Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday January 28 at 7 am. 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).

ANNOUNCEMENTS

!FREE! Avalanche Education in Anchorage this weekend from Alaska Avalanche School.

Avalanche Awareness Lecture Series

(No Registration Required)

WHEN: Saturday Jan. 30, 2010

Time: Seating and sign in begins at 8:45am. Lecture runs from 9:00am to 1:00pm

WHERE: Alaska Pacific University Carr-Gottstein Building, Room 102

4101 University Drive Anchorage AK

DURATION: The Lecture has a run time of 4 Hours

with intermittent breaks throughout.

COST: FREE!!

Avalanche Field Workshop

(Registration is Required: Please Contact the Office to Enroll)

By Popular Demand we’ve scheduled 2 Avalanche Field Workshops

WHEN:Morning Program: Sunday, January 31, 2010: 9:00 am to 1:00 pm

Afternoon Program: Sunday, January 31, 2010: 1:30 pm to 5:30 pm

WHERE:Glen Alps Trail Head (Flat Top Parking Lot)

Chugach State Park

DURATION:Each program will run 4 hours. Please be ready to spend the duration of the program outside.

COST:FREE

WEATHER ROUNDUP

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Current temp is 24 (3 degrees warmer than yesterday). Winds have been light to extreme averaging 12-40 mph out of the E with an extreme max gust of 48 mph

2400′-Seattle Ridge Wx Station-

Winds have been light to moderate averaging light at 3-23 mph out of the SE with strong max gust of 36mph

1800′-Center Ridge Wx Station-

Current temp is 30 (2 degrees warmer than yesterday) .2 inches of water and 1-2 inches of new snow has fallen. Total snowpack depth 65”

Parking Lot Snow Stake Measurements (taken 2pm yesterday 1/27/2010)

Eddies Lot: 1” new snow

Motorized Lot: 1” new snow

Sunburst Lot: 1” new snow

Johnson Pass North Lot: 1” new snow

Nowcast (5am)

Temps are warmer at all wx stations from sea-level to the ridgetops ranging from 30 degrees F at sea level to 24 degrees F at 3800′. Winds are still moderate averaging in the teens with strong gusts in the 30mph range on most ridgetop wx stations this morning. The Middleton radar shows a wall of moderate-strong precip moving west over PWS toward us. The Kenai radar shows light precip over Turnagain Pass.

Forecast (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU JAN 28 2010

…STRONG WIND THROUGH TONIGHT THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM…

.TODAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE AFTERNOON.

SNOW ACCUMULATION UP TO 3 INCHES. HIGHS IN THE 30S. EAST WIND 10 TO

25 MPH EXCEPT EAST 30 TO 45 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM.

.TONIGHT…SNOW AND RAIN IN THE EVENING…THEN SNOW AFTER MIDNIGHT.

SNOW ACCUMULATION UP TO 2 INCHES. LOWS AROUND 30. EAST WIND 10 TO 15

MPH EXCEPT EAST 30 TO 45 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM.

.FRIDAY…SNOW LIKELY IN THE MORNING…THEN SCATTERED SNOW

SHOWERS AND A CHANCE OF RAIN IN THE AFTERNOON. SNOW ACCUMULATION

UP TO 1 INCH. HIGHS IN THE 30S. EAST WIND 10 TO 15 MPH EXCEPT

EAST 15 TO 25 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

Temperature / Precipitation

SEWARD 37 32 37 / 80 90 60

GIRDWOOD 34 31 35 / 50 50 30

Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass

Sea-level: GFS shows .25-.5 inches of water forecasted today

3000′: temps are forecasted between 23-32 degrees F with winds 15-20 mph

6000′: temps forecasted between 23-32 degrees F with winds 35-40 mph

AVALANCHE DISCUSSION

Today’s weather will increase the avalanche danger today at Turnagain Pass due to wind and new precip. Today’s weather forecast does not look like it will pack too big of a punch, but it’s starting build up some stress out there.

We know that we have a persistent weak layer widespread in the Turnagain Arm area. The big question is if and when this weak layer will start to avalanche. We have had significant wind for over 24 hours and the NWS is forecasting more strong wind today.

Small avalanches on the new snow old snow interface will possible today because the old snow surface had surface hoar and some faceted crystals; but, mostly because the old snow surface was cold and light, and the new storm snow that we are getting right now will be denser. The biggest concern is if you trigger a small avalanche in the new storm snow, could it step down to the rain crust and create a much bigger avalanche? Probably not today, but this is becoming more of a concern as more weather moves in.

We have NOT gotten much of a load out of the precip in the past 48 hours, but the wind fits the definition of rapid loading in certain areas.

Above 2000′ we have a persistent weak layer of light density snow sandwiched between the rain crust and 1½ to 2½ feet of powdery snow. For the most part, this weak layer has not been reactive to human triggers since Jan 17. One theory is that it does not have enough of a slab or load on top of it (this could change with new weather), but it shows up in every test pit we dig. In snow stability test pits over the past 10 days, we continue to get similar results from numerous locations. The common theme on both sides of the highway is that the snow continues to fail slightly above the rain crust with smooth failures. Usually, we see improving test scores over a 10 day period, but that has not happened with this particularly persistent weak layer. These test scores make this layer unusual. Whenever I see something unusual with the snowpack, it raises a red flag in my head. Part of the problem is that the snow above the rain crust has a poor structure with all 3 of the main ingredients for avalanches: a bed surface (slippery rain crust), a weak layer (lighter density snow sitting on top of rain crust), and a slab of denser snow on top that weaker snow.

We will most likely not see any major problems till we get more snow or wind. We could have some serious avalanche dangers in the future after the next RAPID change with the weather. This type of avalanche forecasting is difficult; but, since all the ingredients are there, it would be wise to approach the mountains with serious caution if we get any kind of rapid load on top of the current snowpack

A secondary concern exists below 2000′ on facets and surface hoar near the rain crust. This lower elevation problem layer is still showing signs of instability. One of our best observers who spends a lot of time in the mountains in lots of different locations reported, “one of the loudest whoomps I have heard in my life when we were climbing out of a gully onto a deposition pillow” down in the trees near Tincan on Sunday 1/24/2010. This lower elevation weak layer could become a serious problem, especially after the next storm, in places like Placer Valley, Kern Creek, Peterson Creek, or Girdwood Valley. These areas have steep slopes at these lower elevations.

Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Friday January 29th.