Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday January 27 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).

WEATHER ROUNDUP

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Current temp is 21 (6 degrees colder than yesterday). RH increased. Winds have been increasing from calm to light averaging 0-13 mph out of the E with a moderate max gust of 21 mph

2400′-Seattle Ridge Wx Station-

Winds have been increasing averaging light at 6-15 mph out of the ESE with a moderate max gust of 10mph

1800′-Center Ridge Wx Station-

Current temp is 28 (5 degrees warmer than yesterday) Zero inches of water and zero inches of new snow has fallen. RH increased. Total snowpack depth 63” after 1” of settlement

Nowcast (5am)

Temps are warming up at all wx stations below 2000′ this morning by 5-10 degrees. Ridgetop temps are steady or dropping slightly. Current temps range from 26 degrees F at sea level to 21 degrees F at 3800′. There is zero new precip at the snotel sites this morning. Winds are increasing at all ridgetop wx stations averaging light to moderate 1-22mph with strong gusts up to 30mph. RH is increasing at most wx stations and the Middleton radar shows a wall of moderate precip moving west over PWS toward us. The Kenai radar is mostly clear this morning. The weather is changing from how it has been the last couple days.

Forecast (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED JAN 27 2010

.TODAY…NUMEROUS SNOW SHOWERS. SNOW ACCUMULATION UP TO 3 INCHES.

HIGHS IN THE LOWER TO MID 30S. EAST WIND 10 TO 20 MPH.

.TONIGHT…SNOW LIKELY. SNOW ACCUMULATION UP TO 3 INCHES. AREAS OF

BLOWING SNOW. LOWS IN THE MID 20S TO LOWER 30S. EAST WIND 10 TO 20

MPH EXCEPT EAST 20 TO 30 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM.

.THURSDAY…SNOW LIKELY IN THE MORNING…THEN SNOW AND RAIN

LIKELY IN THE AFTERNOON. SNOW ACCUMULATION UP TO 3 INCHES. HIGHS

IN THE 30S. EAST WIND 10 TO 20 MPH EXCEPT EAST 15 TO 30 MPH

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

Temperature / Precipitation

SEWARD 34 30 37 / 70 70 70

GIRDWOOD 32 30 34 / 50 40 50

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

Sea-level: GFS shows .1 inches of water forecasted today

3000′: temps are forecasted between 23-32 degrees F with winds 10-20 mph

6000′: temps forecasted between 14-23 degrees F with winds 20-40 mph

AVALANCHE DISCUSSION

Today’s weather could contribute to the avalanche danger today at Turnagain Pass due to increasing wind this morning.

Today’s avalanche conditions should be generally safe; however, watch out for isolated pockets of wind slabs that could make small human triggered avalanches possible (if the wind continues to blow as it is forecasted by the NWS).

Above 2000′ we have a persistent weak layer of light density snow between the rain crust and the powder on the surface. 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, 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 heavy rapid load on top of the current snowpack. Today’s weather forecast, however, does not look like it will pack too big of a punch.

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. Lisa took a close look at some lower elevations yesterday at Turnagain Pass and reported junky facets underneath the uppermost rain crust that collapsed about an inch during isolated column stability tests.

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 Thursday January 28th.