24-25

Isothermal snow underneath cold pow

Date

Mon, 05/05/2025 - 15:35

Activity

Skiing

S1.5, winds Mod from N, OVC ~ 1400

6-8” of cold snow at Bradley’s Meadow (7,800’) but about 4-5 inches of isothermal snow and a M/F crust interface below.

if temps drop overnight, this could be a problematic layer.

winds scouring some parts of Bradley’s ridgeline and depositing 4f to 1f slabs

Region

Bridger Range

Location (from list)

Bridger Bowl

Observer Name

M Standal

GNFAC Avalanche Forecast for Mon May 5, 2025

Snowpack and Avalanche Discussion

<h3>GENERAL SPRING SNOWPACK AND TRAVEL ADVICE</h3>

NEW SNOW AND WIND LOADED SLOPES

Spring storms are notorious for depositing heavy amounts of snow in the mountains. Even with a deep and generally stable snowpack throughout the advisory area, heavy and rapid loads of new snow will decrease stability. The main problems to look out for are avalanches breaking within the new snow, wind slabs, and loose snow avalanches. The likelihood of triggering an avalanche spikes during and immediately after snowstorms. New snow instabilities tend to stabilize quickly, but it’s a good idea to give fresh snow a day to adjust before hitting big terrain. New snow instabilities can be challenging to assess, and spring storms bond to old snow differently across aspects and elevations. Conservative terrain selection is essential during and immediately following storms. Avoid wind-loaded slopes and slopes steeper than 35 degrees for 24-48 hours after new snow and wind.

New snow can quickly change from dry to wet on a spring day, and stability can decrease rapidly with above freezing temperatures or brief sunshine. New snow may bond well early in the morning and then easily slide later. Wet loose slides are likely during the first above freezing temperatures or sunshine immediately after a storm. Anticipate changes in snow stability as you change aspect or elevation and over the course of the day. An early start is always an advantage. Be ready to change plans or move to safer terrain at the first signs of decreasing stability.

WET SNOW AVALANCHES

Spring and wet snow avalanches go hand-in-hand. Above freezing temperatures, rain, and/or intense sunshine cause the snow to become wet and weak and make wet avalanches easy to trigger or release naturally. Conditions tend to become most unstable when temperatures stay above freezing for multiple days and nights in a row. Avoid steep terrain, and be aware of the potential for natural wet avalanches in steep terrain above you, if you see:

<ul>
<li>Heavy rain,</li>
<li>Above freezing temperatures for more than 24 hours,</li>
<li>Natural wet avalanches,</li>
<li>Rollerballs or pinwheels indicating a moist or wet snow surface,</li>
<li>Or if you sink to your boot top in wet snow.</li>
</ul>

In general, if the snow surface freezes solid overnight, the snowpack will be stable in the morning and stability will decrease through the day as snow warms up. The snow surface hardness, rate of warming, duration of sunshine, aspect and elevation determine how fast stability will decrease through the day. Be aware that sunny aspects may have a wet snow avalanche danger while shadier slopes still have a dry snow avalanche danger. Getting off of steep slopes should be considered when, or before, the above signs of instability are present. Wet snow avalanches, whether loose snow or slabs, can be powerful, destructive and very dangerous. Conservative terrain choices, starting early in the day, and careful observations can keep you safe.

CORNICES

Cornices along ridgelines are massive and can break under the weight of a person (photo). Prolonged above freezing temperatures and rain make them weaker and possible to break naturally. They can break off suddenly and farther back than one might expect. Cornice falls can also entrain large amounts of loose snow or trigger slab avalanches. Stay far back from the edge of ridgelines and minimize exposure to slopes directly below cornices. Regardless of whether a cornice triggers a slide or not, a falling cornice is dangerous to anyone in its path.

DISCLAIMER

It does not matter if new snow falls or not, avalanches will continue to occur until the existing snowpack is mostly gone. Always assess the slope you plan to ride with diligence and safety in mind. Do not let your guard down. Travel with a partner, carry rescue gear and only expose one person at a time in avalanche terrain.

Have a safe and enjoyable spring and summer!

Mark, Alex, Ian and Dave

For more spring travel advice see this <a href="https://www.mtavalanche.com/blog/transitions-spring-snow-avalanche-prob… our GNFAC forecaster blog.

We will continue to share avalanche and snowpack information on our website and social media when available. If you get out, please send us your observations no matter how brief. Submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><spa…; or email <a href="mailto:mtavalanche@gmail.com">…;

Read more about GNFAC Avalanche Forecast for Mon May 5, 2025

Events and Education Calendar

Slide off of The Nose

Date

Sat, 05/03/2025 - 10:55

Activity

Skiing

We were above the entrance to Exit Chute and triggered a slough slide that slid down one of the gullies that emptied into PK bowl. It appears to have followed an existing slide path, terminating in the top of what looked to be a significant existing avalanche runout. The slide looks pretty wide but not deep.

Region

Bridger Range

Location (from list)

Bridger Bowl

Observer Name

Emily Hook

Large recent wet loose avalanches at Bridger

Date

Thu, 05/01/2025 - 10:00

Activity

Skiing

Saw many recent looking wet loose avalanches on east facing slopes at Bridger. We got a good look at the debris pile from one in Z chute and it looked big enough to bury a person (D2) and had run far past the cat track into south bowl.

We encountered a lot of variation in ski penetration with ~1' of loose melt forms in places on north and east facing slopes ~8k' in elevation.

Region

Bridger Range

Location (from list)

Bridger Bowl

Observer Name

Heather Myers

GNFAC Avalanche Forecast for Fri May 2, 2025

Snowpack and Avalanche Discussion

Today and this weekend, the main threat is wet snow avalanches. A minimal refreeze of the snow this week combined with very warm weather the next few days will increase the odds of wet loose avalanches.

Often the main threat is having one start naturally above you. The good news is that the snowpack will most often give clues that it’s starting to warm up enough for wet avalanches to start happening. Areas with exposed rocks heat up the quickest and are often places where wet loose avalanches happen first. Check out this <a href="https://www.mtavalanche.com/node/34962"><… example of a slide</a> I spotted while skiing yesterday.

Make sure to get an early start in the coming days and exit the mountains early. The snow should be lightly refrozen in the mornings, but will quickly break down as soon as the sun climbs into the sky by mid-morning.

Read more about GNFAC Avalanche Forecast for Fri May 2, 2025

Give Big Gallatin Valley

Give Big Gallatin Valley is TODAY! until 6pm

Read more about Wet loose avalanche

This wet loose avalanche is a great example of where they often occur. Rocks absorb extra heat from the sun and can quickly melt and destabilize the snow. Either move under areas like this early in the morning (as we did), or if you have to travel under them later in the day, move quickly.

Forecast link: GNFAC Avalanche Forecast for Fri May 2, 2025 GNFAC Avalanche Forecast for Mon May 5, 2025

Out of Advisory Area, 2025-05-02

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