Avalanche Safety for Backcountry Travelers

The winter can make popular locations your personal sanctuary; however avalanche safety and preparation are crucial to enjoying the pristine conditions.

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by Kevin Sawchuk | 2013-12-03 00:00:00-07

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You’ll have this very popular area all to yourself in the winter. Mt. Ritter from San Joaquin Ridge.

Introduction

Winter is a wonderful time to visit the backcountry! In the winter you’ll have the most crowded locations to yourself. Overused areas are refreshed with a tinsel of snow and places you’ve visited a dozen times are exciting and new! However the snow of winter adds challenges and requires additional skills. You’ve got to know how to stay warm and dry both while moving quickly on sunny and stormy days….and once your activity level drops in camp. Navigation must be performed quickly in stormy conditions with limited visibility...when the trails and even trail signs are buried. The snow that adds so much freshness to the backcountry also adds the deadly danger of avalanches. Before you head into your winter wonderland you’ve got to know the season’s snowpack, the weather you’ll be facing and how to assess the risk of avalanches in the terrain you plan to cover and make the best route decisions to minimize those risks.

Basic Safety!

This article presumes that the reader has a basic knowledge of how snow behaves. It assumes that you will travel in a group and that each group member will carry an avalanche probe, beacon, and metal-bladed shovel and can deploy them within 10-15 seconds. Avalanche probes, beacons, and shovels can save lives but they are no guarantee of safety. While it is critical to know how to use them successfully (and their use is beyond the scope of this article), you cannot count on your beacon and probe to save you! You’ve got to know where, when and how to travel and rigidly follow the rules you’ve set up. You must approach snow with the mindset that coming back alive is more important than completing a route or skiing a fun but dangerous line. That mindset is crucial.

Snowy Myths

Let’s dispel a few myths. First, most avalanches are not huge avalanches that rip out trees and send house-sized boulders cascading into valleys. They are small and release after storms and changes in weather. Second, most avalanches do not kill by burying their victims. They are more likely to kill by sending an unsuspecting skier over a cliff or by smashing them into rocks or trees. Third, most avalanches are not random events from a side ridge. They are usually triggered by their victim. Finally, having a probe and beacon does not guarantee your safety. They may save your life and certainly make it easier to find your body but alone their use means a life threatening event has already occurred. Let’s keep that from happening!

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A small avalanche below a steep glacial slab. Going over the cliff above would not have been healthy.

Knowledge is Light! (Scientiae perfusorius est)

As with so much in lightweight backpacking it’s not what you carry but what you know that keeps you safe. Understanding that a beacon and probe won’t protect you means that you have to carry a cautious attitude and a working knowledge of snow safety into the backcountry when you visit. Fortunately these don’t add anything to your baseweight!

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Sastrugi give evidence to the transformative power of wind.

Snowpack Evaluation and Transformations

Evaluating the snowpack begins with the first snows of the season. This is true even if your trip doesn’t happen until March. I follow the base layers of snow, the temperatures at which they fell and subsequently settled, and any rain especially early in the snow season. Snow falls as a series of layers. Once it falls it is changed by a combination of wind, sun, rain, a high temperature differential between the ground and the air, and warm temperatures. Each of these factors can increase or decrease the avalanche risk.

Temperature

Thin snowpacks and high differential temperatures between the ground (32 F) and air promote the formation of dreaded “depth hoar.” Depth hoar is a type of reformatted snow that develops from the constant melting/refreezing cycles driven by large temperature gradients. Depth hoar has few sharp edges and behaves more like crushed ice. It has little cohesiveness. This is a loose crystal type of snow that is very unstable. Put a load of heavy snow on top and it is prone to slide. Early depth hoar development can leave unstable layers in the snowpack that can last the entire season. And you’ve got to know about them. Rain on top of snow often forms an icy layer that provides another unstable surface prime for avalanches. Really warm days before a cold storm can also lead to icy layers. Icy layers don’t hold snow well. New snow will often release from the top of an icy layer.

Sudden and new increases in the ambient temperature (often increased by the “reflector oven” effect of bowls) result in less bonding force within the snowpack, and this is a major time of increased avalanche risk. If you are traveling on the first unseasonably warm day of the season or any day above recent average temperatures, watch out! In the Sierra we often travel before sunrise and only until 12-1pm on warm days to avoid avalanches. (But if we’re making miles we may start again at dusk and travel well into dark.)

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Fresh snow on top of this icy surface would not hold very well. It is a prime avalanche location.

Wind Loading

When snow falls it usually does not stay where it fell. Storms are almost always associated with wind and inches of snow can be redistributed to the leeward side of ridges and gullies. These “wind loaded” slopes get way more snow deposition that the windward side during a storm. The snow is often packed together into “slabs” that behave as a unit and are much more prone to avalanches until that snow has settled. This is especially true if there is an unstable layer of powder, hoar, or ice beneath it. One of the important wintry backcountry skills is determining where the winds have deposited the last storm’s snow. Just by looking at the scene you need to be able to see how the snow has been influenced by the weather and where possible avalanche sites have formed. Also the wind direction needs to be determined from the current wind direction as well as the snow ridges behind rocks and trees; snow will build up behind trees and rocks on the side away from the wind. Cornices are also a good indicator of where new snow may be deposited and where possible avalanche areas may be found since they form on the leeward side of the ridge. In short, the leeward side of ridges and ribs are much more unstable for several days after a storm. Don’t travel there!

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The illustration below (from Allen & Mike's Avalanche Book by Allen O'Bannon and Mike Clelland) and the video shows how snow loads on slopes.

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Loose windloaded snow pillows--could send you to a permanent sleep. Top of the “Golden Staircase” John Muir Trail.

Slope Angle/Microterrain

Slopes with angles between 30 and 45 degrees of steepness are the most prone to avalanches. Most of our travel occurs on slopes less than 40 degrees so it's critical to pay attention to slopes in the 25-40 degrees. Even slopes less than 20 degrees can avalanche--typically on very warm days. Steeper slopes usually shed their snow in small slides and shallower slopes don’t provide enough kinetic energy for snow to slide unless conditions are unusual. Many compasses have a clinometer and it’s worth having one to measure slope angles.

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An in depth look at the most common slope angles for skope failure. (credit: Allen & Mike's Avalanche Book by Allen O'Bannon and Mike Clelland)

Small features in the terrain also give clues to and dictate avalanche risk. Aside from the obvious tree cleaned avalanche path look for places where the slope angle steepens--this increases the force on the snow pack at the top of the steeper slope and is a more common area for an avalanche to triggers. If chutes and gullies collect snow and increase avalanche risk the top of a ridges or ribs are unlikely to be snow loaded and less likely to avalanche. Mature trees reduce the risk of avalanches--but traveling in trees is no guarantee of safety as summer travelers can attest from the massive piles of downed trees they sometimes see below avalanche chutes.

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They all point one way and that points to how they got there: a massive avalanche! Trees are no guarantee of safety!

If you take an avalanche course you’ll be taught about digging a snow pit to assess for unstable layers. Digging a snow pit can help assess risk--but you need quite a bit of experience digging and interpreting tests for unstable layers. You also have to understand that a snow pit at one elevation and on one aspect of a slope may give very different information from one on another aspect 400 m away or 1000 ft below. Wind loading, sun exposure, and base layers can be dramatically different short distances apart. Don’t be overly reassured by snow pits!

Regional Differences

Snowpacks behave differently in different regions. In the Sierra we get a very heavy “marine” snowfall and most storms are relatively warm. While this means we’re often skiing “Sierra cement” it makes for a safer snowpack. Generally the greater snow density means less blowing snow (but this rule is much less reliable at higher elevations) and more rapid consolidation of new snow. The biggest risks usually come within 48 hours of a snowfall and on the leeward side of peaks and ridges. Three to four inches of snow can translate into 1 to 2 ft in leeward gullies. Big avalanche risks often come late in the season with the first warm days. As the snow warms it loses its cohesiveness and it is less able to support the heavy and deep snow that has fallen. Snow on granite slabs is especially dangerous - melting water percolates through the snowpack and lubricates the snow sitting on smooth slabs. This is a recipe for disaster and is why travel on warmer days is limited to the cooler times of day.

In the Rockies the lighter volume of snow and dramatic temperature difference between the ground (32 F) and air often lead to “depth hoar”* and unstable layers. Many seasons will have persistent unstable layers that develop early and can make for very unsafe conditions through the entirety of the season. The very light powder that falls is a skiers dream: but if it blows into a gully and wind loads it this dreamy powder can quickly become a nightmare.

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High in Cloud Canyon before a ripping descent down Tamarack Canyon. King’s Canyon.

So what’s the bottom line? What is a snowshoer or skier to do to enjoy the backcountry safely? In addition to the mandatory beacon and probe, here’s my approach to researching the avalanche risk and minimizing my chances of meeting one. (They’re as nasty as trolls!)

  1. Check the avalanche risk and weather forecast before you go. Avalanche.Org and NOAA.gov can give detailed avalanche and weather forecasts for specific regions. Don’t travel in avalanche prone terrain if the avalanche danger is more than moderate. If the general risk is lower know the details of what slopes and aspects have a higher avalanche risk. If the big avalanche risk is on the northeast aspect of slopes above timberline don’t travel there. Change your plans to minimize risk.
  2. Pay attention to what you see, feel, and hear where you’re traveling. If you see avalanches even in the distance--especially fresh ones--avoid similar slopes and aspects. If you hear deep “whumps” in the snowpack or trigger small slides go somewhere safer. A whump sound can indicate deeper unstable layers. Pay attention to the signs of wind direction and wind loading--and change your route to avoid wind loaded slopes.
  3.  - 10
    Looks like a fun ski slope! I wonder why there are no trees. Weird?!

  4. Travel spaced out across potential avalanche terrain with beacons on and probes ready to deploy.
  5. Take an avalanche assessment course. Learn even more about how to assess risk and how to (partially) mitigate the risk through specific route choices.
  6. Always choose safety over fun. The mindset and caution you bring into the backcountry is probably the most important guarantee of your safety.

One other consideration

A final additional snow risk to consider is that of collapsing snow bridges - especially over lakes and rivers. (spoiler alert for “The Last Season”) Randy Morgenson, an experienced backcountry ranger, likely died this way in the Window Peak drainage of the Sierra Nevada. Water undercuts snow and especially on a warm day the thin and weakened snow bridge can collapse--and suck you down the river, under the snow. I visited this region a few years ago and identified the location Randy likely fell through the snow: just below an avalanche runout at a geologically determined bend/pond in Window Creek.

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Water undercuts snow. Tyndall Creek is 8 ft down. This weakness is obvious, others aren’t.

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A “crevasse” at the edge of a lake. Another place an unsuspecting hiker could fall in.

Final Thoughts

Winter is a great time to visit the backcountry. Don’t be chilled by the thoughts of cold weather and avalanches! Develop the knowledge and skills to stay warm, travel safely and you’ll open up months of time you can travel in the mountains. Use this knowledge to help make cautious decisions so you can enjoy your private paradise for many years to come!

Additional Information can be found online.

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There’s a lot of fun to be had in the winter if you’re careful. Horse Creek Canyon, Northern Yosemite.


Citation

"Avalanche Safety for Backcountry Travelers," by Kevin Sawchuk. BackpackingLight.com (ISSN 1537-0364).
http://backpackinglight.com/cgi-bin/backpackinglight/avalanche-assessment-sawchuk.html, 2013-12-03 00:00:00-07.

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Forum Index » Editor's Roundtable » Avalanche Safety for Backcountry Travelers


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Maia
(maia) - MLife

Locale: Rocky Mountains
Avalanche Safety for Backcountry Travelers on 12/03/2013 20:16:54 MST Print View

Companion forum thread to:

Avalanche Safety for Backcountry Travelers

Billy Ray
(rosyfinch) - M

Locale: the mountains
Re: Avalanche Safety for Backcountry Travelers on 12/03/2013 20:39:25 MST Print View

here's another great avalanche class:

http://donnersummitavalancheseminars.com/

Billy

Andrew F
(andrew.f) - F - M

Locale: San Francisco Bay Area
Re: Avalanche Safety for Backcountry Travelers on 12/03/2013 21:49:54 MST Print View

An excellent and timely article. Thanks Kevin.

Ian Destroyer of Forums
(IDBLOOM) - MLife

Locale: PNW
Re: Re: Avalanche Safety for Backcountry Travelers on 12/03/2013 22:11:31 MST Print View

Great article!

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Fascinating, but on 12/04/2013 02:24:29 MST Print View

To the best of my knowlegde, there has been just one avalanche in the Australian snow fields over the last 20 - 40 years. I have no idea why, and I suspect >99% of our ski tourers never even think about avalanches.

So interesting stuff, but not something we see in Oz. Weird.

Cheers
Roger

John S.
(jshann) - F
Re: Fascinating, but on 12/04/2013 07:37:44 MST Print View

Australia may have less natural triggering events such as natural seismic activity, earthquakes, blizzards.

Jonathan Shefftz
(jshefftz1) - MLife

Locale: Western Mass.
Some important corrections... on 12/04/2013 11:39:57 MST Print View

I strongly suggest that anyone really interested in safe winter travel disregard this article and instead first read either the book by Bruce Tremper that I assign to my avalanche course students:
http://www.mountaineersbooks.org/Staying-Alive-in-Avalanche-Terrain-2nd-Ed-P512.aspx
... or his new book that is on a more introductory level:
http://www.mountaineersbooks.org/Avalanche-Essentials-P1170.aspx

If you do read this article, then here are some corrections for some of the most egregious aspects:

1. I count seven references each to beacons and probes, yet not a single reference to shovels. Maybe the implicit assumption is that each and every winter traveler will already have a shovel, but still, this has to be some kind of first for an article about avalanche safety to omit any reference to shovels.

2. “Let’s dispel a few myths. [...] Second, most avalanches do not kill by burying their victims. They are more likely to kill by sending an unsuspecting skier over a cliff or by smashing them into rocks or trees.”
- Exactly the other way around, i.e., the usual statistic is about 3/4 asphyxiation (via airway burial) versus 1/4 trauma. (Avalanche deaths for technical climbers can be more like around 1/3 trauma, but the only study I’ve ever seen for a majority of avalanche deaths via trauma is my own analysis of deaths on NH’s Mt Washington.)

3. “Slopes with angles between 25 and 40 degrees of steepness are the most prone to avalanches.”
This statement is very misleading, and the accompany diagram from some book is even worse, both for its portrayal of slopes between 40-45 degrees, and the misuse of the word “Moderate” in this context, since it is one of the descriptors on the five-point avalanche forecasting scale.
The statement is contradicted even by the accompanying diagram, as well as by the typical classification, as found in the older Tremper book:
“Slopes between 35 and 45 degrees cause the vast majority of avalanche fatalities [...]. Recent statistics from Canada and Switzerland indicate that half of human-triggered avalanches occur between 37 and 42 degrees [...].”
... by his newer more introductory book:
“In the steepness graph [...], the bull’s-eye steepness is 39 degrees; nearly three out of four avalanches occur in red-light starting zones (34 to 45 degrees), 10% occur in the yellow-light terrain on the gentle side of the curve (30-34 degrees), 13% on the steep end of the curve, and only 3% on slopes less than 30 degrees.”

4. “If you take an avalanche course you’ll be taught about digging a snow pit to assess for unstable layers.”
Teaching snowpit assessment skills is no longer part of the standard Level 1 three-day curriculum.

5. “In the Sierra we get a very heavy “marine” snowfall [...]”
Tahoe does have a maritime avalanche climate, but not the Eastern Sierra.

6. I’m not going to get into the snow science aspects of the article except to note that depth hoar often seems to be confused here with buried surface hoar.

Jonathan Shefftz
(jshefftz1) - MLife

Locale: Western Mass.
Australia and Avalanche Triggers on 12/04/2013 11:44:18 MST Print View

"Australia may have less natural triggering events such as natural seismic activity, earthquakes, blizzards."
-- I have no idea if Australian above-treeline terrain is less susceptible to snowstorms with heavy wind ... but I do know that most avalanche fatalities are from human-triggered avalanches, and of naturally triggered avalanches, natural seismic activity / earthquakes are an extremely rare cause (e.g., 1970 Huascarán).

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
THANKS! on 12/04/2013 12:26:09 MST Print View

Kevin,

Excellent article with great illustrations. As an avy certified ski patroller in an avalanche prone area (Las Vegas Ski & Snowboard Resort in Lee Canyon, Spring Mountains) I applaud this timely article as not only intertesting but necessary for those travelling in avy territory.

MINIMUM AVALANCHE SAFETY KIT:

1. Avalanche One course
2. avy beacon
3. probe
4. avy shovel (no plastic blades)
5. snow study kit (inclinometer, compass, magnifier, thermometer, etc.)

RECOMMENDED AVY GEAR:

1. snow saw (for Rutschblock and snow pit study)
2. Avalung
3. avy air bag backpack (BCA pack, for ex.)

Then go out with other similarly equipped friends and PRACTICE.
Practice finding a hidden beacon.
Practice team digging for buried beacon using > shaped digging technique and "paddling" movement of snow.

IN AVY TERRAIN:
Practice maximum caution for route selection. Testosterone-charged macho attitudes lead to abandoning proper caution. This is why groups that include females have a much lower chance of being avalanched. (true)

Again Kevin, thanks for a great article. This article, with any needed updates, should be posted EVERY year at this time.

UPDATE: Worldwide statistics show that those avalanched with DEPLOYED airbags have a 90+% chance of survival. Most of the data comes from Europe and North America. The European avy areas are much less forested than in North America. Therefore the statistics are somewhat skewed by the European data. Still, even with an 80% chance of survival an airbag pack should be virtually mandatory for any commercial heli-ski operations and "highly recommended" for backcountry skiers.

Edited by Danepacker on 01/17/2014 12:43:32 MST.

John S.
(jshann) - F
Re: THANKS! on 12/04/2013 14:13:23 MST Print View

Does one typically learn how to really use a snow study kit in an avalanche one course?

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: THANKS! on 12/04/2013 14:30:58 MST Print View

Every avalanche course is different, and they are different across different parts of the country due to huge differences in the makeup of snow.

Sometimes a whole snow study kit is demonstrated in a first-level class, but often it isn't used until a second-level class.

A few of us managed to study the snow very quickly on our first unexpected ride down the hill. For my second event, I had the opportunity to study the snow from the underneath.

--B.G.--

Kevin Sawchuk
(ksawchuk) - BPL Staff - MLife

Locale: Northern California
Re: Some important corrections... on 12/04/2013 15:14:09 MST Print View

Jonathan:

Thank-you for your comments. You obviously have a great background of snow safety. You are absolutely correct, not including a shovel as required gear in avalanche terrain is a major oversight. If you need a probe and beacon you need a shovel to explore for the person (or body) buried. I always carry one and absolutely agree that a plastic bladed shovel is inadequate. When avalanches come to rest the snow is in a very compacted state that is difficult to dig through. I have asked the article be updated with this important point.

I won't debate the other differences of percentage of victims (killed and injured) by burial vs by terrain. The important point is to pay attention to the terrain below you as a very small slide can send you places you don't want to go.

What I was trying to capture in the slope angle is that since we travel much more frequently in more gentle terrain we're more likely to trigger slides in more gentle terrain. It's easy to think of 30-35 degrees as "safe" and not requiring special attention. This type of relaxed attitude is what gets you killed. Only hard core skiers ski 45 degrees--it's double black diamond steepness (and personally very fun) but not visited by snowshoers and backpack tourers often.

Thanks for shedding light and knowledge!

Edited by ksawchuk on 12/04/2013 16:03:15 MST.

Kevin Sawchuk
(ksawchuk) - BPL Staff - MLife

Locale: Northern California
Re: Re: THANKS! on 12/04/2013 15:21:48 MST Print View

When I took my level one course ~5 years ago snow pits and avalanche study kits were covered. Given how differently snow can behave short distances apart I usually dig only 1-2 snow pits per trip just to get a sense of what is happening deeper but I rely on the general information and terrain aspects most.

Billy Ray
(rosyfinch) - M

Locale: the mountains
Re: Re: Some important corrections... on 12/04/2013 15:25:43 MST Print View

Since this site is about saving weight, there is another strategy with regard to the shovel...

Leave it in the car, but make sure the others in the group have shovels! You can save quite a bit of weight...

Think about it. :)

[okay... maybe bad joke on a serious subject... ]

Billy

Kevin Sawchuk
(ksawchuk) - BPL Staff - MLife

Locale: Northern California
Re: Re: Re: Some important corrections... on 12/04/2013 16:04:11 MST Print View

Billy:

Same reason I'm always willing to loan my triple antenna beacon to a newbie with a lesser device! If it's needed you want the person looking for you to have the best.

Edited by ksawchuk on 12/04/2013 16:05:07 MST.

Billy Ray
(rosyfinch) - M

Locale: the mountains
Re: Re: Re: Re: Some important corrections... on 12/04/2013 17:17:24 MST Print View

Kevin...

I have a similar situation with a very old Ortovox and a last year beacon and have had the same thought... great minds (or devious ones anyway) think alike... eh?

Billy

Stuart R
(Scunnered) - F

Locale: Scotland
Regional variations on 12/05/2013 03:46:56 MST Print View

Every avalanche course is different, and they are different across different parts of the country due to huge differences in the makeup of snow.

Indeed, and in different countries too. Here in Scotland windslab avalanches are the most common, so it is important to know the recent wind and temperature history when going out.
The classic text for Scottish conditions is A Chance in a Million?

casey redder
(credder) - MLife

Locale: Rocky Mountains
Avy Classes on 12/05/2013 14:47:53 MST Print View

The avy 1 class i help teach every winter covers the basic whats whys and wheres of avalanches and i think it is a good starter to get people thinking about the mindset you must have in the backcountry...
We teach a go/no-go system, where if one person has a concern about terrain, weather, etc. then the group shouldn't do it... find different terrain to play on.
We also do a full day on gear, from all the manufacuturers, BCA, PIEPs, Mammut etc... the students are encouraged to touch and use all the beacons during the beacon hunt.
Then we do an on-hill day where the students get to use probes and get a feel for what a helmet feels like or a boot or even a torso. Then we dig pits in many different aspects, south facing no trees, north facing in the trees, above and below rock bands (at a ski area so the chance of an avy is minimized of course) just to show someone new to the winter side of BC fun that different parts of the mountain behave differently when it comes to snow. Finally they get to move to a scenario where we've buried some beacons and synthetic humans in snow cat debris and turn them loose... everyone gets to enjoy digging in avy-crete with metal shovels, plastic blades and plastic shovels... by the end the plastic stuff is on the sidelines... i like to finish it off with a quick CPR refresher and some basic first aide while they're still sweating and panting, oh and remind them that they could be miles from thier car... so digging someone out is just the beginning of the fun.

Edited by credder on 12/05/2013 14:52:51 MST.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Avalanche Safety for Backcountry Travelers on 12/05/2013 14:53:00 MST Print View

What some cross country ski groups do is to have a transceiver practice in sloping sand dunes. Basically, one transceiver is left in the transmit mode, and then placed in a plastic bag, and then buried in a sand dune. Then the sand is smoothed over. The trainees arrive, switch over to receive mode, and then look for the target.

It doesn't take too much practice to get the hang of it.

--B.G.--

John S.
(jshann) - F
Re: Avy Classes on 12/05/2013 17:45:47 MST Print View

Sounds like a great course Casey.