ARCHIVED in relation to a serious incident on Feb 17
Backcountry Avalanche Forecast
Flathead Range & Glacier NP

Issued: Saturday, February 17, 2024 - 6:59AM
Expires: Sunday, February 18, 2024 - 6:00AM
Author: Mark Dundas

THE BOTTOM LINE

Natural loose snow avalanches may occur on steep slopes that face the sun or are initiated by riders on shady aspects. It remains possible to trigger a 1-2 foot thick slab avalanche on a buried weak layer where the surface snow is consolidated. Pay attention to changing snow surface conditions throughout the day. 

Avalanche Forecast

Avalanche Danger
Saturday, February 17, 2024
Upper and Mid Elevations Above 5000 ft - Moderate
Low Elevation Below 5000 ft 1 - Low

Avalanche Problems (2)

Problem #1: Dry Loose
Aspect/Elevation: All aspects above 5000 ft
Likelihood: Likely
Size: Small (D1) -  Large (D2)

Cold weather has preserved the recent 1-2 feet of surface snow on many slopes. Today's sunshine and slightly warmer temperatures may initiate loose snow slides on steep slopes that face the sun. Riders may trigger sluffs on steep, shaded terrain. Both of these can potentially entrain substantial snow in large, continuous terrain.  

Snow falling from tree branches, sluffing from rock outcroppings, and small rollerballs are precursors to a loose slide. Either move to a different aspect or choose lower-angle slopes. Manage your sluff and limit time spent above terrain traps and in long-running gullies.

Problem #2: Persistent Slab
Problem Type
Persistent Slab
Aspect/Elevation: NW through E above 6500 ft
Likelihood: Possible
Size: Small (D1) to Large (D2)

It is still possible to trigger a slab that breaks 18 to 24 inches deep on thin layers of weak snow above the very hard, early February ice and crust layer. These layers are better developed on shady, upper-elevation slopes but are also found on isolated sunny and mid-elevation slopes. 

The surface snow in many locations remains soft and unconsolidated. Exceptions to this are where the wind has stiffened the surface or today's warming consolidates the snow into a denser slab. Cracking beneath your boards or machine indicates an unstable slab directing you to lower-angle terrain. 

Forecast Discussion

A Bluebird Saturday is on tap to reward the hard-working mid-week employees. Another cool day is expected, although warmer than yesterday. This morning, temperatures at mid and upper elevations are generally several degrees warmer except in the eastern part of the advisory area, where Marias Pass is +29 F and Shed 7 +16 F from yesterday.

A day of sun and warmer temperatures may initiate natural loose snow avalanches on sunny slopes, especially this afternoon. In most locations, the tree branches still hold substantial snow, as I observed above Essex yesterday. Today's warming may shed this snow, initiating rollerballs or loose slides upon impact with the surface snow.  Rock outcroppings facing the sun will heat and possibly shed their snow cover. These slides will gain mass as they move downhill, perhaps running fast and far in the unconsolidated surface snow. Loose slides in the 1-2 feet of soft surface snow can be triggered by riders on shaded slopes, as this group experienced in Cascadilla yesterday. 

Today's warming may consolidate the surface snow, forming a denser slab on top of potentially weak layers. Note where your boards or machines do not sink as deeply into the snow surface and steer around these areas in favor of softer snow or lower-angle terrain for a more enjoyable and safer experience. 

Winds have shifted to the southwest after a few days of north and easterly flow. We removed wind slab from the problem list, but in isolated locations, riders may still be able to trigger a slide in the dense wind-drifted snow on atypical aspects. An experienced rider identified and avoided these in the southern Whitefish Range in favor of soft boot top powder. 

Weather Forecast

Another day of high pressure will allow clear skies and sunshine before the late afternoon clouds roll in. Temperatures will remain cool but slightly warmer than the past few days. A weak system moves into the area overnight into Sunday with mostly cloudy conditions and minimal snowfall.  Expect an active weather pattern through the week with gradually warming temperatures.