Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday March 23rd, 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).

WEATHER ROUNDUP

-The winds have increased slightly at most ridge top weather stations this morning with moderate average speeds 9-17mph with moderate gusts up to 25mph.

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

0.0 inches of water and 2 inch of snow melting/settlement at Turnagain Pass

0.1 inch of water and 1 inch of snow melting/settlement at Grandview

0.0 inches of water and 0 inches snow melting/settlement at Summit Creek.

-The current radars show moderate precip over the Gulf of Alaska moving North West toward Prince William Sound.

-Temps have increased slightly at most weather stations this morning by 2-5 degrees. Current temps range from 32 degrees F at sea-level and 21 degrees F at 3800′.

AVALANCHE DISCUSSION

Today’s avalanche danger will remain at MODERATE. There have not been any big changes with the weather or snowpack in the past 24 hours, and the weather forecast does not look like it will pack a punch today.

We are keeping the danger at MODERATE because there is a lot of spatial variability in the snowpack right now including multiple layers of buried surface hoar. There are plenty of places in the backcountry where the danger level is hinting towards LOW, but there are a couple of different crusts and layers of buried surface hoar in the top 1-3 feet of snow that create elevated caution in areas like steep rocky terrain.

There are two main concerns today and one future concern right now:

1. A sun crust that is buried 1-3 feet deep (we have found buried surface hoar near this crust)

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

3. A new sun crust on the current surface with surface hoar on top of this crust (future problem)

The recent sun crusts that are buried are very aspect dependent. All of the direct southern aspects and steep SE and SW aspects that have been exposed to the recent intense sun have formed these crusts in the past week.

We know there have been several surface hoar events that have been buried, but it has been very difficult to find these layers of buried surface hoar in any of our snow stability pits; however, we have found surface hoar near the suncrust that is buried 1-3 feet deep in a snow pit on Sunburst. It’s easy to find moderately clean shears with sparkly snow, but we have mostly been find broken stellars on top and underneath these crusts instead of buried surface hoar. It’s hard to tell 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 on top of any crusts. Reguardless of the type of weak layer, our stability tests have been regularly getting smooth shear planes with moderate to hard failures above and below that crust buried 1-3 feet deep; so, this layer is going to be a serious and dangerous weak layer when the next storm, wind slab, or hot sunny day hits our area.

Right now, there is not much of a slab on top of this crust in many places, but this is the type of weak layer that has the potential create one of those surprise avalanches on extreme terrain.

The new sun crust on the surface of the direct southern aspects and steep SE and SW aspects has the latest batch of surface hoar on top of it. This new batch of surface hoar has been observed up high in the starting zones along ridges above 2500 feet, and it has been observed from sea-level to about 1500′. This surface hoar has been difficult to see at mid elevations. Just like the CNFAIC Staff crust, this one has potential to become dangerous when the next storm or wind slab buries this layer.

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 TUE MAR 23 2010

.TODAY…MOSTLY CLOUDY. ISOLATED SNOW SHOWERS EARLY THIS MORNING.

A CHANCE OF SNOW AND RAIN ALONG THE COAST LATE THIS AFTERNOON.

HIGHS 35 TO 40. NORTH TO WEST WIND 10 TO 20 MPH.

.TONIGHT…SNOW…POSSIBLY MIXED WITH RAIN AT SEA LEVEL. SNOW

ACCUMULATION 1 TO 3 INCHES. LOWS IN THE UPPER 20S TO MID 30S.

NORTH TO EAST WIND 10 TO 25 MPH…WITH GUSTS TO 35 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM AFTER MIDNIGHT.

.WEDNESDAY…RAIN AND SNOW SHOWERS. SNOW ACCUMULATION UP TO 1 INCH

AT HIGHER ELEVATIONS. HIGHS 35 TO 40. EAST WIND 10 TO 25 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 40 32 40 / 20 90 60

GIRDWOOD 37 32 38 / 20 80 60

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

Sea-level: temps are forecasted between 32-37 and between 0.1”-0.25” of water forecasted 3000′: temps are forecasted in the range of 23-32 degrees F with winds 10 mph

6000′: temps are forecasted in the range of 14-23 degrees F with winds 15-20 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Current Temp: 21 (3 degrees warmer than yesterday morning)

Winds: Are slightly increasing this morning. In last 24 hours winds have been light to moderate averaging 3-17mph with an moderate max gust of 25mph

2600′-Seattle Ridge Wx Station

Current Temp: 24 (3 degree warmer than yesterday morning)

Winds: In last 24 hours winds have been light averaging 8-14mph with a moderate max gust of 23mph

1800′-Center Ridge Wx Station

Current Temp: 27 (3 degrees warmer than yesterday morning)

Precip: 0 new precip. 2” of melting/settlement

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday March 24, 2010.