THIS AVALANCHE ADVISORY EXPIRED ON February 7, 2016 @ 6:54 am
Avalanche Advisory published on February 6, 2016 @ 6:54 am
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche Danger is MODERATE today. Evaluate all slopes steeper than 30 degrees. Human triggered avalanches are still possible, especially on windloaded slopes over 30 degrees, and in areas with a layer of buried surface hoar(the layer responsible for last weekend's fatality).  Moderate danger means heightened avalanche danger on specific terrain features, careful snowpack and terrain evaluation is essential. Below 6,000 feet generally safe avalanche conditions exist, and the avalanche danger is LOW.

 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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We have plenty of light density snow to move around right now and with Southwest winds gusting into the 20's again today, that snow will be loading the Northerly aspects. With that in mind, wind slabs remain our primary concern. Expect to find wind slabs of varying thickness and hardness on east, north, northeast, northwest and cross loaded west aspects. You are most likely to find these slabs at or near the ridge tops or in exposed terrain above 7,000 feet. They are still relatively widespread in the upper elevations and range in sensitivity from touchy to unreactive. Shallow wind slabs are more likely right now within this week's new snow, but you may also find some deeper ones still lingering deeper below the surface.These slabs range in density between soft to hard, which means they may let you get well out onto them before they fail. Also, keep in mind that some of these wind slabs may be resting on a newer layer of buried surface hoar that was formed early last week, or even worse could step down to the buried surface hoar layer that formed in early January. 

 

Avalanche Problem 2: Persistent Slab
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We currently have 2 different persistent layers that we are tracking: one is relatively shallow and the other relatively deep. Both layers are made up of either buried surface hoar or near surface facets and represent old surface snow that was subjected to the faceting process during periods of high pressure in between snow cycles.  The deeper layer is the one that resulted in the large and fatal slide near Twin Lakes on Sunday and the substantial natural avalanche cycle that we saw following MLK day that continued through Monday of last week.  It is becoming a deep instability problem that is increasingly hard to trigger and not very widespread but is probably unsurvivable if triggered. In hazard evaluation terms it is a LOW probability/HIGH consequence problem.  Its current depth is between 2.5 and 3.5 feet down in the snowpack depending on the windloading on individual slopes.  Unfortunately, this layer is likely to stay where it is for quite some time and Snowmobiles are more likely to trigger it than a skier.  It is also very hard to predict where you will trigger it because of its non-uniform distribution across the larger area and even across individual slopes and small micro features. Shallow wind protected areas well below the ridge tops, areas around rocks or on slopes with rocks sticking out or barely covered that were mostly protected from the winds are our best description for where you might trigger it right now. If you avoid areas with complex or convoluted terrain with lots of varying snow thickness across a slope, you will eliminate a large portion of the risk of triggering this layer, better yet spend your time boondocking through more moderate terrain and leave the steeps alone right now.

The upper layer is also made up of faceted snow or preserved surface hoar that was the snow surface last week before our last round of snowfall.  In addition, we are finding areas with substantial grauple layers that were deposited  a week ago as the last significant storm entered our area. This upper layer is likely to be triggered by skiers or snowmobilers with equal chance due to its proximity to the surface right now. It is also variable where you will find it and what it is comprised of based on the winds, and the type of precipitation that fell on top of it.  If you are skiing or riding on steep Northerly or protected slopes, you are literally rolling the dice on whether you are going to step on a land mine unless you take the time to evaluate the upper snowpack before you commit.  Both of these layers are easily identifiable as a gray line or layer in the snow when you dig through them.

A warming trend beginning tomorrow will add a significant stress to the snowpack as layers begin to melt and add weight and water to the upper snowpack.  Be aware that rapid warming is one of the main red flags and that these will be the warmest temperatures of the winter so far.  The possibility of natural and human triggered avalanches will increase with the temperatures.

 

 

Avalanche Problem 3: Loose Dry
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We saw and started a lot of minor sluffs yesterday as we moved into some steeper pitches of skiing.  These small sluffs are easy to manage unless you are in confined or complex terrain and get caught off guard.  You can easily ski cut before you enter a slope or move across the slope as you ski it to stay out of a sluff's way.  If you do get tangled up in them, they can easily push you where you don't want to go.  As the temperatures increase expect to see more natural sluffs occurring as the snow surface heats up and the dry sluffs become wet and more pushy.  Increasing roller ball activity and the possibility of small wet slides on the sunny aspects should be expected tomorrow and Monday as temperatures soar towards 50 in the mountains. Good bye powder, hello inversion!

advisory discussion

That's right folks, it's almost time for our annual fundraiser...next Saturday at the Little Ski Hill from 6-9 ish.  Spoiler alert: Beer from McCall's own SRB, Waverunner rental from Cheap Thrills and skis from Dynafit! Practice up with those beacons and get ready for some timed becon races with great prizes.  Family Friendly with night skiing and plenty of parking available on both sides of the highway. Thanks to all the donors that have supported us in the past and again this year!

recent observations

We toured near Sawtooth Peak yesterday skiing both E and W aspects of the Sesame Street Ridge.  We found a fair amount of sluffing in the loose faceted snow on the surface on all aspects on steeper pitches. Some of these gouged a thin slab in the upper 6-10 inches of the new snow.  We also found some great skiing on short steep pitches that were not harboring the buried surface hoar layer.  We did find a well preserved layer on a W/NW slope that was at 105 cm down from the snow surface or about 3.5 feet.  Our pit tests continue to show that where we find this layer it is hard to initiate but still has the potential to propagate across a larger area.  We also found the layer of buried grauple at 55 cm on multiple aspects which produced moderate trending toward hard shears with a CT17 Q3/PC on a west aspect.  On the East aspect we also found a density change at 35 cm that produced moderate shears with a CT12 Q3/SC at the interface between the soft snow and the older snow surface from last week, however we could not initiate failure with ski cuts on this layer.  The grauple layer did not fail and was very thin on this aspect.  The snowpack was also warming up yesterday and will be undergoing some serious stresses over the next few days as inverted temperatures in the mountains climb towards the mid 40'starting tomorrow with a climb towards 40.  The early part of the week will bring some of the highest temperatures of the winter so far which means the snow will be changing rapidly.  This warming trend will have the potential to make our buried surface hoar more likely to fail with the added stress of heat and lubrication of the weak layers.

weather

SHORT TERM...WEAK FRONTAL SYSTEM WILL BRING SCATTERED SNOW SHOWERS WITH MINOR ACCUMULATION TO THE WEST CENTRAL IDAHO MOUNTAINS AND HIGHER BOISE MOUNTAINS TODAY. ONLY CLOUDS EXPECTED ELSEWHERE. SYSTEM WILL ALSO BRING ENOUGH WIND TO MIX OUT ANY FOG AND ALLOW TEMPS TO CLIMB TO THE 30S AND 40S. LIGHTER WINDS TONIGHT AND SUNDAY UNDER BUILDING HIGH PRESSURE ALOFT WILL ALLOW PATCHY FOG TO FORM AND ALSO HOLD DOWN DAYTIME TEMPS IN THE VALLEYS AS AN INVERSION BEGINS TO FORM.

LONG TERM...SUNDAY NIGHT THROUGH SATURDAY...HIGH AMPLITUDE UPPER LEVEL RIDGE WILL BE OVER THE REGION THROUGH EARLY NEXT WEEK. THIS WILL BRING A STRONG INVERSION WHICH WILL LIKELY LEAD TO THE DEVELOPMENT OF STRATUS AND FOG IN THE LOWER VALLEYS. TEMPERATURES WILL DEPEND ON HOW MUCH FOG/STRATUS DOES DEVELOP WHICH AT THIS POINT IS HARD TO DETERMINE. CONTINUED THE TREND OF HIGH TEMPERATURES IN THE VALLEYS IN THE 30S WITH TEMPERATURES ABOVE THE INVERSION IN THE 40S AND LOW 50S. UPPER LEVEL RIDGE BEGINS TO BREAK DOWN WEDNESDAY AS ENERGY FROM AN UPPER LEVEL TROUGH TO OUR WEST MOVES INLAND.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Isolated snow showers before 11am. Cloudy, with a high near 32. South wind 5 to 7 mph becoming calm. Chance of precipitation is 20%. Mostly cloudy, with a low around 12. Light and variable wind. Mostly sunny, with a high near 33. Calm wind.
Temperatures: 32 deg. F. 12 deg. F. 33 deg. F.
Wind direction: South Variable Calm
Wind speed: 5-7 Light Calm
Expected snowfall: trace in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Scattered snow showers, mainly before 11am. Cloudy, with a high near 31. Breezy, with a southwest wind 17 to 22 mph becoming light south southwest. Chance of precipitation is 30%. New snow accumulation of less than a half inch possible. Mostly cloudy, with a low around 18. West wind 7 to 13 mph. Mostly sunny, with a high near 36. Northwest wind 8 to 13 mph.
Temperatures: 31 deg. F. 18 deg. F. 36 deg. F.
Wind direction: Southwest West Northwest
Wind speed: 17-22 7-13 8-13
Expected snowfall: Trace in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. 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 at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.