Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday February 3rd 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 only show scattered precip. The surface maps show no major storms near Turnagain Pass. Ridgetop winds have been calm to light at all wx stations in the past 48 hours and are still currently calm to light. Temps have dropped at almost all wx stations this morning by 3-7 degrees F compared to yesterday. Temps range from 27 degrees F at sea-level and 19 degrees at 3800′. There has been zero new snow or water recorded at any of the snotel sites. The weather forecasts listed below do not indicate anything significant that will affect the snowpack today.

AVALANCHE DISCUSSION

Today’s avalanche danger for the Turnagain Pass area will remain at LOW with pockets of MODERATE.

When you are snowboarding, skiing or riding your snowmachine around Turnagain Pass right now, there are not really any signs of instability; however, yesterday we did see a snowmachine triggered avalanche to the lookers right of the middle uptrack out of Main Bowl. We are not sure when this was triggered, but it looks recent and it was confirmed to fail on the rain crust on a steep rollover of 40+ degrees. The slab was about 50 feet wide, 2 feet deep, and ran about 40 feet. Plus, we received a report of a large human triggered cornice release near Resort Bowl along Seattle Ridge from a couple days ago.

CNFAIC Staff than these examples of isolated pockets of MODERATE, it’s hard to remember that we have a potentially dangerous weak layer for the future on that slippery rain crust that is generally buried under about 2 feet of snow; but, it is there. Since Saturday, we have done over 30 stability tests at 1800′, 1900′, 2000′, 2400′ 2500′, 2800′ 2900′, 3000′, and 3500′ on multiple aspects on both the motorized and nonmotorized sides of Turnagain Pass. In some places, we are still are finding some alarmingly clean shears. For an example, take a 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

There continues to be some variability in our test results. Yesterday on Seattle Ridge, we found the most concerning stability test of the week at the top of Widowmaker Peak at about 2500. While over on Cornbiscuit, Lisa and Jon found no failures on the rain crust. Plus, I found lower test scores but improved shear quality in a pit at about 3000′ near Warm Up Bowl on Seattle Ridge.

Take a look in the photo gallery of the picture labeled “Widowmaker Tracks” taken on Jan 24. There have are lots of tracks on this slope, and no avalanches have been triggered; except for the small snowmachine triggered avalanche nearby in Main Bowl. Our stability tests at the top of Widowmaker at about 2500′ yesterday had a clean fast shear like what we saw on Eddies two days ago; except, these test scores showed lower test scores with moderate failures at CTM14Q1@65cm only indicating fair stability. The slab on top of the rain crust slid off rapidly and was clean, smooth and fast. It appears that all the ski, snowboard, and snowmachine tracks are NOT improving stability on that rain crust. There may just not be a big enough slab on top to cause any problems yet, but I would completely avoid Widowmaker Peak after the next storm till we can get an updated impression of stability.

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. Some of these isolated pockets have all the ingredients to be potentially deadly after the next RAPID load. We don’t know where all of those isolated pockets will be; but, based on recent test pit results, I’d guess that the steep slopes in areas like Widowmaker Peak and the west face of Eddies could be some of those landmines.

Below 2500′

There are a lot of different layers of: crusts, buried surface hoar, and junky facets underneath some of those crusts. We have been finding failures above and below the crusts, but generally speaking we have a concerning weak layer about 2 feet deep. Keep in mind that places like the Seattle Ridge Bowls, Placer Valley, Kern Creek, Peterson Creek, and Girdwood Valley all have steep terrain with big consequences below 2500′ that are frequently used by people. Widowmaker Peak is a good example of steep lower elevation terrain. Our recent results on Eddies were 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

Above 2500′

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 99% of the test pits that we dig. For the most part, the actual rain crust goes up to about 3000′, but we have been finding a smooth bed surface up to the ridgetops near 4000′ that formed during the same storm on Jan 7. This bed surface has been showing similar or better 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.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED FEB 3 2010

.TODAY…MOSTLY CLOUDY. PATCHY FOG AND FLURRIES IN THE MORNING. HIGHS

IN THE MID 20S TO MID 30S. LIGHT WINDS. NORTH TO WEST WINDS 15 TO 25

MPH NEAR SEWARD AND WHITTIER.

.TONIGHT…MOSTLY CLOUDY. LOWS 10 TO 25 ABOVE…COLDEST INLAND.

LIGHT WINDS. NORTH TO WEST WINDS 15 TO 25 MPH NEAR SEWARD AND

WHITTIER.

.THURSDAY…CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE 20S. LIGHT

WINDS EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.

Temperature / Precipitation

SEWARD 31 19 26 / 0 0 40

GIRDWOOD 31 12 22 / 0 0 20

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

Sea-level: temps are forecasted between 12-31 with up to 0.1 inches of water today

3000′: temps are forecasted between 14-23 degrees F with winds 5 mph

6000′: temps are forecasted between 14-23 degrees F with winds 5-10 mph

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday February 4th.