Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, February 19, 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-
Temps have increased at lower elevation weather stations by 1-10 degrees, and stayed the same or decreased by 1 degree at ridgetop weather stations. Temps were the warmest between noon and 2 pm yesterday reaching as high as 33 degrees. Its that time of year again when the sun starts to bake the snow. Winds at all ridgetop weather stations have started to increase this morning, but have been light to moderate in the last 24 hours. The SNOTEL sites at Summit, Grandview, and Turnagain Pass all recorded .1 inch of water but zero new snow.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 37 degrees (2 degrees warmer than yesterday) with light winds averaging 10mph out of the NE.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 29 degrees (4 degrees colder than yesterday). 0.1 inches of water and zero 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 21 degrees (1 degree colder than yesterday). Winds have been calm to moderate averaging 2-24mph out of the ESE with a max gust of 36mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….That same storm out in the Bering Sea from yesterday moved NE and became weaker (960-988mb), but its thin outer arm is still pulling moisture up from the south toward us.
The Kenai Radar shows a green monster of precip over Cook Inlet and western Kenai Peninsula moving toward us. The Middleton radar shows that moisture just creeping into view.
Primary avalanche concerns
-Upside down surface slabs on slippery bed surface on alpine slopes above 3000 feet. Some buried surface hoar has been reported in this surface snow at elevations up to 4500 feet.
-Upside down surface slabs on top of rain crust 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. Be very careful in Placer Valley, Seattle Creek, and Girdwood Valley)
AVALANCHE AND SNOWPACK
Extra Caution is advised today. There are pockets of considerable avalanche hazard. The conditions right now are the types of conditions when people get killed in avalanches because human factors and overconfidence in the snowpack intersects with the reality of a problematic snowpack.
See photo gallery for some pictures of recent avalanches
A large natural avalanche was reported in Skookum Valley yesterday. We are not sure when it happened, but it probably avalanched Sunday night or Monday when several CNFAIC Staff natural avalanches ripped out in places like Peterson Creek, Portage Valley, and the northern end of Turnagain Pass. This Skookum avalanche was reported to be 1/2 mile wide at a lower elevation on a NE aspect.
Some skier-triggered avalanches happened yesterday. There was a small slab of that upside down surface snow triggered on Tincan under CFR. Plus, CPG intentionally ski cut some medium sized slabs of surface snow in Upper Girdwood Valley when they increased their slope angles above 30 degrees.
It does not appear that yesterday’s skier-triggered avalanches stepped down to the slippery January monsoon layers like the artillery triggered avalanches did on Monday. However, if we get more snow on top of the already sensitive surface snow, then the chance of triggering larger avalanches will increase.
By definition, considerable avalanche hazard means conditions are dangerous. This has been proven by the natural, artillery, and human-triggered avalanches that have been observed/reported in Girdwood Valley, Peterson Creek, Portage Valley, Skookum Valley, Placer Valley, and Turnagain Pass. The snowpack is tender right now, and it will only get more dangerous if we get hit by this storm.
Safe terrain management is essential today. Stay away from slopes steeper than 30 degrees. A lot of times, we talk about the 24 hour rule, meaning that most avalanches occur during or within 24 hours of a storm. That is not exactly the case with our current weak layers. They have been persitent enough that we will have to be extra careful for several days if not weeks after the next storm.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST THU FEB 19 2009
…STRONG WIND TODAY THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…
…STRONG WIND NEAR SEWARD AND WHITTIER FRIDAY AND FRIDAY NIGHT…
.TODAY…SNOW…MIXED AT TIMES WITH RAIN. SNOW ACCUMULATIONS 2 TO 5
INCHES. HIGHS IN THE 30S. PORTAGE VALLEY AND ALONG TURNAGAIN
ARM…EAST WINDS 30 TO 45 MPH DIMINISHING TO 25 MPH THIS AFTERNOON.
ELSEWHERE…SOUTH TO EAST WINDS 10 TO 25 MPH DIMINISHING THIS
.TONIGHT…SNOW SHOWERS IN THE EVENING…THEN SCATTERED SNOW
SHOWERS AFTER MIDNIGHT. AREAS OF BLOWING SNOW. SNOW ACCUMULATION UP
TO 1 INCH. LOWS IN THE 20S. NORTH TO WEST WINDS 10 TO 20 MPH. GUSTS
TO 35 MPH NEAR SEWARD AND WHITTIER.
.FRIDAY…PARTLY CLOUDY. AREAS OF BLOWING SNOW. HIGHS IN THE MID 20S
TO LOWER 30S. NORTH TO WEST WINDS 10 TO 25 MPH. GUSTS TO 45 MPH NEAR
SEWARD AND WHITTIER.
TEMPERATURE / PRECIPITATION
SEWARD 38 25 31 / 100 40 0
GIRDWOOD 34 27 29 / 100 80 0
This concludes today’s avalanche advisory the next advisory will be on Friday, February 20th. Thanks and have a great day.