Seward & Southern Kenai Mtns

Archives
Issued
Fri, February 9th, 2024 - 7:00AM
Expires
Sat, February 10th, 2024 - 7:00AM
Forecaster
Mik Dalpes
Conditions Summary

Weekend Avalanche Outlook

Saturday, Feb. 10 – Sunday, Feb. 11

Bottom Line: After a month of cold weather and a few small storms a large storm has arrived to the Kenai Mountains. With 12 to 24″ of new snow and 30 to 40 mph ridgetop winds forecast, we expect dangerous avalanche conditions this weekend. Natural and human triggered avalanches 1 to 3′ deep will be likely for a person to trigger. Additionally, there is a layer of weak snow buried in the snowpack that could cause an avalanche to break larger than expected. We recommend avoiding avalanche terrain this weekend and giving the snowpack time to adjust to it’s new load.

Special Announcements

The Chugach National Forest Avalanche Center has issued an avalanche warning through the National Weather Service for Girdwood, Portage, Turnagain Pass, Moose Pass, and Seward that will end at 9pm Saturday, February 10.

The National Weather Service has issued a winter weather advisory for Turnagain Pass through 9pm on Friday, February 9th

Recent Avalanches

Recent Avalanches: I was able to trigger a small loose dry avalanche on a steep roll in the Carter Lake area on February 7. Other than that, there have not been any reported avalanches in the Seward area this week. However, there were three human triggered avalanches reported last weekend in other zones of our forecast areas. We believe these avalanches failed on the weak snow created during the January cold spell that also exists in the Seward zone described below in Problem 2. Two of these avalanches were in the Turnagain forecast zone (Tincan’s Library and Girdwood’s Raggedtop) and one was slightly west of Girdwood in Falls Creek.

Weather Recap: A pattern shift occurred this week bringing warmer temperatures, cloudy skies, light winds and a few small storms. Snow fell to sea level bringing a total of 9″ to the Grouse Creek weather station at Mile 12 of the Seward Highway since last Friday. The Cooper Lake weather station shows a total of 6″ of new snow this week. The temperature at the Grouse Creek weather station is 34 degrees F this Friday morning, and light rain is falling at sea level as a large storm moves into the region.

Weather Forecast: Winds are light and variable in the town of Seward this morning Friday, February 9, but a storm has moved in from the east and winds and precipitation are increasing as of Friday afternoon. In the Lost Lake area today ridgetop winds are forecast to be 30 to 40 mph. Temperatures should be in the mid to upper 20’s F and 6 to 12″ of new snow is forecast by Saturday morning. Temperatures are warmer in the lower elevations and snow line could be as high as 1,400′. Similar weather is forecast on Saturday with temperatures in the mid to upper 20’s F and another 6-12″ of new snow could fall by Sunday morning at Lost Lake. Ridgetop winds on Saturday look to be 30 to 40 mph from the south. Sunday’s weather looks a bit calmer with precipitation tapering off and winds in the 20 to 25 mph range from the south. Temperatures should cool on Sunday to the low 20s F at Lost Lake and snow line should come down to sea level as the storm tapers off.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

With a warm storm forecast to bring 12 to 24″ of new snow by Sunday morning with sustained 30 to 40 mph winds both storm and wind slab avalanches are our main concern this weekend. This is a large amount of stress to add to a snowpack in a short amount of time. In places where 12″ or more snow has fallen withing the last 24 hours we expect that natural and human triggered storm slab avalanches 1 to 2′ deep will be likely. In areas that have recently been wind loaded, natural and human triggered wind slab avalanches 1 to 3′ deep will be likely. It is also possible that the new snow and wind could cause a larger avalanche breaking into weak snow deeper in the snowpack. More on this in problem 2. We recommend giving the snowpack some time to adjust to it’s new load and sticking to terrain below 30 degrees through the weekend. We also recommend making sure you are out of the runout of large avalanche paths.

Snow totals forecast for the Chugach Mountains from 3AM Friday, Feb. 9 to 3AM Saturday, Feb. 10, 2024. Image courtesy of the NWS Anchorage forecast office 2.9.2024 

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

The cold spell in January created a weak layer of near surface facets that was located about 1′ below the surface of the snow before the storm that arrived last night. This new load of snow and wind could be enough to tip the balance causing this layer to fail and create a large avalanche up to 3′ deep or more. We have some uncertainty with this layer because we don’t know how high it exists in elevation, but we have enough information to tell us it exists up to at least 2,500′ and possibly higher. This problem is tricky to assess and the only way to completely avoid it is to stick to slopes less than 30 degrees and give this layer time to strengthen.

Snowpack at Carter Lake prior to the current storm showing weak snow below the surface. A similar set up exists in the Lost Lake area. 2.7.2024

 

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

It has been over two weeks since the last known glide avalanche released in any of our forecast areas. However, last week we observed several recent glide cracks and avalanches in the Snug Harbor area so we are still keeping an eye on this problem. These glide cracks will likely be covered with new snow this weekend so we recommend watching out for them and avoiding them when possible.

Weather
Fri, February 9th, 2024

Weather Forecast Links:

NWS Point Forecast: Point forecast near Lost Lake.

NWS Avalanche Weather Guidance (AVG) forecast page: Zoom into the Anchorage bowl for special detailed winter forecast.

Windy.com Spot Forecast: Spot forecast for Lost Lake. (tip: scroll through models using the links at the bottom of the page, and change locations by clicking on the map).

Weather Stations

Grouse Creek Divide Snotel

Lost Lake Weather Station

Observations
Recent Observations for Seward & Southern Kenai Mtns
Date Region Location
04/16/24 Seward Observation: Lost Lake
04/10/24 Seward Observation: Lost Lake
04/03/24 Seward Observation: Snug Harbor
03/31/24 Seward Avalanche: Lost Lake
03/27/24 Seward Avalanche: Tiehacker Mountain
03/14/24 Seward Observation: Lost Lake via Snug Harbor
03/06/24 Seward Observation: Carter Lake
03/03/24 Seward Observation: Victor Creek, 1k – 1.6k elevation
02/29/24 Seward Observation: Carter Lake
02/26/24 Seward Avalanche: Mt Marathon
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This is a general backcountry conditions summary. This advisory does not apply to highways, railroads or operating ski areas.