Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, January 4th at 7am. 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).
Placer River and the Skookum Drainage closed to motorized use yesterday due to low snow cover and forest resource protection concerns. Recent warm weather and heavy rains have depleted the snowpack in the access areas to minimal or negligible amounts. These areas will be monitored and may open again once we have enough snow coverage to allow protection of the resource from damage.
Today the avalanche hazard is CONSIDERABLE. Natural avalanches are possible, while Human triggered avalanches are likely on steep windloaded terrain. These are still dangerous avalanche conditions, and careful evaluation of the snowpack is essential while travelling around avalanche terrain today. A person would likely trigger small avalanches in many areas, or large avalanches in steep windloaded terrain.
We seem to have made it through the crux of our snow/rain/wind storm, but we are currently far from out of the woods yet. Many steep slopes likely avalanched naturally yesterday, but are potentially unsafe today due to continued loading processes and increased water weight in the upper layers of the snowpack. A good thing to remember is that snow on avalanche-prone slopes can fail and release several times during a storm cycle, so interpreting the stability of a given slope by looking for debris at the bottom could be a poor judgement today.
Two days ago we heard whumphs, saw shooting cracks, and were able to get reactive wind slabs to pop out on small test slopes. I can imagine that conditions are similar right now, and that it will take some time for the energy in our snowpack to lessen to safe levels. For the time being, make sure you know what type of terrain you are travelling on, and have plenty of knowledge about where safe zones are located if you do decide to go into the backcountry today.
The biggest wild card today is trying to figure out how deep of an avalanche a person could trigger. Recent activity suggests that many slides would fail on the interface between the new warm snow and our old and cold snow. It is at this interface that a layer of 5-7mm surface hoar has been observed in many areas. However, a failure at this layer could step down to CNFAIC Staff buried layers of surface hoar, as well as down to the Thanksgiving Rain Crust. If this scenario were to happen, a very large and deadly avalanche could occur. Here is an example of a situation we are talking about:
This was a remotely skier-triggered avalanche that occurred on Sunday down on Tenderfoot in the Summit Lake area, but the image is fairly similar to the activity we saw on Tincan the same day.
One of the biggest take home messages today is that most avalanche fatalities occur during CONSIDERABLE danger days. More people recreate on days like today than on days like yesterday, which had a HIGH danger. Be mindful of this bit of information, because it could keep you from venturing into dangerous terrain, and out of a dangerous situation.
Check out an encyclopedia of terms here: www.fsavalanche.org/Encyclopedia.aspx
The radar images this morning indicate that anCNFAIC Staff wave of heavy precipitation is on its way here. Whether or not it makes it over Portage Pass is a different story, but it does give us the possibility of more precipitation and wind. The Low pressure systems that are giving us this warm wet weather are slowly weakening, but will linger for a few more days. Weather models currently indicate a cooling trend hitting our area on Wednesday night, so we will see then whether or not this prediction is correct. Looking further out, the National Weather Service is predicting clearing skies on Thursday and Friday, so do not forget about this storm and what it has done to our snow. Blue skies do not indicate a stable snowpack by any means.
I will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST TUE JAN 4 2011
.TODAY…SNOW AND RAIN. SNOW ACCUMULATION UP TO 2 INCHES THROUGH
TURNAGAIN PASS. HIGHS IN THE MID 30S TO LOWER 40S. EAST WIND 5 TO 15
MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 25 TO 40
MPH DECREASING TO 15 TO 30 MPH IN THE AFTERNOON.
.TONIGHT…SNOW AND RAIN. SNOW ACCUMULATION UP TO 3 INCHES. LOWS
IN THE UPPER 20S TO MID 30S. LIGHT WINDS EXCEPT EAST WIND 15 TO 30
MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.WEDNESDAY…SNOW AND RAIN LIKELY. SNOW ACCUMULATION UP TO 3 INCHES.
HIGHS IN THE LOWER TO MID 30S. VARIABLE WIND 10 MPH. THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…EAST WIND 15 TO 30 MPH BECOMING VARIABLE
10 MPH IN THE AFTERNOON.
TEMPERATURE / PRECIPITATION
SEWARD 40 36 36 / 100 100 70
GIRDWOOD 38 36 36 / 80 80 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded wind speeds yesterday up to 104mph, and temps from 25F to 27F. This station stopped working at 1:00am, while the current temp was 25F with 32mph winds out of the east-northeast.
-2600′ Seattle Ridge Wx Station-
stopped recording winds two days ago, while temps ranged from 27F to 29F yesterday. The current temp is 29F with 100% relative humidity.
-1800′ Center Ridge Wx Station-
recorded 10″ new snow in the past 24hrs, with 9″ settlement. During this time, the precipitation added .5″ SWE. Temps yesterday ranged from 31F to 34F. The current temp is 33F with a total snowpack depth of 64 inches.