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Issued
Thu, January 21st, 2010 - 7:00AM
Expires
Fri, January 22nd, 2010 - 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 January 22nd 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

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Current temp is 22 (1 degree colder than yesterday) Winds have been light averaging 3-10mph out of the WNW with a light max gust of 14 mph

2400′-Seattle Ridge Wx Station-

Winds have been calm to light averaging 0-4 mph out of the NNW with a light max gust of 8mph

1800′-Center Ridge Wx Station-

Current temp is 15 (12 degrees colder than yesterday) Zero inches of water and zero inches of new snow has fallen.

Nowcast

Temps are colder at all wx stations this morning, especially near valley floors where they dropped 12-16 degrees compared to yesterday. Current temps range from 16 at sea level to 22 at 3800′; so, there is a slight inversion. There is zero new precip at the snotel sites this morning. Winds are currently light at all ridgetop wx stations this morning. The Middleton shows a wall of moderate precip moving our direction, but it is way outside of PWS. The Kenai radar is clear as a bell.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU JAN 21 2010

…STRONG WIND THROUGH FRIDAY AFTERNOON NEAR WHITTIER…

.TODAY…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS ALONG THE COAST IN THE

AFTERNOON. HIGHS IN THE LOWER 20S TO MID 30S…COLDEST INLAND. LIGHT

WINDS EXCEPT NORTH WIND 15 TO 30 MPH NEAR SEWARD. NEAR

WHITTIER…WEST WINDS GUSTING TO 50 MPH.

.TONIGHT…CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE MID

TEENS TO LOWER 30S…COLDEST INLAND. LIGHT WINDS EXCEPT NORTH WIND 15

TO 30 MPH NEAR SEWARD. NEAR WHITTIER…WEST WINDS GUSTING TO 50 MPH.

.FRIDAY…DECREASING CLOUDS. SCATTERED SNOW SHOWERS IN THE MORNING.

HIGHS IN THE LOWER 20S TO LOWER 30S. LIGHT WINDS EXCEPT NORTH WIND 15

TO 30 MPH NEAR SEWARD. NEAR WHITTIER…WEST WINDS GUSTING TO 45 MPH.

Temperature / Precipitation

SEWARD 30 19 28 / 30 40 40

GIRDWOOD 21 14 20 / 0 40 20

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

Sea-level: GFS shows 0.1 inches of water forecasted today

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

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

AVALANCHE DISCUSSION

Today’s weather should not contribute to the avalanche danger today at Turnagain Pass. The NWS is calling for strong winds near Whittier today, but none of the wx stations are reporting any wind yet.

The main avalanche concern today is that slippery rain crust underneath the 1.5-2.5 feet of newer snow especially between 2000′-3000′. This slippery rain crust formed on Thursday Jan 7 and is widespread on all aspects from Girdwood to Seward.

We have been seeing a common feature in the snowpack on both sides of the highway. The newer storm snow likes to fail about ½ inch above the top rain crust with hard failures in the lower 20 range on compression tests with clean shears (Q2) where the shear plane is smooth but does not slide readily.

What this means according to the avalanche guidelines is that these test scores… “generally indicates good stability (in these particular test pit locations) but a compact group of skiers/snowboarders, a snowmachine, or explosives may trigger an avalanche. Natural avalanches are rare”.

These test scores are still on the low end of good stability and the structure of the snowpack is poor right now because it has the three main ingredients for an avalanche: a slab (the new 1.5-2.5 feet of snow) on top of a weaker layer (last week’s 6 inches of light dry snow) on top of a slippery bed surface (rain crust).

Since the snowpack structure is poor and we have been finding consistent failures in multiple locations, the danger level needs to stay at MODERATE until this failure starts to go away. Terrain management is key right now. I think it would be wise to stay away from big lines and stick to more manageable terrain. Actual data is always better for making decisions than opinions; but, for whatever it is worth, I’m not willing to risk my life on big terrain when the stability is on the low end of good. I like to wait till stability is very good at low danger. We will get there again, but the snowpack is not quit there yet.

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 January 22nd.

Thu, January 21st, 2010
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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.