Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday March 25th, 2010 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).

ANNOUNCEMENTS

This week is Telepalooza week at Alyeska Resort. There are lots of great events and a fundraiser for the Friends of the Chugach National Forest Avalanche Information Center. Check Alyeska Resort’s webpage or www.telepalooza.com for a detailed schedule of events.

WEATHER ROUNDUP

-The winds have been averaging light to moderate in the 3-24mph range at all ridge top wx stations with strong gusts up to 36mph at Seattle Ridge

-In the last 24 hours (5am-5am), the snotel sites recorded:

0.2 inches of water with minus 3” of snow due to melting/settlement at Turnagain Pass

0.3 inches of water and minus 3” of snow due to melting/settlement at Grandview

0.0 inches of water and no change to total snowpack depth Summit Creek.

-The current (5am) radars show scattered precip over Prince William Sound Kenai Peninsula

-Temps have decreased slightly at all weather stations this morning by 2-4 degrees compared to yesterday. Temps at 5am range from 35 degrees F at sea-level and 19 degrees F at 3800′. Above freezing temps made it as high as 32 degrees at 2800′ at 2pm yesterday.

AVALANCHE DISCUSSION

Today’s avalanche danger is MODERATE, due a complex and fairly poor structured snowpack in the top 3 feet of snow. There are layers of buried surface hoar on all aspects and suncrusts on southern aspects. It is spring; so, we have to be careful with rapidly warming temperatures. Avalanche danger will increase to CONSIDERABLE on all southern aspects…IF… the sun breaks out and rapidly warms these slopes.

The weather forecast is not calling for intense sun today, but sometimes it only takes an hour or two of direct sun to get fresh snow to start avalanching in the spring time. Direct sun is one of those red flags that we need to watch out for this time of year.

Even under relatively cloudy skies, yesterday’s temperatures around Turnagain Arm made it as high as 40 degrees at the highway elevation and 32 degrees at 2800′. If there was direct sunlight associated with these warm temps, then avalanche danger could increase rapidly. Generally speaking, the warmest temps are being recorded between noon and 5pm, but the hours between 2pm-3pm were the warmest for the majority of the weather stations yesterday.

There are three main problem layers in the snowpack right now:

1. A sun crust with surface hoar on top of this crust is now buried under Tuesday’s new 4-6 inches of new snow. We observed surface hoar on top of this crust in multiple locations. This layer could create small human-triggered avalanches on steep slopes where wind has deposited deeper snow.

2. A sun crust that is buried 2-3 feet deep (we have observed surface hoar near this crust) We have been finding moderate to hard failures with smooth shear planes on top and underneath this crust. It might become more reactive with a heavier load on top of it, or small avalanches might step down to this layer making medium sized avalanches.

3. Multiple layers of buried surface hoar in the top 1-3 feet of snow

There is a lot of spatial variability in the snowpack right now including multiple layers of buried surface hoar and buried suncrusts in the top 3 feet of snow. At lower elevations, there is a 1 inch thick breakable crust on all aspects up to about 1500-2000′ which is now buried under 4-6 inches of wet snow. Mid elevations to ridge top elevations generally have multiple buried suncrusts on southern aspects, but these crusts are very aspect-dependent and do not wrap around to CNFAIC Staff aspects. The uppermost suncrust was thin but it had surface hoar on top of it. Northern aspects at Turnagain Pass are generally thin, cold, and faceted especially in rocky areas.

We know there have been several surface hoar events that have been buried over the past couple weeks, but it has been very difficult to find these layers of buried surface hoar in any of our snow stability pits; however, some layers of buried surface hoar have been confirmed in places like: Sunburst, Cornbiscuit, and Spokane Creek.

In our stability tests, it’s been easy to find smooth shears with sparkly snow on top of these smooth shear planes. We have mostly been finding broken stellars on top and underneath these crusts instead of buried surface hoar. It’s hard to tell the difference with the naked eye; so, it would be wise to take a closer look with a magnifying glass to confirm if the slope you are about to ski has surface hoar on top of any crusts. We know that the surface hoar is buried out there in isolated pockets, but it has been difficult to find it in our pits.

There is not a huge slab on top of these crusts and layers of buried surface hoar in many places, except for isolated wind slabs. These types of weak layers, however, have the potential create those surprise avalanches in places like steep rocky terrain or basketball shaped rollovers on wind loaded slopes.

Glide cracks are secondary concern today. These crevasse like features are those cracks that go all the way to the ground. One of these glide cracks avalanched on Friday or Saturday on the southern aspect of Tincan to the lookers left of Tincan Proper (see photo gallery).

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT THU MAR 25 2010

.TODAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS 35 TO 40.

LIGHT WINDS.

.TONIGHT…MOSTLY CLOUDY IN THE EVENING THEN BECOMING PARTLY

CLOUDY. ISOLATED SNOW SHOWERS ALONG THE SOUND IN THE EVENING.

LOWS IN THE LOWER 20S TO LOWER 30S. LIGHT WINDS.

.FRIDAY…MOSTLY CLOUDY. A SLIGHT CHANCE OF SNOW SHOWERS IN

THE AFTERNOON. HIGHS IN THE MID 30S TO LOWER 40S. VARIABLE

WIND 10 MPH EXCEPT NORTH 15 TO 25 MPH NEAR SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 38 27 39 / 40 0 20

GIRDWOOD 38 23 37 / 40 0 0

Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass

Sea-level: temps are forecasted between 23-38 and between 0.0-0.25” of water forecasted

3000′: temps are forecasted in the range of 23-32 degrees F with winds 5-10 mph

6000′: temps are forecasted in the range of 14-23 degrees F with winds 5-10 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Temp (5am): 19 (4 degrees colder than yesterday morning)

Winds: In last 24 hours winds have been light to moderate averaging 6-19mph with a strong max gust of 34mph

HIGH TEMP 25 at 4pm

2600′-Seattle Ridge Wx Station

Temp (5am): 23 (4 degrees colder than yesterday morning)

Winds: In last 24 hours winds have been light to moderate averaging 3-24 mph with a strong max gust of 36mph

HIGH TEMP 30 at 2pm

1800′-Center Ridge Wx Station

Temp (5am): 26 (3 degrees colder than yesterday morning)

Precip: 0.2 new water minus 3” snow

HIGH TEMP 39 at noon

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Friday March 26, 2010.