AVALANCHE WARNING IN EFFECT. The avalanche danger is HIGH. 3.2 inches of snow water equivalent has accumulated over the past 24 hours in the Swan Range. Continued heavy snow and wind will continue through today. Both natural and human triggered avalanches are likely. Travel in avalanche terrain is not recommended. Stay off of and out from underneath slopes steeper than 30 degrees. Avalanches may run long distances and can reach into mature forests.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
Dangerous avalanche conditions exist. This new snow is accumulating on weak layers and/or crusts that formed recently. Surface hoar from early January and near surface facets (small, weak snow grains just under the snow surface) exist throughout the advisory area though the distribution is somewhat spotty. Last week's snowfall buried these weak layers under 2-3 inches of snow, but with this additional load overnight and today they are likely to become reactive. On sunny aspects, a sun crust formed last week that will be a potential bed surface for storm slabs today. On Wednesday, parts of our advisory area received freezing rain from valley floors to upper elevations. This crust could also serve as a potential bed surface. Surface hoar is notorious for propagating long distances across and up a slope. Avalanches can be triggered from flat runout zones below slopes so avoid being underneath slopes.
Heavy, dense snow coupled with moderate winds and strong gusts will form fresh wind slabs on top of a variety of surfaces including sun crusts, freezing rain crusts and buried weak layers. Wind slabs are likely to be thicker in the precipitation favored Swan Range and in areas near the Continental Divide where wind speeds have been stronger. Look for smooth, rounded features on the slope especially on steep convex rollovers, on leeward sides of ridges and cross-loaded gullies.
Tricky conditions with buried surface hoar. Surface hoar has been observed in all ranges throughout the advisory area, but not on all slopes. This makes it tricky. Some slopes (or even parts of one slope) may avalanche on this layer and others may not. The nature and distribution of this weak layer requires cautious route-finding and conservative decision making.
Deeper layers in the snowpack like the December 9 rain crust and weak snow near the ground in areas with a shallow snowpack are unlikely to be awakened during this storm, but it's not impossible. As you dig deep into the snowpack you will encounter the remnants of the December 9 rain crust. Currently it is located about 2/3 below the snow surface. This crust/ice mass is a good landmark to monitor as the season progresses.
An avalanche accident occurred in the St. Regis Basin area yesterday along the Idaho/Montana border near Lookout Pass. This area is within the Idaho Panhandle National Forest Avalanche Center advisory area. Early information states injuries were sustained, but there were no fatalities. Our thoughts go to all involved for a swift recovery.
In the Marion Lake/Dickey Creek area of the Flathead Range yesterday I observed active wind loading and a developing wind slab on near surface weak layers (observation, video). Yesterday, skiers in the southern Whitefish Range found buried surface hoar about 4-5 inches below the surface, and noted localized shooting cracks on this layer (observation). Skiers in the Skyland area yesterday found buried facets a few inches below the surface and recent wind slab activity on Slippery Bill Mountain (observation).
On Tuesday, a party of skiers in the Middle Fork reported triggering 2 thin wind slabs (photo). They also reported a freezing rain crust that extended from the valley floor to the upper elevations (observation). Also on Tuesday, GNP rangers outside the advisory area in Boundary Creek in northern Glacier Park found very reactive buried surface hoar in their stability tests and observed sensitive wind slabs on convex rollovers (observation).
Last Saturday, Mark traveled to Baldhead Mountain in the Flathead Range. He found soft, cohesionless wind drifted snow on leeward aspects and buried surface hoar 2-4 inches deep (photo). We also noted weak snow near the ground that was unreactive in stability tests (observation). Also on Saturday, skiers in the Marion Lake area, also in the Flathead Range found a shallow snowpack (about 3 feet deep). On sunny aspects they found a 1 inch crust with 2 inches of recent snow on top. Below the crust they noted weak snow that failed and propagated in stability tests.
Last Friday, Todd and I traveled up a ridge that divides the Lost Johnny and Wounded Buck drainages in the Swan Range. We observed buried surface hoar and near surface facets in the top 2-3 inches of snow. The snowpack in this area was deep and uniform (photo, video).
Thanks to everyone for submitting observations. They are extremely useful for everyone.
Visit our Observations page and our You Tube channel for more observations from the entire season.
Please let us know what you are seeing out there. Your observations are important and valued.
HOW TO SUBMIT OBSERVATIONS:
Email: [email protected]
Call and leave a message: 406.387.3821
You can also submit quick observations via text: 406.241.4571 (FAC mobile)
OR
Submit Snowpack Observations: http://www.flatheadavalanche.org/node/add/snowobs
Submit Avalanche Observations: http://www.flatheadavalanche.org/node/add/avyobs
A very wet storm system gained momentum overnight and will continue through today for the advisory area. The fire hose is currently pointed at the Swan Range which has recieved 2.5 inches of snow water equivalent (SWE) over the past 24 hours. The rest of the advisory area has not received as much, but more snow and strong winds are expected today. Storm totals as of 5:00 am this morning range from 6-10 inches of snow with 0.5 to 3.2 inches of snow water equivalent.
Currently, mountain weather stations report temperatures ranging from 23 - 29º F at upper elevations and winds are out of the southwest at 5-12 mph with gusts up to 19 mph. Today, expect snow to continue through the day with the snow level lowering and winds moving out of the southwest at 15-20 mph with gusts to 35 mph in the Swan, Flathead, and Glacier Park ranges. The Whitefish Range should see less wind. New snow amounts today range from 3-15 inches favoring the Swan Range.
| 0600 temperature: | 23-29 deg. F. |
| Max. temperature in the last 24 hours: | 28-33 deg. F. |
| Average wind direction during the last 24 hours: | SW |
| Average wind speed during the last 24 hours: | 10-19 mph |
| Maximum wind gust in the last 24 hours: | 17-34 mph |
| New snowfall in the last 24 hours: | 3-12 inches |
| Total snow depth: | 49-62 inches |
| Thursday | Thursday Night | Friday | |
|---|---|---|---|
| Cloud Cover: | Snow with lowering snow levels. Swan Range favored. | Tapering snow. | Lingering snow showers. |
| Temperatures: | 27 to 35 deg. F. | 14 to 22 deg. F. | 22 to 29 deg. F. |
| Wind Direction: | Southwest | Southwest | Southwest |
| Wind Speed: | 10-15 mph with gusts to 30 mph. | 5-10 mph gusts to 20 mph. | 4-5 mph. |
| Snowfall: | 4-15 in. | 0-2 in. | 1-2 in. |
| Snow Line: |
This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
