Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, November 29th 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).
Turnagain Pass and Johnson Pass North Trailhead motorized areas are open for snowmachine use. Adequate snow is present to prevent resource damage. These areas consist of the lands on the west side of the Seward Highway between the Turnagain Arm and Sixmile Creek and the drainage southwest of Bench Creek adjacent to the Johnson Pass North Trailhead south to Bench Lake. Center and Divide Creek drainages are closed to snowmachine use. All CNFAIC Staff areas of the Chugach NF are closed to motorized use until December 1st or until adequate snow falls to prevent resource damage.
The tail end of a weak low pressure system dropped 1 inch of new snow in Turnagain Pass yesterday morning before skies cleared. Most of the strong north winds stayed confined to sea level along Turnagain Arm yesterday, although I did see quite a bit of snow pluming off the peaks on the northern end of Turnagain Pass. The Sunburst and Seattle Ridge weather stations somehow recorded light winds yesterday averaging 5-10mph out of the northwest with gusts in the 20’s on Seattle Ridge. Mountain temps took a nose dive yesterday into the single digits and remain there this morning. Ridgetop winds in Turnagain Pass are currently averaging 5-10mph out of the northwest (while moderate winds averaging 20-25mph with gale force gusts in the 40’s are blowing in Portage Valley and on the ridges south of Turnagain Pass). Expect clear and cold weather for most of the week with strong northwest winds persisting through Tuesday.
Today the avalanche hazard will remain at MODERATE on steep windloaded slopes greater than 35 degrees while slopes not affected by the wind will have a LOW danger. New windslabs on top of a slick ice crust will be our main concern today. Small to medium sized human-triggered avalanches 1-2 feet deep will be possible on steep windloaded slopes while natural avalanches are possible on actively loading slopes. Glide cracks continue to avalanche unpredictably and remain a secondary concern today.
Despite the ridgetop weather station readings in Turnagain Pass, the north winds yesterday hit some areas and spared CNFAIC Staffs. Expect more of the same today. Any new windslabs will be sitting on top of a super slick ice crust that formed during the freezing rain event last Monday. We’re now calling this ice layer the “Thanksgiving Rain Crust”, or TRC for short, because I have a feeling we will be writing about it for a long time. Keep in mind this is no ordinary rain crust. At the higher elevations it looks like a pane of glass and shatters like one too. Matt and I toured up to the Sunburst weather station Saturday and confirmed that the ¼ to ½ inch thick ice crust extends to 4000 feet elevation and most likely higher. Since the TRC formed, 7-10 inches of fluff has fallen in Turnagain Pass. In non wind-affected areas, the soft snow is slowly settling into more of a slab. Even moderate winds will drive this snow into dense soft slabs that will slide easily on the rain crust.
We are still in an active glide avalanche cycle that has been going on for the past 3 weeks. Be aware of your travel routes and try to avoid spending time below the gaping cracks.
Kevin 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-
500 AM AKST MON NOV 29 2010
…STRONG WIND THROUGH TUESDAY AFTERNOON NEAR SEWARD AND WHITTIER…
.TODAY…PARTLY CLOUDY. HIGHS IN THE 20S. WEST WIND 55 TO 65 MPH NEAR
WHITTIER. NORTH WIND 35 TO 50 MPH NEAR SEWARD. NORTHWEST WIND 15 TO
30 MPH ELSEWHERE.
.TONIGHT…MOSTLY CLEAR. LOWS IN THE TEENS. WEST WIND 55 TO 65 MPH
NEAR WHITTIER. NORTH WIND 35 TO 50 MPH NEAR SEWARD. NORTHWEST WIND 15
TO 30 MPH ELSEWHERE.
.TUESDAY…SUNNY. HIGHS 15 TO 25. WEST WIND 40 TO 55 MPH NEAR
WHITTIER. NORTH WIND 30 TO 45 MPH NEAR SEWARD. NORTHWEST WIND 10 TO
20 MPH ELSEWHERE.
TEMPERATURE / PRECIPITATION
SEWARD 25 16 23 / 0 0 0
GIRDWOOD 20 10 17 / 0 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light northwest winds yesterday averaging 3-8mph and temps dropping from 15F to 5F. The current temp is 3F with winds averaging 5mph out of the northwest.
-2600′ Seattle Ridge Wx Station-
recorded light northwest winds yesterday averaging 2-13mph and temps dropping from 15F to 9F. The current temp is 10F with winds averaging 5-10mph out of the northwest.
-1800′ Center Ridge Wx Station-
recorded 1 inch of new snow and 0.1” water in the last 24 hours. Temps yesterday dropped from 17F to 13F. The current temp is 11F with a total snowpack depth of 46 inches (1 inch of settlement).