Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, March 23rd 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).
Today, the avalanche danger remains at LOW. We have received 1 inch of snow overnight, making this the 2nd largest snowstorm in the past month. This new snow, coupled with strong winds into the 30s, has started to fill the divots in the surface snow caused by wind, but we are still a ways away from having a continuous, trigger-able slab on top of the various crusts, near-surface facets, and surface hoar.
Normal hazard conditions continue in Turnagain Pass, but we are watching anCNFAIC Staff concerning set of instabilities emerge. There is still an isolated chance of breaking off an old wind slab on steep unsupported slopes, and cornices could fail if stressed too much by sun or weight, which could become a problem for a person travelling beneath or on them.
The conditions we will be monitoring closely over the next while will be mostly confined to how the new snow and old snow bond together. With observations of surface hoar, near surface facets, and all around hard snow surfaces, I am skeptical of how “nice” this new snow could become. With strong winds pushing around 1 inch of snow at 1800 feet, the likelihood of deeper snow on top of these surface features exists at higher elevations in wind-loaded start zones. Isolated pooling areas for this snow could start becoming reactive to human triggers if the snow keeps falling.
The recent Hatcher Pass avalanche brings back thoughts about how dangerous a weak and shallow snowpack can be in areas that usually get more snow. Turnagain Pass is currently at 60% of its normal SWE, Summit Lake is at 78% (though inherently thin on a good year), Alyeska Resort is at 55%, and Hatcher Pass is less than 50% of its snow water equivalent, loosely signifying a snowpack less than its usual height. Thin snow tends to mean weak snow, and weak snow should be thought of as “guilty until proven innocent.” Summit Lake has shown signs of a shallow snowpack all winter, so any new stresses to the old snow could reinvigorate any currently dormant instability. Isolated spots in steep, rocky, unsupported terrain of Turnagain Pass have also shown signs of a shallow snowpack, so this local terrain is not out of the woods yet. New precipitation can help us test this hypothesis.
Encyclopedia of avalanche terms.
Winds are forecasted to be similar to yesterday, reaching into the 30 mph range again. Temperatures should be similar to yesterday, approaching the freeze threshold in the afternoon if the sun comes out. New precipitation is forecasted at over 50%, making it likely to NWS personnel. These weather factors could start increasing the avalanche danger in Turnagain Pass, so we will see if the forecasts actually become verified.
Kevin 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-
500 AM AKDT WED MAR 23 2011
.TODAY…SNOW SHOWERS IN THE MORNING…THEN NUMEROUS SNOW AND RAIN
SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION 1 TO 3 INCHES. HIGHS IN
THE MID 30S TO LOWER 40S. EAST WIND 10 TO 25 MPH.
.TONIGHT…NUMEROUS SNOW SHOWERS. SNOW ACCUMULATION 1 TO 4
INCHES…HIGHEST AMOUNTS AT HIGHER ELEVATIONS. LOWS IN THE 20S. EAST
WIND 10 TO 20 MPH.
.THURSDAY…NUMEROUS SNOW SHOWERS IN THE MORNING…THEN NUMEROUS
SNOW AND RAIN SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION 1 TO 3
INCHES. HIGHS IN THE MID 30S TO LOWER 40S. EAST WIND 10 TO 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 39 28 39 / 80 80 70
GIRDWOOD 37 25 37 / 60 50 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
17 degrees. East wind 18mph gusting to 25mph.
-2600′ Seattle Ridge Wx Station-
21 degrees. Southeast wind 11mph gusting to 14mph.
-1800′ Center Ridge Wx Station-
24 degrees. 1 inch new snow.