Spring Avalanche Safety Considerations

In previous years we’ve seen many big snow storms pass through western Montana in April and May, this year should be no exception.  These spring snows typically come in at much warmer atmospheric temperatures so it tends to bond to the old hard snow surface and settle quickly.  The storm snow avalanche hazard usually abates within 24-48 hours.

Recently wind loaded terrain steeper than 35 degrees should be treated with caution during and immediately after a storm.

As soon as skies clear and temperatures warm above freezing, the wet snow avalancheAn avalanche caused by snow losing its strength after becoming damp, moist or saturated with water. danger can escalate especially on steep slopes that have recent new snow.  These wet slides can entrain a lot of snow and potentially step down into the deeper, weaker snow at the ground.

Be alert to what the temperature is doing and watch slopes that have early exposure to the sun.  Wet, point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet snow avalanches area good sign that slope stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). is rapidly decreasing.  Once you see these, or start punching through the upper snowpack, move to the more shaded northerly aspects.

Much of our area has already been through several days of melt down and even rain up to 7000 feet so the bottom of the snowpack is wet and rotten and now capped with a solid melt-freeze layer several inches thick.  Several melt-freeze cycles will allow for good skiing and riding conditions early in the day or during cool weather.  Once it warms up again, pay attention to how the snow feels.

Cornices can be very touchy this time of year.  The best advice we can offer is to stay well back on the windwardThe upwind side of an obstacle such as a ridge. Usually snow is eroded from windward slopes making them relatively safer. side of ridges and avoid travel directly underneath them.  Big cornices have a nasty habit of breaking further back than you might expect and can entrain a lot of snow, kind of like a bulldozer, as they roll downhill.

Thank You!

We’re at the end of what will be remembered as an exceptionally safe winter. There were no avalanche fatalities in Montana this winter!  It’s been a long time since we could say that.  Locally, we issued only one warning for high avalanche danger in early January and investigated one avalanche incident that had a positive outcome (details here).

This can be attributed to a mostly stable early season snowpack, good assessment skills by many of you and, in some cases, shear luck. More people are recreating in avalanche terrain than ever and this year is no exception.

Our Friends group, the West Central Montana Avalanche Foundation (WCMAF), really stepped up to the plate this year.  The level of service we provide would not be possible without their monetary support.  This partnership between the Lolo Forest and the WCMAF has been very successful and will continue for many years, but it needs your continued support.  100% of the local fund-raising efforts by the WCMAF along with your donations pay for data collection, avalanche advisories and public avalanche education programs in west central Montana.

Thanks to all of you for your dedication to staying safe and for your support of the avalanche advisory and education program here.  Have a safe, excellent summer and we’ll see you again next season!

Steve Karkanen, Dudley Improta, Tim Laroche.

Good morning!  This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Friday, April 5, 2013.  This is the final avalanche advisory for the season.  Springtime avalanche information will be posted in the next few days.

Weather and Snowpack

A cold front is passing through western Montana this morning with light precipitation.  Mountain temperatures are in the 30′s with SW winds 10-15 with gusts to 40 mph.  Nighttime mountain temperatures have remained above freezing for several days now.

Yesterday, we found mostly stable and hard snow early in the day. By 1 pm,  all but the more northerly aspects were punchy and difficult to ski, especially near rocky areas or trees. Many point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet slides and roller balls were observed on the steeper slopes above 6000 feet.

The forecasted cooler weather arriving today will set things up like concrete.

What’s Important Now

Mountain temperatures are expected to drop below freezing which will make for great travel and stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). conditions.  Until then, it will be important to avoid steep open terrain during warm or sunny days, or during periods of rain.  Easily punching deep into the snow or seeing pinwheels gaining size are good clues that it’s time to move to safer terrain.

Weather Forecast and Avalanche Outlook

Missoula Weather is forecasting a series of wet weather systems to pass over our area starting today.

A cold front is predicted to move into the area with snow levels expected to drop from 6000 feet today to 4000 feet by Sunday. Winds are expected to be in the 10-15 mph range from the SW with 3 to 5 inches of snow.

With these cooler mountain temperatures, the avalanche danger will remain LOW.

When temperatures climb above freezing, there will be an increase in the risk of wet snow avalanches especially at elevations that receive new snow.

Season End

We’re at the end of what will be remembered as an exceptionally safe winter. No avalanche fatalities in Montana this winter!  It’s been a long time since we could say that.  Locally, we issued only one warning for high avalanche danger in early January and investigated one avalanche incident that had a positive outcome (details here).

This can be attributed to a mostly stable early season snowpack, good assessment skills by many of you and, in some cases, shear luck. More people are recreating in avalanche terrain than ever and this year is no exception.

Thanks to all of you for your dedication to staying safe and for your support of the avalanche advisory and education program here.

A general springtime avalanche safety information statement will be posted in the next few days.

Conditions are generally safe, but unstable snow may exist on isolated terrain features.  Isolated pockets of instability may be found in steep, rocky areas where the snowpack is thin or on terrain steeper than 35 degrees exposed to the sun.

Good morning! This is Steve Karkanen with the Friday, March 29,  avalanche advisory from the West Central Montana Avalanche Center.

Weather and Snowpack

Very little (if any) precipitation fell in the mountains since Tuesday.  SNOTEL sites have been recording afternoon temperatures in the forties and fifties with overnight readings dropping below freezing.  This morning, temperatures are just above freezing with 15 mph southwest winds. Temperatures are expected to warm a couple of degrees beyond yesterdays high temperature.

The overall snowpack stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). is very good.  Last week’s new snow is well consolidated and has gone through a few melt freeze cycles.

Melt-freeze cycles strengthen snow and can create great skiing and travel conditions. It’s not quite like the corn snowLarge-grained, rounded crystals formed from repeated melting and freezing of the snow. the ski areas now have but it’s close.

What’s Important Now

The biggest hazard will be loose snow avalanches on terrain steeper than 35 degrees during warm afternoons.  Seeing pin wheels, point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet slides or sinking up to your knees in wet snow are good indicators of changing and possibly more dangerous conditions.  Move to the more shaded and cooler terrain.

Large cornices can be especially touchy and unpredictable during warm weather so avoid walking or riding on or underneath them.

Weather Forecast and Avalanche Outlook

A weak disturbance is moving through the area this morning with widespread shower activity with snow levels above 6000 feet.  A ridge of high pressure will build over the Northern Rockies Saturday and Sunday causing a warming and drying trend. Temperatures will be near to slightly above normal for this time of year. This means freezing temperatures overnight and warm temperatures in the afternoon.

Expect LOW avalanche danger in the morning increasing to MODERATE on steep terrain in the afternoon.

I will issue the final avalanche advisory for the season next Friday, April 5, 2013.  Have a safe and sunny weekend!

On sunny days or whenever the surface temperature warms to 32 degrees F on slopes steeper than 35 degrees, the avalanche danger will increase to MODERATE (Level 2). Expect to see point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet snow avalanches involving the new snow we received this past week.  Some of these can get quite large on the longer paths as more snow is entrained as they move down slope.

Good morning, this is Steve Karkanen with the Tuesday, March 26, 2013 avalanche advisory from the West Central Montana Avalanche Center.  This will be the final Tuesday avalanche advisory for the season.

Weather and Snowpack

In the past week our mountains picked up anywhere from 8 to nearly 16 inches of new snow through Saturday. Mountain temperatures have stayed below normal for this time of year which made for exceptional skiing and riding this past weekend. The clouds cleared Sunday and although air temperatures remained cool, the sun rapidly warmed things up especially on any slope with a steep sun angle.

With the cooler and clear conditions all aspects on the north half of the compass remain powdery while aspects on the south half get baked.  This snow bonded well to the crustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind. that formed more than 10 days ago and no major sloughs or loose snow avalanches were seen or reported on the steep lines people were skiing this weekend.  Many skiers and riders reported wet snow conditions on the southerly aspects by early afternoon Sunday.

Temperatures dropped back into the teens again early Monday then warmed into the thirties by afternoon.  This morning, temperatures are in the twenties and are expected to ramp back up into the forties this afternoon.  Ridge top winds are light this morning.

What’s Important Now

This diurnal temperature variation puts all but the most shaded snow into a melt/freeze cycle, which is good for stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human)., maybe not so good for skiing. For a sled however, this is go-anywhere snow. You just have to pay attention to the steep, sunny aspects and avoid them when things warm to the melting point.

Seeing pin wheels, point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet slides or sinking up to your knees in wet snow are good indicators of changing and possibly more dangerous conditions.  Move to the more shaded and cooler terrain.

Cornices grew even bigger during the 40-70mph winds we experienced last week and they will be touchy as it warms up.  Give them a wide berth. Don’t tempt fate by hucking off of or high-marking a slope directly underneath one of these monsters.

Weather Forecast and Avalanche Outlook

Missoula Weather is forecasting a ridge of high pressure to linger over the Northern Rockies for much of the week. The atmosphere will continue to warm and there’s a chance for minor showers. Temperatures above 6000 feet will continue dropping well below freezing at night and warm into the forties in the afternoon.

Avalanche danger will remain similar under these conditions with LOW danger on most slopes bumping up to MODERATE on steep terrain exposed to the sun.

I will issue the next advisory this Friday, March 29, 2013.

Friday, April 5, 2013 will be the last advisory of the season.

The avalanche danger is LOW on terrain that does not have a wind load and is less steep than 35 degrees. Small avalanches in isolated areas or extreme terrain.

Good Morning. This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Friday, March 22nd, 2013.

Weather and Snowpack Analysis

All advisory area locations picked up fresh snow the past few days. Most mountain locations picked up 4-7 inches of new snow since Wednesday. The wind blew hard from the west and southwest, gusting into the 40 mph range at times (photo). Temperatures hovered in the twenties. This morning at 4am, winds have calmed to 4-6 mph out of the west and southwest, temperatures are generally in the teens, and widely scattered light snow continues to fall.

The relentless wind this past week created soft and hard wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. on leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. slopes and terrain features at upper and mid elevations. During stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). testing, we are getting the soft slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. to fail on a melt-freeze crustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind.A Melt-Freeze CrustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind. results from a period of melt-freeze metamorphism and is typically a few centimeters thick. that is buried 1-2 feet deep. These 3 pit profiles highlight the layer of concern in 3 different locations (profile, profile, profile). This weakness is mostly found on the coldest aspects of north and northeast that have not experienced the sun exposure that other aspects have this past week. These are also the aspects that received the most wind load and where you will find the softest skiing and riding at upper elevations. The hard wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. that formed are smooth, rounded, and hollow sounding and can be found on multiple aspects. They will be stubborn to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche ., but could break 1-2 feet deep and well above you on a slope.

The secondary avalanche concern is for loose snow avalanches in steep terrain. The new snow we are receiving is coming in cold and will easily sluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff. on the buried melt-freeze layers that formed this past week. When the sun comes out, it will quickly warm the new snow and loose wet slides will be a concern on aspects exposed to the sun. These conditions are generally manageable, but should not be over-looked if you are recreating in high consequence terrain.

The snow and wind we have been receiving continues to add weight to the hefty cornices that now hang above leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. slopes. These tend to break further back than one might expect. Use caution when recreating around these features.

Weather Forecast and Avalanche Outlook

Cold temperatures and scattered snow showers will stick around through the weekend, but we should see much less wind than recent days. Most advisory area locations should receive another 2-4 inches of new snow. High temperatures will be in the twenties and lows in the teens to single digits. Winds will be out of the northwest at 6-10 mph.

Cold temperatures will likely help to keep the upper snow pack instabilities weak. Therefore, I expect the avalanche danger to remain at the MODERATE level.

Steve will issue the next advisory on Tuesday, March 26th.

If you get out and have the time to send us some information about what you are seeing, please use our “public observations” link on our website or send us a quick note at info@missoulaavalanche.org. Thank you for your continued support!

Have a Great Weekend!

Good Morning. This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Tuesday, March 19th, 2013.

Weather and Snowpack Analysis

Winter returned to west central Montana the past few days with a juicy storm that deposited over 20 inches of new snow in the Bitterroot, southern Mission, and southern Swan Mountains since Sunday. The Rattlesnake Mountains received about a foot of new snow. This latest storm dramatically improved skiing and riding conditions throughout our advisory area. The wind blew hard, gusting in the upper 30 mph range from the west and southwest until switching to the northwest late last night and calming to the mid teens. Currently, the bulk of the storm system has exited to the east, mountain temperatures are hovering in the low twenties, and winds are blowing from the west at 15-20 mph.

The primary avalanche concern is fresh wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. that have formed on upper elevation ridgelines and cross-loaded gullies. The new snow sits on a stout melt-freeze crustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind.A Melt-Freeze CrustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind. results from a period of melt-freeze metamorphism and is typically a few centimeters thick. that developed last week during warm weather and has now frozen. During field assessments yesterday, we found the new snow bonded to this crustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind., but you will have to assess each slope to see if this is the case where you are recreating. On Sunday, skiers in the Bitterroot Mountains turned around when they experienced instabilities created by the storm snow that had not yet bonded to the underlying surface (public observation).  The new snow should settle out fairly quickly, but until it does be aware of the potential to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . fresh wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. that formed the past few days.

The secondary avalanche concern is for storm snow avalanches. There are variable weaknessesA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. in the new snow due to differing temperatures and precipitation rates. These weaknessesA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. will be sensitive to human triggers today on steep slopes. The storm snow is fairly cold, so expect loose snow avalanches in steep terrain where the wind has not yet formed a slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.. These sluffs could catch and carry you down slope if you are not suspecting them.

Watch for the snow to change today on aspects that receive sun. Wet loose slides will occur as the sun comes around and warms the southerly facing aspects. Stay off and out from underneath any steep slopes that start to get damp. Visual indicators are small point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. slides starting from rock outcrops and pinwheels that roll down steep slopes and gather snow as they descend.

Weather Forecast and Avalanche Outlook

Today will be a mostly dry day under a slight ridge of high pressure. Winds will be light out of the south with temperatures reaching the mid 30’s under partly cloudy skies. Beyond today, expect another round of precipitation and for unsettled weather to continue through the week.

I expect the avalanche danger to decrease as the new snow settles and until the next cold front arrives and delivers another round of precipitation.

I will issue the next advisory on Friday, March 22nd.

If you get out and have the time to send us some information about what you are seeing, please use our “public observations” link on our website or send us a quick note at info@missoulaavalanche.org. Thank you for your continued support!

Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s advisory for Friday March 15, 2013.

Weather and Snowpack Analysis

Mountain temperatures did not reach the freezing point last night. Temperatures are in the thirties and forties. High elevation winds are strong out of the west and southwest gusting 20 to 30mph. The winds aren’t moving snow though, the warm temperatures have made things quite heavy. The warming has lasted a few days. Many mountain locations in the region have stayed above freezing for over 48 hours.

The warm temperatures have settled out the wind-slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. potential but made the surface snow quite weak. I observed lots of debris in the Rattlesnakes yesterday from ubiquitous loose, wet snow releases (photo 1) (photo 2).  Observers in the Lost Trail area noted debris from loose, wet avalanches on steeper slopes. Most of the wet releases at Lost Trail and in the Rattlesnakes were observed on slopes with northerly aspects. Steve was in the Bullion Pass area (southeast of Lookout Pass) and found loose, wet unconsolidated snow also.

We had a second hand report of wet avalanches that ran to the ground in the southern Swans. Steve did find water pooled on crusts in the snow and near the bottom of the snowpack in his pits southeast of Lookout Pass. This is something to keep in mind on very open, big unanchored slopes.

The Bottom Line

The Moderate danger is related to terrain and timing. On slopes steeper than 35 degrees, expect the danger of wet slides to elevate during the warmest part of the day.  Rain above 6000 feet will also increase the avalanche danger.  The chances for corniceA mass of snow deposited by the wind, often overhanging, and usually near a sharp terrain break such as a ridge. Cornices can break off unexpectedly and should be approached with caution. failure increase as the warming causes the entire snowpack to creep downhill.

Weather Forecast and Avalanche Outlook

Forecasts call for temperatures to be a few degrees cooler today. Rain is predicted for up to 6000 feet on Saturday; then a return to winter may happen (weather story). The colder temperatures will stiffen things up and likely stabilize the snowpack. Snow is expected to accompany this change in the weather; time will tell if the weekend system produces enough snow to create surface instability. New snow would be welcome; with the warm temperatures we’re experiencing, and the cold change predicted, backcountry skiing and riding conditions might prove challenging.

Public Observations

I would like to extend a note of thanks to all those who have sent in observations. Some are posted on the website; some folks request they not be posted. Some of the observations are just quick e-mails from an iPhone. The one thing they all have in common is they are valuable.

Consider sending in observations either this season or next. You can be vague about the area; maybe just name a drainage, aspectThe compass direction a slope faces i.e. North, South, East, West. and elevation. The more info we have, the better the advisories. Observations aren’t for the avalanche center; they’re for your compadres. If you would like to report on avalanche or snow conditions use our public observations form or send us a note at info@missoulaavalanche.org .

Tim will issue the next advisory on Tuesday, March 19.

Ski and ride safe and have a great weekend.

Good Morning! This is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for Tuesday, March 12, 2013.

Weather and Snowpack Analysis

Mountain temperatures are mostly in the mid-twenties this morning. Above 7000 feet, winds are blowing at 20mph, generally out of the west and northwest. Wind, warm temperatures and light accumulations of snow were the weather story over the weekend. Yesterday, weather stations recorded winds steady in the 20mph range, with gusts to 40mph at 7000-8000 feet. Temperatures reached 38 degrees F at 7900 feet in the Bitterroots on Saturday.

While the warm temperatures have helped settle the snow; the relentless winds have moved what snow was available to the leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. slopes and created unstable pockets with wind-slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.. On Saturday we had a report of a skier-triggered wind-slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. on a northeast aspectThe compass direction a slope faces i.e. North, South, East, West. at 8000 feet in the southern Missions. This wind-slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. was 12 inches deep and ran a 100 feet. Yesterday, in the Rattlesnakes, Steve and I found small, sensitive wind-slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. on an east aspectThe compass direction a slope faces i.e. North, South, East, West. at 7100 feet. We could observe snow being transported on more open, exposed ridges.

The other avalanche problem is a persistent weak layerA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. that has been noted in observations from the Rattlesnakes to Lost Trail Pass. This weak layerA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. formed in February and continues to show some energy when it fails in our stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). tests (VIDEO) . This is a classic “low probability/high consequence” avalanche problem. This situation seems to be confined to high elevations where the snowpack is 5 feet or less in depth.

The Bottom Line

Our snowpack is mostly stable, although the warm weather has limited opportunities to ride soft powder. Wind-slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are a potential problem on steep, open, exposed slopes above 7000 feet. The persistent layer (mentioned above) deserves consideration if riding or skiing steep terrain above 7000 feet; particularly if the total snow depth is less than 5 feet. During the warmest parts of the day or if it rains at elevation (yes, spring is coming), steer clear of the large cornices that have developed.

Weather Forecast and Avalanche Outlook

Accumulations of snow should be on the light side this morning. High pressure is expected to build this evening with” warmer than normal temperatures”.  Some precipitation is expected Wednesday with rain up above 6000 feet by Thursday.

If the winds abate, and with the warmer temperatures predicted, I would expect the snow to settle. However, possible rain above 6000 feet has my attention. The immediate effect of the rain will destabilize the snow and the large cornices.

If you would like to report on avalanche or snow conditions use our public observations form or send us a note at info@missoulaavalanche.org .

I will issue the next advisory on Friday, March 15.

Ski and ride safe and have a great week.

The avalanche danger may quickly rise to CONSIDERABLE (Level 3) for wet snow avalanches on steep slopes exposed to solar radiation today and through the weekend.

Hello!  This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Friday, March 8, 2013.

Weather and Snowpack

Short, intense pulses of moisture moved through the area Wednesday and Thursday.  SNOTEL  sites report small gains in snow water equivalent (SWE or roughly 4-6 inches of new snow) since Tuesday. Higher ridges were again slammed by high winds that moved a lot of snow forming fresh wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. and gave already large cornices another growth spurt.

Mountain temperatures stayed mostly below the freezing point but in areas where the sun had a chance to warm the snow, wet point-release loose snow avalanches were observed on some steep slopes.  The forecast is for 2 or 3 days of nice sunny weather so I expect to see many of these avalanches on steep sun exposed terrain this weekend.

In shallow areas with a weaker snow structure, it is possible for the added weight of heavy wet snow moving down a slope to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . the more deeply buried facet layers we have been describing for the past few weeks.   It is a good idea to avoid these slopes when you start seeing roller balls or small point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. slides during warm sunny conditions.

At the sites where observers performed stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). assessments yesterday in the Rattlesnake, Lost Trail, Lolo, Hoodoo and Lookout Pass areas we are finding weak faceted snowAngular snow with poor bonding created from large temperature gradients within the snowpack. near the ground in shallow pockets and a more widespread and deeply buried persistent weak layerA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. on and under the crusts that formed in February.

These features are showing good strength but we get consistent propagationThe spreading of a fractureThe physical separation of the slab from the bed surface and surrounding snow during the initiation of a slab avalanche. or crackThe spreading of a fractureThe physical separation of the slab from the bed surface and surrounding snow during the initiation of a slab avalanche. or crack within the snowpack. within the snowpack. in extended column testing with fast clean shears (ECTP20 -22) in some pits in the Rattlesnake and near Lost Trail Pass.  Other pits on similar aspects and elevations don’t show this problem. The issue is trying to figure out where these features exist.  The only way to know for sure is to dig down and look for them.  We don’t find this to be a problem in snow deeper than 150-200cm (60-80″).  In the southern Swan for example, Tim and Dave checked on a much deeper snowpack (250cm) and felt that the avalanche danger there is LOW .

What’s Important Now

It’s hard to say what the biggest threat to your safety is right now. We have been at the MODERATE danger rating since the first week in February and don’t have any obvious stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). problems. We’ve been tempted to drop the rating to LOW but we continue to find many different types of land mines out there not to mention that we’re going into a period where the snowpack will be subjected to rapid change in many isolated pockets over a widespread area.

• Large, touchy cornices may very well be the biggest problem but they are so obvious and scary looking that I shouldn’t have to say anything more. These cornices are very sensitive now and will be dangerously unstable when it warms up.

• The primary and sneakier avalanche problem today is recently formed wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. on the upper portion of fetch areas on leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain at elevations above 7000 feet.  These slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. can take you for a nasty ride if you happen to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . one.
• Loose (dry and wet) snow avalanches.  Yesterday we were able to easily triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . small sluffs involving the newest dry snow on 40+ degree terrain. Later today and during the next couple of sunny days, wet, loose snow avalanches will be possible on steep, sun exposed terrain.
• Persistent weak layersA snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures.A snowpack layer with less strength than adjacent layers. Often the layer in the snowpack where an avalanche fractures. exist in shallow snow where wind has scoured and reloaded higher exposed terrain. You have to dig down to find this weakness. If you dig more than 3 feet down and don’t see it, it’s probably not a problem.

Weather Forecast and Avalanche Outlook

A broad trough of low pressure remains over the northern Rockies today with lingering showers. The atmosphere becomes unstable this afternoon slightly increasing the chance for showers.  Not much precipitation is expected.  The Missoula Weather Service Office is forecasting a ridge of high pressure to build into the weekend with clear skies and temperatures rising into the mid-thirties and low forties.  The ridge begins to break down by Sunday afternoon with increasing cloud cover and potential for light showers by Monday.

Expect the avalanche danger to increase to CONSIDERABLE if temperatures quickly rise above freezing and when the sun warms the snow on east-south-and westerly aspects.

Although we are in a mostly stable condition, snow does not like rapid change, and if the above forecast is true, it will be subject to rapid change this weekend.

Dudley will issue the next advisory on Tuesday, March 12.  Have a safe weekend!

On all other terrain and elevations the avalanche danger is LOW.  Natural and human triggered avalanches are unlikely. Small avalanches are possible in isolated areas or on extreme terrain.

Good morning, this is Steve Karkanen with the March 5, 2013 avalanche advisory from the West Central Montana Avalanche Center.

Weather and Snowpack

March came in like the lion it’s said to be with rain up to 6000 feet Friday, sunny and warm on Saturday, then cold, snowy and windy on Sunday. Monday was calm and cool.

SNOTEL sites recorded temperatures into the high forties on Friday and Saturday. By Sunday these same locations were recording temperatures in the teens and twenties.  This morning, mountain temperatures are in the low teens with a brisk south-southeast wind gusting into the twenties.

Most sites picked up a few inches of snow with the Rattlesnake and higher elevations in the Bitterroot each receiving close to a foot of new snow during the past few days. High northerly winds Sunday redistributed much of the new snow onto east and south facing aspects.

Tim and I toured into the Rattlesnake Monday and we received a great report from the Bitterroot near Hamilton from Doug Brinkerhoff who described much of the current concerns in his observation posted here yesterday.

What’s Important Now

• Once again, recently formed wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. are the primary avalanche problem.  Sunday’s high wind moved a lot of snow onto terrain that doesn’t normally see wind slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. formation.  The wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. we were seeing Monday were thin and stubborn, but it is still possible to get into trouble if you happen to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . one in gnarly terrain.
• Persistent slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers..  We still find one or two now deeply buried facet layers (about 25 to 30 inches deep) that react when enough force is applied in our stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). tests. This condition can be found in nearly all aspects and elevations above 7000 feet.  While it is unlikely to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . these with the weight of 1 person, a big shock in the right place may be enough to pull out a deep hard slabA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.. This is a classic low probability high consequence scenario that demands sticking to safe travel practices (one at a time) on steep terrain.
• Loose snow avalanches.  Tim and I found excellent dry powder on our tour in the Rattlesnake. This new snow is bonding to the old surface but on terrain steeper than 40 degrees it is possible to get it moving. On sunny days expect to see wet snow avalancheAn avalanche caused by snow losing its strength after becoming damp, moist or saturated with water. activity on southeast to southwest aspects.
• Cornices are now huge and can’t be trusted.  We’re hearing about and seeing several natural corniceA mass of snow deposited by the wind, often overhanging, and usually near a sharp terrain break such as a ridge. Cornices can break off unexpectedly and should be approached with caution. falls recently especially during the warmer days so avoid them as they are touchy and mean.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting a sunny morning today as a ridge of high pressure moves through the area. This afternoon, a moist southwest flow will raise potential for valley rain and mountain snow until late Wednesday when a cold front pushes into the area.  Snow levels will lower into the valleys but not much precipitation is expected with this system.

Expect the avalanche danger to slowly improve under the current conditions.  The angle of the sun is now high enough that solar radiation rapidly warms the snowpack during periods of clear skies.  The avalanche danger can quickly rise to CONSIDERABLE during these periods.

I will issue the next advisory on Friday, March 8.

Level 1 Avalanche Class

We are offering another Level 1 class next week. Details are here.  This class is limited to 8 students so register ASAP if you are interested.