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Issued
Thu, December 10th, 2009 - 7:00AM
Expires
Fri, December 11th, 2009 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday December 10th 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, these colder temps down low are really helping these areas.

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-

Temps are approaching the 4th day in a row since 2pm 12/6/09 of sustained above freezing temps. They ranged 35-38 degrees and the warmest reading was at 10am yesterday. Temps have been decreasing slightly. Winds have remained calm averaging 0-7 mph out of the WSW with a max gust of 9 mph.

2600′-Seattle Ridge Wx Station-

Winds have been calm averaging 0-4 mph out of the NE with a max gust of 6 mph

1800′-Center Ridge Wx Station-

Precip: 0 inches of water and 0 inches of new snow

minus 1” of total snowpack due to settlement for total depth of 58 inches

Temperature Range: 23-31 (highest temp recorded 5am yesterday morning) Temps have been decreasing. The snowpack at this elevation has settled 8″ since Sunday, which is about normal.

Nowcast

Skies are foggy in Girdwood as of 5am, but the Middleton and Kenai Radars are clear as a bell. Every weather station that I checked this morning had decreased temps from yesterday by 3-8 degrees. Temps currently range from 17 degrees at sea level to 35 degrees at 3800′; so, the inversion is still happening. Winds are still calm at all ridgetop wx stations.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 10 2009

.TODAY…MOSTLY SUNNY EXCEPT FOR AREAS OF FOG. HIGHS IN THE LOWER 20S

TO MID 30S…COLDEST INLAND. LIGHT WINDS.

.TONIGHT…MOSTLY CLEAR. PATCHY FOG. LOWS IN THE LOWER TEENS TO LOWER

30S…COLDEST INLAND. LIGHT WINDS EXCEPT WEST INCREASING TO 20 TO 30

MPH NEAR WHITTIER.

.FRIDAY…MOSTLY SUNNY. PATCHY MORNING FOG. HIGHS IN THE MID 20S TO

MID 30S. LIGHT WINDS EXCEPT WEST 20 TO 30 MPH NEAR WHITTIER.

.FRIDAY NIGHT…MOSTLY CLEAR. LOWS IN THE LOWER TEENS TO LOWER

30S…COLDEST INLAND. LIGHT WINDS EXCEPT NORTH 15 TO 25 MPH NEAR

SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 33 25 32 / 0 0 0

GIRDWOOD 26 17 27 / 0 0 0

Short Term Weather Models

Some models show the higher elevations around the Kenai Mountains near Turnagain Pass looking similar to yesterday, but they do show temps around 3000′ on the eastern Kenai Peninsula flirting with the freeze line, but above 6000′ temps appear to be staying warm and above freezing.

Sea-level: 0 inches of water forecasted today

3000′: temps forecasted above freezing today around 35-40 degrees with winds 5-10mph

6000′: temps forecasted above freezing today around 40 degrees with winds 5-10mph

AVALANCHE DISCUSSION

Today’s weather could contribute to the avalanche danger. This will be the 4th day in a row of unusually warm temps at the upper elevations; however, temps have backed off a little which might give the surface snow a little rest. We observeed very isolated and small sun sluffs and roller balls on southern aspects on Tuesday, but yesterday’s observations on Seattle Ridge showed that sun and warm temps were not significantly affecting the snow. We also recieved observations from Summit Lake from a southern aspect near Puluki Bowl with nothing remarkable to note. No new avalanches have been reported or observed since Monday near Summit Lake.

On Monday afternoon, we took a closer look at the snow temps on a ESE aspect on Seattle Ridge. We found the top 6 inches of the surface snow was warming up. Yesterday, we took anCNFAIC Staff look on a direct southern aspect at about 3000′ on Seattle Ridge on the highway side accross from Warm Up Bowl. We found the top 6 inches of the surface snow was warming up. These observations were spaced out by two full days of above freezing temps on slopes that get direct sunlight, and we did not see any significant change between these two locations. The sun was warm enough to slowly melt some snow off my skis while we were digging this pit, but there have been no alarming signs of instability on the surface.

The only concerning weak layer in the snowpack that this warming surface snow could trigger are the facets on the ground. With that being said. Areas of shallow snowpack will be the most likely area for an avalanche if the temps, sunlight, and aspect are all perfectly aligned. The NWS is still confident that today will have warm temps in the upper elevations.

Due to insignificant results in recent snowpits, a lack of recent natural or human-triggered avalanches since Monday around Summit Lake, and a similar weather forecast from the NWS, today’s avalanche danger level has returned to LOW. 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.

Normal Caution is advised.

Be carefull not to discredit sunsluffs near or above your location.

The secondary concern today are glide cracks. Tincan in particular has lots of these crevasse like features. People and dogs have fallen into these before in the past, and they can be very difficult to crawl out of. Make sure your partner knows where you are around these glide cracks.

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

Thu, December 10th, 2009
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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This is 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.