Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday January 13th 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).

ANOUNCEMENTS

Thanks to the group that removed the snowmachine jump structure on the motorized side of the highway so quickly.

WEATHER ROUNDUP

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temperatures ranged between 18 to 23 degrees F with light to moderate average winds between 7-17 out of the E with a strong max gust of 27 mph

Current temp is 23

2400′-Seattle Ridge Wx Station-

Winds have been light to moderate averaging 1-22 mph out of the SE with a strong max gust of 30mph

1800′-Center Ridge Wx Station-

Precip: 0.3 inches of water and 7” of new snow *(see parking lot totals for ground truth snow depths from yesterday. This weather station was a bit behind in reporting snow depths yesterday due to the very light consistency of the snow; so, the 7” of blower powder that is recorded today actually represents yesterday’s snowfall)

Total depth of 61 inches

Temperatures have increased 20 degrees.

Current temp is 30

Parking lot snow stake measurements taken at 10 am yesterday 1/12/10.

Eddies Lot: 7” new snow

Motorized Lot: 6” new snow

Sunburst Lot: 5” new snow

Johnson Pass North Lot: 3” new snow

Nowcast

Temps have increased at almost all wx stations this morning. Mid elevations around 1800′ warmed up by 18-20 degrees, but all CNFAIC Staff weather stations are showing increased temps of 5-9 degrees compared to yesterday morning. Currently, its 21 degrees at sea level and 23 degrees at 3800′. Winds have backed off a bit since last night and are currently light at all ridgetop wx stations this morning. Precip totals are consistent at all wx stations with about .3-.4 inches of water and 6-7” of new snow; however, this snow actually fell yesterday based on our ground truths yesterday at Turnagain Pass. The Middleton radar shows moderate precip mostly over Cordova, and the Kenai radar is mostly clear.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED JAN 13 2010

.TODAY…SNOW LIKELY IN THE MORNING…THEN SCATTERED SNOW SHOWERS

IN THE AFTERNOON. SNOW ACCUMULATION 1 TO 3 INCHES. HIGHS IN THE

MID 20S TO MID 30S. LIGHT WINDS EXCEPT NORTH 10 MPH NEAR SEWARD.

.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE

LOWER 20S TO LOWER 30S. LIGHT WINDS EXCEPT NORTH 10 MPH NEAR

SEWARD.

.THURSDAY…A CHANCE OF SNOW IN THE MORNING…THEN SNOW LIKELY IN

THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE UPPER

20S TO MID 30S. LIGHT WINDS EXCEPT NORTH 10 TO 15 MPH NEAR

SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 34 24 35 / 60 40 60

GIRDWOOD 29 24 34 / 60 40 50

Short Term Weather Models (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass

Sea-level: GFS shows 0.1 inches of water forecasted today

3000′: temps forecasted between 23 and 32 degrees F with winds 5 mph

6000′: temps forecasted between 23 and 32 degrees F with winds 5 mph

AVALANCHE DISCUSSION

Today’s weather should not contribute to the avalanche danger today at Turnagain Pass, but the winds on Seattle Ridge increased last night and may have formed a few small wind slabs because yesterday’s 6 inches of light fluffy snow was easy for the wind to transport. The NWS is not calling for any major weather today and the models over Turnagain Pass are only calling for up 0.1 inches of water with light winds; so, today’s weather forecast does not look like it will pack too big of a punch.

Today’s avalanche danger will remain at LOW with pockets of MODERATE due to small wind slabs near ridgetops, and easily triggered small slabs on steep rollovers at all elevations. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human triggered avalanches unlikely (except glide cracks are possible). Small avalanches in isolated areas of extreme terrain. MODERATE is defined as heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely, human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.

In simple terms, we have a variety of weak layers below 3000′ and one weak layer at higher elevations between 2800′-3800′.

The big picture right now is that the rain crust that formed up to 3000′ has a lot of potential to become a very dangerous weak layer in the future. Turnagain Pass has plenty of terrain steep enough to avalanche from valley floors up to 3000′ including the bowls along Seattle Ridge. It’s difficult to say exactly how this rain crust will react to new snow on top; so, we all need to take it easy once the next big storm comes in.

Yesterday, we found that slippery and supportable rain crust at 3000′ in Warm Up Bowl on Seattle Ridge. The 6 inches of yesterday’s new snow failed very easily starting as sluffs which ran far and easily entraining snow as it plowed down to the valley bottom. There was a little propagation yesterday when the snow was light; so, use elevated caution if you find any stiff wind slabs deeper than a foot today, because this type of slab will avalanche very easily on top of that slippery bed surface. We also were able to easily ski cut lots of small slabs on any steep rollover skiing down Repeat Offender above the snow machine up-track to Seattle Ridge. Lisa and Jon found similar results on Tincan yesterday. The reason the danger level is LOW-MODERATE today is because there is not enough snow on top of the slippery rain crust to create large avalanches. If there was 3 feet of new snow, then avalanche conditions would be deadly today. Things are not looking good for the avalanche danger after the next storm, but it will all depend on how the next storm comes in.

A wild card right now are the glide cracks. One of these crevasse like features avalanched last week for no obvious or apparent reason (see photo gallery). Nostradamus couldn’t have predicted that one; so, it adds to the theory that glide cracks are like cornices in that they are very difficult to predict. Sometimes they avalanche when it’s cold, sometimes when it’s warm, sometimes when it rains. We have not seen or had any reports of any more glide crack failures in the past week, but it would still be wise to avoid traveling on, near, or underneath the path of any glide cracks.

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 Thursday January 14th.