately. Skies are mostly cloudy right now, and temperatures currently range from 24F at sea level to 19F at 3800 feet. A weak low pressure over the western sound will park itself, bringing much needed snowfall to our area over the next few days. Valdez and Cordova stand to gain the most snow from this system as it trends eastward. Snow totals will remain on the light side today for us with only 2 inches forecasted. We could, however, get more snow than expected depending on the whims of a cold upper level low as it drops south. Ridgetop winds will remain light today with mountain temps in the low to mid 20’s.
-The Center Ridge Wx Station at 1800 feet/Turnagain Pass-
recorded no new snow in the last 24 hours with temps in the low 20’s. The current temp is 24F (same as yesterday) with a total snowpack depth of 54 inches (1 inch of settlement since yesterday).
-The Sunburst Wx Station at 3800 feet/Turnagain Pass-
recorded light southeasterly winds yesterday averaging 5-10mph. Temps decreased from 29F in the morning to 17F in the evening. The current temp is 19F (10 degrees colder than yesterday).
-The Summit Lake Wx Station at 1200 feet-
recorded no new snow in the last 24 hours with temps ranging from 14-21F. The current temp is 20F (6 degrees warmer than yesterday) with a total snowpack depth of 25 inches (same as yesterday).
-The Fresno Ridge Wx Station at 3400 feet/Summit Lake-
recorded light and variable winds yesterday with temps ranging from 25F in the morning to 18F in the evening. The current temp is 20F (5 degrees colder than yesterday).
The weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST MON DEC 14 2009
.TODAY…SNOW LIKELY ALONG THE COAST AND ALONG TURNAGAIN ARM.
A CHANCE OF SNOW ELSEWHERE. SNOW ACCUMULATION UP TO 2 INCHES.
HIGHS IN THE LOWER 20S TO LOWER 30S…COLDEST INLAND. LIGHT WINDS.
.TONIGHT…SNOW. SNOW ACCUMULATION 1 TO 3 INCHES. LOWS IN THE 20S.
.TUESDAY…SNOW LIKELY…ESPECIALLY ALONG THE SOUND. SNOW
ACCUMULATION UP TO 2 INCHES. HIGHS IN THE LOWER 20S TO LOWER
30S…COLDEST INLAND. VARIABLE WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 32 26 30 / 50 70 50
GIRDWOOD 28 25 28 / 60 90 60
Today, the avalanche danger will remain LOW on all slopes which means that natural and human-triggered avalanches are unlikely. We are looking at generally stable avalanche conditions today with the addition of only 1-2 inches of new snow and light winds. If anything, it may be possible to trigger some shallow sluffs on steep, previously windhammered slopes later in the day if we get more snow than expected. Watch for isolated pockets of shallow windslab anywhere the wind sneaks up and is actively loading lee aspects. As always, evaluate the snow and terrain carefully and always use good travel habits.
It has been 12 days since our last reported avalanche at Turnagain Pass, and the snowpack has shown no obvious signs of instability. Folks have been skiing, riding, and highmarking steep slopes without incident. This new snow will fall on a variety of snow types including dry faceted powder, surface hoar, supportable windslab, windhammered crust, windbuffed powder, and a thin sun crust on direct southern aspects up high. The next weak link in our snowpack is anywhere surface hoar formed, especially at the mid to lower elevations. Huge feathery crystals up to 1 inch in size were observed on Saturday up to 1600 feet elevation along with smaller crystals up to ¼ inch in size up to 2500 feet elevation. Above freezing temps at the higher elevations kept the surface hoar from forming thankfully. Once buried with enough snow, we may see some action on this layer.
Depending on how this new snow bonds with the old snow surfaces, along with the intensity and duration of the snowfall, we may see some instabilities develop over the next few days at the new snow/old snow interface. We’ll keep you posted.
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.