Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday April 13th, 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).
Skookum Valley and Skookum Glacier are closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses.. This closure is directed in the current Chugach National Forest Land and Resource Management Plan. Placer River Drainage remains open for motorized use to Spencer Glacier.
-The winds are strong to our south at Summit Lake, but light to moderate CNFAIC Staffwise this morning averaging 2-26 mph with some extreme gusts up to 47mph down at Fresno Ridge
-The 24 hour snotel sites are reporting:
-0.2 inches of water, 3-4inches of new snow, and 3” of melting/settlement at 1800′ at Turnagain Pass
-0.3 inches of water, 2 inches of new snow, and 4” of melting/settlement 1100′ at Grandview
-0.3 inches of water, 3 inches of new snow, and 0 inches of melting/settlement at 1400′ at Summit Creek.
-This morning’s (5am) radars show lots of precip hitting eastern PWS between Cordova and Valdez
-Temps are starting off about the same this morning at most weather stations as they did yesterday morning. Above freezing temps made it up to 40 degrees at 1800′ yesterday. This morning’s temperature range is 33 degrees F at sea-level and 22 degrees F at 3800′.
Today’s avalanche danger will start out as MODERATE, but could rapidly increase to CONSIDERABLE on any sunny slopes IF the sun comes out like the NWS is forecasting. There should be small to medium sized wind slabs sitting on top of buried surface hoar on top of a sun crust in many places, especially up high in the starting zones.
The primary snowpack concerns today are: recently formed winds slabs sitting on top of a sun crust with buried surface hoar and/or facets on top of that crust. Small to medium human-triggered avalanches are possible on these pockets of instability, and natural avalanches will become possible IF the sun comes out. Recent natural slab avalanches triggered during sunny days have occurred as early as 11am on SE aspects over the past couple of weeks. The warmest ambient air temps yesterday were recorded between 12-3pm.
Before the new precip starting falling Saturday night, surface hoar was observed on Tincan, Pastoral, Twin Peaks, and Pete’s North, and Cornbiscuit. On Sunday we found this surface hoar buried and standing up on a small wind lip on Tincan. This small pocket was very reactive to human triggers. Yesterday, we tried to confirm this same layer of buried surface hoar on Sunburst, but could not find it. We did, however, find facets on top of the most recent sun crust instead of the surface hoar. Recent observations have described this surface hoar as large above 3200′ (up to 1cm).
Even though it has not been actually observed except for on Tincan, it’s a pretty good guess that there will be pockets of buried surface hoar that have survived the recent ridgetop winds. There has not been very much precip lately, but the wind has been moving some enough snow around for some isolated wind slabs.
The sun is the critical “watch out” situation this time of year. April sun and temps can change the snowpack much more drastically than January or February sun. Avalanche danger can increase rapidly during periods rapidly warming temps and direct sunlight especially when the sun hits fresh snow like we have right now.
Glide cracks are secondary concern today. These crevasse like features are those cracks that go all the way to the ground. Avoid traveling underneath these cracks. Glide cracks and full depth release avalanches have been occurring on warm sunny days. We are seeing more and more of these glide cracks form everyday.
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT TUE APR 13 2010
.TODAY…MOSTLY CLOUDY WITH SCATTERED RAIN AND SNOW SHOWERS
EARLY THIS MORNING…THEN BECOMING MOSTLY SUNNY. HIGHS AROUND 40.
SOUTH TO WEST WIND 10 TO 20 MPH.
.TONIGHT…INCREASING CLOUDS WITH SNOW DEVELOPING AFTER MIDNIGHT.
SNOW ACCUMULATION 1 TO 3 INCHES. LOWS IN THE MID 20S TO LOWER 30S.
VARIABLE WIND TO 10 MPH.
.WEDNESDAY…SNOW AND RAIN. SNOW ACCUMULATION UP TO 2 INCHES.
HIGHS IN THE 30S. VARIABLE WIND TO 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 39 32 37 / 0 80 80
GIRDWOOD 38 31 37 / 30 80 80
Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass
Sea-level: temps are forecasted between 31-38 and between 0.0-0.05” of water forecasted
3000′: temps are forecasted in the range of 23-32 degrees F with winds 10-20 mph
6000′: temps are forecasted in the range of 14-23 degrees F with winds 20-30 mph
WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS
3800′-Sunburst Wx Station
Temp (5am): 22 (2 degrees colder than yesterday morning)
Winds: In last 24 hours winds have been light-moderate averaging 10-25mph with an extreme max gust of 42mph
HIGH TEMP of 23 between 12-5pm
2600′-Seattle Ridge Wx Station
Temp (5am): 25 (one degree warmer than yesterday morning)
Winds: In last 24 hours have been light to strong averaging 2-32mph with an extreme gust of 48mph
HIGH TEMP of 26 between 11am-4pm
1800′-Center Ridge Wx Station
Temp (5am): 28 (1 degrees colder than yesterday morning)
Precip: 0.2 inches of water, 3-4 inches of new snow
HIGH TEMP 40 at 11am
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday April 14th, 2010.