2020-21 West Central Montana Avalanche upates: 4/8/2021 END OF FORECAST SEASON REPORT

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Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Mar 20, 2021 06:49 am
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Avalanche Advisory for March 20, 2021​

low danger
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The avalanche danger in the west central Montana backcountry is LOW.
Good Morning. This is Jeff Carty with the West Central Montana Avalanche Center advisory on Saturday, March 20, 2021. This advisory is sponsored by REI. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Snowpack and weather
After a very warm week that culminated with all elevations remaining above freezing on Thursday night, we are back to cooler temperatures. Mountain temperatures dipped to 20º last night and are expected to reach 38º today. Cloud cover should keep solar warming to a minimum, but the sun may come out and affect southern aspects. 0.1″-0.2″ SWE fell in the past 24 hrs, snow accumulation was negligible due to warm temperatures. Elevations below 5500′ received rain. 1″-2″ of snow is forecast today, and up to 3″ tonight. Light winds, with strong gusts, will be out of the northwest.
All elevations and aspects were affected by above freezing temperatures yesterday. The dry snow that had been preserved on north faces is gone and was moist to a foot down in the snowpack. Pockets of dry snow may be preserved above 8000′ feet.
Despite the week of warmth, we were able to find faceted layers at the base of the snowpack on the north, They were rounding and gaining strength, but it is worth noting that they are out there in isolated locations. They would be unlikely to trigger in the location found yesterday given the depth and the density of the overlying slab. Isolated pockets of facets may still exist in other locations. There remains a very slight possibility that just the right trigger point or cornice fall could trigger a persistent slab.
All other aspects but north were saturated to ground yesterday. Some spots were approaching isothermal, with noncohesive snow below a deteriorating crust. It’s conditions such as this that can lead to large wet spring avalanches. However, cold temperatures last night have locked the snowpack in place with a stout supportive crust. The cold nights and mild days in the forecast should keep the whole snowpack refrozen. Avalanche hazard will remain low as long as the snowpack remains solidly frozen, or unless enough snow accumulates to create new problems.
Sun, rising temperatures, or rain could cause a rise in hazard. If the snowpack is saturated more than a few inches below the surface, if you sink into softened snow to mid boot, or if you are punching through the crust into wet snow, it’s time to go. Any rain on snow should be cause for concern.
The minimal amount of snow forecast for today is unlikely to create any instabilities. By tomorrow there may be enough, combined with wind, to create small wind slabs.
Cornices and glide cracks will be with us for the rest of the season. These are two unpredictable avalanche problems. The cornices left after the warmth are a hazard that will increase with warmth, sun, or rain. Give them a wide berth above and stay out from underneath. Glide cracks will have opened and accelerated with the warmth. While slowed, they are still opening despite cold temperatures as the ground beneath the snowpack remains unfrozen. They can fail unexpectedly, creating full-depth avalanches. Stay off slopes where they are present.
The bottom line
The snowpack has refrozen, and the hazard is low. Warming or rain may cause the hazard to rise. If you are sinking into moist snow or breaking through the supportable crust, it is time to head home. Reassess conditions throughout the day and stay alert for signs of instability. Look for red flags. Carry a beacon, shovel, and probe.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.

The post Avalanche Advisory for March 20, 2021 appeared first on Missoula Avalanche.
 

Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Mar 23, 2021 06:10 am
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Avalanche Advisory for March 23, 2021​

moderate danger
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The avalanche danger in the west central Montana backcountry is MODERATE. New snow and winds have created avalanche conditions.
Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Tuesday, March 23, 2021. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Temperatures range from 17 to 26 degrees this morning. Over the last 24 hours .3 to .6 inches of SWE have been recorded. Winds will be light today.
Yesterday we found upper elevation start zones and leeward aspects to have wind slabs. These slabs ranged in depth from a couple of inches to 10 inches. These slabs will be sensitive to humans today.
New snow has not bonded to old snow s surfaces. Use test slopes to see how the new snow is bonding. These are small slides but could knock a rider off their feet. Terrain traps such as gullies can concentrate the depth and strength of these slides, obstacles such as cliffs or rocks will increase the likelihood of trauma.
We found propagation in our pit on a north facing slope on facets. This is not a widespread problem but when found should dial back objectives for the day.
Cornices and glide cracks will be with us for the rest of the season. These are two unpredictable avalanche problems. The cornices left after the warmth are a hazard that will increase with warmth, sun, or rain. Give them a wide berth above and stay out from underneath. Glide cracks will have opened and accelerated with the warmth. While slowed, they are still opening despite cold temperatures as the ground beneath the snowpack remains unfrozen. They can fail unexpectedly, creating full-depth avalanches. Stay off slopes where they are present.
Bottom Line
Winter weather is back. Look for sheltered slopes today. Choose slopes with a supportable crust. On these slopes managing your sluff will be important. Dig a pit. Search for instabilities not stability. Use test slopes and hand pits to see how the new snow is bonding. Reassess conditions throughout the day and stay alert for signs of instability. Look for red flags. Carry a beacon, shovel, and probe.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.

The post Avalanche Advisory for March 23, 2021 appeared first on Missoula Avalanche.
 

Scott

Scott Stiegler
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Lifetime Membership
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Current West Central Montana Avalanche Advisory
Posted: Mar 25, 2021 06:17 am
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Avalanche Advisory for March 25, 2021​

moderate danger
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The avalanche danger in the west central Montana backcountry is MODERATE. New snow and winds have created avalanche conditions.
Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Thursday, March 25, 2021. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Temperatures range from 23 to 29 degrees this morning. Over the last 24 hours, .3 to .7 inches of SWE have been recorded. Winds will be gusting into the 20’s today.
Yesterday, we found that the new snow was not bonding well to old snow surfaces. The new snow has fallen slick crusts. We found facets in the upper third of the snowpack that should be investigated before committing to any steep terrain. We found wind slabs that were sensitive to human triggers on leeward slopes.
The new snow yesterday was easily triggered and ran long distances as sluffs. Use test slopes to see how the new snow is bonding to old snow surfaces. Terrain traps such as gullies concentrate the depth and strength of these slides. Obstacles such as cliffs or rocks will increase the likelihood of trauma. Today with more loading look for these sluffs to gain consolidation and create storm slabs. Cracking from skis or machines will be good indicators of this problem.
Winds have created small to large wind slabs on ridges and start zones. Shooting cracks are a sign of instability.
Facets are in our snowpack buried in the top third of the snowpack. Not reactive yesterday, but should be investigated with more loading today.
Cornices and glide cracks will be with us for the rest of the season. These are two unpredictable avalanche problems. The cornices remaining after the warmth are a hazard. This hazard will increase with warmth, sun, or rain. Give them a wide berth above and stay out from underneath. Glide cracks will have opened and accelerated with the warmth. While slowed, they are still opening despite cold temperatures as the ground beneath the snowpack remains unfrozen. They can fail unexpectedly, creating full-depth avalanches. Stay off slopes where they are present.
Bottom Line
Use caution today and do your homework before committing to steep terrain. Seek slopes sheltered from the wind. Use small test slopes and hand pits to check new snow depth and bonding to old snow surfaces. Dig a pit. Pay attention to terrain traps. Search for instabilities, not stability. Reassess conditions throughout the day and stay alert for signs of instability. Look for red flags. Carry a beacon, shovel, and probe.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.
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Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Mar 27, 2021 06:16 am
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Avalanche Advisory for March 27, 2021​

moderate danger
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The avalanche danger in the west-central Montana backcountry is MODERATE.
Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Saturday, March 27, 2021. This advisory is sponsored by Loose Caboose. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Temperatures range from 25 to 31 degrees this morning. .1 to .3 SWE in the last 24 hours. Winds will be increasing over the weekend potential gusts greater than 50 mph by Sunday.
Yesterday we found the new snow was not bonding well to old snow surfaces and interfaces. The new snow was easy to trigger as sluffs and where it was deeper than 8 inches or warming was propagating and producing shooting cracks form skis. Loose wet was observed on slopes below 5500 ft. With warming temperatures and sun expect loose wet to increase throughout the day. Terrain traps such as gullies concentrate the depth and strength of these slides. Obstacles such as cliffs or rocks will increase the likelihood of trauma. Cracking from skis or machines will be good indicators of this problem.
Winds have created small to large wind slabs on ridges and start zones. Shooting cracks are a sign of instability.
Facets are in our snowpack buried in the top third of the snowpack. Not reactive yesterday, but should be investigated.
Cornices and glide cracks will be with us for the rest of the season. These are two unpredictable avalanche problems. The cornices remaining after the warmth are a hazard. This hazard will increase with warmth, sun, or rain. Give them a wide berth above and stay out from underneath. Glide cracks will have opened and accelerated with the warmth. While slowed, they are still opening despite cold temperatures as the ground beneath the snowpack remains unfrozen. They can fail unexpectedly, creating full-depth avalanches. Stay off slopes where they are present.
Bottom Line
Use caution today and do your homework before committing to steep terrain. Warming temperatures will increase avalanche danger throughout the day. Roller balls are signs to change aspect.Use small test slopes and hand pits to check new snow depth and bonding to old snow surfaces. Dig a pit. Pay attention to terrain traps. Search for instabilities, not stability. Reassess conditions throughout the day and stay alert for signs of instability. Look for red flags. Carry a beacon, shovel, and probe.
Upcoming Education Events
Please visit our education page for an up-to-date list of regional events and course offerings. Below are new educational opportunities to check out this week.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.
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Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Mar 30, 2021 06:48 am
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Avalanche Advisory for March 30, 2021​

considerable danger
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The avalanche danger in the west-central Montana backcountry is CONSIDERABLE. New snow, wind and buried facets have created dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.
Good Morning. This is Jeff Carty with the West Central Montana Avalanche Center advisory on Tuesday, March 30, 2021. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Winter has returned. In the last 48 hrs the mountains have received between 0.3″ SWE at Stuart Mt. and 2.2″ SWE at Twin Lakes in the central Bitterroot. Much of the forecast area has 12″+ of new snow. Temperatures this morning are 17º at 7400′. Winds have been strong out of the west. Scattered snow showers are possible today with minimal accumulation, westerly winds will be moderate with strong gusts. Temperatures will remain below freezing above 6000′.
There are currently three problems contributing to touchy avalanche conditions:
Up to 24” of new snow in the past 48 hrs has created storm slab conditions. This has not yet bonded to underlying snow surfaces and shooting cracks were common yesterday indicating unstable snow. Storm slab avalanches are likely on convexities and slopes greater than 33º.
Strong to extreme wind has loaded leeward slopes and created very deep drifts. These were very touchy yesterday and have the potential to create large avalanches. Wind slab was remotely triggered yesterday from ridge top in the Bitterroot, and easily triggered by skis in the Rattlesnake. Crown depths were 12″ to 24″, the potential for much deeper avalanches exists. Winds continued overnight adding to the depth and size of wind slabs. Windloaded slopes greater than 30º should be avoided.
Facets that formed around crusts in the upper part of the snowpack during the past two weeks have been overloaded and are propagating easily in tests. Storm slab and wind slab may run on these layers or step down to them, with depths to 36”. These are not layers to mess with. It’s best to give these time to round out and enjoy low angle powder, less than 30º.
Cornices have been reloaded by the storm and are a hazard. Stay out from underneath and well away from the top as they can break farther back than expected.
The storm snow will need some time to settle out and bond. Conservative decisions and mellow terrain are a good idea for today. Warming temperatures tomorrow may help the snowpack bond but will also lead to a new set of wet snow problems as temperatures rise above freezing and the sun comes out.
The Bottom Line
Dangerous avalanche conditions exist and multiple problems complicate management. Human triggered avalanches are likely. Travel in terrain less than 30º is recommended. Avoid traveling under avalanche slopes. Stay alert for red flags such as whumphing and shooting cracks. Carry a beacon, shovel, and probe.
Upcoming Education Events
Please visit our education page for an up-to-date list of regional events and course offerings. Below are new educational opportunities to check out this week.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.

The post Avalanche Advisory for March 30, 2021 appeared first on Missoula Avalanche.
 

Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Apr 01, 2021 06:57 am
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Avalanche Advisory for April 1, 2021​

considerable danger
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The avalanche danger in the west-central Montana backcountry is MODERATE this morning and CONSIDERABLE this afternoon.
Good Morning. This is Jeff Carty with the West Central Montana Avalanche Center advisory on Thursday, April 1, 2021. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Mountain temperatures this morning ranged from 28º to 32º and were climbing by 5:00 am. They are expected to reach 57º above 6000’ today. Skies will be clear and the sun will be out rapidly warming southern aspects. Winds will be moderate out of the southwest.
In the past 48hrs the weather has done a complete 180º. From mid winter weather and touchy avalanche conditions to spring high pressure and wet snow problems.
The warmth that began yesterday will continue through at least Saturday with progressively warmer temperatures. A mild freeze last night above 5000’’ has frozen snow surfaces and they will warm rapidly today. Freezing levels may rise to 9000’ and could affect north aspects as well.
With the warming we are at risk for wet slab avalanches. The new snow sits on a couple of very stout crusts that will provide both a barrier to free water moving through the snow pack and a very slick bed surface if lubricated by water. The new snow is up to 24” thick and could form large destructive wet slabs.
In addition, in many areas the snowpack is only frozen 18 to 25 inches deep. Below this the snowpack remains moist and packable. This snowpack will warm quickly and poses the problem of isothermal snow and much larger wet slides as the whole snowpack loses cohesion.
Pay close attention to the temperature and solar warming over the next few days. As the snowpack warms up, roller balls will start to fall off steeper rocks followed by warming of the snow surface and finally, the crusts will break down. If you are punching into wet snow more than a few inches deep it’s time to move to shadier aspects or home. If you are punching through moist crusts exercise extreme caution and avoid all avalanche terrain. If the snow surface does not freeze overnight then the risk of wet slides increases.
North aspects remained cold and dry yesterday. That may change with rising freezing levels today. Yesterday we found much better bonding of the new snow, but were still able to get propagation at the new snow/old snow interface on facets and around two crusts in the upper part of the snowpack. These should be investigated before committing to north facing terrain greater than 35º. Any propagation on facets is cause for concern.
Timing is everything with spring conditions. Stability will be higher in the morning and decrease throughout the day. Late afternoon is when the greatest wet slide hazard exists. Caught at the right time, when just the top couple inches of the snowpack is warmed, corn skiing will be good. This will be a very short window today.
The Bottom Line
Rapidly rising temperatures combined with sun warming make wet slab avalanches likely today. Move to shadier aspects as roller balls start and you sink past mid boot in wet snow. Plan your exit from the backcountry so you are not crossing southerly or westerly avalanche terrain late in the day. On north slopes, faceted layers have potential to propagate. Avoiding north slopes over 35º is the easiest management. Stay alert for red flags. Carry a beacon, shovel, and probe.
Upcoming Education Events
Please visit our education page for an up-to-date list of regional events and course offerings. Below are new educational opportunities to check out this week.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.
The post Avalanche Advisory for April 1, 2021 appeared first on Missoula Avalanche.

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 you can use the information we provide to help you make more informed decisions regarding travel in avalanche terrain for the next few days.

Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to Hoodoo Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Avalanche information for the Lookout Pass/St. Regis Basin is available from the Idaho Panhandle Avalanche Center.
 

Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Apr 03, 2021 06:54 am
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Avalanche Advisory for April 3, 2021​

considerable danger
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The avalanche danger in the west central Montana backcountry is CONSIDERABLE.
Good Morning. This is Jeff Carty with the West Central Montana Avalanche Center advisory on Saturday, April 3, 2021. This advisory is sponsored by Spark R&D. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Weather and Snowpack
Mountain temperatures this morning ranged from 30º to 41º to. There was an inversion last night with higher temperatures at upper elevations. Temperatures are forecast to reach 59º above 6000′ today. Freezing levels will be at least 7500’, potentially climbing to 10000’. The sun will rapidly warm southern aspects. Winds will be light out of the southwest.
Last night was the second in a row with elevated temperatures that did not dip below freezing. Temperatures remained higher than the previous night so less cooling of the snow surface occurred. Strong sun and high temperatures yesterday added considerable warmth to the snowpack, saturating the snow on all solar aspects. Any freeze that happened on the snow surface last night will be shallow. By noon yesterday, the snowpack at 7600’ on south aspects was saturated throughout. Small loose wet slabs were easy to trigger and the snowpack lost cohesion throughout the day. This will happen earlier today.
The risk of large wet avalanches increases today. Freezing levels rising to above 7500’ and solar warming will destabilize the snow further. Loose wet avalanches could entrain considerable snow and have the potential to be much larger than the slides seen yesterday. The potential also exists for very large wet slabs to release. The January 13th crust still exists deep in the snowpack. While bonded when dry, warm wet conditions could reawaken it or other dormant layers.
Once the snow warms up, is saturated, or you are punching past mid boot, it’s time to move to shadier aspects. If you are post-holing in wet snow stay well away from avalanche terrain.
North aspects were dry yesterday above 6800’ in the Rattlesnake. However, last night’s elevated temperatures may have affected the snow. We were still able to find isolated pockets of buried surface hoar and near surface facets yesterday on the north. There is a slight possibility to trigger a slide on these in steep, unsupported terrain. Avoiding convexities over 35º is one way to manage this problem.
Timing will be difficult today, and the time window for stable corn skiing may not exist at all, with most slopes not refreezing overnight. Given the unpredictability of wet slides, and the generally poor skiing and riding conditions of saturated snow, avoiding all avalanche slopes with solar warming is a good risk management option today.
The Bottom Line
Above freezing overnight temperatures combined with sun warming make loose and wet slab avalanches likely today. The extended warmth increases the potential size of avalanches and we may see very large avalanches in specific locations. Move to shadier aspects as roller balls start and you sink past mid boot in wet snow. Plan your exit from the backcountry so you are not crossing southerly or westerly avalanche terrain late in the day. On north slopes, above 6800’, faceted layers have a slight potential to propagate. Avoiding convex north slopes over 35º is the easiest management. Stay alert for red flags. Carry a beacon, shovel, and probe.
Public Observations
Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. You can now text us your observations to (406) 219-5566 when you don’t have time to fill out the observations page.
Ski and ride safe.

The post Avalanche Advisory for April 3, 2021 appeared first on Missoula Avalanche.
 

Scott

Scott Stiegler
Staff member
Lifetime Membership
Nov 1, 1998
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Current West Central Montana Avalanche Advisory
Posted: Apr 06, 2021 06:19 am
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Avalanche Advisory for April 6, 2021​

moderate danger
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The avalanche danger in the west-central Montana backcountry is MODERATE.
Good Morning. This is Travis Craft with the West Central Montana Avalanche Center advisory on Tuesday, April 6, 2021. This is our last regular advisory of the season. This advisory does not apply to operating ski areas and expires at midnight tonight. The USDA Forest Service is solely responsible for its content.
Today’s advisory is dedicated to you, everyone that sent in observations, read the forecast, took an avalanche class, or donated money, time or equipment. This resource is the result of continued community support and partnerships. On behalf of the WCMAC, thank you for another great season.
Weather and Snowpack
Over the last 48 hours, the snowpack has refrozen above 5000 feet. Temperatures range from 21 degrees to 31 degrees this morning. Over the last 24 hours, the advisory area has accumulated 3 to 5 new inches of snow. The weather continues to alternate between winter and spring in the mountains.
The refreezing of the snowpack will keep wet avalanche problems in check until we have another warm-up. The new snow is sitting on a refrozen surface. Look for loose dry avalanches to be small today. If the sun comes out look for the loose dry to change over to loose wet avalanches on sun-exposed slopes. If you see roller balls or start to punch through the snowpack it is time to find shadier aspects.
Timing is everything with spring conditions. Stability will be greater in the morning and decrease throughout the day.
The Bottom Line
Warming temperatures will increase avalanche danger throughout the day. Roller balls are signs to change aspect. Use small test slopes and hand pits to check new snow depth and bonding to old snow surfaces. Dig a pit. Pay attention to terrain traps. Search for instabilities, not stability. Reassess conditions throughout the day and stay alert for signs of instability. Look for red flags. Carry a beacon, shovel, and probe.
Special Announcements
We want to reiterate our most sincere thanks for your support this season. Providing west-central Montana’s avalanche forecasts and free education programs is made possible in part through your generosity and our gracious sponsors’ help. This winter, we succeeded in reaching more people than ever before and provided new educational opportunities for all backcountry user groups. Together, we can save lives and continue creating the most fun, safe, and responsible backcountry community possible. Again, thank you for your continued support. We couldn’t do it without you!
The post Avalanche Advisory for April 6, 2021 appeared first on Missoula Avalanche.
 

Scott

Scott Stiegler
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Current West Central Montana Avalanche Advisory
Posted: Apr 08, 2021 08:06 am
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Avalanche Special Update – A season recap and spring avalanche problem refresher – April 8, 2021​

norating danger
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Good morning, this is Jeff Carty with the West Central Montana Avalanche Center on Thursday, April 8, 2021. Regular avalanche advisories with avalanche danger ratings have ended. This does not mean the end of avalanches. Spring storms and warm temperatures may make avalanche danger rise. We will continue to post public observations, so please keep submitting them as you get out in the mountains. Below are a season recap and review of common spring avalanche problems.
We issued our final avalanche advisory for the 20/21 winter season on April 6, 2021. It caps a busy and challenging season. A proliferation of faceted layers and spatial variability made forecasting and recreating safely a challenge this year.
We issued our first avalanche advisory on December 1st this year in response to higher than average backcountry use, and enough snowpack to create avalanche conditions. In total, we issued 63 forecasts this year. Underlining the challenging conditions, only 6 were low hazard days, 5 in early December and 1 in March. Conversely, we issued 5 avalanche warnings, had 12 days of high hazard, 18 of considerable. This meant that 30 out of 63 forecast days this year had elevated avalanche hazard. Facets featured as a problem layer in almost all forecasts this season. The January 13th crust, created by rain to 8000’, featured as a prominent problem layer that contributed to faceting within the snowpack.
Despite conditions that we usually associate with bonding and rounding in the snowpack, such as warmth and depth, facets and persistent layers continued developing and propagating in tests. This added complexity and was compounded by drastic spatial variability. Stability varied widely over short distances, from drainage to drainage, and aspect to aspect, making both forecasting and risk management a challenge.
Weather Recap and Outlook

The weather contributed to the challenging conditions this year. Despite La Niña, abundant early season snow and predictions of heavier than average snowfall, it felt more like an El Niño year. In early November, the snowpack throughout the advisory area was 201% of average. However, the region experienced above-average temperatures and lower than average snowfall in December and January. Drought conditions reduced the snowpack to 89% of average by early December, and depth hoar began to form. By late January, snow totals dropped as low as 80% of average. February brought snow, and we received up to 12″ of SWE or roughly 120” of snow. The snowpack rose above 110% of average. Following a warm March with lower than average precipitation, we are currently sitting between 105% and 93% of the snowpack average.

Our first avalanche warning and high danger rating on December 20th were in response to loading on top of facets and crusts. This pattern was repeated 4 more times throughout the winter. January 13th delivered rain to 8000’ and created an ice crust that formed facets around it. This layer lingered throughout the region and contributed to the persistence of the facets in the snowpack. This layer was likely the culprit in the Lost Horse slide on February 21, 2021, that ran full path.
Finally, the last week brought 72 hrs of above-freezing temperatures to the mountains. This period underlines the unpredictability of forecasting wet snow problems. Despite a snowpack saturated to ground, and intense sun and warmth, conditions that often result in very large wet avalanches, we did not see a significant avalanche cycle.
What does the rest of the season hold? NOAA predicts cooler than average temperatures with lower than average precipitation over the next 10 days. This likely means cold nights, clear skies, and warm days. Good conditions for corn skiing, and easier conditions for avalanche management. The one-month outlook shows west-central Montana with approximately average temperatures and precipitation for this time of year.

Spring Avalanche Problems
Spring can be a challenging time for avalanche conditions. Dramatic swings in weather and snow conditions are possible. As we’ve seen in the past week, we can move from mid-winter problems to wet snow problems within 24 hrs. Understanding avalanche problems can help us plan for successful days in the backcountry. You can read more about avalanche problems here.
We have a decent understanding and tests for dry avalanche problems. We know that propagations within a weak layer can travel horizontally under a slab, delaminating it from the bed surface in dry snow environments. If the slope’s steepness is enough to overcome the friction between the delaminated slab and bed surface, we get an avalanche. This is why the extended column test is such a good test; it gives us an idea of the propagation likelihood.
Wet problems have less understood mechanics and predictability. Standardized tests also become ineffective. As snow warms up, it loses cohesion, and water is introduced into the snowpack. The weight of the water can cause the release of wet loose or wet slab avalanches. Roller balls (pinwheels) indicate water in the snowpack and signal that the snowpack is losing cohesion. With continued warmth and water in the snowpack, we can get wet loose and wet slab avalanches. The rate of thaw that results in a wet slab avalanche is variable and unpredictable.

We know that the snowpack is stable when it is refrozen, and stability decreases as it thaws. With repeated cycles of daily freeze and thaw, called the diurnal cycle, the snowpack gets more dense and stable. With this pattern, instabilities become isolated to the upper snowpack that melts daily. This changes when we receive new snow that delivers a new load or have multiple nights with above-freezing temperatures that allow the snowpack to thaw to the ground and move moisture into underlying weak layers. Rain will also quickly destabilize the snowpack.
Without tests for stability assessments, we must rely on observations to make decisions. This method lends itself to all avalanche problems, often simplifying the decision-making process.
Trask Baughman, an educator with the West Central Montana Avalanche Foundation (WCMAF) explains:
With the conclusion of the 20-21 avalanche forecast season, you will have to gather and observe all necessary data to plan your adventures and make on slope go or no-go decisions. Bruce Tremper, the author of Staying Alive in Avalanche Terrain, writes, “good habits are what will save your life”. Having easy to use tools will help build those good habits and aid with decisions in the complex, dynamic mountain environment. All backcountry users, regardless of experience, can use rule-based decision-making.
A powerful tool is ALPTRUTh, a mnemonic to help memorize and remember red flags and key terrain features. To utilize this tool, you note the factors and add them up. ALPTRUTh can be incorporated in a pre-trip checklist or a final check before committing to a slope. When 3 or 4 clues are present, extra caution and careful terrain management are needed (93% of accidents in North America have 3 or more factors present). If you have 5 or more factors present, it is recommended you push pause and carefully find an alternative path.

Avalanches, in the last 48 hours?
  • Using resources like the Missoula Backcountry Facebook page and the WCMAC public observations page is an excellent place to find this information when planning your tour. When in the field, if you see avalanches on similar aspects and elevations that you want to ski, nature is screaming danger.
Loading, by snow, wind, or rain in the last 48 hours?
  • Snow doesn’t like rapid changes; it takes time for it to settle and bond. Your pre-tour ritual should include looking at weather data for the last few days.
Path. Are you skiing an avalanche path?
  • The “Path” in ALPTRUTh is for easily recognizable avalanche terrain. When choosing to ski avalanche terrain, it is essential to make sure no other factors are present and to use best travel practices like skiing one at a time.
Terrain Traps. Are there any terrain traps?
  • Imagine the consequence of being caught? Any terrain features like gullies, trees, and cliffs will significantly increase the severity of being caught, even by a small loose wet slide.
Rating considerable or higher hazard on the current avalanche bulletin?
  • Without an avalanche bulletin, assume the danger rating is Considerable. Only with careful consideration over days without significant weather change and no other red flags being present would I drop the danger rating to Moderate. Often in a spring diurnal cycle, the danger starts at low in the morning and rising throughout the day.
Unstable Snow. Has there been any collapsing, cracking?
  • Like recent avalanches, collapsing and cracking are clear signs of avalanche potential. Careful decision-making and terrain choices are recommended.
Thaw Instability. Is the temperature rising?
  • When temperatures rise above freezing, the snowpack’s cohesion quickly falls apart, leading to thaw instability. Keeping an eye on the time of day and rising temperatures is the name of the game in the spring. Looking at weather data to see if it is freezing at night will help give you a go or no-go decision before leaving your house.
In my assessment continuum, I rely on observing red flags and weather trends that are listed in ALPTRUTh first and use data from snow pits last. If ALPTRUTh is indicating dangerous conditions then pits and stability tests are unnecessary. Stability tests do not reliably predict wet problems, and you should never use a single pit to make decisions when choosing to ski a slope. A quick hand pit can be helpful when investigating how saturated the snow surface is. Skiing a test slope is also a great way to gather information on surface conditions. When I decide that it is safe to ski avalanche terrain, I slowly step into more committing terrain in a systematic approach. Roger Atkins’ strategic mindset is a great tool, more can be read here.

The public observations page is a great asset to learn about conditions, but it is only effective if observations are being submitted. It may be more important than ever this time of year. Don’t feel obligated to submit complex observations, anything is helpful, and pictures speak a thousand words. Pertinent negatives are also helpful, if you didn’t see any red flags and found stable conditions, let people know.
Useful online resources:
  • Weather
    • The NOAA backcountry forecast page has a number of useful links including local SNOTEL sites.
    • The NOAA home page also has good info, check out the discussion for more detailed weather information
    • Montana MDT has Cams at Lolo, Lost Trail, and other roads, giving a visual on weather conditions.
    • Snow-forecast.com Has good weather maps that show snowfall, freezing level, cloud cover, wind, ect.

Ski and ride safe. See you next year!

The post Avalanche Special Update – A season recap and spring avalanche problem refresher – April 8, 2021 appeared first on Missoula Avalanche.
 
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