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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, December 19th, 2008 - 7:00AM
Expires
Sat, December 20th, 2008 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, December 19, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm (Turnagain Pass is the core advisory area). Local variations always occur. Note: We are now issuing regular advisories 5 days a week Wednesday-Sunday.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

-The Center Ridge weather station at 1800 feet in Turnagain Pass-

Recorded zero new precip. Current temperature is 21 degrees F (1.5 degrees colder than yesterday morning). Total snowpack depth is 53 inches. with a total of 15 inches of settlement since last Tuesday’s (12/9/08) storm.

-Sunburst weather station at 3800 feet in Turnagain Pass-

Recorded light winds averaging 0-11 mph mostly from the east with a moderate gust of 18 mph. Current temperature is 19 degrees F (same as yesterday)

-Surface Analysis Maps-

From 3 am Thursday to 9pm last night, the maps shows that storm building over the Aluetians (988-990), but it is staying in one place.

-Jet Stream-

I was unable to get jet stream info this morning

-Satellite-

As of 6:00 am this morning…shows that storm over the Aleutians pulling up some haze from the Gulf of Alaska towards us.

-Radar-

The Middleton radar shows some very scattered precip.

The Kenai radar shows precip over Homer moving west.

-General Weather Observations-

Temps are about the same as yesterday at all weather stations. Winds have still been very light, but are showing signs of picking up this morning.

PRIMARY AVALANCHE CONCERNS

-Terrain Management

-Shallow Snow

-Chocolate Chip Rocks (see photo)

-Cliff Bands

-October Facets

-Buried Surface Hoar

SECONDARY AVALANCHE CONCERNS

-Glide Cracks (see photo)

AVALANCHE AND SNOWPACK DISCUSSION

Dan and I went up to Cornbiscuit yesterday. We wanted to do a crown profile on last Saturday’s avalanche. I wanted to wait a couple days to let the snow mellow out in that area, and I studied that areial photo and maps for a safe way to get to that crown face. It looked simple and safe enough to approach that avalanche from the lower angle slope above it. When we got there, however, I got a case of the “ooga-boogas” and did not like how the slope rolled over above that complex terrain with a gully that had not yet avalanched; so, I decided not to go all the way over to the crown face. Even though it probably would have been ok, I decided that probably was not good enough. I ended up digging a pit at a similar elevation to the old crown face, but on a different aspect. I dug a pit in 4 feet of total snow depth, and found similar results to CNFAIC Staff recent pits. There were those October facets on the ground that are rounding out and bonding to each CNFAIC Staff with about 3 feet of consolidated slab on top of it. It was very very difficult to get those October facets to fail.

What does all this mean? Our snowpit data keeps indicating good stability, but we know there are isolated pockets of instability out there. Snow pits are only one small piece of the entire avalanche puzzle. Terrain management is the key to safety right now. You can still see the features of the mountains under a lot of slopes, indicating shallow snowpack. There are lots of steep rollovers and rocks out there that will be the most likely areas for a human-triggered avalanche. The most recent human-triggered avalanches did not propogate across an entire slope. They stayed confined to isolated terrain features.

Here are my avalanche speculations for today…

-Dangerous avalanche conditions still exist on some terrain features (see photo). Evaluate the snow and terrain carefully and use good travel habits.

-Shallow snow seems to be where most of the human-triggered avalanche activity is happening.

-The general snowpack gets more and more shallow the further south you drive; so, places like Cornbiscuit almost always have less snow than places like Tincan. Summit Lake is even thinner, colder, and weaker.

-There is a possibilty of triggering small to medium sized avalanches on isolated terrain features like: steep rollovers near rocks or cliffs, wind scoured ridges where the snow depth tapers from shallow to deep

It is still early season, and we have an early season intermountain style snowpack. This is not the best time of year for big steep Alaskan lines. There will be opportunity for that later in the season. Avoid any sort of complex terrain, stick to simple planar slopes, and enjoy the great powder.

Future avalanche problems will be glide cracks (see photo gallery), which are very difficult to predict. Treat them like cornices and realize that they could avalanche at any time for wierd reasons; so, don’t travel on or underneath those things. The good news is that glide cracks are very easy to avoid because you can see them!

The next big problem will be the surface hoar and rimed surface snow that has been forming all over the place.

WATCH OUT SITUATIONS

-Rocky terrain with shallow snow connected to deeper snow (photo gallery)

-Steep rollovers (photo gallery)

-If you hear any “whumpfing” or feel any collapsing, then get to safe terrain immediately and call it a day.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 18 2008

.TODAY…CLOUDY WITH ISOLATED SNOW SHOWERS. HIGHS IN THE 20S TO MID

30S. VARIABLE WIND 15 MPH OR LESS.

.TONIGHT…CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE 20S.

VARIABLE WIND 10 MPH EXCEPT EAST WIND 10 TO 20 MPH THROUGH PORTAGE

PASS AND TURNAGAIN ARM.

.FRIDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE

AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS IN THE LOWER

TO MID 30S. EAST WIND 10 TO 25 MPH.

.FRIDAY NIGHT…SNOW…MIXED WITH RAIN ALONG THE COAST. LOWS IN THE

20S TO LOWER 30S. EAST WIND 15 TO 20 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 30 28 33 / 20 40 80

GIRDWOOD 27 24 34 / 0 20 20

Fri, December 19th, 2008
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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This is 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.