Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday March 16th, 2010 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 winds have been light to moderate averaging 4-22mph with gust up to 32mph and are currently light averaging 4-5mph.

-In the last 24 hours (5am-5am), the snotel sites recorded: 0.0 inches of water and 3” of snow melting/settlement at Turnagain Pass, 0.1 inch of water and 5 inches of snow melting/settlement at Grandview, and 0.1 inches of water and 1 inches snow melting/settlement at Summit Creek.

-The current radars are mostly clear.

-Temps have cooled off at most weather stations by 0-5 degrees since yesterday morning. The Turnagain Pass wx stations recorded the highest temps of the day at 12:00, but all CNFAIC Staff weather stations recorded the highest temps between 2-5pm. Temps made it as high as 32 degrees at 3300′ and 42 degrees at 1800′. Current temps are 29 degrees F at sea-level and 24 degrees F at 3800′.

AVALANCHE DISCUSSION

Today’s danger level will start at MODERATE, but the danger will increase in the afternoon on steep sunny slopes. Today’s temps are forecasted to be 2-3 degrees warmer today than yesterday.

A human-triggered slab avalanche was reported at 3600′ on the west side of the Seward Highway across from Lower Summit Lake yesterday. Estimates from the reporting party describe the avalanche as 300′ wide, 1′ deep, which ran 2000′ and sympathetically triggered anCNFAIC Staff avalanche 150′ wide. The bed surface/failure layer was a recent crust. The slope angle at the trigger point was estimated to be 35 degrees on shallow rocky terrain that was slightly wind loaded. The snowboarder that triggered the avalanche started to get partially buried on the way down, but luckily was spit out on top of the debris at the bottom. No injuries reported.

Winds were stronger at Summit yesterday compared to Turnagain Pass, but I think the warm temps and sun shine are the big picture right now. As far as the snowpack is concerned, this sunny weather is putting stress on it just like any CNFAIC Staff storm would. In CNFAIC Staff words, it may not feel like a storm, but the current warm sunny weather should be treated just like any CNFAIC Staff storm hitting our snowpack because it is causing rapid changes to the snow.

Yesterday on Sunburst, the snow was light and fluffy as we hiked up, but noticeably changed to denser and wetter snow after just 2-3 hours. We found a denser layer/potential suncrust buried about 5 inches deep. This smooth dense layer/crust probably formed on 3 days ago on Saturday 3/13/2010. Now there is the new snow 5-7 inches of new snow sitting on top of that slippery surface. Some areas will be deeper due to recent wind. This slippery layer will be the problem layer today providing a slippery surface for the snow snow to slide and entrain snow.

There were widespread loose snow point release natural avalanches observed yesterday, but only a few small slabs were naturally triggered. Many of these small natural avalanches ran 500′-1000′ on steep sun effected slopes. The warmest temps of the day were recorded at noon at Turnagin Pass, but between 2:00-5:00 pm at all CNFAIC Staff weather stations. Temps made it as high as 32 degrees at 3300′ yesterday.

The temps dropped below freezing last night, so the snow will have set up a little more compared to how yesterday started, but avalanches on sun effected slopes will be the main concern today for small to medium sized avalanches that are clearly large enough to bury injure or kill a person in some isolated areas.

Glide cracks are secondary concern today. These crevasse like features that are cracks that go all the way to the ground appeared to have opened up a bit more in the past 24-48 hours. Glide cracks are like cornices in that they are wild cards that are very difficult to predict. Stay far away from these cracks today since they are actively moving right now.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT TUE MAR 16 2010

.TODAY…PARTLY CLOUDY. AREAS OF FOG REDUCING VISIBILITIES TO ONE

HALF MILE DURING THE MORNING NEAR WHITTIER AND PORTAGE VALLEY. HIGHS

AROUND 40. NORTHEAST WIND 10 TO 15 MPH EXCEPT NORTH 10 TO 20 MPH NEAR

SEWARD.

.TONIGHT…PARTLY CLOUDY. PATCHY FOG. LOWS IN THE LOWER 20S TO LOWER

30S. VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 10 TO 15 MPH.

.WEDNESDAY…MOSTLY SUNNY. HIGHS IN THE 30S. LIGHT WINDS EXCEPT

NORTH 10 MPH NEAR SEWARD.

Temperature / Precipitation

SEWARD 41 25 39 / 0 0 0

GIRDWOOD 39 24 39 / 0 0 0

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

Sea-level: temps are forecasted between 24-39 and between 0.0” of water forecasted

3000′: temps are forecasted in the range of 23-32 degrees F with winds 10 mph

6000′: temps are forecasted in the range of 14-23 degrees F with winds 15-20 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 24 (same as yesterday morning)

Winds: In last 24 hours winds have been calm to light to moderate averaging 4-22mph with a strong max gust of 32mph

HIGHEST TEMP: 26 @ 12:00

2600′-Seattle Ridge Wx Station

Winds: In last 24 hours winds have been light to moderate averaging 4-17mph with an moderate max gust of 26mph

1800′-Center Ridge Wx Station

Current Temp: 25 (5 degrees colder than yesterday morning)

Precip: 0 new precip. 3” of melting/settlement

HIGHEST TEMP: 42 @ 12:00

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday March 17, 2010.