Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday March 31st, 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 will be closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses after March 31, 2010. This closure is directed in the current Chugach National Forest Land and Resource Management Plan.
-The winds are increasing at most ridge top weather stations this morning and the weather forecasts and models are all calling for strong to extreme wind today as highs as 60mph on ridges
-The snotel sites are not working this morning, but yesterday they recorded:
-A high temp of 47 degrees at 3pm 1800′ at Turnagain Pass
-A high temp of 39 degrees between 11-12 at Grandview
-A high temp of 44 degrees between 12-2 at Summit Creek.
-The current (5am) radars are mostly clear right now, but the satellite image shows a big storm heading our way from the Aleutians. The models show the bulk of the precip hitting our area later today.
-Temps have cooled off slightly at ridge top weather stations this morning by 1-3 degrees compared to yesterday. Temps at 5am range from 35 degrees F at sea-level and 24 degrees F at 3800′. Temps made it above freezing higher than 3800′ yesterday. The wx stations recorded the warmest temps between 11-6pm.
Today’s avalanche danger will remain at CONSIDERABLE, due a heavy slab on top of a variety of crusts and weak layers of buried surface hoar. In the past 3 days, numerous natural and human triggered avalanches have been occurring on all aspects. The avalanches that have been ripping out are big enough to bury, injure, or kill a person.
It was very easy for the warm direct sun to trigger natural slab avalanches yesterday. Even though most slopes are now pre-cooked, the ease at which these slabs were triggered yesterday, and the long width of the propagation has to be respected. Once again, we have a widespread slab sitting on top of multiple weak layers including suncrusts and buried surface hoar. We are still within 24 hours of a VERY active natural avalanche cycle.
The buried surface hoar is a serious concern today. A party reported a large collapse near the top of Sunburst yesterday. In the past week, there have been several human-triggered avalanches that have occurred on one of the MULTIPLE layers of buried surface hoar (mostly on northern aspects). The pre-cooked surface snow can still act as a slab on top of this surface hoar which is protected further down in the snowpack.
Due to the intense sun yesterday, numerous natural avalanches occurred. We went up Seattle Ridge and observed small natural slab avalanches that had occurred within 24 hours on the southern aspect of Warm Up Bowl, northern aspect of Zero Bowl. We also saw some medium sized avalanches that had occurred on and east and southeast aspects of Big Chief and CNFAIC Staff unnamed slopes on the opposite side of Seattle Creek. At 12:15, we observed ~700 wide natural slab avalanche actively rip out on an eastern aspect on the CNFAIC Staff side of Seattle Creek. We turned around and were back at our truck and out of the mountains by 12:30.
CNFAIC Staff recent avalanches that have been failing on our current weak layers include:
-An eastern aspect avalanched on Pyramid (3/30/2010)
-We also saw new slab avalanches on the southern aspect of Cornbiscuit (3/30/2010)
-There was a small slab under some rocks on the western aspect of Lipps (~48 hours old)
-A very large avalanche occurred in Portage Valley on Williwaw Peak 2 days ago 3/29/2010.
-Additionally, a large glide crack avalanched all the way to the ground at the lower elevation of Goat Ridge in Girdwood Valley (3/30/2010)
-Large natural avalanches occurred 3/29/2010 due to the intense sun and warm temps. An avalanche on Sunnyside across from the motorized parking lot at Turnagain Pass was clearly big enough to injure, bury or kill a person.
-I was able to easily trigger a medium sized slab avalanche that failed on a crust on a steep rollover on Tincan 2 days ago on 3/28/2010. If this slab would have occurred on bigger terrain it would have been big enough to injure, bury or kill a person.
-Several natural avalanches occurred 3/27 or 3/28/2010 on steep slopes like Tincan Proper and along the Library on Tincan Ridge
– North aspect of Granddaddy Chute (Bertha Creek drainage), 2.5 feet deep, 150-200 feet wide (probably buried surface hoar).
-North aspect of Magnum at Taylor Pass between Sunburst and Magnum, triggered while skinning, 3400 feet elevation, 80-90 feet wide, 1.5-2 feet deep, ran 300 feet on layer of (buried surface hoar).
-South face of Sunburst at highest point, triggered while skiing on convex rollover, 6-9 inch deep crown face, ran 3/4 of the way to the bottom, happened at 12:30pm (failed on suncrust).
– North face of Sunburst near the top of Elevator Shaft. The skier triggered it on his third jump turn from the top. It broke 2-3 feet deep and ran 1000 feet (probably buried surface hoar).
-South face of A1 in the Upper Girdwood Valley between 4000 and 5000 feet.
There have been too many avalanches to list, but we covered a lot of the most significant ones.
Terrain management is the key right now. Keep your slope angles below 35 degrees. AVOID traveling on any sunny slopes IF the sun comes out (the sun is not forecasted today, but this is a critical “watch out” situation with our current snowpack)
In summary, it appears that northern aspects are holding layers of buried surface hoar and southern aspects have a crust. Either way, we have a dense heavy slab on top of these weak layers and avalanches have occurred as recently as yesterday afternoon.
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. A large glide crack avalanched on lower Goat Ridge in Girdwood Valley on 3/30/2010.
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT WED MAR 31 2010
…STRONG WIND EARLY THIS AFTERNOON THROUGH LATE WEDNESDAY NIGHT
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…
.TODAY…RAIN SHOWERS NORTH OF MOOSE PASS. ELSEWHERE…CLOUDY WITH
SCATTERED RAIN AND SNOW SHOWERS BECOMING NUMEROUS IN THE AFTERNOON.
NO SNOW ACCUMULATION. HIGHS IN THE LOWER TO MID 40S. VARIABLE WIND 15
MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND
25 TO 35 MPH INCREASING TO 35 TO 50 MPH IN THE AFTERNOON.
.TONIGHT…RAIN…MIXED WITH SNOW AT TIMES. LITTLE OR NO SNOW
ACCUMULATION. LOWS IN THE UPPER 20S TO MID 30S. VARIABLE WIND 15 MPH
EXCEPT EAST 35 TO 50 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.THURSDAY…RAIN SHOWERS…MIXED WITH SNOW AT TIMES IN THE MORNING.
NO SNOW ACCUMULATION. HIGHS IN THE LOWER TO MID 40S. EAST WIND 15 TO
20 MPH EXCEPT EAST 15 TO 30 MPH THROUGH PORTAGE VALLEY AND
TEMPERATURE / PRECIPITATION
SEWARD 45 33 45 / 60 80 80
GIRDWOOD 43 31 44 / 80 100 70
Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass
Sea-level: temps are forecasted between 31-43 and between 0.5” of water forecasted
3000′: temps are forecasted in the range of 23-32 degrees F with winds 15-25 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): 24 (1 degree colder than yesterday morning)
Winds: In last 24 hours winds have been light averaging 1-14mph with a strong max gust of 28mph
HIGH TEMP 36 between 4pm
2600′-Seattle Ridge Wx Station
Temp (5am): 28 (same as yesterday morning)
Winds: In last 24 hours winds have been light to moderate averaging 1-21 mph with a strong max gust of 30mph
HIGH TEMP 38 at 2pm
1800′-Center Ridge Wx Station
Temp (5am): not working this morning
Precip: not working this morning
HIGH TEMP 47 at 3pm
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday April 1st, 2010.