Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday March 17th, 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 averaging 1-10 mph with light gusts up to 15mph and are currently light averaging 3-6mph.

-In the last 24 hours (5am-5am), the snotel sites recorded: 0.0 inches of water and 2” of snow melting/settlement at Turnagain Pass, 0.0 inch of water and 2 inches of snow melting/settlement at Grandview, and 0.0 inches of water and 1 inches snow melting/settlement at Summit Creek.

-The current radars are mostly clear.

-Temps are in a melt-freeze cycle at all weather stations. The highest temps of the day were recorded between 2pm-6pm. Above freezing temps made it as high as 33 degrees at 3800′ and 45 degrees at 1700′. Current temps are 2-4 degrees colder this morning compared to yesterday with temps of 23 degrees F at sea-level and 24 degrees F at 3800′. Summit Lake had the biggest change of 10 degrees colder this morning.

AVALANCHE DISCUSSION

Today’s danger level will start at MODERATE, but the danger will increase to CONSIDERABLE in the afternoon on sunny slopes. Today’s temps are forecasted to be about as warm as yesterday. *NOTE-The North American Avalanche Danger Scale is not a perfect fit for current conditions. The important point today is that natural and human-triggered avalanches will become likely on sunny slopes this afternoon. Read the narrative below for more detailed information about recent avalanche hazard.

AnCNFAIC Staff human-triggered slab avalanche was reported yesterday 3/16/2010. The slab was triggered under the foot of the second person skinning up a South East aspect. The party heard a couple of “whumphs” before the avalanche a ripped out a few hundred feet wide. It ranged in depth from 1-4 feet deep. It failed on top of a recent sun crust (potentially with facets on top of the crust) on a sun baked slope at about 2:20pm on Tuesday 3/16/2010. No injuries or burial reported. The location was reported at TT43? The reporting party found similarities with the weak layer of this avalanche to the larger one that occured on Cornbiscuit last week.

See the photo gallery for pictures of the human-triggered slab avalanche that was reported on Monday 3/15/2010 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 foot 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.

Widespread natural point release avalanches were observed yesterday, and several natural slab avalanches were also observed. See photo gallery for a picture of a slab on a thin rocky sun baked slope at the southern end of Turnagain Pass.

We toured up Seattle Ridge yesterday and found a 1” thick breakable suncrust on the surface of the sun effected slopes. This crust became soft and pushable by 3pm. A previous sun crust/density change that formed on Saturday 3/13/2010 is providing a slippery sliding surface for the new 5-7 inches of snow to slide on. Some areas will have slabs with tapered depths from shallow to a couple feet deep in areas due to recent wind loading that occurred on Sunday. A future concern will be from the new layer of surface hoar that we observed on top of the current suncrust observed along the Seattle Ridge.

Our current weather may not feel like a storm, but the warm sunny weather must be treated just like any CNFAIC Staff storm hitting our snowpack because it is causing rapid changes to the snow. The sun is causing widespread point release avalanches and it is causing the surface snow to slab up during the warmest part of the day between 2-6pm.

The temps dropped below freezing again last night; so, the snow will have a melt freeze crust on the surface this morning that will soften and become more dangerous in the afternoon. 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.

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 over the past 2-3 days. 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 WED MAR 17 2010

.TODAY…SUNNY. AREAS OF LOW CLOUDS AND FOG WITH VISIBILITIES TO ONE

HALF MILE AT TIMES THROUGH PORTAGE VALLEY AND ALONG EASTERN TURNAGAIN

ARM THIS MORNING. HIGHS AROUND 40. SEWARD…NORTH WINDS TO 15 MPH

WITH GUSTS TO 30 MPH THIS MORNING. WHITTIER…WEST WINDS 15 MPH WITH

GUSTS TO 35 MPH THIS MORNING. LIGHT WINDS ELSEWHERE.

.TONIGHT…INCREASING CLOUDS WITH A CHANCE OF SNOW AFTER MIDNIGHT.

LOWS IN THE MID TEENS TO LOWER 30S…COLDEST INLAND. VARIABLE WIND TO

10 MPH.

.THURSDAY…RAIN AND SNOW LIKELY IN THE AFTERNOON. SNOW ACCUMULATION

UP TO 1 INCH. HIGHS IN THE MID 30S TO LOWER 40S. NORTH TO EAST WINDS

10 TO 20 MPH. GUSTS TO 35 MPH THROUGH PORTAGE VALLEY AND ALONG

TURNAGAIN ARM.

Temperature / Precipitation

SEWARD 39 27 42 / 0 30 70

GIRDWOOD 38 20 40 / 0 20 30

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

Sea-level: temps are forecasted between 20-38 and between 0.0” of water forecasted

3000′: temps are forecasted in the range of 23-32 degrees F with winds 5-10 mph

6000′: temps are forecasted in the range of 23-32 degrees F with winds 5-10 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 1-10mph with a light max gust of 15mph

HIGHEST TEMP: 33 @ 6pm

2600′-Seattle Ridge Wx Station

Current Temp: 24

Winds: In last 24 hours winds have been light to moderate averaging 1-6mph with a light max gust of 10mph

HIGHEST TEMP: 33 @ 5pm

1800′-Center Ridge Wx Station

Current Temp: 22 (3 degrees colder than yesterday morning)

Precip: 0 new precip. 2” of melting/settlement

HIGHEST TEMP: 42 @ 2pm

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday March 18, 2010.