Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday December 17th 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).

ANNOUNCEMENTS

All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. These areas are periodically patrolled by law enforcement. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow. We checked out 20 mile on Wednesday 12/16/09. Its still very shallow with lots of alders, but the ground water is frozen solid.

WEATHER ROUNDUP

Will recent weather effect avalanche conditions today?

Well, let’s take a closer look at the precip, winds, and temps.

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temperatures have dropped from 15 to 2 degrees F with increasing winds averaging 2-33 mph from the E with a strong max gust of 46 mph

2400′-Seattle Ridge Wx Station-

Winds have been increasing averaging 0-16 mph from ESE with a max gust of 29 mph

1800′-Center Ridge Wx Station-

Precip: 0.4 inches of water and 4 inches of new snow

Total depth of 60 inches

Temperatures have dropped from 12-4 degrees F

Yesterday (12/16) afternoon’s snow stake totals

Eddies Lot: 4″ new

Motorized Lot: 4″ new

Sunburst Lot: 4″ new

Johnson Pass North Lot: 3″ new

Nowcast

Light snow is falling in Girdwood as of 5am. The Middleton radar is not working and the Kenai radar shows light precip over Anchorage. Temps are colder at all wx stations this morning with temps ranging from 12 degrees F at sea-level to negative 1 degree at 3300′. Winds have increased at all ridgetip wx stations.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 17 2009

…STRONG WIND THROUGH FRIDAY MORNING…

.TODAY…SNOW SHOWERS. SNOW ACCUMULATION 2 TO 4 INCHES. AREAS OF

BLOWING SNOW. HIGHS 10 TO 20 ABOVE…COLDEST INLAND. WEST WINDS 20 TO

30 MPH WITH GUSTS TO 45 MPH NEAR WHITTIER THIS MORNING DIMINISHING TO

25 MPH THIS AFTERNOON. NORTH TO WEST WINDS 10 TO 20 MPH ELSEWHERE.

.TONIGHT…MOSTLY CLOUDY. ISOLATED SNOW SHOWERS. AREAS OF

BLOWING SNOW. LOWS 10 BELOW TO 10 ABOVE…COLDEST INLAND.

NEAR WHITTIER…WEST WINDS INCREASING 30 MPH WITH GUSTS TO 50 MPH IN

THE EVENING. NEAR SEWARD…NORTH WINDS INCREASING 20 TO 30 MPH WITH

GUSTS TO 45 MPH BY MIDNIGHT. WEST WINDS 15 MPH ELSEWHERE.

.FRIDAY…AREAS OF BLOWING SNOW IN THE MORNING. PARTLY CLOUDY

WITH ISOLATED SNOW SHOWERS. HIGHS ZERO TO 15 ABOVE…COLDEST

INLAND. NEAR WHITTIER…WEST WINDS 15 TO 30 MPH WITH GUSTS TO 50 MPH

IN THE MORNING. NEAR SEWARD…NORTH WINDS INCREASING 15 TO 25 MPH

WITH GUSTS TO 45 MPH ENDING IN THE MORNING. WEST WINDS 5 TO 15 MPH IN

THE MORNING ELSEWHERE.

TEMPERATURE / PRECIPITATION

SEWARD 18 5 8 / 50 20 20

GIRDWOOD 13 2 2 / 100 20 0

Short Term Weather Models (NAM, WRF, QPF) for the Kenai Mountains near Turnagain Pass

Sea-level: 0.0 – 0.05 inches of water forecasted today

3000′: temps forecasted between 5 and negative 4 degrees F with winds 5-10mph

6000′: temps forecasted between negative 3 and negative 13 degrees F with winds 10-15mph

AVALANCHE DISCUSSION

Today’s weather will contribute to the avalanche danger today at Turnagain Pass. The NWS is talking about strong winds through Friday. They have not issued any sort of advisory or warning about the wind yet, but all the ridgetop weather stations are indicating increased winds since last night. Our parking lot snow stakes have measured 7-9 inches of new snow at Turnagain Pass between Tuesday and Wednesday. Plus, the Center Ridge wx station is reporting anCNFAIC Staff 4 inches of snow from last night bringing the total to about 12″ of new very light density snow in the past 3 days at Turnagain Pass. That is not very much snow, but its very light and will transport very easily with wind. There will probably be lots of very small to small windslabs today that will be easy to trigger today on slopes steeper than 38 degrees. Large avalanches will be unlikley today.

Due to a lack of deep instability, the biggest avalanche conern today is recent snow on the surface. Today’s avalanche danger level will remain at LOW although it is getting close to bumping up to MODERATE due to today’s wind. If larger avalanches were possible, then the danger would increase. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Very small avalanches in widespread areas; or small avalanches in isolated areas.

AnCNFAIC Staff concern today will be the glide cracks. Tincan in particular has lots of these crevasse like features which will be hidden due to recent wind. Watch your partners. We had a report of a guy who fell into a four foot glide crack this week.

The next avalanche concern that we are watching out for is near the surface snow. There are widespread firm or slippery surfaces created by the wind, sun, and warm temps from last week. Surface hoar formed from sea level to as high as 2800′, however, the most defined surface hoar and faceted surface snow is below 1600′; so, due to the slippery surfaces and formation of surface hoar and faceted sugary surface snow, the worst weak layer in the near future will be below 2800′. These mid to lower elevations could become our next big problem when we get the next big weather event. Just as a reminder, most of the bowls along Seattle Ridge are below 2800′. CNFAIC Staff areas with steep terrain below 2800′ include but are not limited to the lower part of Eddies, Pete’s North, and the terrain behind the “Welcome to the Kenai” sign near Pyramid along Seattle Ridge.

Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Friday December 18.