Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, March 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).
After a beautiful bluebird day yesterday, anCNFAIC Staff major storm moved onshore early this morning. Hold onto your hats as this storm is shaping up to be like last Friday’s storm. The NWS has issued a blizzard warning in effect until 6pm tonight. It started snowing around 3am this morning, so only a couple inches of snow have fallen so far. Ridgetop winds started to pick up around midnight last night and are currently averaging 40-50mph out of the east gusting to 63mph. Temperatures have increased by about 10 degrees in the last 6 hours and currently range from 30F at sea level to 12F at 3800 feet. It is snowing sideways in Girdwood right now, and the winds are plastering the snow to my window as I write. We could get up to 2 feet of snow at the higher elevations today with an additional 6-14 inches this evening. Gale to storm force easterly winds averaging 40-65mph and hurricane force gusts over 75mph are forecasted for today.
The avalanche danger will increase to HIGH today as this storm progresses. Human-triggered avalanches will be very likely on steep windloaded slopes with natural avalanches likely on actively loading slopes greater than 35 degrees. Storm force easterly winds and up to 2 feet of snow today at the higher elevations equals dangerous avalanche conditions. Travel in avalanche terrain is not recommended.
The cold light density snow that is falling right now at the higher elevations will be the foundation for the rest of today’s snowfall, so I would expect the initial bonding with the old snow surface to be poor. The old snow surface varies from powder to soft windslab to supportable hardslab to windhammered boilerplate. There are probably thin suncrusts on southerly aspects as well from yesterday’s intense sunshine. In CNFAIC Staff words, there are many areas with slick bed surfaces for today’s avalanches. As temperatures warm up and the wind continues to form fresh windslabs, an increasingly top-heavy slab will form on top of the lighter density snow creating unstable conditions. Visibly drifting snow and shooting cracks are the most obvious clues to windslab formation.
A glide crack in the upper Girdwood Valley around 2300 feet avalanched yesterday morning when temperatures bottomed out to the low single digits. We also received a report of some wet loose snow sluffs triggered by skiers yesterday on the steep southerly slopes of Goat Mountain in the upper Girdwood Valley. Despite the single digit temperatures, the March sun was strong enough to melt the snow surface.
Matt will issue the next advisory tomorrow morning at 7am. Thanks and have a great day.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST MON MAR 8 2010
…BLIZZARD WARNING NOW IN EFFECT UNTIL 6 PM AKST THIS EVENING
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…
.TODAY…SNOW. SNOW AND BLOWING SNOW REDUCING VISIBILITY TO ONE
QUARTER MILE OR LESS THROUGH PORTAGE VALLEY AND TURNAGAIN ARM. SNOW
MAY BE HEAVY AT TIMES IN THE MORNING. SNOW ACCUMULATION 5 TO 12
INCHES…HEAVIEST NORTH OF MOOSE PASS. HIGHS IN THE LOWER 30S. NORTH
TO EAST WIND 15 TO 30 EXCEPT EAST 50 TO 65 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM.
.TONIGHT…SNOW…POSSIBLY MIXING WITH RAIN AT SEA LEVEL IN THE
EVENING. SNOW ACCUMULATION 2 TO 6 INCHES. LOWS IN THE MID 20S TO
LOWER 30S. NORTH AND EAST WIND 15 TO 30 MPH BECOMING SOUTH AND EAST
AFTER MIDNIGHT. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND
30 TO 45 MPH DECREASING TO 15 TO 30 MPH AFTER MIDNIGHT.
.TUESDAY…SNOW SHOWERS. SNOW ACCUMULATION 1 TO 4 INCHES. HIGHS
IN THE MID 20S TO LOWER 30S. SOUTHEAST WIND 10 TO 25 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 33 30 30 / 100 100 80
GIRDWOOD 31 27 29 / 90 90 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light winds yesterday averaging 5-15mph out of the west shifting to the south. The current temp is 12F (14 degrees warmer than yesterday) with gale force winds averaging 40-50mph out of the east gusting to 63mph.
-2600′ Seattle Ridge Wx Station-
is currently recording moderate southeasterly winds averaging 20mph with gusts to 34mph.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. The current temp is 19F (13 degrees warmer than yesterday) with a total snowpack depth of 122 inches (3 inches of settlement since yesterday).