Posted:
Apr 7, 2017 @ 5:33 am

This is Travis Craft with a Spring conditions update.

SPRINGTIME SNOW SAFETY CONSIDERATIONS

Spring time is a mixed bag of conditions. It can feel like winter and summer all in the same day. The primary considerations are looking at Snotel data to see if upper elevations have frozen overnight and what the weather forecast is for the day. You have to pay attention to changing conditions throughout the day.

The main avalanche problems are loose wet avalanches, cornices, wet slab avalanches; and also in the alpine, wind slabs and new snow bonding to old snow surfaces.

Loose wet avalanches can entrain a large amount of snow and carry a rider into a terrain trap. When the snow surface starts producing roller balls and pinwheels it is time to change to a shadier aspect.

Cornices are starting to weaken. These beasts are unpredictable, give them a wide berth because they break farther back than expected. Avoid traveling under slopes with cornices during the middle of the day.

Wet slab avalanches are very unpredictable. When you start to punch into the snowpack up to your knees or below the melt freeze crust, change your aspect and avoid steep slopes.

In higher elevations, where new snow is still falling, pay attention to how new snow is bonding to old snow surfaces. Shooting cracks give you bullseye data that the new snow is not bonding to the old snow surface.

Wind slabs will be present in the higher elevations on leeward slopes. Identify these features and how sensitive they are when traveling by looking for shooting cracks.

The take home points. If temperatures did not freeze overnight, instabilities in the snowpack will rapidly increase and the avalanche danger will rise throughout the day. Pay attention to changes throughout the day with weather and temperature.

This is our last information statement for this season. We will continue to monitor and post any public observations as we receive them and will post updated information if conditions change dramatically. If you get out and see something worth passing along, please send us an email or use the form available on our website at missoulaavalanche.org. The information provided might keep someone out of trouble.

Thanks for another great season and all the support this year! We couldn’t do it without your financial help, and it is deeply appreciated. A special thank you goes out to the dedicated board members of the West Central Montana Avalanche Foundation, our non-profit support organization.

Ski and ride safe.

 

READ FULL ADVISORY  

Problem 1 - Loose Wet

  • TYPE

    loose-wet

    Loose Wet

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

Problem 2 - Loose Dry

  • TYPE

    loose-dry

    Loose Dry

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

Problem 3 - Cornice

  • TYPE

    cornices

    Cornices / Cornice Fall

    Release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the down-wind side. They range from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (~10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice fall can entrain loose surface snow or trigger slab avalanches.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

Problem 4 - Wind Slabs

  • TYPE

    wind-slabs

    Wind Slabs

    Release of a cohesive layer of snow (a slab) formed by the wind.  Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side.  Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

  • SIZE

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

In higher elevations.

Problem 5 - Wet Slabs

  • TYPE

    wet-slabs

    Wet Slabs

    Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet slabs can be very destructive.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    The likelihood of an avalanche resulting from this problem.

 

FORECAST & OUTLOOK

  • Danger Trend

    same

    Same Danger

  • Area Forecast

 

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.