Moderate Danger

January 9, 2018

Warm and Shifting Conditions

Posted:
Jan 9, 2018 @ 6:54 am

The current avalanche danger is Moderate in the West Central Montana backcountry. Human triggered avalanches are possible and have the potential to be large in isolated areas. Carefully evaluate snowpack and terrain to identify areas of greatest concern.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for January 9th, 2018. This danger rating does not apply to operating ski areas, expires at midnight tonight and is the sole responsibility of the U.S. Forest Service.

Weather and Snowpack

Mountain temperatures this morning are just above freezing in the low to mid thirties. Winds are calm at Point 6 and 19 mph gusting to 28 mph from the SE at Deer Mountain. Light showers delivered .1-.3 inches of snow water scattered across the region. More precipitation is expected later today with rain lines around 5,000 feet.

Travis and I were in the Rattlesnake yesterday and Tim and Greg were in the Southern Swans. We all found snow that is continuing to settle along with warm and mild conditions.

The most significant concern this morning are the deep persistent slabs. The Thanksgiving crust and facets continue to heal but have the potential to still cause very large avalanches. This layer continues to gain strength but with the consequences so high it demands respect. Avoid shallow or rocky areas where it may be easier to trigger this layer. Thoroughly consider the consequences of this layer failing before committing to avalanche terrain.

Consequences continue to be the theme today as the secondary concern is loose wet avalanches. Although very small in nature a wet loose slide can pack a punch. Avoid terrain traps where you have the possibility of getting carried into rocks, tress, or gullies where deep burials are possible. Lots of roller balls and wet point releases were observed yesterday and with todays warm temperatures and moisture coming it will be a growing concern.

Wind slabs are the third concern today. Tim reported the presence of large wind slabs in the Southern Swan but wind slabs have slowly been gaining strength over the last few days. Wind slab activity has decreased and with clam winds in the north and minimal snow for transport in the south, growth has diminished. Identify terrain that is wind loaded and carefully evaluate the possibility of triggering a wind slab, especially if there is potential to step down to the deep persistent layers.

A warm wet system is moving into the region later today and into tomorrow morning. Rain lines will be high and a significant load of wet heavy snow is possible. Conditions can deteriorate rapidly with a new heavy load of snow, stay aware of avalanche conditions as they change through the day today.

If you are out in the backcountry, please send us your observation, these are very helpful in producing the advisory. A weather update will be issued on Wednesday, January 10th.

Ski and ride safe.

READ FULL ADVISORY

Problem 1 - Deep Persistent Slab

TYPE

Deep Persistent Slabs
Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar, deeply-buried surface hoar, or facets surrounding a deeply-buried crust. Persistent, Deep-Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply-buried over time.
SIZE

3 (Large-Very Large)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Unlikely/Possible
The likelihood of an avalanche resulting from this problem.

Thanksgiving crust is gaining strength and less reactive, but still has the potential to produce very large avalanches if triggered.

Problem 2 - Loose Wet

TYPE

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

< 1 (Small)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Possible/Likely
The likelihood of an avalanche resulting from this problem.

Warm temperatures are making for moist and heavy surface snow. The addition of rain at lower elevations will only further this problem today.

Problem 3 - Wind slabs

TYPE

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

1-2 (Small-Large)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Unlikely/Possible
The likelihood of an avalanche resulting from this problem.

Wind slabs have been gaining strength all week and are becoming more difficult to trigger.

VIDEO

GALLERY

Morrell Ridge

Studyplot01_08_18-08-Jan

Pit Snake 01:08:2018

1/8/18

Point 6 on 1/8/18

Morell Ridge

FORECAST & OUTLOOK

Danger Trend

Increasing Danger
Area Forecast

Warm and Wet

As moisture moves through the region today rain will be possible up to 5,000 feet. There is potential for up to a foot of wet heavy snow through tomorrow morning. with the addition of a wet heavy load of snow avalanche danger will increase.

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.