Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, 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).
AnCNFAIC Staff 1 inch of new snow fell in the last 24 hours in Turnagain Pass, bringing our snowfall total for the last 36 hours to around 13 inches of snow and 1 inch of water. Actual amounts vary from 6 inches on the southern end of the pass to 14 inches on the northern end. Yesterday ridgetop winds were ripping, averaging 15-45mph out of the east and southeast with gusts in the 40’s, 50’s, and 60’s. Mountain temps dropped about 10 to 15 degrees to the mid to upper teens by the end of the day. Ridgetop winds died down around midnight last night and are currently light. Sea level winds, however, picked up around midnight and are currently averaging 15-20mph out of the northeast. Temperatures this morning range from 13F at 3800 feet to 24F at sea level. It is currently snowing in Girdwood with an additional 6-8 inches falling last night on top of the 12-18 inches that fell in the last day and a half. A weak low moving into western Prince William Sound may bring an additional 1-3 inches of snow today. Expect mountain temps in the teens with easterly ridgetop winds averaging up to 15-20mph. Skies will clear up tomorrow ahead of the next low that will impact us Tuesday.
Today the avalanche danger is rated CONSIDERABLE on windloaded slopes steeper than 35 degrees. All CNFAIC Staff slopes have a MODERATE danger. Thirteen inches of new snow and strong easterly winds in the last 36 hours means human-triggered avalanches are likely on steep windloaded slopes and cross-loaded gullies. Terrain management is key today as our snowpack adjusts to the new load.
There was no shortage of action yesterday once the skies cleared by midday. Jon and I watched a skier trigger an avalanche on a southwest aspect of Tincan at 3000 feet in an area called the Kitchen Wall. The skier was caught, carried, and partially buried but able to dig himself out. We estimated the slide at 150 feet wide, 200 feet long, 14 inches deep at the crown face, and 39 degrees at the trigger point. The slide failed below a windslab on a possible melt-freeeze layer or sun crust. A second skier immediately skied down next to the first avalanche and triggered a smaller slide but was not buried. Check out our photo and video gallery for a picture of this slide and CNFAIC Staff photos/videos from yesterday. During our tour up Tincan, we got numerous shooting cracks on steep rollovers breaking down about a foot deep and found that any recently formed windslabs (2-6 inches thick) were especially reactive, fracturing 25-60 feet wide on leeward slopes. One of our observers reported seeing numerous small slides on steep rollovers in the alpine in addition to substantial windslabs at the higher elevations. Whumphing was also reported below 2000 feet on Sunburst.
We saw evidence of only a few natural avalanches up at the pass that most likely happened during the height of the storm, the most obvious one being just below the corniced ridge on Tincan (CFR) that ran about 500 feet into the trees. The crown faces were blown in on most of them, so it was difficult to judge the depth of the fractures. Nothing seemed to step down to the buried Jan. 7 rain crust, now buried 2-4 feet deep and even deeper on leeward aspects. That’s not to say it’s not possible. I think a big enough avalanche could easily step down to this persistent weak layer and create an even bigger slide, especially on the northern end of the pass where we found buried surface hoar lurking on top of this slick crust and clean fast Q1 shears in our 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.
I 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.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SUN FEB 7 2010
.TODAY…CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE LOWER 20S
TO LOWER 30S. SOUTHEAST WIND TO 15 MPH.
.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS 10 TO 20
ABOVE. VARIABLE WIND 10 MPH.
.MONDAY…PARTLY CLOUDY. HIGHS 15 TO 25 ABOVE. LIGHT WINDS. NEAR
WHITTIER…WEST WIND 10 TO 20 MPH BECOMING VARIABLE 10 MPH IN THE
.MONDAY NIGHT…CLOUDY. LOWS 10 TO 20 ABOVE…COLDEST INLAND. EAST
WIND 10 TO 20 MPH. NEAR SEWARD…NORTH WIND 10 MPH INCREASING TO
10 TO 25 MPH AFTER MIDNIGHT.
.TUESDAY…SNOW. HIGHS IN THE MID 20S TO LOWER 30S. EAST WIND
15 TO 25 MPH EXCEPT SOUTHEAST 25 TO 35 MPH THROUGH PORTAGE VALLEY AND
TEMPERATURE / PRECIPITATION
SEWARD 31 10 19 / 40 40 0
GIRDWOOD 32 24 26 / 40 40 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded moderate to gale force easterly winds yesterday averaging 15-45mph with gusts to 68mph. The current temp is 13F (13 degrees colder than yesterday) with winds averaging 8mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded moderate to strong southeasterly winds yesterday averaging 15-30mph with gusts to 53mph. Winds are currently averaging 2mph out of the southeast.
-1800′ Center Ridge Wx Station-
recorded 1 inch of new snow and 0.1 inches of water in the last 24 hours. The current temp is 18F (14 degrees colder than yesterday) with a total snowpack depth of 72 inches.