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Issued
Sun, February 21st, 2010 - 7:00AM
Expires
Mon, February 22nd, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, February 21st at 7am. 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

In the last two weeks Turnagain Pass received 7.5 feet of snow and over 9 inches of water, with consistent rain below 1000 feet from Feb 10-19. Gale to storm force easterly winds pummeled us the last three days of the storm. Yesterday was the first day since Feb. 4 we did not record any precipitation. Temperatures have been ridiculously warm the last two days…near 50F at sea level and in the low 40’s at 1800 feet. Temps above 3500′ were in the upper 20’s. Yesterday winds averaged 20-35mph out of the east with gusts in the 40’s while skies were mostly cloudy. The sun actually peeked through for a few hours, and it felt strangely like April while the freezeline went as high as 3000 feet. As of 4am this morning, ridgetop winds are light averaging 5-15mph out of the east. Temperatures are above freezing at all weather stations, ranging from 32F@3800′ to 35F@1800′ to 33F@sea level. A weak shortwave riding the southerly jet will bring cloudy skies today, continued warm temps in the upper 20’s to mid 30’s, and light to moderate easterly winds up to 20mph.

AVALANCHE DISCUSSION

Today the avalanche danger is rated CONSIDERABLE which means that dangerous avalanche conditions still exist. Human-triggered avalanches are likely on slopes steeper than 35 degrees. Natural avalanches will be possible on southerly aspects if the sun comes out for any extended period. We are coming off of six straight days of High or Extreme avalanche danger and the biggest storm of the season, so conservative decision-making is essential today. Although we are past the apex of the avalanche cycle, the avalanche hazard remains elevated due to unusually warm temperatures. We need some solid below freezing temperatures before conditions improve.

Days like today are when most people get caught and killed in avalanches. If skies clear you will be tempted to push into steeper terrain. Reason #1 to back off: we are less than 36 hours removed from the biggest storm of the season, and our snowpack is still adjusting to this massive load. Many of the slopes that avalanched naturally simply reloaded during Friday’s high winds. If you trigger an avalanche today it will be huge and most likely unsurvivable. Check out our photo gallery for some pics of recent avalanche activity.

It is going to take some time to get reacquainted with our snowpack after our recent pummeling. We have some significant deep slab instabilities in the snowpack right now, most notably several layers of buried surface hoar and the Jan. 7 rain crust. Numerous natural and explosive-triggered avalanches ran on the deeply buried Jan. 7 rain crust during this latest storm. And the buried surface hoar was responsible for many natural and human-triggered slides before the storm really got cranking. I’m guessing that a majority of the natural avalanches that happened during the storm ran on or stepped down to these layers. An avalanche triggered today could easily do the same.

I will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN FEB 21 2010

.TODAY…CLOUDY WITH A CHANCE OF RAIN AND SNOW. PATCHY MORNING FOG.

HIGHS AROUND 40. VARIABLE WIND TO 10 MPH. THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…EAST WIND INCREASING TO 15 MPH IN THE AFTERNOON.

.TONIGHT…MOSTLY CLOUDY. A CHANCE OF SNOW AND RAIN IN THE

EVENING. LOWS IN THE MID 20S TO MID 30S. VARIABLE WIND TO 10 MPH.

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 10 TO 20 MPH.

.MONDAY…MOSTLY CLOUDY WITH A CHANCE OF RAIN AND SNOW. HIGHS IN THE

MID 30S TO LOWER 40S. VARIABLE WIND TO 10 MPH. THROUGH PORTAGE VALLEY

AND TURNAGAIN ARM…VARIABLE WIND 10 MPH INCREASING TO EAST 15 TO 30

MPH IN THE AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 39 32 39 / 60 40 30

GIRDWOOD 39 29 37 / 20 20 0

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded moderate to strong easterly winds yesterday averaging 20-30mph with gusts in the 40’s. The current temp is 32F (6 degrees warmer than yesterday) with winds averaging 13mph out of the east.

-2600′ Seattle Ridge Wx Station-

recorded strong southeasterly winds yesterday averaging 25-35mph with gusts in the 40’s. Winds are currently light averaging 2mph out of the east.

-1800′ Center Ridge Wx Station-

recorded no new snow in the last 24 hours. The current temp is 35F (same as yesterday) with a total snowpack depth of 96 inches (7 inches of settlement since yesterday, 18 inches settlement since 2/18). The temperature has been above freezing for 72 hours.

Sun, February 21st, 2010
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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.