Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday March 2nd 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 increased this morning at all ridge top weather stations. Sunburst at 3800′ and Seattle Ridge at 2600′ at Turnagain Pass are both recording strong to extreme average wind speeds between 39-47mph and are both recording extreme gusts between 59-67mph.

-In the last 24 hours (5am-5am), the snotel sites recorded 1.1 inches of water at Turnagain Pass with 5 inches of wet snow, .7 inches of water at zero new snow at Grandview, and 0 inches of water and snow at Summit Creek.

-The current radars show a moderate band of precip over PWS moving WNW toward the southern Kenai Mountains near Seward.

-Temps are about the same this morning at all weather stations compared to yesterday plus or minus 1-3 degrees Temps range from 37 degrees F at sea-level and 25 degrees F at 3800′. High temps made it as high as 32 degrees at 2800′ yesterday.

AVALANCHE DISCUSSION

Today’s avalanche danger will remain at CONSIDERABLE on specific terrain features due to precip/winds in the last 24 hours.

Last night, the Center Ridge weather station recorded about twice as much water as it did the previous night. Yesterday, it required large triggers to create small to medium sized avalanches. Today these same sized avalanches might require less of a trigger. Or the avalanches might be bigger. Or the recent wind and precip may have already stressed the snowpack enough that it will be difficult to trigger an avalanche. In CNFAIC Staff words, we have some question marks about whether or not a skier, snowboarder, or snowmachiner will trigger an avalanche large enough to bury, injure or kill a person today; so, don’t push your luck. There are some dangerous avalanche conditions out there right now.

Most of the danger will be isolated to pockets of wind slabs on specific terrain features like: ridges, shoulders, wind lips, ribs, and slopes steeper than 35 degrees on unsupported slopes above cliffs. Plus, natural avalanches are possible due to the strong winds forecasted today.

The structure of the snowpack is fair right now with 2 out of the 3 main ingredients for an avalanche. We have a bed slippery bed surface all the way to ridges, we have slab of denser snow on top of weaker snow. The ingredient that is questionable right now is a significant weak layer. We do have an upside down snowpack with density changes between the old light density snow and the new storm snow. The light density snow has been very easy to sluff recently, but it probably lacks the potential for large propogation like a layer of buried surface. Once again, this is a question mark with the snowpack today. Remember, it does not take a large avalanche to bury a person; so, don’t take your chances today on big terrain.

We also received a report that the glide cracks on Tincan are getting big enough for a dog or person to fall into. Many of these crevasse like features could be covered up by the recent wind.

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST TUE MAR 2 2010

…STRONG WIND THROUGH LATE TONIGHT THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…

.TODAY…RAIN. HIGHS 35 TO 40. NORTH AND EAST WIND 10 TO 20 MPH

EXCEPT EAST 45 TO 60 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.TONIGHT…RAIN AND SNOW. SNOW ACCUMULATION UP TO 2 INCHES OVER THE

HIGH ELEVATIONS. LOWS IN THE 30S. NORTH AND EAST WIND 10 TO 20 MPH

EXCEPT EAST 45 TO 60 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.WEDNESDAY…RAIN. HIGHS IN THE MID 30S TO LOWER 40S. SOUTHEAST WIND

10 TO 20 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 25

TO 40 MPH DECREASING TO 15 TO 20 MPH IN THE AFTERNOON.

Temperature / Precipitation

SEWARD 43 38 40 / 100 100 80

GIRDWOOD 42 34 39 / 80 100 80

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

Sea-level: temps are forecasted between 34-42 and between 0.5” of water forecasted 3000′: temps are forecasted in the range of 23-32 degrees F with winds 25 mph

6000′: temps are forecasted in the range of 14-23 degrees F with winds 35-40 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 25 (1 degrees warmer than yesterday)

Winds: In last 24 hours winds have been light to extreme averaging 13-47mph with extreme gusts up to 67mph

2600′-Seattle Ridge Wx Station

Winds: In last 24 hours winds have been light to extreme averaging 7-41mph with an extreme gust of 62mph

1800′-Center Ridge Wx Station

Current Temp: 30 degrees (same as yesterday)

Precip: 1.1” new water, 5” new wet snow, total snowpack depth of 105”

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday March 3, 2010.