Good Morning backcountry travelers, this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday, February 21, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Nuking winds dominated the weather and landscape yesterday in all of the advisory area. We didn’t get the storm precipitation that we expected but the active wind loading that occurred yesterday certainly put allot on new snow on leeward aspects. Ridge top wind gust to 89 mph were recorded yesterday afternoon. Gust to 40 at sea level indicate that this wind event mixed down to all elevations. Although this event was predominately associated with northeast winds, variable winds from the south and west were reported at lower elevations in Turnagain Pass.
Current NE winds have decreased to moderate with clear skies this morning and partly cloudy this afternoon.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 31 degrees (3 degrees cooler than yesterday) with light winds averaging 3-6 mph out of the NW.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 16 degrees (6 degrees colder than yesterday). 0 inches of water and 0 inches of new snow has been recorded. Total snowpack depth is 68″.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Shows a temperature of 10 degrees (7 degree colder than yesterday). Winds are still moderate with strong gusts in the 20’s
-Surface Analysis Maps-
A high pressure ridge has developed over much of AK. A 1046 mb high is set mid state and 1016 mb low setting in the gulf. These two systems are responsible for the pressure gradient that is driving our NE winds.
Pretty clear on the radar, but the satellite images show a cloud band moving into the area for this afternoon. There doesn’t look like any moisture associated with it.
Primary avalanche concerns
-Dense wind slabs overlying less dense facets snow. Very high winds yesterday re-energized our wind slab problem. The size of these slabs has grown, up to 4+foot crowns observed!
-Denser snow on top of lighter density snow teetering on top of a weak rain crust layer below 3000 feet. (Avalanches have been common and widespread on this lower elevation instability. There is a layer of faceted snow on top of this rain crust. Areas of concern include but are not limited to: Placer Valley, Seattle Creek, and Girdwood Valley)
AVALANCHE AND SNOWPACK
Extra Caution is advised today. There are pockets of considerable avalanche hazard at multiple elevations and aspects today. Yesterday’s strong winds dominated all peaks and all elevations throughout the advisory area. AnCNFAIC Staff large skier triggered avalanche in Skookum Valley yesterday proved just how sensitive our current snowpack is! Long time mountain guides reporting this avalanche occurred on lower angle slopes they never see avalanche and was considered low risk. Good travel management was once again key!
We have to think of yesterday’s wind event just like we would a precipitation event! Large amounts of snow were blown into the air and redeposited on leeward aspects. These leeward aspects will be very sensitive today with dense wind slabs over weaker snow.
Managing your terrain should be job number one this weekend. Clear, blue bird skies could give false confidence that nothing can go wrong. That thought process could get you killed. Choosing terrain less than 30 deg, with smooth run outs and escape routes will be key.
See photo gallery for some pictures of recent avalanches
Large natural avalanches occurred in Skookum, Peterson Creek, Portage Valley, and the northern end of Turnagain Pass earlier this week, just to mention a few. This northern edge of the advisory area received more snow load than did interior areas of Turnagain and Summit Passes. However, the same weak layers exist. This means that T. Pass has not yet hit the stress over strength point on the scale that an avalanche will occur at. A trigger is the something or someone that slides the scale to the tipping point and causes an avalanche. A trigger could be a skier, snowboarder, snowmachiner, or a wind driven snow flake. Use increased caution if our winds pick up. Actively loading slopes will be areas of increased hazard.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SAT FEB 21 2009
…STRONG WIND THROUGH THIS MORNING NEAR SEWARD AND WHITTIER…
.TODAY…MOSTLY SUNNY IN THE MORNING THEN BECOMING PARTLY CLOUDY.
HIGHS IN THE MID 20S TO LOWER 30S. SEWARD AND WHITTIER…NORTH TO
WEST WINDS 40 TO 50 MPH THIS MORNING DIMINISHING 15 TO 25 MPH THIS
AFTERNOON. ELSEWHERE…NORTH TO WEST WINDS TO 20 MPH DIMINISHING TO
10 MPH THIS AFTERNOON.
.TONIGHT…SKIES BECOMING MOSTLY CLOUDY. LOWS IN THE TEENS. VARIABLE
WIND TO 10 MPH EXCEPT NORTH TO WEST 15 MPH NEAR SEWARD AND WHITTIER.
.SUNDAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
SUNNY. HIGHS IN THE UPPER 20S TO MID 30S. LIGHT WINDS EXCEPT
NORTH TO WEST NEAR SEWARD AND WHITTIER.
.SUNDAY NIGHT…PARTLY CLOUDY. LOWS IN THE MID TEENS TO LOWER
20S. LIGHT WINDS. NEAR SEWARD…LIGHT WINDS BECOMING NORTH 15 MPH
.MONDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
SUNNY. HIGHS IN THE 30S. VARIABLE WIND TO 10 MPH.
.MONDAY NIGHT…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW. LOWS
IN THE UPPER TEENS TO MID 20S.
TEMPERATURE / PRECIPITATION
SEWARD 30 17 32 / 0 0 0
GIRDWOOD 25 12 27 / 0 0 0
This concludes today’s avalanche advisory the next advisory will be on Sunday, February 22nd. Thanks and have a great day.