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Issued
Wed, March 24th, 2010 - 7:00AM
Expires
Thu, March 25th, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday March 24th, 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 backed off and are averaging light to moderate in the 1-25mph range at all ridge top wx stations with strong gusts up to 33mph at Sunburst

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

0.4 inches of water and 6 inches of new snow at Turnagain Pass

0.6 inches of water and 7 inches of new snow at Grandview

0.0 inches of water and 0 inches of new snow Summit Creek.

-The current radars show scattered moderate precip circulating over Prince William Sound and light precip over the southern Kenai Peninsula

-Temps have increased slightly at all weather stations this morning by 1-3 degrees. Temps at 5am range from 30 degrees F at sea-level and 23 degrees F at 3800′.

AVALANCHE DISCUSSION

Today’s avalanche danger has increased to MODERATE with pockets of CONSIDERABLE, due to new snow and wind on top fairly poor structured snowpack with buried surface hoar on top of a crust in the top 3 feet.

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. There is a 1 inch thick breakable crust on all aspects up to about 1500-2000′. 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. Northern aspects at Turnagain Pass are generally thin, cold, and faceted similar to intermountain or continental snowpacks in the lower 48.

There are three main concerns right now:

1. A sun crust with surface hoar on top of this crust is now buried under yesterdays snow. We observed surface hoar on top of this crust in multiple locations. There will likely be some small wind slabs out there today sitting on top of this weak layer on wind loaded slopes.

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.

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

Yesterday on a northern Cornbisuit chute, we found a really bad weak layer of facets on top of a block of melt-freeze snow. This adds one more item to our list of spatial variability. It’s important to remember that the northern aspects at Turnagain Pass have a completely different snowpack than the southern aspects that most people ski through the season. It’s common for people to start exploring these northern aspects this time of year. It’s a good idea to approach northern aspects with a different mindset. These aspects are commonly thin and rocky due to predominant winds, and colder due to aspect. It is common to find more facets near these rocky northern aspects.

We know there have been several surface hoar events that have been buried on all aspects over the past couple weeks, but it has been very difficult to find these layers of buried surface hoar in most 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 moderately clean shears with sparkly snow on top of the shear plane, but we have mostly been find 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 buried surface hoar on top of any crusts. We know that the surface hoar is buried out there in isolated pockets, but its hard to say exactly where.

There is still not a huge slab on top of these crusts and layers of buried surface hoar in many places, but these types of weak layers have the potential create those surprise avalanches in places like steep rocky terrain or on 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 WED MAR 24 2010

.TODAY…NUMEROUS RAIN AND SNOW SHOWERS. UP TO 2 INCHES WET

SNOW ACCUMULATION THROUGH TURNAGAIN PASS. HIGHS 35 TO 40.

NORTH TO EAST WIND 10 TO 25 MPH BECOMING VARIABLE 5 TO 15 MPH

IN THE AFTERNOON.

.TONIGHT…MOSTLY CLOUDY. SCATTERED SNOW AND RAIN SHOWERS

IN THE EVENING…THEN ISOLATED SNOW SHOWERS AFTER MIDNIGHT.

LOWS IN THE LOWER 20S TO LOWER 30S…COLDEST INLAND.

VARIABLE WIND TO 15 MPH.

.THURSDAY…MOSTLY CLOUDY. SCATTERED RAIN AND SNOW SHOWERS

ALONG THE COAST. HIGHS AROUND 40. VARIABLE WIND TO 10 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 38 28 38 / 60 20 30

GIRDWOOD 39 27 40 / 60 30 0

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

Sea-level: temps are forecasted between 27-39 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 10-20 mph

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Temp (4am): 23 (3 degrees warmer than yesterday morning)

Winds: In last 24 hours winds have been light to moderate averaging 3-23mph with a strong max gust of 33mph

2600′-Seattle Ridge Wx Station

Temp (4am): 27 (3 degree warmer than yesterday morning)

Winds: In last 24 hours winds have been light to moderate averaging 1-18mph with a moderate max gust of 32mph

1800′-Center Ridge Wx Station

Current Temp: 30 (3 degrees warmer than yesterday morning)

Precip: 0.4 new water 6” new snow

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday March 25, 2010.

Wed, March 24th, 2010
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Dangerous avalanche conditions. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Observations
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This is 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.