Chugach National Forest

[ace44]

Current Advisory
Tuesday, December 15th 2009
Created: Dec 15th 7:01 am
Updated: Dec 15th 7:20 am

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday December 15th 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
All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. These areas are periodically patrolled by law enforcement. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow, these colder temps down low are really helping these areas.




AVALANCHE DISCUSSION
Recent weather will not contribute to the avalanche danger today, and the NWS is not forecasting much precip or wind for the Turnagain Pass area.

Due to insignificant results in recent snow stability test pits, zero significant natural or human-triggered avalanches reported or observed recently, and a mild weather forecast from the NWS, today’s avalanche danger level will remain at LOW. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Very small avalanches in widespread areas; or small avalanches in isolated areas.

Normal Caution is advised.

The next avalanche concern that we are watching out for is on the current surface snow. There are widespread firm or slippery surfaces created by the wind, sun, and warm temps from last week. Surface hoar formed from sea level to as high as 2800', however, the most defined surface hoar and faceted surface snow is below 1600'; so, due to the slippery surfaces and formation of surface hoar and faceted sugary surface snow, the worst weak layer in the near future will be below 2800'. These mid to lower elevations could become our next big problem when we get the next big weather event. Just as a reminder, most of the bowls along Seattle Ridge are below 2800'. Other areas with steep terrain below 2800' include but are not limited to the lower part of Eddies, Pete's North, and the terrain behind the "Welcome to the Kenai" sign near Pyramid along Seattle Ridge.

Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday December 16.

[nuckinfuts]

Chugach National Forest Avalanche Info Center....

http://www.cnfaic.org/

[nuckinfuts]

Created: Dec 16th 7:07 am

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday December 16th 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
All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. These areas are periodically patrolled by law enforcement. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow, these colder temps down low are really helping these areas.

AVALANCHE DISCUSSION
The weather should not contribute significantly to the avalanche danger today at Turnagain Pass. The NWS and weather models directly over Turnagain Pass are not forecasting much wind for the Turnagain Pass area. Plus the models really jive with the NWS forecast because they show most of the precip between Whittier and Girdwood and not in the Kenai Mountains.

Due to insignificant results in recent snow stability test pits, zero significant natural or human-triggered avalanches reported or observed recently, and a lack of wind forecasted from the NWS, today’s avalanche danger level will remain at LOW. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Very small avalanches in widespread areas; or small avalanches in isolated areas.

Normal Caution is advised.

Yesterday's snow stake totals
Eddies Lot: 3" new
Motorized Lot: 4" new
Sunburst Lot: 5" new
Johnson Pass North Lot: 4" new

*These parking lot totals show a bit more snow than was recorded by the Center Ridge wx station yesterday morning which reported 2".


Nowcast

Light snow is falling in Girdwood as of 5am. The Middleton radar shows moderate precip moving north mostly over PWS and Cordova and the Kenai radar shows light precip moving north toward Anchorage. Temps are 3-10 degrees colder at most wx station with temps ranging from 18 degrees at sea-level to 15 degrees at 3800'. Winds are calm to light at all ridgetip wx stations this morning.

Forecast

WESTERN PRINCE WILLIAM SOUND-
INCLUDING...WHITTIER...SEWARD...GIRDWOOD...MOOSE PASS
500 AM AKST WED DEC 16 2009

.TODAY...SNOW. SNOW ACCUMULATION UP TO 3 INCHES EXCEPT 6 TO 12
INCHES FROM WHITTIER TO GIRDWOOD. HIGHS 15 TO 25. VARIABLE WIND
TO 10 MPH. NEAR SEWARD...NORTH WIND TO 15 MPH SHIFTING TO SOUTH
15 TO 25 MPH IN THE AFTERNOON.
.TONIGHT...SNOW IN THE EVENING FROM WHITTIER TO GIRDWOOD WITH
UP TO 4 INCHES ADDITIONAL ACCUMULATION. OTHERWISE...SCATTERED
SNOW SHOWERS. LOWS 5 BELOW TO 15 ABOVE...COLDEST INLAND. SOUTH
TO EAST WIND TO 15 MPH.
.THURSDAY...MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS
5 TO 15 ABOVE. VARIABLE WIND TO 10 MPH. NEAR WHITTIER AND
SEWARD...LIGHT WINDS BECOMING NORTH TO WEST 15 TO 30 MPH IN
THE AFTERNOON.

TEMPERATURE / PRECIPITATION

[nuckinfuts]

AVALANCHE DISCUSSION
Due to lack of information and a questionable weak layer underneath a fresh load of heavy snow, the avalanche danger needs to stay at CONSIDERABLE. Not enough new information has come to light, in order, to drop the danger yet.

We still have some uncertainty with the snowpack. We tried to get some higher elevation observations yesterday on Tincan, but the visibility was very poor. We only made it up to 2500’; so, we don’t have much information about the snowpack in the steeper starting zones along the ridges. The only information we have about these upper elevations is that AK RR shot along the tracks south of Girdwood yesterday, and we did not see very much new avalanche debris in any of those paths between 20 Mile and Girdwood, except, for a medium sized pile in the path closest to Kern Creek.

Up to 2500’ on Tincan, we did not see any obvious signs of instability yesterday. We left the skin track in spots to jump around on steep test slopes, and we dug some pits on a steep roll. We felt no collapsing, I had one shooting crack that was only about 4 feet long in the top 2 inches of the snow, and the apprx 12” of storm snow did not appear to have any energy. The surface snow was like heavy tooth paste up to 1800’ and lighter density snow above 1800’.

The biggest danger for a human triggered avalanche today will be a new storm snow slabs on top of the thin breakable melt-freeze layer that has surface hoar on top of it on steep rollovers greater than 35 degrees. Since we have seen surface hoar on top of a crust in several locations, we have to give this type of weak layer lots of respect. We always have multiple layers of buried surface hoar in our snowpack. A lot of times they don’t do much of anything, but this layer has my attention. This is the type of weak layer you hear old-timers talking about because the surface hoar is on top of a crust. This combination is probably responsible for the majority of surprises and fatalities. It is easy to forget about this type of weak layer, especially when the snowpack was showing very good stability in spots on Monday (see “backcountry artillery” in the forecasters video or on YouTube).

My general impression yesterday was that the snowpack was adjusting well to its new load, but now there is an additional .7 inches of water weight and apprx 9 inches of new snow. That brings the storm total up to 1.5 inches of water weight and 14” of new snow at Center Ridge. As usual, this is a general number and there will be more snow at the northern end of Turnagain Pass and less snow on the southern end.


There are two main weak layers in our snowpack.
1.A thin breakable melt-freeze crust with surface hoar on top of it. We have seen this weak layer up to 3000’ on multiple aspects on both sides of highway at Turnagain Pass. This weak layer is generally buried 1 ½ to 2 ½ feet deep. Of course it will be buried deeper in areas where wind slabs formed. We were getting moderate failures with clean fast shears on this layer along Seattle Ridge on Monday 2/8/2010, but this weak layer was not reactive to human-triggers in certain locations on Monday (see forecasters video link for “backcountry artillery). Surface hoar has been observed on top of this layer in several pits. Not all pits show the surface hoar, and these feathery crystals get smaller as you gain elevation. This is the same weak layer that was responsible for the skier-triggered avalanches on Tincan on Saturday 2/6/2010. Plus I suspect this was the same weak layer that failed creating a natural avalanche on Widowmaker on Saturday 2/6/2010 as well (see photo gallery). This particular weak layer will be the likely culprit for human-triggered avalanches today.

2.The Jan 7 rain crust is generally buried 3-5 feet deep and it qualifies as a deep slab instability. As of yesterday 2/10/2010, it was still showing moderate failures with clean smooth shears. This weak layer is still showing significant signs of instability, but the question is what kind of trigger could create an avalanche on this weak layer? It appears that this weak layer will require a big trigger or more weight on top of it. This weak layer is widespread on all aspects between 2000-3000 feet.

WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
INCLUDING...WHITTIER...SEWARD...GIRDWOOD...MOOSE PASS
500 AM AKST THU FEB 11 2010

...STRONG WIND LATE TONIGHT THROUGH FRIDAY AFTERNOON THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM...

.TODAY...RAIN SHOWERS DIMINISHING THIS AFTERNOON. PATCHY FOG.
HIGHS IN THE MID 30S TO LOWER 40S. NORTH TO EAST WIND 10 TO 20 MPH.
.TONIGHT...A CHANCE OF RAIN IN THE EVENING...THEN RAIN LIKELY
AFTER MIDNIGHT. LOWS IN THE MID 30S. NORTH TO EAST WIND 10 TO 20 MPH.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM...EAST WIND 10 TO 20 MPH
INCREASING TO 30 TO 45 MPH AFTER MIDNIGHT.
.FRIDAY...RAIN LIKELY. HIGHS IN THE MID 30S TO LOWER 40S.
NORTH TO EAST WIND 15 TO 30 MPH BECOMING SOUTH TO EAST IN
THE AFTERNOON. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM...EAST
WIND 35 TO 50 MPH.

[LiveAlaska]

Originally Posted by alaskabackcountry

Hi everyone, this is Lisa Portune at the Chugach NF Avalanche Center in Girdwood. Just wanted to give a heads up to the dangerous avalanche conditions up at Turnagain Pass today. Below is a copy of today's advisory...
Here's a link to our website with the daily avalanche advisory: http://cnfaic.org/advisories/current.php
Thanks and stay safe!!

BOTTOM LINE
Today the avalanche hazard has increased to HIGH on all windloaded slopes greater than 30 degrees. Non wind-affected slopes and rain-saturated terrain at the lower elevations will have a CONSIDERABLE danger today. Large natural and human-triggered avalanches are likely! 9-18 inches of new snow, hurricane-force winds, and heavy rain at the lower elevations equals dangerous avalanche conditions. Today is not the day to be in the mountains.

AVALANCHE DISCUSSION
Today’s advisory is pretty straightforward…stay out of avalanche terrain. It's a skull and crossbones kind of day. Natural avalanches are most likely happening as I write this morning. The NWS has forecasted up to 10 inches of additional snow today at the higher elevations along with continued hurricane-force winds out of the east. Winds on Sunburst hit 104mph at 6am this morning.

Yesterday Jon and his partner intentionally triggered a 60 ft. wide windslab on a small test slope at 2000 feet that stepped down to several different layers of buried surface hoar as well as the Thanksgiving Rain Crust (TRC) three feet down. It looks like we have hit the tipping point. All of the heavy dense snow from the last five days (20”+) fell on a very weak upper snowpack littered with multiple layers of buried surface hoar, weak faceted snow, and the TRC. Any avalanches triggered today have the potential to step down to these deeper weak layers, creating a much larger avalanche than anticipated.

Keep in mind that whenever the weather happens to mellow out, natural avalanches will subside but most steep slopes at the mid and upper elevations will be hair-trigger for the following 24 hours.

http://www.backcountryrebels.com/sho...&postcount=506

Copied from Turny Thread

[ChugachAvalanche]

Hey All-
As many of you already know, riding conditions in south-central AK have been unbelievably good! I am happy to report that ALL snomachine areas on the Glacier and Seward Ranger Districts are open! For the specifics please check out cnfaic.org or call the Glacier Ranger District (Girdwood) at 783-3242.

Have fun and stay on top out there!