Fall Update

Though it’s still technically summer for a few more days, we here at the Flathead Avalanche Center (FAC) hope everyone is enjoying their fall. The sight of snow in the mountains last week conjured up images of winter, and we just wanted to send out a quick update to let folks know what is going on at the FAC. So here is what is going on:

September snow on the shaded north facing aspects already.

September snow on the shaded north facing aspects already.

  • We are diligently devising the education calendar in cooperation with the Friends of the Flathead Avalanche Center (FOFAC) for this fall and winter and hope to have that finalized in October. We’ve already had inquiries about classes for the upcoming winter and that is fantastic.
  • Erich Peitzsch is now the Director of the FAC after serving as the interim director last season.
  • FOFAC, a non-profit devoted to avalanche education and supporting the FAC, will be hosting a number of functions this fall and winter. A description of their mission and what they are all about will be on the website soon. First, they will be hosting the social event after the Northern Rockies Avalanche Safety Workshop (NRASW) on Saturday, October 25, 2014. The workshop is an extremely educational, fun, and social event centered around avalanche safety. There is a fantastic line-up of speakers this year, and it’s a great way to kick off the season. Registration opens soon.
  • FOFAC will also host a Snowball in early December. Look for details in the near future on the website about this fun event that benefits avalanche education and the FAC.
  • Speaking of website, FAC will unveil a fresh, new website at the NRASW on Oct. 25, and discuss how to utilize FAC products in your backcountry decision making process.
  • Finally, a new weather station exists at the summit of Big Mountain at Whitefish Mountain Resort. This sophisticated weather station was made possible by donations and grants from BNSF Railway Foundation, the Northern Rockies Avalanche Safety Workshop, and Whitefish Mountain Resort, and will continue as a collaboration between these entities and the FAC, Flathead Nordic Backcountry Patrol, and the Flathead National Forest. Check out the article about it from the Flathead Beacon. Final touches on the system are being made to ensure accuracy and reliability, and we will post the link to the weather data once available. This station will be hugely beneficial to not only our operations here at the FAC, but to the recreating public as well.
  • Whew! Well, that’s it for now, and check back periodically for updates this fall and feel free to drop us a line: fac.admin@flatheadavalanche.org

2013-2014 Flathead Avalanche Center Annual Report

The final 2013-2014 Flathead Avalanche Center Annual Report is available. Thanks again to everyone for supporting and assisting the FAC this season in many ways. We greatly appreciate it, and look forward to working with and serving the community again next winter. Until then, have a great spring, summer, and fall.

2013-2014 Flathead Avalanche Center Annual Report

Cheers!
The Flathead Avalanche Center Staff
Erich Peitzsch
Todd Hannan
Seth Carbonari
Tony Willits

 

Spring Avalanche Information

SPRING AVALANCHE INFORMATION

Spring in northwest Montana brings a mixed bag of weather. We can see snow, rain, sun and everything in between all in one day. This can greatly affect avalanche conditions. Thus, it is essential to pay attention to changing conditions as these changes can happen rapidly and stability can also deteriorate fairly quickly. Avalanches (and sometimes big ones) still happen in the spring and it is important to not let your guard down. There are a few things to keep in mind while out riding or skiing and enjoying the longer and sunnier days this spring. 

 

Loose WetLOOSE WET AVALANCHES

This is probably the most common type of avalanche during the spring in northwest Montana. Wet loose avalanches are a 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. 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. Some of these avalanches may seem harmless, but can be deadly in high consequence terrain like above cliffs or a terrain trap. An important point to remember is that loose wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushy. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Wet SlabWET SLAB AVALANCHE

Wet slabs could be a very real possibility this spring given our current snow structure. We have numerous layers within the snowpack that could produce wet slab avalanches if the right weather conditions develop this spring. Wet slab avalanches are a release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet slabs can be very destructive. Hopefully, the weak layers behave this spring and don’t turn into nasty gremlins when hit with free water this spring.

Avoid terrain where and when you suspect wet slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty of this type of wet snow avalanches. It is important to pay attention to rapid warming especially with light or no refreeze overnight or rain on snow events. Free water in the snowpack acts a lot like the water in your sink drain pipes. Once you turn off the water there is a bit of a lag and water still moves through the drain. Imagine the snowpack as the drain with some layers of snow impeding water from moving directly down to the ground like a turn in the drain pipes. If a weak layer exists anywhere along the way and enough water affects the bonds of that weak layer then wet slab avalanches could occur. Thus, wet slab avalanches can even occur after prolonged sunny days or rain events (when the water shuts off).

A glide avalanche (crown circled in red) released and triggered a destructive wet slab avlanche (outlined in red line) in Glacier National Park in the spring of 2012.

A glide avalanche (crown circled in red) released and triggered a destructive wet slab avlanche (outlined in red line) in Glacier National Park in the spring of 2012.

 

 

 

 

 

 

 

 

 

 

 

GlideGLIDE AVALANCHES

Earlier in the winter glide cracks and avalanches made an unwanted appearance then went away for a while. In our travels over the past couple of weeks, we noticed glide cracks beginning to rear their ugly heads again. Glide avalanches are, unfortunately, a rather common spring occurrence here in northwest Montana, and are a release of the entire snow cover as a result of gliding over the ground. Adding insult to injury this type of avalanche is rather poorly understood and it is difficult to predict when they might fail (or even if the glide crack might fail at all). Thus, it is best to avoid slopes where glide cracks exist. 

Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage. Safe travel relies on identifying and avoiding those slopes. Glide cracks and recent glide avalanches are a good indicator of future glide avalanche activity.

Glide avalanche activity in Glacier National Park on numerous aspects (2013).

Glide avalanche activity in Glacier National Park on numerous aspects (2013).

 

 

 

 

 

 

 

 

 

 

 

Cornice

CORNICE FALL

Cornice fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice fall can entrain loose surface snow or trigger slab avalanches. Cornices are susceptible to failing particularly on warm, sunny days.

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridge line areas with cornices. They often overhang the ridge edge and can be triggered remotely. Avoid areas underneath cornices. Even small cornice fall can trigger a larger avalanche and large cornice fall can easily crush a human. Periods of substantial temperature warming are times to be particularly aware.

Massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

Massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

 

Debris from massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

Debris from massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

 

Debris from massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

Debris from massive cornice failure in John F. Stevens Canyon, Lewis Range, southern Glacier NP. 4/7/2014.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Storm SnowSTORM SNOW

Large storms can occur every spring. It is not uncommon to have spring storms drop 2-3 feet of new snow at upper elevations. So, just like in the winter it is best to give the snowpack ample time to adjust to the new load. Often in the spring this new snow will fall on melt-freeze crusts (sun or rain crusts). This crust provides a great bed surface for the new snow to slide on. Storm slabs are a release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm slab problems typically last between a few hours and few days. It is also important to pay attention to wind slabs that form both during a storm and during high wind events.

You can reduce your risk from storm slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Deep SlabDEEP SLAB

We dealt with some pretty tricky avalanche conditions this winter, and one of them was a nasty persistent slab with a crust/facet layer that formed in late January/early February. This persistent slab as well as weak layers at the ground/snow interface still lurk. Deep persistent slabs are a 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 or facets surrounding a deeply buried crust. Deep persistent 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. Deep persistent slabs are destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

 

On that note, enjoy the spring as it can be a great time of year to get out and enjoy the mountains, but keep your avalanche eyeballs open at all times. We will be working on the Flathead Avalanche Center Annual Report and will post it on the website as soon as it is complete. Please send in your observations as you are out and about this spring as they are still valuable to us (fac.admin@flatheadavalanche.org or call 406.261.9873). For now, thanks for all of the observations, feedback, and general support of the Flathead Avalanche Center this year.

Happy Spring!

Avalanche Advisory – 3/29/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 29, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Saturday, March 29, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Sunday, March 30, 2014.


MOUNTAIN WEATHER

WeatherGraphicA series of moist and progressively warmer storms impacted the advisory area over the past 48 hours. The current stream of moisture from the southwest is pointed directly at us. Currently, remote weather stations and SNOTEL sites report temperatures from 24 to 34°F with winds out of the southwest at 10-20 mph and gusts into the 30 mph range. Snowfall should continue at upper elevations with rain at lower elevations through the morning. Colder air should move into the region by this afternoon causing snow levels to drop a bit. Expect another 3-6 inches through the day with temperatures in the upper 20s to mid 30s F. Wind should be out of the southwest today at 10-25 mph and gusts into the 40 mph range particularly near the Continental Divide.

Storm totals over the past 48 hours:
Noisy Basin SNOTEL: 14 in. snow, 2.5 in. SWE
Stahl Peak SNOTEL: 10 in. snow, 1.9 in. SWE
Flattop SNOTEL: 9 in. snow, 1.1 in. SWE
Pike Creek SNOTEL: 12 in. snow, 0.7 in. SWE
Shed 7 weather station: 10 in. snow


RECENT OBSERVATIONS

RecentObservationsGraphic

It is spring and the mixed bag of weather continues as do the avalanches. Rain on new snow and heavy snow at upper elevations continue to fall throughout the advisory area. This will cause a slew of problems that include storm slabs, wind slabs, and wet avalanches. The Swan Range has received the most precipitation with impressive snow water equivalent totals (2.5 inches) over the past 48 hours.

Wind slabs were the biggest problem yesterday when we rode into Lost Johnny and Doris Creek drainages in the Swan Range. We found about 10-12 inches (25-30 cm) of new snow from Thursday into Friday (video). Moderate to strong winds created sensitive wind slabs on leeward slopes. We observed four natural slides that occurred on wind loaded slopes along the Swan crest. We also triggered two smaller wind slabs (10-20 inches deep) from the top of a ridge just by approaching the slopes (photo 1, photo 2). This evidence combined with the shooting cracks and unstable results in our stability tests (snow profiles) kept us far away from any wind loaded slope. Given the new load and the potential for storm slabs, we also stayed away from slopes steeper than 35 degrees. These problems will become even worse today with additional precipitation and continued moderate to strong winds.

We found a melt-freeze crust on all but the most shaded slopes underneath the new snow (photo) and also found this crust in the Middle Fork corridor in the Flathead Range on Thursday. This crust could provide a good bed surface for the new snow to slide on.

BNSF avalanche safety reported small wet, loose sluffs in John F. Stevens Canyon yesterday as well as other avalanche debris but did not observe any crown lines. However, they suspect these crown could have already reloaded with new and wind transported snow.

Glide cracks are beginning to rear their ugly heads again this spring. We noted a couple of glide cracks yesterday in the Swan Range (photo), and Glacier National Park rangers noted a few in the park this past week.

We received no other observations within the past 48 hours from any other locations.

 

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

 

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 10-20 inches. Width: 100 ft. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 10-20 inches. Width: 100 ft. 3/28/2014.

 

Generalized upper snowpack structure on two different aspects in the Swan Range. 3/28/2014.

Generalized upper snowpack structure on two different aspects in the Swan Range. 3/28/2014.

 

 


 SNOWPACK DISCUSSION

Avalanche Problem #1

Storm Snow

Storm slabs and wind slabs are the main problem with heavy, new snow at upper elevations (particularly in the Swan Range) and moderate to strong winds the past 48 hours. Wind slabs were breaking yesterday about 10-20 inches deep and up to 200 feet wide. These wind slabs are sensitive particularly along ridges and cross-loaded terrain features like gullies. Avoid wind loaded terrain and stick to lower angled slopes today. Expect new storm slabs today as well with the new snow at upper elevations. Large cornices exist and with warming temperatures this time of year they can become particularly sensitive. Longer days with even short periods of more intense sun can make them unstable. Give cornices a wide berth when travelling around them and avoid travel below them.


Avalanche Problem #2

WetAval

It is hard to pin down the exact elevation of the rain/snow line this morning, but, regardless, wet avalanches will be a problem today. Rain on snow is never a good thing. We could see the whole gamut of wet avalanches today: wet loose, wet slab, and maybe even glide avalanches. Rain can accelerate the glide process so we can’t rule those out. Wet, loose avalanches can start as small point releases, but are able to entrain recent storm snow and present a slow moving but increasing hazard particularly near terrain traps. Wet slabs are difficult to predict but rain on this new storm snow could cause wet slabs at mid and lower elevations. Avoid slopes greater than 35 degrees and think about turning around when it begins to rain as conditions can change rapidly.


Avalanche Problem #3

Deep Slab

Deep slabs are still a problem given the weak snow found in shallow areas (video) as well as the rain crust from early March. Though these layers are deeply buried and difficult to trigger the possibility of an avalanche breaking on these layers still exists. The recent load placed on the snowpack combined with a human trigger in the right spot may be the tipping point for a deep slab. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. While the chances of triggering a slide on these layers may be low the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.


 BOTTOM LINE

With continued new snow, strong wind, and rain on snow  the avalanche hazard is CONSIDERABLE on most slopes and  HIGH on wind loaded slopes steeper than 35 degrees above 6,000 feet. This means that human triggered avalanches are likely, particularly on steep wind loaded slopes, and natural avalanches are possible to likely. Tricky and dangerous avalanche conditions exist so conservative decision making and terrain selection will be important today. Avoid wind loaded slopes and slopes steeper than 35 degrees. Recent and new wind and storm slab instabilities exist at higher elevations with wet avalanche problems at lower elevations. Periods of heavy snow, rain, and daytime warming effects can quickly change the likelihood of avalanches and the hazard could rise if more snow and rain fall than expected. 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

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 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Information Update – 3/28/2014

Good Morning! This is Erich Peitzsch with the Flathead Avalanche Center with an avalanche information update. The next regularly scheduled advisory will be issued Saturday, March 29, 2014. 

Mountain Weather

A moist system moved through the advisory area yesterday and overnight dropping 6-9 inches of new snow and 0.5 – 1.5 inches of SWE.  Storm total from the past 24 hours at SNOTEL sites and remote weather stations:
Noisy Basin (Swan Range): 10 inches snow, 1.5 inches SWE.
Stahl Peak (Whitefish Range): 7 inches snow, 1.0 inches SWE.
Flattop Mountain (Glacier Park): 6 inches snow, 0.4 inches SWE.
Pike Creek (Flathead Range): 7 inches snow, 0.3 inches SWE.
Shed 7 (Glacier Park): 6 inches snow.

Temperatures currently range from 22-29° F with winds out of the southwest at 5-20 mph and gusts into the 30 mph range. Another moist system moves into the region this afternoon/evening with snow levels potentially up to 5000 feet.

Snowpack Discussion

Substantial weight was recently added to the snowpack, particularly in the Swan Range which saw the largest accumulation of 1.5 inches of SWE in 24 hours. Weak layers and crusts are now buried by this new snow with additional wind transported snow from strong winds.  Expect to encounter storm slabs and wind slabs on any aspect, and cross loading can create wind slabs in gullies and exposed terrain features at any elevation. Surface crusts previously existed on all but the most shaded slopes from the most recent warm and sunny periods. These crusts provide a great bed surface for this new snow to slide on. Allow the snowpack time to adjust to this new load, and avoid steep and wind loaded slopes. Avalanches can fail within the new storm snow or at the new and old snow interface. Of course, these avalanches still have the potential to step down into deeper weaker snow in the snowpack as we still contend with a deep slab avalanche potential. Also be aware of avalanche terrain above you and avoid runout zones of avalanche paths.

The next regularly scheduled advisory will be Saturday, March 29, 2014.

 

Avalanche Advisory – 3/23/2014

THIS ADVISORY HAS EXPIRED

Issued: March 23, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Sunday, March 23, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Wednesday, March 26, 2014.


MOUNTAIN WEATHER

WeatherGraphicYesterday’s sunny weather transitioned to a quick moving disturbance that dropped 1-6 inches of new snow overnight throughout the advisory area. Winds shifted back to the southwest yesterday. Currently, remote weather stations and SNOTEL sites report temperatures from 18 to 23 °F with winds out of the southwest at 5-15 mph and gusts into the 20 mph range. Snowfall should taper through the day and may linger in locations closer to the Continental Divide. Expect another 1-3 inches through the day with temperatures in the mid-20s to mid-30s F. Wind should be out of the west today at 10-20 mph. High pressure builds into the region tonight into tomorrow bringing drier weather.

Storm totals over the past seven days:
Flattop SNOTEL: 33 in. snow, 4.4 in. SWE
Stahl Peak SNOTEL: 24 in. snow, 3.8 in. SWE
Noisy Basin SNOTEL: 20 in. snow, 3.0 in. SWE
Pike Creek SNOTEL: 16 in. snow, 0.6 in. SWE
Shed 7 weather station: 31 in. snow


RECENT OBSERVATIONS

RecentObservationsGraphic

Given that wind slab is our primary concern we traveled in the Lewis Range in the southern part of Glacier National Park yesterday on the hunt for this problem. We found them particularly above 6500 feet. We observed both hard and soft wind slabs on numerous aspects. These slabs were shallow (less than a foot) in the areas we investigated, but we purposefully stayed away from large, steep, wind loaded slopes. These slabs failed easily in stability tests (video) and we also observed minor cracking of wind slabs on small rollover test slopes. BNSF Avalanche Safety also observed active wind loading on Thursday in an adjacent area (observation). We also observed a skier triggered slab in Cascadilla Creek drainage (Flathead Range) yesterday morning (photo). We are not sure on the exact timing, but it occurred before Saturday morning.

We also observed weak faceted snow near the ground that failed and propagated in our stability tests (profile), and is still a concern for persistent slab potential in areas of shallow snow. These results are consistent with BNSF Avalanche Safety observations over the past 10 days in a nearby area.

The early March rain crust is noticeable in every snow pit, and appears to be behaving itself so far. However, on Thursday in the northern Whitefish Range, this layer showed the potential to propagate a fracture in our stability tests (video). On Friday, Todd was in the Six Mile Peak area in the Swan Range where he observed active wind drifting on high peaks. He found the early March rain crust buried 2-3 feet deep and the snow above and below was fairly consolidated relative to the rest of the snowpack (photo).

Skiers in the southern Whitefish Range yesterday noted a sun crust that formed Friday afternoon on most sun exposed slopes, but found soft, unconsolidated snow on shaded aspects with no obvious signs of instability and small recent activity on sun exposed slopes from Friday.

 

Cascadilla Creek basin, Flathead Range ,Middle Fork Corridor. Observed 3/22/2014.

Cascadilla Creek basin, Flathead Range ,Middle Fork Corridor. Observed 3/22/2014.

General snow profile on east aspect in the Six Mile Peak area. Swan Range 3/21/2014

General snow profile in the Six Mile Peak area. Swan Range 3/21/2014

Generalized image of upper snowpack highlighting the March 9 rain crust about 2-3 feet below the surface. Red Meadow, Whitefish Range. 3/20/2014.

Generalized image of upper snowpack. Red Meadow, Whitefish Range. 3/20/2014.


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabThe recipe for wind slab formation exists with over 20-30 inches of new snow in the past seven days accompanied by strong winds. The new snow overnight has even slightly buried these wind slabs so they may not be as obvious or visible. It can take up to a week for wind slabs to stabilize. These wind slabs are sensitive particularly along ridgelines and cross-loaded terrain features like gullies. Recent north winds also caused drifting snow along high elevation ridgelines potentially forming new wind slabs on slopes that are typically windward. Avoid wind loaded terrain steeper than 35 degrees and stick to non-wind affected slopes. In addition to wind slabs, cornices formed over the season can become particularly sensitive this time of year. Longer days with even short periods of more intense sun can make them unstable. Stay well clear of cornices when travelling near them and avoid travel below them.


Avalanche Problem #2

Deep Slab

Though deeply buried and difficult to trigger, the late January/early February crust/facet layer in addition to weak, faceted snow near the ground still lurks in the snowpack. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. The rain event that provided the trigger for that large avalanche cycle in early March formed a thick rain crust that now sits about 2-3 feet from the surface. This layer has shown instability in recent stability tests. The chances of triggering an avalanche on these layers may be low, but the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether. 

 


Spring can bring a mixed bag of weather and snow conditions. While overnight storm amounts aren’t particularly impressive, this new snow came in with warmer temperatures than the previous snow over the past 48 hours. Above freezing temperatures combined with any sunshine this afternoon could cause loose, wet sluffs. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions this time of year. Pay particular attention to sun exposed slopes as the day progresses.


BOTTOM LINE

For today, the overall avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes and areas of shallow snow where deeper instabilities exist in the snowpack. It is also possible to trigger an avalanche within the recent storm snow from over the past week. Wind loaded slopes above 6500 feet and steeper than 35 degrees are rated as CONSIDERABLE meaning that human triggered avalanches are possible to likely in these areas. Avoid wind loaded slopes particularly at upper elevations, along ridges, and on convex rollovers.

Moderate_2

 Considerable

 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

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 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Advisory – 3/19/2014

THIS ADVISORY HAS EXPIRED

Issued: March 19, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Wednesday, March 19, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, March 22, 2014.


MOUNTAIN WEATHER

WeatherGraphicThe most recent storm dropped up to 10-18 inches within our advisory area and tapered late Monday night (SNOTEL and remote weather stations). Winds gusted into the 25-30 mph range. Partly to mostly cloudy skies dominated yesterday with moderate wind. Currently, mountain temperatures range from 17-25 °F with winds out of the southwest at 5-30 mph with gusts to 45 mph in southern Glacier Park. No new snow fell overnight, but another disturbance rolls through the area this afternoon through tomorrow. Today, temperatures should range from the mid-20s to low 30s F with winds 10-20 mph and gusts to 30 mph. Snow should begin this afternoon and we could see up to 6 inches by tomorrow morning at upper elevations within the advisory area.


 RECENT OBSERVATIONS

RecentObservationsGraphic

On Tuesday we traveled in the Middle Fork corridor of the northern Flathead Range. We found up to 12-18 inches (30-45 cm) of new snow. On leeward slopes we found sensitive wind slabs (photo). These were easily triggered and up to a foot thick. As they traveled downhill they would entrain both dry and wet (depending on aspect and elevation) sluffs that ran several hundred vertical feet. These sluffs were also fairly easy to trigger on steep, small test slopes (photo).

We also found the early March rain crust about 30 inches (80 cm) from the surface (profile). This crust is about 8 inches (20 cm) thick and harbors softer moist, weak snow below it (video). Most sun exposed slopes formed yet another sun crust on the surface by late in the day. The new snow on these slopes became wet and heavy throughout the day.

BNSF Avalanche Safety reported three small soft slab avalanches in John F. Stevens Canyon in southern Glacier Park yesterday involving the new storm snow. These occurred on high elevation east facing slopes and probably during the storm on Monday (photos). These slabs ran about 100-200 vertical feet. They also reported 12 inches (30 cm) in the canyon floor and 18 inches (45 cm) at upper elevations.

Skiers in the Essex area in the Flathead Range on Monday reported a few natural sluffs within the new snow and localized cracking while skiing during the storm. They found various layers to be somewhat reactive with moderate to hard force in their stability tests including the layer of moist, weak snow below the thick early March rain crust.

We received no observations from the Swan Range or the Whitefish Range so our confidence in these areas is fair.

Wind slabs were sensitive and easy to trigger. They weren't very wide, but were up to a foot deep. 3/18/2014.

Wind slabs were sensitive and easy to trigger. They weren’t very wide, but were up to a foot deep. 3/18/2014.

Both loose wet and loose dry avalanches were easy to trigger on slopes steeper than 35 degrees. 3/18/2014.

Both loose wet and loose dry avalanches were easy to trigger on slopes steeper than 35 degrees. 3/18/2014.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.


 SNOWPACK DISCUSSION

Avalanche Problem #1

Wind Slab

Wind slabs were easy to trigger yesterday, and should be again today. Increasing winds and a bit of new snow this afternoon will continue to form wind slabs. These slabs weren’t particularly wide, but even a slab up to a foot deep can have high consequences. The slabs observed by BNSF Avalanche Safety occurred on easterly aspects which were loaded by wind during the recent storm. Look for and avoid convex pillows of wind-drifted snow on the lee side of ridges and other terrain features. Wind slabs are confined to leeward slopes and cross-loaded terrain features and can be avoided by sticking to sheltered or wind-scoured areas. 


Avalanche Problem #2

Persistent Slab

Several layers within our snowpack pose a persistent slab and deep persistent slab threat. The late January/early February crust/facet layer that was the weak layer responsible for the large, natural avalanche cycle almost two weeks ago still lurks. Even though it is buried deeply the possibility for avalanches to fail or step down on this layer still exists, particularly in areas of shallow snow as demonstrated by BNSF Avalanche Safety less than a week ago (video). The rain event that provided the trigger for that large cycle formed a thick rain crust that now sits about 2-3 feet from the surface. Weak, moist snow sits below this crust and is also a concern. While we have yet to hear or observe any reactivity of this layer it cannot be ruled out as a potential persistent slab problem. These layers may be harder to trigger now, but the consequences of an avalanche breaking on these layers are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.

Also, cornices are ripe and ready to fail especially during times of warm weather or rain. They can trigger deeper layers when they hit the slope so stay off of and out from underneath these giant monsters.


Oh, Spring in northwest Montana! Spring can bring a mixed bag of weather and snow conditions. It is not uncommon to have sun, snow, and rain in the mountains all in one day during this time of year. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions. Pay particular attention to sun exposed slopes as the day progresses as well as rain on snow as wet avalanche conditions can change quickly.


BOTTOM LINE

For today, the avalanche hazard is CONSIDERABLE on wind loaded slopes and MODERATE on all other slopes This means that human triggered avalanches are likely on slopes where wind formed sensitive wind slabs. Deeper instabilities within the snowpack exist and it is still possible to trigger an avalanche on these deeper layers particularly in areas of shallow snow and steep slopes. It is also possible to trigger an avalanche involving the recent storm snow. Cautious routefinding and conservative decision making are essential. Identify areas of wind drifted snow and weak layers buried deeper in the snowpack and avoid these areas.

Considerable

 

Moderate_2 

 


 

Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

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 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.