Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, February 4th 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 hazard rating is MODERATE. The storm just ended yesterday so new snow instabilities are still present. Older persistent instabilities will be a major concern today and through the weekend. Human triggered avalanches were happening before the storm and new snow, rain, and wind all conspire to tip the balance further toward failure.
Natural avalanche activity was observed with good visibility in the mountains yesterday. Along Turnagain arm, Portage, and into Turnagain pass there were natural avalanches evident that happened during the storm. Overall, activity was less then I expected, but some odd examples in mid slope terrain with deep fractures underline the need to expect the worst if traveling in the backcountry today.
Temperatures have dropped about 10 degrees since the storm was most intense. Generally this will freeze the rain saturated lower elevations and lock it in place quickly. That was also the zone where we had the largest surface hoar, so large collapses are still possible below tree line. Above the rain line (2000 feet) the temperatures stayed below freezing and we simply don’t know yet how tempermental this new load will be when subjected to backcountry travelers.
Just prior to this storm there were a number of human triggered avalanches region-wide breaking down to old January and December persistent weak layers. Some of these events were “close calls” and involved serious injuries. The new storm will add stress on top of an already weak structure, but it also adds strength and insulation from being affected by a person’s weight. At this point it is extremely difficult to tell how touchy the snow will be. Today, being just 24 hours out from the end of the storm is a good day to keep terrain choices mellow. Giving the snow time to adjust to the new stress keeps us out of the hazard during the most dangerous time. My own uncertainty about the likelihood of human triggered avalanches is high until time passes and we get more information about the new snow. Public observations this weekend will be vital to getting a clear picture of the changing hazard.
Terrain choice will be a critical factor to stay safe today. The people who survive a lifetime in the backcountry don’t depend on luck, they use timing after storms and careful route-finding as well as safe travel techniques to increase their chances of a safe backcountry day.
Two specific concerns are present today. The new storm snow is still possible to trigger region wide. This concern will likely bond and become stable soon. Old persistent instabilities will be a major concern today and through the weekend. These layers of facets and buried surface hoar have been causing problems for the last month and they will remain a problem. Most likely trigger points will be in shallow areas near rocks, ridges and gullies. Steeper, advanced terrain is most likely to show the exposed rocks and have the angle sufficient to promote avalanches.
Encyclopedia of avalanche terms.
The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it!
The storm finished yesterday. Total storm accumulation ranged from only 8 inches in Summit to over 50 at upper elevations in Girdwood. Turnagain pass was middle range with about 29 inches up high. Rain to 2000 feet saturated the lower elevations and should be evident with a crust below treeline. Wind during the storm trended from the East with gusts into the 60s at the ridge-tops. Wind drifting and a textured snow surface was obvious yesterday. Temperatures have dropped since the storm started diminishing. A few inches of colder snow fell at the end of the storm. Today clear skies, moderate temperatures, and light wind are expected.
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 AKST FRI FEB 4 2011
.TODAY…MOSTLY CLOUDY IN THE MORNING WITH PATCHY FOG…THEN
BECOMING MOSTLY SUNNY. HIGHS IN THE MID 20S TO LOWER 30S.
NORTH TO WEST WIND TO 15 MPH. NEAR SEWARD…NORTH WIND INCREASING
TO 15 TO 25 MPH. NEAR WHITTIER…WEST WIND INCREASING TO
15 TO 25 MPH WITH GUSTS TO 35 MPH.
.TONIGHT…CLEAR. LOWS 5 TO 15 ABOVE INLAND AND 20 TO 25 ALONG
THE COAST. LIGHT WINDS EXCEPT NORTH TO 15 MPH NEAR SEWARD.
.SATURDAY…MOSTLY SUNNY. HIGHS IN THE 20S. VARIABLE WIND TO
.SATURDAY NIGHT…MOSTLY CLEAR. LOWS 5 TO 15 ABOVE INLAND AND
20 TO 25 ALONG THE COAST. VARIABLE WIND 10 MPH.
.SUNDAY…PARTLY CLOUDY EXCEPT MOSTLY CLOUDY ALONG THE GULF
COAST WITH A CHANCE OF SNOW SHOWERS. HIGHS IN THE LOWER 20S
TO LOWER 30S. VARIABLE WIND TO 10 MPH.
.SUNDAY NIGHT…PARTLY CLOUDY. A CHANCE OF SNOW SHOWERS ALONG
THE GULF COAST. LOWS IN THE TEENS.
.MONDAY AND MONDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF
SNOW SHOWERS. HIGHS 25 TO 35. LOWS IN THE TEENS.
.TUESDAY…RAIN AND SNOW LIKELY. HIGHS IN THE 30S.
.TUESDAY NIGHT…CLOUDY WITH A CHANCE OF SNOW. LOWS IN THE 20S.
.WEDNESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE 30S.
.WEDNESDAY NIGHT AND THURSDAY…MOSTLY CLOUDY. A CHANCE OF SNOW
SHOWERS. LOWS IN THE 20S. HIGHS 25 TO 35.
TEMPERATURE / PRECIPITATION
SEWARD 30 20 28 / 0 0 0
GIRDWOOD 28 15 24 / 0 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature is 17 and steady. Wind is light.
-2600′ Seattle Ridge Wx Station-
Temperature 19 degrees. Wind gauge iced up.
-1800′ Center Ridge Wx Station-
Temperature 23. Two inches of light snow fell yesterday as the storm finished.