Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday March 3rd, 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 are still moderate to strong at all ridge top weather stations this morning averaging 18mph-30mph with extreme gusts as high 48mph at Sunburst at 3800′ at Turnagain Pass.

-In the last 24 hours (5am-5am), the snotel sites recorded: 1.2 inches of water at Turnagain Pass with 9 inches of new snow, 0.5 inches of water and 5 inches of new snow at Grandview, and 0.2 inches of water and zero snow at Summit Creek.

-The current radar shows Prince William Sound full of precip spinning counter clockwise toward us.

-Temps are colder this morning at all weather stations compared to yesterday by 2-5 degrees ranging from 34 degrees F at sea-level and 20 degrees F at 3800′.

AVALANCHE DISCUSSION

Today’s avalanche danger will increase to CONSIDERABLE with pockets of HIGH due to a recent rapid load of precip and wind in the last 48 hours. Very dangerous avalanche conditions exist on slopes steeper than 35 degrees today. The size of avalanches will likely increase from yesterday.

Yesterday, the snowpack was reactive to human triggers and natural triggers. We found it easy to get shooting cracks below 2500′ on Tincan, and we were able to trigger an avalanche on a small test slope when the slope angle got just right (steeper than 35 degrees). Click on forecastors video at top of this page to see one of yesterday’s stability tests. These intentionally triggered avalanches on these test slopes failed about 2 feet deep down to the most recent rain crust that formed during the big February storm. Plus, small to medium sized natural avalanches were observed in Portage Valley.

The structure of the snowpack is too weak on steep slopes for this recent rapid heavy load of dense snow and wind slabs right now.

Today, the size of avalanches will likely be bigger today than the small to medium sized avlanches observed yesterday because we just got an additional 1.2 inches of water with strong to extreme winds at Turnagain Pass.

Traveling on slopes steeper than 35 degrees today is not recommended and stay away from traditional avalanche paths today. The slab avalanches that we triggered yesterday required the right slope angle before they would fail. This is dangerous because these are the types of conditions where the 2nd, 3rd, or 4th person finds that specific trigger point or puts enough weight on the slab too create a deep avalanche that is too difficult to escape.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED MAR 3 2010

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

AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS IN THE MID 30S

TO LOWER 40S. NORTH TO EAST WIND 10 TO 20 MPH. THROUGH PORTAGE VALLEY

AND TURNAGAIN ARM…SOUTHEAST WIND 25 TO 40 MPH DIMINISHING TO 15 MPH

BY AFTERNOON.

.TONIGHT…SNOW SHOWERS. SNOW ACCUMULATION 2 TO 4 INCHES. LOWS IN THE

UPPER 20S TO MID 30S. VARIABLE WINDS 10 MPH.

.THURSDAY…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS. HIGHS IN THE MID

20S TO MID 30S. VARIABLE WINDS 10 MPH.

Temperature / Precipitation

SEWARD 39 33 34 / 100 80 20

GIRDWOOD 40 32 37 / 100 80 40

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

Sea-level: temps are forecasted between 32-40 and between 0.5-0.75” 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 15-30 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 20 (4 degrees colder than yesterday)

Winds: In last 24 hours winds have been strong to extreme averaging 30-51mph with extreme gusts up to 71mph

2600′-Seattle Ridge Wx Station

Winds: In last 24 hours winds have been moderate to extreme averaging 20-39mph with an extreme gust of 59mph

1800′-Center Ridge Wx Station

Current Temp: 28 degrees (3 degrees colder than yesterday)

Precip: 1.2” new water, 9” new snow, total snowpack depth of 114”

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday March 4, 2010.