Weather and Snowpack Analysis

The mountain snowpack in western Montana has experienced several melt-freeze cycles the past 14 days with afternoon temperatures reaching into the 40‘s and 50’s then dropping back into the twenties and teens. This back and forth (temperature exchange) has strengthened the snowpack greatly but there are a few exceptions to keep in mind. 

The weak faceted layers that formed in late January and February have not completely gone away and still fail cleanly during stability testing but only when shocked with an unusual amount of force. The important exception to this is when temperatures rise above freezing and stay there for several hours (especially overnight) or if rain water percolates down to one of these weak layers or an old crust.

We found a very strong, thick crust Thursday which struggled to warm up under partially sunny skies. Beneath this armor is a pencil hard snowpack that is still moist from the melting experienced during warmer weather the past few days.  Above 8000 feet the northern aspects will hold drier snow but even after a big storm, the powder days will be short lived.  Only an inch or two of snow has been recorded at advisory area SNOTEL sites this week.

The primary concern will be how well any new snow bonds to this hard surface with wind loaded terrain being the most sensitive after heavy snowfall.  Until it snows heavily or warms up, there is very little chance of triggering an avalanche.

SNOTEL sites report a trace of new snow with NW winds at Point Six hitting 27 mph at 0600 this morning.  Mountain temperatures are in the teens and low 20′s.

Weather Forecast and Avalanche Outlook

The Missoula office of the National Weather Service is forecasting a spring snow storm to impact areas south of Missoula Friday into Saturday with the Lost Trail Pass area having the best chance for significant accumulating snowfall. 9-15 inches of new snow is possible in the Lost Trail Pass area with less accumulation as the storm moves north.

High pressure builds back Saturday through Sunday with valley temperatures warming back into the 50′s and 60′s and mountain temperatures in the 40′s and 50′s. The high pressure ridge will remain for the early part of next week with temperatures warming 15 to 20 degrees above normal.

As temperatures remain close to seasonal norms, expect LOW avalanche danger in the mornings and on shaded slopes throughout the day. As the day warms up, the avalanche danger becomes MODERATE and the avalanche danger will quickly rise to CONSIDERABLE on aspects exposed to the sun or whenever temperatures remain above freezing overnight.

In locations that receive heavy new snow, pay close attention to how well the snow bonds to the now hard old snow surface. Expect this new snow to easily sluff on terrain steeper than 35 degrees immediately after a storm then again when it begins to be affected by warm temperatures or rain.

It’s a bad deal anytime it rains when you are playing on snow. Mostly because it isn’t any fun but more importantly rain quickly creates instability.

If this happens, expect the avalanche danger to rise to CONSIDERABLE or HIGH immediately.

Good clues of imminent avalanche danger in the spring are roller balls gaining size as they roll downhill, small point release avalanches entraining much larger amounts of snow or sinking easily past your boot tops or up to your knees in heavy wet snow. Move off of and out from under large open slopes and seek out the more shaded and cooler northerly aspects.

This is the last official advisory for the season but we will continue to post any observations sent in through the spring.  So please do send us your reports.  They are very helpful for the hard core skiers and riders chasing winter for as long as possible.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 30th, 2012.

Weather and Snowpack Analysis

The snowpack has been experiencing a melt-freeze cycle this past week. Daytime temperatures have been in the mid forties and nighttime temperatures have been in the mid twenties. Most locations received 1-2 inches of new snow and the wind has been blowing mostly out of the south at 8-10 mph and gusting into the low thirties. Currently, mountain temperatures are in the mid thirties, winds are blowing out of the south and west at 12-14mph gusting to 26mph with light snow above 7000 feet and light rain below.

We are now in a classic Spring like pattern of weather and snow. Most advisory locations have a thick and supportable crust on all aspects. Watch for this crust to break down and become wet if it gets rain or sun. This condition will increase the avalanche danger and produce wet loose slides on steep slopes. Once initiated, these slides could step down to deeply buried weak layers in the snowpack.

Observers in the northern Bitterroots reported deeply buried weak layers that were failing cleanly in stability tests. It took a lot of force for these layers to fail, but they did fail with a lot of energy. If this area receives heavy rain or snow, it will increase the avalanche danger. Observers in other locations are not reporting these deeper instabilities and the snowpack is generally more stable.

Where precipitation is falling as snow, it is falling on a variety of surface crusts. Watch for fresh wind drifts to fail easily on leeward ridgelines and cross-loaded gullies at the highest elevations. In the Rattlesnake area, we observed a thick layer of graupel on all aspects above 6500 feet yesterday. This condition will provide a slick sliding surface for any new snow deposited on top of it.

When the sun comes out this week, pay attention to how the snow is changing. It will warm the surface snow quickly and begin to produce wet loose snow slides in steep, rocky terrain first. This is a good indicator of changing conditions and decreasing stability. Stay off and out from underneath any steep exposed slopes, especially those with cornices or glide cracks.

Weather Forecast and Avalanche Outlook

A warm, moist weather system is entering our area and will affect the Northern Rockies through Saturday. We could see 6-10 inches of heavy, wet snow in the upper elevations and rain is likely below 7000 feet. Winds will be blowing out of the south and west with speeds in the 20mph range. Temperatures will be warm and the snow level should hover around 7000 feet until Saturday night, when a cold front arrives. The cold front will lower snow levels and could deliver another 6-10 inches of snow above 3000 feet.

In areas that experience heavy rain or snow, I expect the avalanche danger to rise through the storm period. Otherwise, I expect the avalanche danger to remain the same.

Steve will issue the last advisory of the season on Friday, April 6th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.

Hello, this is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Monday March 26, 2012.

Weather and Snowpack Analysis

Since Friday, mountain weather has moderated with temperatures climbing into the 40′s and 50′s  in the afternoons then dropping back to near freezing at night.  The sun was out in full force Sunday so many slopes with direct exposure to the sun were active with natural point release wet snow avalanches involving last weeks new snow.  SNOTEL sites this morning are reporting that overnight temperatures remained above freezing.

Continued warm temperatures are bringing the overall snowpack to an isothermal condition which means that the temperature of the snow is the same from the surface to the ground. In this case 0 degrees c or 32 degrees F.  When a snowpack becomes isothermal it becomes unstable. At least until it goes through several melt-freeze cycles giving melt water a chance to form channels and adjust to the change in condition.

Weather Forecast and Avalanche Outlook

An approaching weather system will bring a good chance for showers and cooler temperatures in the next 48 hours. Initially this storm comes in warm with rain possible at elevations above 6000 feet.  Any rain introduced onto the snow will immediately add weight and weaken the snow structure.  During periods of rain the avalanche danger on any slope steeper than 30 degrees will quickly escalate to CONSIDERABLE where human triggered avalanches are likely and natural avalanches are possible.

As the storm front passes and cools, the avalanche danger will drop back to a MODERATE condition where human triggered avalanches are still possible but natural avalanches unlikely. A solid freeze will lock things up tight.

This will be the last Monday avalanche advisory of the season.  We will continue to post regular Friday morning advisories until April 6 which will be the last planned avalanche advisory of the season.

Tim Laroche will issue the next advisory on Friday, March 30, 2012.

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for March 23, 2012.

Weather and Snowpack Analysis

Spring officially began Tuesday, and it can be cold and snowy or warm and sunny; yesterday it was both. Since Monday the advisory area received 12 to 18 inches of snow, packing up to 4 inches of snow water equivalent. The storms mainly hit the central to northern Bitterroots along the Idaho border. Variable winds accompanied the storms and loaded leeward slopes. Yesterday afternoon winds were predominately out of the southwest. The area should pick up another inch or two of snow this morning.

Slopes throughout the advisory area had surface releases on Wednesday. At Lolo Pass, where it rained up to 5000 feet on Wednesday, some slides on the road cuts went to the ground. This activity shows the immediate, destabilizing effect rain can have on the snowpack.

Yesterday, in the Rattlesnakes, we saw surface debris on all aspects from loose snow avalanches that ran on Wednesday; and one small soft slab avalanche that appeared to be skier or snowboard triggered. The Snow Bowl Patrol had a soft slab release on a southwest exposure with their explosives yesterday morning. We posted this video that shows some of the layers from this week’s storms.

Our main concern is the storm snow from the past week and the wind-loading that occurred. If you are recreating on steep slopes this weekend you should look for instabilities in the top 2 to 3 feet of the snowpack.

This week’s storm bypassed the southern part of the advisory area and things are a bit different. Near Lost Trail Pass, observers felt that wet slabs or large wet sluffs during the afternoon are currently the main avalanche concerns.

Any rapid warming or rain will immediately weaken the snowpack and the large cornices that have formed this year.

Weather Forecast and Avalanche Outlook

Light snow this morning should give way to a weak high pressure lasting through Saturday and Sunday. Sunday may see the warmest temperatures of the year (possibly in the high 40’s at 7000 feet) with a return to cooler conditions Monday.

The avalanche danger will rise with the very warm temperatures predicted. Any rain on the snowpack will also elevate avalanche danger. During warm temperatures and/or rain beware of the possibility of cornice failure.

If you head into the backcountry this weekend, as always, ski and ride safe!

Steve will issue the next scheduled advisory Monday, March 26.

As we slide toward the end of another great skiing & riding season; I would like to extend thanks to all the folks who posted public observations or sent us reports and information. We have a large forecast area and it helps to hear if you missed something or get a confirmation of the forecast. I believe everyone who uses the advisory appreciates those contributions.

There is LOW Avalanche Danger on all other terrain in the advisory area.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Monday, March 19th, 2012.

Weather and Snowpack Analysis

Advisory area locations picked up 7-12 inches of snow since Friday, the southern Bitterroot Mountains receiving the higher amounts. The winds were moderate out of the south and west and mountain temperatures were in the low to mid thirties during the day. Currently, temperatures are in the mid twenties, winds are out of the north and west at 5-8 mph, and it’s snowing.

The new snow we have received is bonding well to the sun crusts that developed early last week. It is settling quickly, but there are multiple weaknesses within the storm snow that are releasing easily on steep slopes with a human trigger. Watch for recently formed soft slabs and loose snow sluffs to fail easily on steep terrain. Standard sluff management techniques will work well to keep you from getting caught by the loose debris.

Look for fresh wind drifts on leeward sides of upper elevation ridges, as well as cross-loaded terrain features like gullies and sub ridges. These drifts are about a foot deep and should be mostly manageable if you are not caught by surprise.

The buried surface hoar layer, down 2-3 feet, that has been the cause of recent human triggered slides has continued to gain strength. This weak layer takes a lot of force to fail, but should still not be trusted. A slide initiated in the upper snow pack could step down to this layer. So, dig down and look for this weakness before you commit to a steep slope.

When the sun comes out this week, pay attention to how the snow is changing. It will warm the surface snow quickly and produce wet surface snow slides on the buried sun crust. When the snow starts getting damp, move off the slope in search of colder snow.

Weather Forecast and Avalanche Outlook

There is a Winter Weather Advisory posted for our advisory area until noon today. Forecasts are calling for an additional 3-8 inches of snow in the higher terrain of west central Montana. Temperatures will stay cool until Tuesday when the next storm system arrives. The wet storm pattern will stay with us delivering moderate amounts of snow until Thursday, when we should see a brief break in the active pattern.

I expect the avalanche danger to remain the same with small doses of new snow accumulations throughout the week.

Dudley will issue the next advisory on Friday, March 23^rd.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.

Heavy wet snow and a rain-on-snow scenario has elevated the avalanche danger overnight.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 16th, 2012.

Weather and Snowpack Analysis

Advisory area snotel sites are showing .8 to 1.6 inches SWE in the past 24 hours. The exception is Saddle Mountain, only recording .2 inches SWE. Mountain temperatures were in the low forties yesterday and are starting to cool back down to near freezing at 4am this morning near 7000 feet. Precipitation is falling as a mix of rain and snow. Winds are currently blowing 8-12 mph out of the south and east.

Areas near the Idaho border received 12-18 inches of snow this past weak. Other advisory area locations picked up 4-6 inches of snow. We are now seeing steady rain up to 7000 feet which will cause the snow to become saturated. Watch for heavy wet slides at all elevations until the temperatures cool down later this morning.

The warm weather and sun of last week helped to settle and strengthen the snowpack, but left a stout sun or melt-freeze crust on most aspects at all elevations. Observers reported mixed results on this crust yesterday in stability tests, but with heavy wet snow or rain now affecting most of the advisory area we can expect this crust to be reactive to the new load for the next 24 hours. The main concern today will be heavy, wet snow releases on the sun and melt-freeze crust in the upper part of the snowpack and density changes within the new storm snow.

The buried surface hoar layer, down 2-3 feet, that has been the cause of recent human triggered slides has continued to gain strength. This weak layer takes a lot of force to fail, but should still not be trusted. Yesterday, we found this weak layer buried almost 3 feet deep on a northeast aspect at 7400 feet. The faceted crystals are well preserved and still quite large. So, dig down and look for this weakness before you commit to a steep slope.

Cornices are big and have started to slump with the recent warm weather pattern. Keep your distance when traveling on ridges and move quickly if you have to cross beneath these features.

Weather Forecast and Avalanche Outlook

A cold front will continue to push into west central Montana this morning. Snow levels should fall causing the rain to turn to snow down to about 4500 feet. Snow is expected to continue today with totals ranging from 7-10 inches at higher elevations. Winds will be out of the southwest at 12-20 mph. I am expecting this warm, wet pattern to stay with us through the weekend bringing additional snow accumulations and fluctuating mountain temperatures.

I expect the avalanche danger to stay the same with the chance of more snow and fluctuating temperatures through the weekend.

I will issue the next advisory on Monday, March 19^th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.

Good morning, this Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for March 12, 2012.

Weather and Snowpack Analysis

The weather was sunny and warm Friday and Saturday and numerous wet surface slides were noted throughout the area. Some had significant debris; as you can see in this picture of a wet point release that ran Friday in the Rattlesnakes on a west slope.  A bit more cloud cover yesterday cooled things down a bit and mountain temperatures are much colder this morning. The cooler temperatures helped avoid the rapid warming in the afternoon and stabilized the snowpack.

The very warm weather created a melt-freeze crust on northerly aspects and a sun crust on southerly exposures. We can expect that any new snow will be sitting on these crusts. It started snowing yesterday and the Idaho border has picked up most of the snow (3 to 4 inches of new snow this morning).  The winds started picking up yesterday afternoon also; with gusts up to 50mph on the ridge tops. Steep leeward slopes will be most susceptible to producing small slides.

The persistent surface hoar layer from early February appears to have strengthened. We took this video yesterday to show the layer and the use of the Propagation Saw Test (PST). The PST works well to test a deeper weak layer for propagation. If a weak layer, you have identified with a Compression Test, will not propagate with the Extended Column Test, the PST may get that layer to react. Here is a link to a site that shows how to perform the PST.

Weather Forecast and Avalanche Outlook

It looks like we’re headed into a series of Pacific storm systems and the temperatures will warm again.  Snow levels will generally be above 4500 feet but the possibility of snow levels rising to 7000 feet exists on Wednesday.

I would expect the avalanche danger to rise with accumulations of wet, heavy snow. Remember the melt-freeze and sun crusts this new snow will be sitting on. With any rain at elevations up to 7000 feet the snow will become very unstable. Wind-loaded slopes and cornices will be very hazardous with high temperatures, wet snow accumulation and/or rain.

If you head into the backcountry this week, as always, ski and ride safe!

Tim will issue the next scheduled advisory Friday, March 16.

Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for March 9, 2012.

 Weather and Snowpack Analysis

On Monday Tim reported on a persistent weak layer from surface hoar that formed in the early part of February. This layer is the primary concern right now. Over the last week I have found this layer in snow pits near Lost Trail Pass, in the Rattlesnakes, and in the crown of an avalanche near Seeley Lake. It was the weak layer in this snowmobile-triggered avalanche that happened last Sunday. You can read Steve’s incident report from this link or look in the documents link on our home page.

Yesterday in the Rattlesnakes this layer was failing with high stability scores that indicate strength; but when it does fail,  it fails very clean with lots of energy. This layer is 80cm to 1 meter (2.5 to 3 feet) from the surface of the snowpack. Observers near Lookout Pass, Lost Trail Pass and Hoodoo Pass also noted this layer and the possibility of a failure. As you can see in this photo it is a significant slab.

We found the slab to be most reactive during the heat of the afternoon. I would be extra cautious in the afternoon and take note of when the surface snow starts to move (about 1pm yesterday). It’s great to get out in the mountains during the warm weather; pick your terrain carefully during the warmest part of the day.

A secondary concern would be steep wind-loaded slopes above 7000 feet. We got a report from Downing Mountain Lodge of skier triggered slabs on 40 degree slopes this week. The winds have been pretty fierce over the week and steep leeward slopes above treeline may harbor wind slabs.

The accident near Seeley Lake was a bad deal; it looks like a sledder from another party triggered the slide that buried two people (fortunately, they were dug out unscathed) and it appears to be a “hit  and run”. The third sledder may not have known or looked for people on the slope below him; either way he didn’t stick around. There are a lot of folks out there recreating; I will quote from Steve’s accident report:

“In this era of powerful machines and lightweight efficient skis there are many more people recreating in remote, often dangerous, terrain. It is paramount that skiers and riders have a high level of situation awareness and be aware of not only the terrain and snow conditions, but also of the location of other people in the area. The actions of a single person can affect the safety of many.”

Weather Forecast and Avalanche Outlook

A ridge of high pressure is expected to continue over the region today. Then the weather will come from the southwest and warm temperatures will continue on Saturday with possible snow. A cold front will arrive Sunday causing a return to winter and possible significant snowfall; particularly over the Idaho border.

I expect the avalanche danger to remain the same with caution advised during the heat of the day on Saturday. The attention will then shift to the predicted new snowfall for Sunday.

I would like to thank the folks who are sending in public observations again. It’s great for all of us to have the extra information.

If you get out and see avalanche activity or want to send us quick snow observations please use our public observations form link on our home page or write us at info@missoulaavalanche.org with any observations or questions.

Have a great weekend and ski and ride safe!

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Monday, March 5th, 2012.

Weather and Snowpack Analysis

Spring rolled in this past weekend and mountain temperatures soared into the low to mid forties on Sunday at all advisory area locations above 6000 feet in elevation. Winds blew hard out of the west and south most of the weekend gusting into the 50mph range in some locations. Currently, temperatures are in the low to mid thirties and the winds are out of the south and west at 8-10 mph under partly cloudy skies.

The sun crust that formed a week ago is now providing a slick sliding surface for the new snow that we received late last week. This crust is most pronounced on south and east aspects. The new snow of 6-10 inches is failing easily in our stability tests on these aspects during this period of warm weather. This condition however, is not a big concern unless a slope fails on a persistent weakness deeper in the snowpack. This is not likely, since it is taking a lot of force in our stability tests to get it to fail.

North facing aspects do not have the sun crust in the upper snowpack, and this is where you will find the softest snow. These aspects are staying cool at upper elevations and providing the best opportunity for recreation. The concern on these slopes is the buried surface hoar layer that is down 2-3 feet. This weakness has gained strength the past few weeks and stability tests have consistently been improving. You will still want to look for this weakness before riding a steep open slope.

Now that warmer temperatures have arrived it is important to pay attention to how the snow is changing during the day, and even hour by hour. You will want to move off steep terrain once the snow becomes damp. Temperatures remained warm last night so look for snow conditions to deteriorate quickly today. Temperatures will cool significantly tonight with the arrival of a cold front and this will help to improve avalanche conditions. When the warm temperatures return later this week, be sure to pay attention to dormant weak layers becoming more reactive, weakening cornices, and for point release slides on steep solar aspects.

We received a report late last night of a live recovery of a snowmobiler caught and buried in a slide near Seeley Lake. The details are vague and Steve will be up there today to investigate. He will post more information on our website under the Documents/Accident Reports tab.

Weather Forecast and Avalanche Outlook

Mountain temperatures will warm into the forties this afternoon and southwest winds will increase ahead of a cold front arriving tonight. The cold front could bring 5-10 inches of new snow by Tuesday morning with gusty west winds to 40 mph. Cooler temperatures and a few lingering snow showers are forecast for Tuesday. Then, a ridge of high pressure builds over our area starting Wednesday bringing rising temperatures through the end of the week.

I expect the avalanche danger to increase with the new snow load followed by warming temperatures.

Dudley will issue the next advisory on Friday, March 9^th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.

Observers in the Hoodoo and Lookout Pass areas reported natural slides that were deeper and more dense than the activity reported elsewhere. For this reason, the avalanche danger is rated CONSIDERABLE on all wind-loaded steep slopes.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 2nd, 2012.

Weather and Snowpack Analysis

All advisory area locations received new snow the past couple of days. The Hoodoo Basin area received 10 inches (1.2”SWE) since Wednesday, while all other advisory area locations received 4-7 inches (.4-.9”SWE) of fresh snow. The winds blew steady mostly from the West and temperatures hovered in the low twenties during the day. Currently, winds are blowing out of the West and Northwest from 4-7mph and temperatures are in the mid to upper teens under mostly cloudy skies.

The sun and warm temperatures we experienced on Monday and Tuesday helped to settle and strengthen the snowpack. It also left a sun crust on all but true North facing slopes, which is where you will find a thin buried surface hoar layer that formed on Monday and Tuesday and got buried by the new snow on Leap Day. The new snow has already sluffed off the steeper slopes and has appeared to buckle in this area of the Rattlesnake mountains (photo), where the slope was not quite steep enough for the snow to slide, even though the slope angle was 37 degrees. Where the new snow has not released, expect it to sluff easily on steep slopes.

The main concerns are fresh wind drifts that have formed on leeward aspects, new snow instabilities, and the potential for triggering a stiff slab on the old buried surface hoar layer that formed in early February now down 1.5-2 feet below the snow surface. This weakness has been slowly strengthening and has been less reactive in stability tests lately. However, we have received some reports of failures in the moderate range on this weak layer and it would be wise to look for this weakness on the slope you plan to ride. It is mostly found on shaded aspects at upper elevations.

If the sun comes out and temperatures rise during the next few days, you will want to pay attention to how the snow is changing. Watch for dormant weak layers to become more reactive and for point release slides on solar aspects especially around steep rock outcrops.

Weather Forecast and Avalanche Outlook

We should see some light snow showers today but not much accumulation, temperatures in the mid to upper twenties and moderate winds out of the West. The next weather system moves in on Friday night and Saturday and should produce another round of snow in the 5-8 inch range. This system is forecasted to come in warm and for snow levels to rise to 4500 feet by Saturday night. Winds will increase with this system blowing from the West.

I expect the avalanche danger to increase if we get forecasted snow amounts with increasing temperatures.

I will issue the next advisory on Monday, March 5^th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.