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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 5th, 2009 - 7:00AM
Expires
Fri, February 6th, 2009 - 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 Thursday, February 5, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

-General Weather Observations-

Temperatures have warmed up at all weather stations again this morning by 6-11 degrees. In addition to the previous day, temps at places like Sunburst have increased 26 degrees in the past 48 hours. All the ridgetop weather stations have recorded light average winds. No new snow yet.

The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet

Is recording a temp of 17 degrees (7 degrees warmer than yesterday) with calm winds.

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

Has a temp of 17 degrees (8 degrees warmer than yesterday). Zero new precip. Total snowpack depth is 64″ after 1 inch of settlement.

The Sunburst weather station at 3800 feet in Turnagain Pass

Shows a temperature of 14 degrees (11 degrees warmer than yesterday). Winds have been light to moderate averaging 5-15 mph out of the E with a max gust of 24 mph.

-Surface Analysis Maps-

There are two storms out there. One in the Bering Sea and one in the Gulf of Alaska. The one in the gulf is getting weaker (986-993mb) and it looks like it is headed more toward SE AK. The one in the Bering Sea is still pretty far away from us, but it is a good sized storm and its gaining strength (970-968mb).

-Radar-

There is not much going on with the Middleton or Kenai radars this morning CNFAIC Staff than some scattered blue haze. It looks like the precip that the NOAA forecast is calling for is still over the Alaska Peninsula on the King Salmon radar.

AVALANCHE HAZARDS

Primary avalanche concerns

-Surface wind slabs on slippery bed surface on alpine ridges above 3000 feet

Secondary avalanche concerns

-Rain crust (ice layer) from January hurricane below 3000 feet.

AVALANCHE AND SNOWPACK

Bottom Line

Normal Caution is still advised for Turnagain Pass today, however, there are still some isolated pockets of elevated caution on really steep convoluted terrain along ridges where you might find windslabs on top of a slippery wind buffed layer.

Discussion

People continue to report triggering wind slabs on steep terrain near ridges. The latest significant wind slab occured on Tincan Proper, where a skier triggered one of those isolated pockets than ran the entire length on that large southern face. Most of these wind slabs are relatively small compared to the enitre slope, but you don’t want to get caught in one on really steep terrain because several of these have been running 1000-2000 feet all the way down to the valley bottoms. These small slabs are carrying so far because the are sitting on such a slippery bed surface. That slippery bed surface is the big story for elvations above 3000 feet. If you see a pocket of snow that looks fat, then it might avalanche on you; so, either avoid it or know how to manage your terrain.

If some of these old wind slabs don’t like to stick to it that slippery bed surface today, then how do you think new storm snow will stick to it tomorrow? My guess is not very well at first. Let’s be careful and drop our slope angles below 35 degrees if we get that 7-16 inches new snow that NOAA is calling for over the next day or two.

I know its been lots of fun out there, and we’ve been having a good stability window but it is our job at the avalanche center to look for problems in the snowpack. I don’t like to dwell on the negatives, but there are some things we all need to think about concerning some potential future problems.

In addition to the slippery bed surface from ridgetops down to 3000 feet, we also need to think about the rain crust that formed during the January hurricane up to 2800 feet. That rain crust has turned into more of an ice layer with a bad temperature gradient underneath it. The reason why I am so concerned with this layer is that it is located at a bad elevation for the starting zones in the bowls along Seattle ridge. It feels like you are up high on Seattle Ridge, but you are really spending most of your time below 3000 feet where there is a lot of steep terrain. There is a chance that I am blowing smoke about this particular weak layer. It might not avalanche at all during or after the next storm, but it raises a big uncertain question mark in my head. Crusts are bad. A lot of people have died in avalanches where a crusty ice layer was the bed surface. If the right kind of storm hits us, then we might have very dangerous avalanche conditions on steep terrain below 3000 feet. NOAA does not make this next storm sound super powerful. I’d be more worried about a pineapple express, but lets be cautious with that weak layer especially once it gets 3 feet or more new snow on top of it. That might not happen for a while, but this layer concerns me.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU FEB 5 2009

.TODAY…SNOW DEVELOPING IN THE MORNING. SNOW ACCUMULATION 3 TO 8

INCHES. HIGHS IN THE LOWER 20S TO LOWER 30S. VARIABLE WIND 10 MPH

INCREASING TO SOUTHEAST 15 TO 20 MPH IN THE AFTERNOON.

.TONIGHT…SNOW TAPERING OFF AFTER MIDNIGHT. SNOW ACCUMULATION 3 TO 6

INCHES. LOWS 5 TO 25 ABOVE…COOLEST INLAND. VARIABLE WIND TO 10 MPH.

.FRIDAY…NUMEROUS SNOW SHOWERS IN THE MORNING…THEN SNOW IN THE

AFTERNOON. SNOW ACCUMULATION 1 TO 2 INCHES. HIGHS IN THE MID 20S

TO LOWER 30S. VARIABLE WIND TO 10 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 33 20 32 / 100 40 80

GIRDWOOD 25 17 33 / 100 80 60

This concludes today’s avalanche advisory the next advisory will be on Friday, February 6th. Thanks and have a great day.

Thu, February 5th, 2009
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.