Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday January 7th 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).
A large snowmachine jump was found on U.S. Forest Service land near the motorized parking lot at Turnagain Pass. Permits are required for private structures on federal land. This structure must be removed by the private party, or the Forest Service will remove and claim this property.
Hindcast (Last 24 hours)
3800′ -Sunburst Wx Station-
This wx station stopped recording at 10pm last night. Up to that time, temperatures ranged from 23 to 29 degrees F with light to extreme winds averaging 7-38 mph from the normal Easterly direction with a max gust of 57 mph
2400′-Seattle Ridge Wx Station-
This wx station stopped recording at 10pm last night. Up to that time, winds were light to strong averaging 14-31 mph from the normal ESE direction with a max gust of 52 mph
1800′-Center Ridge Wx Station-
Precip: 0.1 inches of water and 1” of new snow
Total depth of 57 inches
Temperatures ranged from 29-37 degrees F current temp is 34
Most of the wx stations stopped working last night; so, real time wx data is a bit limited this morning. The temp at 1800 feet at Turnagain Pass is above freezing at 34 degrees, and winds are still moderate averaging in the 20mph range with strong gusts into the 30mph range at 3400′ near Summit Lake on Fresno Ridge. The temp at 3400 feet is getting close the freezing mark at 28 degrees F (3 degrees warmer than yesterday). The Middleton radar is showing a couple bands of moderate precip building into heavy precip over the Gulf of AK and some scattered precip over Prince William Sound. The Kenai radar is clear.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST THU JAN 7 2010
.TODAY…PATCHY MORNING FOG. RAIN ALONG THE COAST THIS MORNING…
SPREADING INLAND THIS AFTERNOON. HIGHS AROUND 40. NORTH TO EAST
WIND 10 TO 25 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST
WIND 15 TO 25 MPH INCREASING TO 25 TO 40 MPH IN THE AFTERNOON.
.TONIGHT…RAIN LIKELY IN THE EVENING…THEN A CHANCE OF RAIN
AFTER MIDNIGHT ALONG THE COAST. LOWS IN THE UPPER 20S TO MID
30S…COLDEST INLAND. NORTH TO EAST WIND 10 TO 25 MPH BECOMING
LIGHT AFTER MIDNIGHT.
.FRIDAY…MOSTLY CLOUDY. HIGHS IN THE 30S. LIGHT WINDS EXCEPT
NORTH WIND TO 15 MPH NEAR SEWARD.
TEMPERATURE / PRECIPITATION
SEWARD 39 33 37 / 70 60 0
GIRDWOOD 39 34 37 / 70 50 0
Short Term Weather Models (NAM, WRF, QPF) for the Kenai Mountains near Turnagain Pass
Sea-level: 0.25 inches of water forecasted today
3000′: temps forecasted between 32 and 40 degrees F with winds 15-40mph
6000′: temps forecasted between 23 and 32 degrees F with winds 20-40mph
Today’s weather could contribute to the avalanche danger today at Turnagain Pass. The weather forecast is not calling for very much precip today, only quarter of an inch for Turnagain Pass; so, it does not look like today’s weather will pack too big of a punch. The wind is a more of an issue. We have enough data with recent winds and a forecast for more wind today to say that wind slabs will be possible on specific terrain features, especially near ridges. Due to a lack of significant buried weak layers in the upper elevations above 2200′, the main concern today will be newly formed wind slabs that could be small to medium in size.
Today’s avalanche danger will remain at MODERATE. MODERATE is defined as: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely (except glide cracks are possible) and human triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.
The big surprise this week is that a glide crack naturally avalanched recently on the southern aspect of Eddies (see photo gallery).
There are three main points of interest in the current snowpack. 2 of these future concerns are defined by elevation.
1.Below 2200′, there is a layer buried surface hoar generally buried about 10-12 inches deep. Plus there is an ice layer/rain crust at these lower elevations. These could become very dangerous weak layers in the future. Luckily they are confined to lower elevations. We will have to be careful at lower elevations in places like Sunnyside and Repeat Offender on the motorized side after the next couple storms till we can see how these weak layers will react to a new load on top. We took a close look at Repeat Offender along Seattle Ridge recently and found that same rain crust/ice layer up to 2200′. Plus anCNFAIC Staff layer of surface hoar formed with the largest crystals in the bathtub ring where the fog layer was hanging out on the valley walls like the water in a bathtub.
2.Near ridgetops, we continue seeing an instability 6-12 inches deep under the surface. It only shows itself in isolated column stability tests, but it has not been reactive to skis, snowboards, or snowmachines. As of Monday 1/4/10, this layer was reported on Lipps failing with easy to moderate shears in a compression test. Plus it was observed along Seattle Ridge on Tuesday 1/5/10.
3.A glide crack avalanched at about 2800′ on the southern aspect of Eddies. It failed all the way to the ground and ran most of the way to the valley floor. Since this glide crack failed, we have to assume that it is possible for CNFAIC Staff glide cracks to fail. There were no obvious signs leading up to this glide crack avalanche. It is a good reminder of how unpredictable glide cracks can be. Plus, these avalanches are destructive when they fail. Avoid traveling underneath or near any glide cracks. It is very difficult to forecast when this type of avalanche occurs. They are wild cards just like cornices.
Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Friday January 8th.