Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, April 13th 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).
The avalanche danger today remains at LOW with pockets of MODERATE. The pockets of MODERATE include steep sun-affected slopes in the afternoon which could potentially fail naturally if the sun beats down again like it did yesterday. North facing slopes at upper elevations that are showing reactive buried layers of surface hoar also fit into this pocketed category.
We are not at a full-on LOW danger rating, so steeper slopes over 35 degrees should be approached with caution if you are uncertain of their stability.
Our primary concern is switching toward usual spring-time instabilities. This time frame has historically shown that the hazard is dramatically higher mid-day than in the morning on solar aspects. Wet slab avalanches on steep slopes directly facing the sun during the warmest part of the day (1:00pm-6:00pm) are starting to pop out. This hazard may be less dramatic today than yesterday, due to an increase in clouds. Any rain associated with a passing Low Pressure system may help induce wet slabs at lower elevations today.
This specific wet slab started as a point release beneath some rocks on a steep slope at 2:00pm yesterday, quickly entraining more snow and ripping out deeper pockets of snow on its travels to the valley bottom.
Steep East, South, and West facing slopes that have not yet shed their upper layers of snow could be some of the most hazardous places to be around lunch time and soon after. If lower slopes facing these directions are becoming saturated on the ascent, it is likely that the steep upper slopes are already weak and could be triggered by additional weight. Sinking into snow beyond your ankles should clue you into this increasing instability. If you observe this, try to get to cooler snow immediately.
As a secondary concern, persistent slabs failing on layers of buried surface hoar are still possible to trigger, but would likely take a large amount of stress to get them going. Looking for these layers on Northern slopes will give you a good idea of how deep any potential avalanche would break, but stability tests performed may show a full spectrum of results. Never base a go or no-go decision on results from one snow pit.
On a final note, we have also been seeing an increase in glide crack activity in the area. These features look like dark frowns in the snow, and should be avoided since they are unpredictable and can fail at any time. Luckily, we are able to see this hazard and avoid it versus the CNFAIC Staff concerns
Encyclopedia of avalanche terms.
Winds are not likely to increase significantly, therefore will not affect the snowpack adversely. Temperatures should be reaching into the upper 30’s, potentially affecting the stability on lower elevation slopes, as well as on sunny aspects during the afternoon. There is a chunk of precipitation moving around in Prince William Sound, but radar, satellite, forecasts, and models all point to a small impact in Turnagain Pass. It could rain a bit at lower elevations while it spits snow at upper elevations.
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-
500 AM AKDT WED APR 13 2011
.TODAY…MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE MORNING…
THEN SCATTERED RAIN AND SNOW SHOWERS IN THE AFTERNOON. HIGHS IN THE
MID 30S TO MID 40S. NEAR SEWARD…NORTH WIND 10 TO 20 MPH. NEAR
WHITTIER…WEST WIND 15 TO 30 MPH…DIMINISHING IN THE AFTERNOON.
VARIABLE WIND TO 10 MPH ELSEWHERE.
.TONIGHT…MOSTLY CLOUDY. SCATTERED SNOW AND RAIN SHOWERS IN THE
EVENING…THEN SCATTERED SNOW SHOWERS AFTER MIDNIGHT. LOWS IN THE
LOWER 20S TO LOWER 30S. LIGHT WINDS EXCEPT NORTH 10 MPH NEAR SEWARD.
.THURSDAY…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE
MORNING…THEN ISOLATED RAIN AND SNOW SHOWERS IN THE AFTERNOON. HIGHS
IN THE LOWER TO MID 40S. VARIABLE WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 44 30 46 / 40 50 30
GIRDWOOD 45 24 46 / 30 30 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
21 degrees. NE wind 3mph gusting to 5mph.
-2600′ Seattle Ridge Wx Station-
21 degrees. NNE wind 5mph gusting to 8mph.
-1800′ Center Ridge Wx Station-
24 degrees. No new snow.