Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday January 6th 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).

ANOUNCEMENTS

An illegal structure was found on US Forest Service land near the motorized parking lot at Turnagain Pass. Permits are required for private structures on federal land. This snowmachine jump is in violation of the code of federal regulations and could result in fines up to $5000 and/or up to 6 months in jail. This structure must be removed by the private party, or the Forest Service will remove and claim this property.

WEATHER ROUNDUP

Will recent weather effect avalanche conditions today?

Well, let’s take a closer look at the precip, winds, and temps.

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temperatures have ranged from 26 to 29 degrees F with light to strong winds averaging 4-38 mph from the normal Easterly direction with a max gust of 57 mph

2400′-Seattle Ridge Wx Station-

Winds have been light to strong averaging 9-31 mph from the normal SE direction with a max gust of 52 mph

1800′-Center Ridge Wx Station-

Precip: 0.0 inches of water

Total depth of 57 inches

Temperatures ranged from 32-39 degrees F

Nowcast

Although none of the wx stations are recording any precip, the Middleton radar is full moderate precip moving northwest directly toward Turnagain Pass, and the Kenai radar shows a patch of moderate precip directly over Turnagain Pass. Compared to yesterday, temps are currently warmer at all valley floor wx stations by 3-5 degrees F, and colder at all weather stations above 1800′ including ridgetops with temps currently 0-4 degrees colder than yesterday. Temps range from 33-39 degrees F on valley floors to 25-28 degrees F on ridgetops. Winds have increased since yesterday at Sunburst, Seattle Ridge, and Fresno Ridge with strong average wind speeds above 30mph, but the winds have not picked up as much in Girdwood yet.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED JAN 6 2010

…STRONG WIND THROUGH LATE THIS AFTERNOON THROUGH PORTAGE

VALLEY AND TURNAGAIN ARM…

.TODAY…RAIN DEVELOPING BY AFTERNOON. HIGHS IN THE MID 30S

TO LOWER 40S. NORTH TO EAST WIND 10 TO 25 MPH EXCEPT EAST

WIND 30 TO 45 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.TONIGHT…RAIN. LOWS IN THE 30S. NORTH TO EAST WIND 5 TO 20 MPH

EXCEPT EAST WIND 15 TO 30 MPH THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM.

.THURSDAY…RAIN LIKELY…MAINLY ALONG THE COAST. HIGHS AROUND 40.

NORTH TO EAST WIND 10 TO 20 MPH EXCEPT NORTH 15 TO 30 MPH

NEAR SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 37 34 38 / 80 80 70

GIRDWOOD 40 35 39 / 80 80 60

Short Term Weather Models (NAM, WRF, QPF) for the Kenai Mountains near Turnagain Pass

Sea-level: 0.5 inches of water forecasted today

3000′: temps forecasted between 23 and 32 degrees F with winds 10-15mph

6000′: temps forecasted between 23 and 32 degrees F with winds 20-40mph

These models show the temps staying below freezing at 3000′ all day today, they don’t crawl above freezing till 3pm on Thursday

AVALANCHE DISCUSSION

Today’s weather will contribute to the avalanche danger today at Turnagain Pass. Yesterday, it was reported easy to trigger very small avalanches near ridgetops, and the increased wind reported at the weather stations could have created small, but somewhat larger avalanches this morning. The NWS is not calling for very much precip today, only ½ an inch for Turnagain Pass, but combined with the strong average winds, the size of avalanches will start getting bigger if the weather forecast holds true. Wind slabs are typically very reactive and easy to trigger during the wind event.

The big surprise yesterday was that we observed a glide crack that avalanche recently on the southern aspect of Eddies at about 2800′ (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 at these lower elevations. These could become very dangerous weak layers in the future. Luckily they are confined to lower angle slopes at lower elevations. There are some places, however, where the slope angles are steep below 2000′ We will have to be careful highmarking 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 yesterday and found that same rain crust/ice lense up to 2200′ that we have been seeing is all locations. 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 1/4/09, this layer was reported on Lipps failing with easy to moderate shears in a compression test. This same layer was seen on Repeat Offender above the snowmachine up-track, but had moderate to hard test scores on a compression test.

3.A glide crack avalanched 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 has been zero significant weather that would make me think was the cause of this 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.

Due observed strong winds and the weather forecast, the avalanche danger for Turnagain Pass will increase today to MODERATE on and near ridgetops. MODERATE is defined as: heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas. As of this morning, it appears unlikely for new wind slabs to step down to any buried layers; so, we are mostly concerned with new storm snow.

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 Thursday January 7th.