Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday December 9th 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).
All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. These areas are periodically patrolled by law enforcement. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow, these colder temps down low are really helping these areas.
Will recent weather effect avalanche conditions today?
Well, let’s take a closer look at the precip, winds, and temps.
Hindcast (Last 24 hours)
3800′ -Sunburst Wx Station-
Stopped reporting at 8pm last night, but recorded temps as high as 48 degress yesterday. Plus, temps have been above freezing at this wx station since 2pm 12/6/09.
2600′-Seattle Ridge Wx Station-
Stopped reporting at 5pm last night.
1800′-Center Ridge Wx Station-
Precip: 0 inches of water and 0 inches of new snow
minus 1” of total snowpack due to settlement for total depth of 59 inches
Temperature Range: 30-40 (highest temp recorded at noon)
Most weather stations stopped reporting yesterday, but we still have a few to go with for current conditions. Fresno Ridge at 3400′ near Summit is currently reporting a temp of 36 degrees (6 degrees colder than yesterday) with calm winds. Center Ridge at 1800′ in Turnagain Pass is reporting a temp of 30 degrees (5 degrees colder than yesterday). Despite of the limited wx station data, we can still say that this wierd temperature inversion is still in place, and that jives with the NWS discussion and forecast below. Temps have come down a little on Fresno Ridge, but they are still above freezing.
Skies are clear in Girdwood as of 5am, and the Middleton and Kenai Radars are clear as a bell.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST WED DEC 9 2009
.TODAY…MOSTLY SUNNY. AREAS OF FOG WILL LOCALLY REDUCE VISIBILITIES
UNDER ONE MILE DURING THE MORNING. HIGHS IN THE LOWER 20S TO MID 30S.
.TONIGHT…MOSTLY CLEAR. LOWS IN THE LOWER TEENS TO LOWER 30S.
LIGHT WINDS EXCEPT NORTH 10 MPH NEAR SEWARD.
.THURSDAY…MOSTLY SUNNY. HIGHS IN THE MID 20S TO MID 30S. LIGHT
.THURSDAY NIGHT…MOSTLY CLEAR. LOWS IN THE LOWER TEENS TO LOWER
30S…COLDEST INLAND. VARIABLE WIND 10 MPH EXCEPT WEST 20 TO
30 MPH NEAR WHITTIER.
TEMPERATURE / PRECIPITATION
SEWARD 32 27 33 / 0 0 0
GIRDWOOD 27 20 27 / 0 0 0
Short Term Weather Models for higher elevations around the Kenai Mountains near Turnagain Pass look similar to yesterday, but they do show 3000′ temps dropping below freezing tomorrow with 6000′ temps strangly staying above freezing tomorrow. However, we are only really interested in what is happening today.
Sea-level: 0 inches of water forecasted today
3000′: temps forecasted above freezing today around 40 degrees with winds 5-10mph
6000′: temps forecasted above freezing today around 40 degrees with winds 5-10mph
Today’s weather could contribute to the avalanche danger. The unusually warm temps at the upper elevations are a becoming more concerning. Today at 2pm will mark 3 straight days of above freezing temps on the ridgetops. As of Monday afternoon, the top 6 inches of the surface snow was warming up, and yesterday we observed small sun sluffs or rollerballs on slopes getting direct sunlight. The surface snow continues to get warmer and warmer since it is not getting a break from the above freezing temps. These sunsluffs are small but they are technically avalanches and they can sometimes trigger larger avalanches.
The only concerning weak layer in the snowpack that this warming surface snow could trigger are the facets on the ground. With that being said. Areas of shallow snowpack will be the most likely area for an avalanche if the temps, sunlight, and aspect are all perfectly aligned. Since the NWS is confident that today will have the similar warm temps like we have been seeing up high on the ridges, we have to increase the avalanche danger today.
We recieved a very concerning observation from the Summit Lake area yesterday. This person reported seeing natural avalanches failing on the facets on the ground. The exact days that these avalanches were observed was unclear, but the person reported them happening during the last couple days during these warm temps. If natural avalanches have been occuring as recently as yesterday or the day before, then that is very serious and dangerous. We do not have enough data from the Summit Lake area or from that observation to speculate too much, but I am taking this persons observations very seriously. Thank you for submiting that information.
Due to the sustained above freezing temps for 3 days straight, the observation from Summit Lake, CNFAIC Staff recent observations of sunsluffs, and an increasing level of uncertainty, today’s avalanche danger level has increased to between MODERATE and CONSIDERABLE. CONSIDERABLE is defined as: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential. Natural avalanches possible; human-triggered avalanches likely. Small avalanches in many areas or; large avalanches in specific areas or; very large avalanches in isolated areas.
Areas of shallow snow will be the most likely areas for avalanches today, IF they happen. The level of uncertainty with this avalanche forecast is pretty high. With that being said. Be conservative out there today. Be carefull not to discredit sunsluffs near or above your location. Strange things happen after 3 days of sustained above freezing temps. This weather is very unusual for December making avalanche forecasting more difficult.
The secondary concern today are glide cracks. Tincan in particular has lots of these crevasse like features. People and dogs have fallen into these before in the past, and they can be very difficult to crawl out of. Make sure your partner knows where you are around these 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