Turnagain Pass Avalanche Forecast

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday March 4th, 2010 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

-The winds have backed off at all ridge top weather stations this morning. Average winds speeds are light this morning between 5mph-16mph with strong gusts up to 34mph.

-In the last 24 hours (5am-5am), the snotel sites recorded: 1.2 inches of water at Turnagain Pass with 11 inches of new snow, 1.4 inches of water and 14 inches of new snow at Grandview, and 0.2 inches of water and 6 inches snow at Summit Creek.

-The current radar shows most of the precip over Prince William Sound hitting Cordova, but the Kenai radar shows quite a bit of precip directly over the Kenai Mountains.

-Temps the same at most weather stations compared to yesterday ranging from 32 degrees F at sea-level and 20 degrees F at 3800′.

AVALANCHE DISCUSSION

Today’s avalanche danger will decrease to CONSIDERABLE due to a less intense weather forecast for the next 24 hours, but dangerous avalanche conditions still exist. Natural avalanches occurred yesterday morning 3/3/2010 and are still possible today, but the more dangerous aspect to today’s snowpack will be human triggered avalanches which will be likely on slopes steeper than 35 degrees.

Yesterday, the snowpack was reactive to a variety of triggers. Human and artificially triggered avalanches created medium sized avalanches in the top 1-2 feet of new storm snow. Natural avalanches were observed on Lipps and Pyramid around Turnagain Pass, and several naturals were reported in Girdwood Valley. Most of these avalanches probably happened early yesterday morning 3/3/2010, but the wind covered them up and made them difficult to see from a distance. Odds are,there were more natural avalanches around the area Turnagain Arm area, but we could not see them. Long story short, whenever natural avalanches happen, it’s wise to give the snowpack at least 24-48 hours to settle down before venturing into aggressive terrain. Remember that 90% of avalanches happen during storms and within 24 hours following a storm. We are still in that window, don’t take your chances on steep slopes today.

The structure of the snowpack has been showing signs for the past 2 days that it is too weak on steep slopes for this recent load of snow and wind slabs. Most of the observed or reported avalanches have been small to medium in size, but that is all it takes to bury a skier, snowmachiner, or snowboarder.

Today, the size of avalanches could be bigger because Turnagain Pass received anCNFAIC Staff 1.2” of water and 11” of snow in the last 24 hours. That brings the total to 3.5 inches of water and over 25 inches of new snow at 1800′ (more snow at higher elevations) in the past 72 hours. All this new snow is sitting on top of a slippery bed surface. There is over 3 feet of snow on top of that slippery bed surface in places like Tincan; so, that layer is becoming a deep slab problem. We need to give the mountains some time to adjust to this new snowpack.

Traveling on big slopes steeper than 35 degrees will be dangerous today. The type of storm snow that we have is tricky because these are the types of conditions that require precise trigger points where the 2nd, 3rd, or 4th person finds that specific trigger point and creates a deep avalanche that is too difficult to escape. A lot of times these trigger points are on steep rollovers in the middle of a slope where you are too committed to escape the slab. Slabs underneath rock bands are anCNFAIC Staff common trigger point in these types of conditions.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

510 AM AKST THU MAR 4 2010

…HIGH WIND WATCH IN EFFECT FROM FRIDAY MORNING THROUGH FRIDAY

EVENING THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…

.TODAY…SNOW IN THE MORNING…THEN SCATTERED SNOW SHOWERS IN THE

AFTERNOON. SNOW ACCUMULATION UP TO 3 INCHES. HIGHS IN THE MID 20S

TO MID 30S. VARIABLE WIND 10 MPH BECOMING SOUTHEAST 10 TO

20 MPH IN THE AFTERNOON.

.TONIGHT…SCATTERED SNOW SHOWERS IN THE EVENING…THEN SNOW

AFTER MIDNIGHT. AREAS OF BLOWING SNOW WILL REDUCE VISIBILITIES TO

LESS THAN A MILE AT TIMES. SNOW ACCUMULATION 2 TO 5 INCHES. LOWS IN

THE MID 20S TO LOWER 30S. SOUTHEAST WIND 15 TO 30 MPH. THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM…SOUTHEAST WIND 15 TO 25 MPH

INCREASING TO 35 TO 50 MPH AFTER MIDNIGHT.

.FRIDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE

AFTERNOON. SNOW ACCUMULATION 3 TO 7 INCHES. HIGHS IN THE 30S.

SOUTHEAST WIND 15 TO 30 MPH EXCEPT SOUTHEAST 65 TO POSSIBLY 85 MPH

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

Temperature / Precipitation

SEWARD 33 26 37 / 80 80 80

GIRDWOOD 36 27 36 / 100 60 80

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

Sea-level: temps are forecasted between 27-36 and between 0.25” of water forecasted

3000′: temps are forecasted in the range of 23-32 degrees F with winds 10 mph

6000′: temps are forecasted in the range of 14-23 degrees F with winds 10-30 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 20 (same as yesterday)

Winds: In last 24 hours winds have been light to strong averaging 5-32mph with extreme gusts up to 52mph

2600′-Seattle Ridge Wx Station

Winds: In last 24 hours winds have been light to moderate averaging 5-25mph with an extreme gust of 41mph

1800′-Center Ridge Wx Station

Current Temp: 27 degrees (same as yesterday)

Precip: 1.2” new water, 11” new snow, total snowpack depth of 121”

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Friday March 5, 2010.