Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Thursday, January 20th 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).
The avalanche hazard rating is MODERATE today. A couple of inches of new snow fell last night, and a little more is expected today. Any new weight on our current snowpack will add stress to a poor structure, but this small amount will probably not affect the overall danger rating. IF we do get a significant amount of snow the hazard will INCREASE.
We’re finally changing weather patterns! Since yesterday the region got 1-2 inches of new snow. Not a lot, but it’s a start. More snow is forecasted for the next couple days. The big question is, “How is this going to affect backcountry stability?” Let’s look at our weather history to answer that.
Since early December we’ve had 6 out of 7 weeks with clear weather. The storm over New Years gave us a quick taste of how new snow sticks to the snowpack produced by high pressure weather: not very well. All that clear and cold weather produced significant weaknesses in the form of facets and surface hoar.
We grew some truly monster size surface hoar over the last 2 weeks. In the flats around Turnagain pass it’s like skiing through large potato chips. At higher elevations the crystals thankfully reduce in size, but you can generally still find surface hoar. I wouldn’t bet on finding “stable” areas around ridge tops because you think the wind destroyed it all. Even if that wind did some good there is the depth hoar and near surface facets to keep us all honest.
So that leads back to the original question. To answer it we have to know how much new snow we’re dealing with. I’ll throw that question over to our friends at the National Weather Service. They are predicting only anCNFAIC Staff 1 inch today, and small amounts the next few days.
Hypothetically, if we got a foot of snow with wind the hazard rating would automatically increase one level to CONSIDERABLE. In that case I expect natural avalanches to be possible and human triggered avalanches likely. Pay attention to the new snow amount if you travel in the backcountry this weekend. The hazard rating of the old snow (everything that fell before last week) was a steady moderate with poor structure but little reactivity. Any new weight and slab in the form of new snow is going to have a bad foundation (all that old faceted snow) and likely high reactivity. The more snow we get and the quicker it accumulates, the higher the likelihood of avalanches. The best answer today is that the danger rating is a moving target, but it’s directly tied to the amount of new snow we get.
Encyclopedia of avalanche terms.
Temperatures have risen, clouds have taken over, and snow is falling. Wind was blowing strong yesterday with some ridgetop gusts into the 40s and 50s. 1-3 inches of new snow have fallen since yesterday. This looks like a weak storm for Turnagain arm, but is worthy of our attention nonetheless. Temperatures have stayed in the high teens to low 20s (relatively cold for snowfall temps), which will inhibit bonding between the new and old snow. The forecast looks like more of the same with small amounts of new snow over the weekend.
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 THU JAN 20 2011
.TODAY…SNOW TAPERING OFF TO ISOLATED SNOW SHOWERS NORTH OF MOOSE
PASS THIS MORNING. MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS
ELSEWHERE. SNOW ACCUMULATIONS AROUND 1 INCH. HIGHS IN THE LOWER 20S
TO LOWER 30S…COOLEST INLAND. VARIABLE WIND TO 10 MPH. NEAR
SEWARD…NORTH WIND 15 MPH WITH GUSTS TO 25 MPH THIS MORNING.
.TONIGHT…A CHANCE OF SNOW IN THE EVENING…THEN SNOW AFTER
MIDNIGHT. SNOW ACCUMULATION UP TO 2 INCHES. LOWS IN THE MID TEENS
TO LOWER 30S. VARIABLE WIND 10 MPH.
.FRIDAY…SNOW LIKELY IN THE MORNING…THEN SNOW AND RAIN LIKELY
IN THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE
UPPER 20S TO MID 30S. VARIABLE WIND TO 10 MPH. NEAR WHITTIER…EAST
WIND 10 TO 15 MPH.
.FRIDAY NIGHT…CLOUDY. A CHANCE OF SNOW AND RAIN. LOWS IN THE MID
TEENS TO LOWER 30S. VARIABLE WIND 10 MPH.
.SATURDAY…CLOUDY. A CHANCE OF SNOW AND RAIN SHOWERS. HIGHS IN THE
MID 20S TO MID 30S. LIGHT WINDS.
.SATURDAY NIGHT…SNOW LIKELY. LOWS IN THE 20S.
.SUNDAY THROUGH MONDAY…RAIN AND SNOW LIKELY. TEMPERATURES IN THE
UPPER 20S TO UPPER 30S.
.MONDAY NIGHT THROUGH TUESDAY NIGHT…CLOUDY WITH A CHANCE OF SNOW.
LOWS 15 TO 25. HIGHS 25 TO 35.
.WEDNESDAY…RAIN AND SNOW LIKELY. HIGHS IN THE UPPER 20S TO UPPER
TEMPERATURE / PRECIPITATION
SEWARD 30 24 34 / 40 80 80
GIRDWOOD 22 17 29 / 60 70 70
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Rising temperature trend, currently 20. Wind diminishing, light from WNW.
-2600′ Seattle Ridge Wx Station-
Rising temperature trend, currently 21. Wind gauge stopped last night.
-1800′ Center Ridge Wx Station-
Temperature 22 degrees. 1-2 inches of new snow. 63 inches total depth.