Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, January 18th at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (advisory does not apply to highways, railroads, or operating ski areas).

ANNOUNCEMENTS

There are still spots available for next weekend’s snowmachine avalanche workshop in Turnagain Pass. Sign up at the Alaska Avalanche School (alaskaavalanche.com) or call (907)345-0878. They will cover rescue procedures and snow assessments with some class room and lots of field work.

WEATHER ROUNDUP

AnCNFAIC Staff 2 inches of new snow fell in the last 24 hours in Turnagain Pass, bringing our snowfall total for the week to around 24 inches of snow and 2 inches of water. Actual amounts from this past week vary from 16 inches on the southern end of the pass to 28 inches on the northern end. Yesterday ridgetop winds averaged 10-20mph out of the east and southeast with gusts in the 20’s and 30’s. Mountain temperatures ranged from the low to high 20’s while the freezeline hovered around 500-700 feet. As of 4am this morning, ridgetop winds are averaging 15mph out of the east and southeast with gusts in the 20’s. Skies are mostly cloudy right now while temps currently range from 22F at 3800 feet to 36F in Portage. A dissipating low over the Kenai peninsula will bring continued snow showers today mixed with rain near sea level. We may get an additional 1-3 inches this morning but things should taper off by afternoon. Mountain temps will remain in the 20’s while winds will average 10-15mph out of the south and southeast.

-The Center Ridge Wx Station at 1800 feet/Turnagain Pass-

recorded 2 inches of new snow and 0.2 inches water in the last 24 hours. The current temp is 28F (same as yesterday) with a total snowpack depth of 71 inches.

-The Sunburst Wx Station at 3800 feet/Turnagain Pass-

recorded light to moderate easterly winds yesterday averaging 15-20mph with gusts in the 20’s and 30’s. The current temp is 22F (same as yesterday) with winds averaging 15mph out of the east.

-The Summit Lake Wx Station at 1200 feet-

recorded 2-3 inches of new snow in the last 24 hours. The current temp is 27F (4 degrees warmer than yesterday) with a total snowpack depth of 32 inches.

-The Fresno Ridge Wx Station at 3400 feet/Summit Lake-

recorded light to moderate southeasterly winds yesterday averaging 10-20mph with gusts in the 20’s and 30’s. The current temp is 23F (1 degrees warmer than yesterday) with winds averaging 5mph out of the southeast.

The weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST MON JAN 18 2010

.TODAY…PERIODS OF SNOW. MIXED WITH RAIN AT TIMES NEAR WHITTIER AND

THROUGH THE PORTAGE VALLEY. ADDITIONAL SNOW ACCUMULATION 1 TO 3

INCHES. TEMPERATURES IN THE 30S. VARIABLE WINDS 10 MPH EXCEPT EAST

WIND 10 TO 25 MPH THROUGH PORTAGE VALLEY IN THE MORNING AND THEN

NORTH 15 MPH NEAR SEWARD IN THE AFTERNOON.

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

TEENS TO UPPER 20S. COLDEST INLAND. LIGHT WINDS EXCEPT NORTH WIND 10

TO 25 MPH NEAR SEWARD.

.TUESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE

UPPER 20S TO MID 30S. VARIABLE WINDS 10 MPH EXCEPT NORTH 15 TO 30

MPH.

TEMPERATURE / PRECIPITATION

SEWARD 35 25 33 / 80 40 40

GIRDWOOD 34 25 31 / 80 40 30

AVALANCHE DISCUSSION

Today, the avalanche danger remains at CONSIDERABLE on steep unsupported slopes greater than 35 degrees. We now have 16-28 inches of new snow on top of a slick crust, with even more on windloaded slopes at the higher elevations. The buried rain crust extends to about 3000 feet with buried wind crusts at the higher elevations. The wind was actively loading leeward aspects near the ridgetops yesterday, adding energy to an already unstable snowpack. Human-triggered avalanches are likely today on steep unsupported slopes over 35 degrees while natural avalanches are unlikely.

Matt, Jon, and I toured up Tincan yesterday and found widespread signs of instability on the rain crust buried under two feet of new snow. We got 15-20 ft. long shooting cracks on steep rollovers and heard quite a bit of whumphing between 1000 and 2000 feet elevation. In one instance the whumph knocked snow off a tree 150 feet away. That will get your attention! Ski cuts triggered 24 inch thick soft slabs running on the crust on steep rollovers at treeline and below, with the fractures propagating 10-40 feet wide. We topped out at 2500 feet due to bad visibility, but felt that these instabilities extended to the higher elevations as well where the crust is buried even deeper on windloaded slopes. Time will tell how quickly this new snow bonds to the crust, so for now I’d stick to the lower angle slopes. Terrain management is key.

The snow that fell this past week came in “upside down”, meaning it started off light and dry last Monday and is now warm and heavy…not the ideal setup for snow accumulating on top of a slick crust. The light, dry snow did not initially bond well with the crust, and now we have an increasingly thick and heavy slab forming on top….a sure recipe for avalanches. Layers of facets and surface hoar exist on top of and below the crust at the lower and mid elevations, which means we’ll be dealing with instabilities on this layer for an unfortunate while. In an extended column test at 1800 feet on Tincan yesterday, an avalanche class got full propagation underneath the rain crust along with easy failures during their compression tests.

Some Summit Lake observations from yesterday…one of our observers reported northeast winds transporting snow to leeward aspects near the ridgetops. He noted that the 6 inches of new snow from this past week was bonding well with the old snow surface and not reactive to ski cutting on a 35 degree W/SW slope. He saw no signs of instability or natural avalanches. During a stability test, however, he got a clean, fast Q1 shear on a layer of facets about 2 feet down.

Matt 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.