Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Saturday, March 21st, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday through Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Yesterday skies were sunny and clear, the third day in a row of perfect spring weather. Ridgetop winds were light and variable, and mountain temperatures were a bit cooler, topping out in the teens to low 20’s. Sea level winds in Portage, however, averaged 10-20 mph out of the northwest from 10am to 5pm yesterday. As of 4am this morning, mountain temperatures ranged from 7-10 degrees F with light and variable winds at all locations. Portage is our cold sink this morning at -12F. Expect sunny skies this morning with clouds moving in by afternoon as a low pressure moves into the gulf. Ridgetop winds will continue to be light with mountain temperatures reaching the teens to low 20’s. Snow is on tap for tonight, tomorrow, and Monday along with warmer temps and strong easterly winds.
-The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass-
recorded no new snow. The current temp is 8F (3 degrees colder than yesterday) with a total snowpack depth of 77 inches. The snowpack has settled 7 inches since the St. Paddy’s Day storm that dropped 18” of new snow and 1.1” water
-The Sunburst weather station at 3800 feet in Turnagain Pass-
recorded light northwesterly winds averaging 5-10 mph all day yesterday. The current temp is 8F (3 degrees colder than yesterday)
Primary avalanche concerns
-Below 3000 feet, the “January Hurricane” rain crust is now buried 2-5 feet deep. There is a layer of weak sugary faceted snow surrounding this hard rain crust. Stability tests on this layer continue to show clean shears on top of this rain crust, a sign of lingering instability.
-From sea-level up to at least 3800 feet, a thin “glazed donut” freezing rain crust that formed 3/5/09 is now buried 1-2 feet deep. This layer was responsible for some of our most recent human-triggered avalanches.
AVALANCHE AND SNOWPACK DISCUSSION
Today, a LOW avalanche danger exists on all slopes with isolated pockets of MODERATE hazard on slopes steeper than 38 degrees. We are looking at generally stable avalanche conditions, but as always, watch for unstable snow on isolated terrain features. Several skier-triggered avalanches were reported as recently as yesterday. Evaluate the snow and terrain carefully and use good travel habits.
The stars aligned these last few days with perfect weather, mostly stable conditions, and incredible snow. People are skiing and riding big lines everywhere, but there are still a few pockets of instability out there that could catch someone off guard. The most recent human-triggered avalanches occurred yesterday on the backside of A-1 in the Girdwood Valley and on Cornbiscuit in Turnagain Pass. The slide on A-1 was a skier “body-bomb” at 2500′ on a SE aspect (see photo gallery). Also, one of our observers saw a skier kick off a small slab on the north side of Cornbiscuit yesterday, but it was small and manageable. Judging by the size and depth of these slabs, I’m guessing they failed at the new snow/old snow interface.
Several CNFAIC Staff human-triggered avalanches occurred Wednesday, the day after the St Paddy’s Day storm dropped 1-2 feet of new snow throughout the advisory area. One was an intentional ski-cut that triggered a 3 ft. deep by 200 ft. wide slab on North Bench Peak (see photo gallery), and the CNFAIC Staff was a 2 ft. deep by 20 ft. wide soft slab on a NNW facing couloir off Cornbiscuit at 3500 feet. It sounds like the culprit was new storm snow failing on the thin freezing rain crust that formed 3/5/09. This new snow has settled out, and the bond with the thin crust seems to have strengthened in most areas.
We have been talking ad nauseum about the facets above the January rain crust that caused many avalanches the third week of February. I wish we could stop talking about them, but the reality is they are a persistent weak layer and proving to be unpredictable. Last week we had widespread collapsing and shooting cracks at the lower elevations (in addition to clean fast Q1 shears in numerous stability tests on this layer), but for some reason 1-2 feet of new snow was not enough to tip the balance. What gives? At the latest, we will see this layer fail when the snowpack starts to go isCNFAIC Staffmal in the spring. But between now and then, be extra cautious if we get rain on snow, anCNFAIC Staff heavy load of snow, or prolonged warming with above freezing temps for more than 3 days.
The next weak link in our snowpack is the current snow surface, especially on south and southwest aspects where recently formed surface hoar is sitting on a 1 inch thick melt-freeze/sun crust. This monster-sized surface hoar has been reported throughout our advisory area from sea level to the ridgetops. Once buried with enough snow, we’ll probably see some action on this layer.
This concludes today’s advisory; the next advisory will be Sunday, March 22nd. If you are out in the backcountry and have the chance, please send us your observations. Simply click on “Submit a snow observation online” at the top of the advisory page and fill in the blanks. Thanks and have a great day!
The weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT SAT MAR 21 2009
.TODAY…INCREASING CLOUDS. A CHANCE OF SNOW IN THE AFTERNOON. HIGHS
IN THE 20S. VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 15 MPH.
.TONIGHT…SNOW. SNOW ACCUMULATION UP TO 9 INCHES. LOWS IN THE
MID TEENS TO LOWER 20S. LIGHT WINDS.
.SUNDAY…SNOW. SNOW ACCUMULATION 2 TO 6 INCHES. HIGHS IN THE
UPPER 20S TO MID 30S. NORTH TO EAST WIND 5 TO 15 MPH.
.SUNDAY NIGHT…SNOW. LOWS IN THE MID 20S TO LOWER 30S. NORTH TO EAST
WIND 15 TO 30 MPH.
.MONDAY…SNOW AND RAIN. HIGHS IN THE MID 30S TO LOWER 40S. NORTH TO
EAST WIND 15 TO 30 MPH.
.MONDAY NIGHT…SNOW LIKELY. LOWS IN THE 20S.
TEMPERATURE / PRECIPITATION
SEWARD 28 20 33 / 20 60 100
GIRDWOOD 26 19 29 / 20 100 100