Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday, February 19th 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).
AnCNFAIC Staff wave of wind and rain is currently moving through the area. This round of wetness has the snowline pushed way up to 3200 ft. Very strong easterly winds are again present with gusts over 90 at Turnagain ridgetop elevations. The radar shows heavy precipitation moving into our area. The models indicate this weather will move through the area by this afternoon. The jet stream continues to bump into the panhandle and Olympic ridge and turn north right at us. This strong south to north flow is responsible for our warm wet weather. This jet stream pattern is expected to break up next week.
Today’s avalanche danger is HIGH due to the heavy precipitation and wind that is being forecasted by the National Weather Service. This means we have very dangerous avalanche conditions and travel in avalanche terrain is not recommended. Natural avalanches likely and human triggered avalanches very likely.
Yesterday, we saw more natural and human triggered avalanches from Girdwood to Summit Lake. DOT, AK Rail Road, and Alyeska Ski Patrol crews reported significant avalanche activity. Avalanches covered the Seward Highway and the AKRR.
I think we probably reached the apex of the storm and avalanche cycle yesterday morning; however, very strong winds and additional rain and snow are assaulting the mountains again today. With weather like this starting zones reload very quickly. In addition, we are seeing rain pushing back up in elevation. This will add additional stress to the snowpack.
As we look into the weekend and see the weather letting up, we need to keep ourselves in check. This is the exact setup we had two years ago when we had a fatal avalanche in Seattle Creek, followed by a very large storm, followed by anCNFAIC Staff large human triggered avalanche on Sunburst that buried a skier for 15-20 minutes. The Sunburst avalanche happened with the same type of weak layers present and the same 5-10 feet of new storm snow.
We already have one avalanche recovery effort still underway. Don’t charge the backcounty this weekend. Give the mountains and your mCNFAIC Staff a break from the stress.
There are two main weak layers in our snowpack:
1.A thin breakable melt-freeze crust with surface hoar on top of it. We have seen this weak layer up to 3000′ on multiple aspects on both sides of highway at Turnagain Pass. This weak layer is generally buried 4-6 feet deep. Surface hoar has been observed on top of this layer in several pits, as recently as Sunday 2/15/2010. This surface hoar has not been seen in all pits, and these feathery crystals get smaller as you gain elevation, but you have to give a weak layer like this lots of respect. This combination of surface hoar on top of a crust is historically responsible for the majority of avalanche surprises and fatalities.
2.The Jan 7 rain crust is generally buried 6-8 feet deep. This particular weak layer has been reactive to explosive triggers and most likely has been naturally triggered during our current avalanche cycle. This persistent weak layer has been showing significant signs of instability since its formation last month. This weak layer is widespread on all aspects up to 3000 feet.
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST FRI FEB 19 2010
…URBAN AND SMALL STREAM FLOOD ADVISORY REMAINS IN EFFECT THROUGH
1000 AM AKST THIS MORNING…
…STRONG WIND THROUGH THIS AFTERNOON THROUGH PORTAGE VALLEY AND
.TODAY…RAIN. HIGHS IN THE 40S. EAST WIND 10 TO 15 MPH EXCEPT EAST
35 TO 50 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.TONIGHT…RAIN LIKELY IN THE EVENING…THEN A CHANCE OF RAIN AND
SNOW AFTER MIDNIGHT. LOWS IN THE UPPER 20S TO MID 30S. EAST WIND 10
TO 15 MPH EXCEPT EAST 15 TO 30 MPH THROUGH PORTAGE VALLEY AND
.SATURDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN. HIGHS
IN THE MID 30S TO LOWER 40S. VARIABLE WIND 10 MPH EXCEPT EAST
10 TO 20 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.SATURDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN.
LOWS IN THE MID 20S TO MID 30S. VARIABLE WIND 10 MPH.
.SUNDAY…SNOW AND RAIN LIKELY. HIGHS IN THE MID 30S TO LOWER
40S. VARIABLE WIND 10 MPH.
.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW AND RAIN.
LOWS IN THE 20S.
.MONDAY…PARTLY CLOUDY. HIGHS 35 TO 45.
TEMPERATURE / PRECIPITATION
SEWARD 44 32 40 / 100 70 50
GIRDWOOD 43 32 41 / 60 40 40
WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS
3800′-Sunburst Wx Station
Current Temp: 27 degrees F
Winds: very string to extreme with easterly averages in the 30’s and gusts over 90 mph.
2600′-Seattle Ridge Wx Station
Broken. We will fix as soon as possible.
1800′-Center Ridge Wx Station
Current Temp: 35 (5 degree warmer than yesterday)
Precip: .5 inches of water and approx. 6 inches of new snow. Total snowpack depth is 109 inches.
Thanks for checking today’s avalanche advisory. I will post again tomorrow morning February 20th by 0700.