Turnagain Pass

Good morning backcountry travelers. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, February 7th at 7am. 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).

BOTTOM LINE

The avalanche danger is MODERATE in shallow snowpack areas for deep slab avalanches. Triggering an avalanche from either a thin spot in rocky terrain or areas with a thin overall snowpack is possible. Potentially large avalanches are most prone in areas with an overall shallow snow cover.

AVALANCHE DISCUSSION

There was one human triggered avalanche in our advisory area yesterday. This was on an east facing slope around 1500′ on Seattle Ridge and was approximately 100′ wide and 1-3′ deep (photo below). CNFAIC Staffwise, the several folks that were out over the weekend ski and rode without incident. However, many were staying in lower angle terrain with deeper snowpacks.

Several reports did come in yesterday of especially large ‘whoomphing’ and long shooting cracks in regions ranging from Glacier Valley to Summit Lake. All reports were from shallow snowpack areas with one party finding an immediate desire to go watch the superbowl. My own party felt a tree shaking collapse on the eastern end of Raggedtop above Girdwood (video of pit results and description from this area below). The snow structure we have been seeing in these thin regions is a classic slab avalanche recipe: 6” to 2′ of weak faceted snow under a 2-4+’ hard slab. In many areas the early season crusts are intact and intermixed with the weak faceted snow providing a good bed surface for sliding.

Due to the below average, and variety, in the snow cover this year there seem to be two different ways to trigger a deep slab. One is in the higher rocky terrain where a scattered distribution of thin spots exist and a person could collapse an old buried weak layer and release a slide. The CNFAIC Staff is in regions where the overall snow depths are low and triggering a slope remotely, or that propagates above or next to you, is LIKELY and wider spread (Johnson Pass and south through Summit Lake and north in the Glacier Valley area). Avalanches in these locations have the potential to be large with high consequences, avoiding slopes above the low 30’s is recommended.

Above is a slide that occurred yesterday on the east side of Seattle Ridge on Repeat Offender. It was triggered by two snowboarders riding over it from above. More details and CNFAIC Staff photos are in the photo gallery.

Above is an Extended Column Test (ECTP 15 Q1) failing and propagating around 20″ below the surface in a ~10 cm faceted layer above a few cm crust. This was on the far east side of Raggedtop on a 27 degree slope east facing at 2200′. The test was performed after a very large whoomph was heard/felt in the area. AnCNFAIC Staff party in a similar area had a very large whoomph as well.

Encyclopedia of avalanche terms.

ANNOUNCEMENTS

The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it!

Click here to take survey

or cut and paste the address directly:

https://www.surveymonkey.com/s/THWXVCD

WEATHER ROUNDUP

The past few days have been generally nice with some sun. The easterly winds decreased yesterday. Overnight temperatures were in the upper teens in the valleys and low 20’s on the ridges. Winds have been in the single digits and gusting into the 20’s from the east on the peaks. Today should be fairly nice with temperatures in the upper 20’s. We should see light winds with partly cloudy skies becoming mostly cloudy in the afternoon. Tonight there is a possibility for snow showers with a few inches accumulating. Its looks as if the winds are going to ramp up on Tuesday.

Jon will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST MON FEB 7 2011

…STRONG WIND LATE TUESDAY MORNING THROUGH TUESDAY NIGHT THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM…

.TODAY…MOSTLY SUNNY IN THE MORNING THEN BECOMING PARTLY CLOUDY.

HIGHS IN THE MID 20S TO MID 30S…WARMEST ALONG THE COAST.

LIGHT WINDS. NEAR WHITTIER…WEST WIND 20 TO 35 MPH IN THE

MORNING BECOMING LIGHT BY AFTERNOON.

.TONIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS IN THE

EVENING ALONG THE COAST…THEN SNOW DEVELOPING AFTER MIDNIGHT.

SNOW ACCUMULATION UP TO 2 INCHES. LOWS IN THE 20S. NORTH TO EAST

WIND TO 15 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST

WIND INCREASING TO 15 TO 30 MPH TOWARD MORNING.

.TUESDAY…SNOW CHANGING TO RAIN IN THE AFTERNOON. SNOW ACCUMULATION

1 TO 3 INCHES EXCEPT 3 TO 6 INCHES THROUGH TURNAGAIN PASS. HIGHS

IN THE 30S. NORTH TO EAST WIND INCREASING TO 15 TO 30 MPH. THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 20 TO 35 MPH INCREASING

TO 35 TO 50 MPH IN THE AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 34 29 37 / 20 100 100

GIRDWOOD 30 25 35 / 0 90 90

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

Temperature 22, on a rising trend. Winds are light, steady at 4-8mph from the NNE currently.

-2600′ Seattle Ridge Wx Station-

Temperature 24 degrees. Recent winds have switched around to the NW and are blowing in the teens.

-1800′ Center Ridge Wx Station-

Temperature 19 degrees. No new snow.