Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday February 2 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

The radars are clear. There are no major storms near the Gulf of Alaska. Ridgetop winds have been calm to light at all wx stations in the past 24 hours and are currently calm to light. Temps have dropped at all wx stations this morning by 2-4 degrees F compared to yesterday. Temps are mild ranging from 29 degrees F at sea-level and 25 degrees at 3800′. The weather forecasts listed below do not indicate anything significant that will effect the snowpack today.

AVALANCHE DISCUSSION

Today’s avalanche danger for the Turnagain Pass area will remain at LOW.

However, there are some serious concerns with the future our snowpack. The rain crust that formed on Jan 7 is still showing signs of instability in many of our pits. The stability test scores have become variable in different locations, but we still are finding some alarmingly clean shears

-look on the forecasters video button on the top left of this screen or click on http://www.youtube.com/user/ChugachAvalanche#p/a/u/0/5awB3GZSWwU

Until recently, we have been finding very consistent failures slightly above that crust. Now we are finding a wider range of stability test results from moderate failures to no failures.

We are having a hard time finding a pattern with recent stability tests, CNFAIC Staff than we are getting variable results. Maybe this variability indicates that we are moving away from a widespread future avalanche concern to more of an isolated pocket avalanche concern. We don’t know where all of those isolated pockets will be; but, based on the results that you can see in the video, I’d guess that the steep rolls below 2000′ on the west face of Eddies could be one of those landmines.

Below 2000′

There are a lot of different layers of crusts, buried surface hoar, and junky facets underneath some of those crusts at lower elevations. Keep in mind that places like Placer Valley, Kern Creek, Peterson Creek, and Girdwood Valley all have terrain that is steep with big consequences at these lower elevations. Part of the reason why our recent results on Eddies were so noteworthy is because there was a layer of surface hoar on top of the rain crust. We have not seen surface hoar on top of that crust in any of our CNFAIC Staff pits. Around Turnagain Pass, we know that the biggest surface hoar crystals this year have formed at elevations less than 2000′. We need more information about this dangerous combination, but I don’t like it.

Above 2000′

We have a persistent weak layer of light density snow between the rain crust and the softer snow on the surface. For the most part, this weak layer has not been reactive to human triggers since Jan 17, but it shows up in most of our test pits. One theory is that it does not have enough of a slab or load on top of it yet. For the most part, the actual rain crust goes up to about 3000′, but we have been finding a smooth bed surface up to ridgetops near 4000′ that formed during the same storm on Jan 7. This bed surface has been showing similar results as the rain crust.

Part of the reason we keep dwelling on this problem is because 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 a RAPID change of snow, wind, or temperature.

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 Wednesday February 3.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST TUE FEB 2 2010

.TODAY…SKIES BECOMING PARTLY CLOUDY BY AFTERNOON. AREAS OF FOG IN

THE MORNING. HIGHS IN THE UPPER 20S TO MID 30S. LIGHT WINDS EXCEPT

NORTH 15 MPH NEAR SEWARD.

.TONIGHT…PARTLY CLOUDY IN THE EVENING…THEN MOSTLY CLOUDY WITH

ISOLATED SNOW SHOWERS AFTER MIDNIGHT. PATCHY FOG AFTER MIDNIGHT.

LOWS 10 TO 25 ABOVE. LIGHT WINDS EXCEPT NORTH 15 MPH NEAR SEWARD AND

WEST 15 MPH NEAR WHITTIER

Temperature / Precipitation

SEWARD 34 22 24 / 0 20 20

GIRDWOOD 32 21 21 / 0 20 0

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

Sea-level: GFS shows .05 inches of water forecasted today

3000′: temps are forecasted between 23-32 degrees F with winds 5 mph

6000′: temps forecasted between 14-23 degrees F with winds 5 mph