Turnagain Pass Avalanche Forecast

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday December 29th 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 on the Chugach National Forest are open to snowmachines except Placer and 20 Mile. Please remember that Center and Divide Creeks near the Johnson Pass Trailhead are always closed due to the current Forest Plan.

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 increased from 26 to 28 degrees F with decreasing winds averaging 7-20 mph from the E with a strong max gust of 31 mph

2400′-Seattle Ridge Wx Station-

Winds have been decreasing averaging 8-20 mph from SE with a strong max gust of 32 mph

1800′-Center Ridge Wx Station-

Precip: 0.0 inches of water

Total depth of 62 inches

Temperatures have dropped 2 degrees F current temp 31

Nowcast

A few stars are visible over Girdwood as of 5am. The Middleton and Kenai radars are clear. Compared to yesterday, temps are colder at all valley bottom wx stations and similar to slightly warmer at all ridgetop wx stations this morning. Temps range 30 degrees F at sea-level to 28 degrees F at 3800′. Winds have decreased at all ridgetip wx stations. Summit Creek is the odd ball this morning showing a temp of 18 degrees.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST TUE DEC 29 2009

.TODAY…PARTLY CLOUDY. PATCHY MORNING FOG. HIGHS IN THE

UPPER 20S TO UPPER 30S. VARIABLE WIND TO 10 MPH.

.TONIGHT…PARTLY CLOUDY. PATCHY FOG AFTER MIDNIGHT. LOWS 15 TO

25. LIGHT WINDS EXCEPT NORTH AND WEST WIND 15 MPH NEAR SEWARD AND

WHITTIER.

.WEDNESDAY…MOSTLY CLOUDY. HIGHS IN THE LOWER 20S TO LOWER 30S.

LIGHT WINDS EXCEPT NORTH AND WEST WIND 15 MPH NEAR SEWARD AND

WHITTIER.

TEMPERATURE / PRECIPITATION

SEWARD 36 22 24 / 0 0 0

GIRDWOOD 32 19 24 / 0 0 0

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

Sea-level: 0.0 inches of water forecasted today

3000′: temps forecasted between 23 and 32 degrees F with winds 0-5mph

6000′: temps forecasted between 23 and 32 degrees F with winds 10-15mph

AVALANCHE DISCUSSION

Today’s weather should not contribute to the avalanche danger today at Turnagain Pass.

Sunburst has been the subject of the Avalanche Center’s most recent snow study. Between Saturday and Monday there have been 20 different compression tests and 1 extended column test at multiple elevations at 1500′, 2000′, 2500′, 3000′, and 3500′. Sometimes it’s good to focus on one mountain to try to find any patterns and combine the results from CNFAIC Staff nearby locations for a good general impression of snowpack over a larger area. Our main area of interest has been how the snow changes through different elevations. Similar observations were reported yesterday from Magnum and Center Ridge.

There are three main points of interest in the current snowpack

1.The buried surface hoar is generally confined to elevations below 2000′ and has been observed buried about 10-12 inches deep.

2.Old wind slabs near ridgetops that are about 6 inches deep near the surface still failed easily in yesterdays compression tests with scores as low as CTE2Q2@15cm. These wind slabs did not appear reactive to ski or snowboard tracks.

3.The facets on the ground are strangely starting to show slightly decreased stability since last week. These facets are generally rounding out, but have shown moderate failures with test scores as low as CTM13Q3@70cm. They show more activity where the snowpack is less than 3 feet deep, but were reactive as of yesterday 12/28/09 in a 5 foot deep isolated column. I’m not that concerned with these facets, but it does raise a few eyebrows. This data jives with a recent report where somebody observed some small slabs stepping down to the ground on steep terrain at about 1800′. Maybe these facets will show themselves during the next big pineapple express.

These 3 points of interest are not overly concerning for today’s avalanche danger. Due to a lack of significant weak layers and a mild weather forecast, the avalanche danger for Turnagain Pass will decrease today to LOW. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain.

AnCNFAIC Staff concern today will be the glide cracks. A couple of large glide cracks have opened north of the snowmachine uptrack to Seattle ridge. Odds are there are numerous more of these crevasse like features which may be difficult to see. People and dogs have fallen into these cracks before, and they can be very difficult to get out of. Sometimes these glide cracks will avalanche, but this does not appear to be a concern today. It’s always a good idea to treat glide cracks like cornices and avoid traveling underneath their path. Like cornices, glide cracks are very difficult to predict.

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 Wednesday December 30.