Thunderstorms can occur any time warm, moist air collides with cold. Even in typically "dry" areas, subtropical moisture can move in and in just a few hours a full scale electrical storm can develop. In mountainous areas, the rider may not be aware of an approaching thunderstorm which can seem to materialize without warning.

Indicators:

"Gray" horizons and rainbows are signs of high humidity. High humidity means dew or frost, greater difficulty for your mount in warm weather, and the potential for thunderhead development.

A corona or halo around the sun or moon indicates moisture in the air, a typical sign of an approaching or departing disturbance in the weather.

The movement of high clouds is significant. Continuous movement in the same direction could simply indicate the passage of air from a high pressure area to a low. If the clouds start to move in different directions, pay attention. A low pressure zone is probably close. Wind changes and increased development of heavy, ominous clouds usually precede a storm which could be intense in nature. (In contrast the apparent rising of clouds and breakups of the cloud mass typically indicate that the disturbance is passing.)

The sound of thunder is an obvious indication that you may be in for a rough time, and in mountainous areas where your view of the sky is limited, thunder may be your first indicator that a storm may be just beyond the horizon.

Products of Thunderstorms:

Thunderstorms can produce massive amounts of rain, generally falling from intense cells of activity. In certain parts of the country you could be peacefully enjoying some tranquil narrow canyon unaware that a significant amount of storm runoff is headed your way. Any time you hear thunder when you are in flash flood country (areas of long, narrow drainages) be alert to any changes in streams or any water running in dry creek beds.

In some areas, flash floods can be severe enough to wash automobiles off of roadways. More typically, water can rise to the point that riders and hikers can no longer safely make stream or creek bed crossings and could be effectively trapped until the water subsides.

Winds can be sudden, significant, and change directions. In weaker stands of trees, dead wood can become dislodged and small, dead branches can take flight. The combination of wind and "nature's own" tree pruning can prove to be too much for some horses, so be prepared to deal with this situation.

By far the most dangerous element of a thunderstorm is lightning. Lightning kills about 300 people in the U.S. every year, more than any other weather related hazard. Most of these deaths could have been prevented had proper precautions been taken. The outdoor rider must take lightning seriously.

Lightning:

Thunderstorms generate electrical discharges of incredible voltage, which are visible as lightning bolts. Atmospheric lightning bolts can extend for miles through clouds, and are not dangerous. They can provide useful information. Sound travels approximately one mile every five seconds, so by counting "One thousand one, one thousand two, etc." as soon as a lightning bolt is seen until the thunder clap is heard, a rider can estimate how far away the storm is. By comparing intervals, an estimate can be made as to whether the storm is approaching and if so, how fast.

Lighting discharges from clouds to ground, and from ground to clouds, are common and can be extremely dangerous. Humans and horses do not have to be struck by a lightning bolt to be killed. Being in the dispersion path along the surface of the ground can provide enough current to stun the heart. When caught in a thunderstorm, avoiding areas that are probable targets should be your primary concern.

Locations of Strikes:

Any tall objects, particularly those that reach above surrounding contours, make probable targets for lightning. These objects may include a lone tree, a small stand of trees surrounded by clear ground, an exceptionally tall tree within a canopy of trees, or even the earth itself where it forms a ridge, peak or promontory point. "Moving targets" often include humans, riders and pack animals who are traveling on exposed domes and flat areas, tall boulders and rugged mountain areas.

A very common lightning target is the sharp edge of a vertical cliff, particularly when clouds are hanging low in mountain valleys. Lightning bolts seem to more often strike larger, sharp edged rocks than those with smooth, round surfaces.

Lightning can blast through metal, melt rocks into a mass of bubbles and instantaneously turn water into super heated steam. The rapid expansion of this steam can cause trees and moisture laden rocks to explode, and huge trenches to be blasted out of moist, grassy ground.

"Lightning never strikes twice" is an old saying that is in an odd sense true. Lightning typically strikes more than twice. A normal lightning strike consists of three to four strokes and can have as many as twenty strokes. If the cloud recharges before it moves on, it can repeat this series of strikes many times. It takes the typical cloud about a minute to recharge itself. If lightning strikes near you, use that minute to find a safer spot!

Hazards to Humans and Horses:

Obviously a direct up or downstroke of lightning contacting a human or horse has lethal potential. Side flashes can occur when a person or horse is standing near an object, such as a tree. A living body provides an efficient electrical conductor and the lightning bolt can leave the tree and enter the body in order to reach the ground. Ground currents radiating away from the strike can travel significant distances and can be extremely dangerous.

To die or not to die!

Lightning downstrokes are the least fatal of the "direct hits". These occur in flat areas such as in an open meadow. The air surrounding the target can absorb part of the discharge and over 70% of humans struck by downstrokes will survive.

Lightning upstrokes are always fatal. The entire current is drawn upward through the body and discharged to the clouds above. Upstrokes rarely occur on flat areas or on bodies of water. Lightning strikes on mountain peaks and promontories are always upstrokes.

Death from radiated ground currents depends on many factors; the proximity to the strike, the type of ground surface (how well it can absorb the discharge) and how the person is positioned when the charge passes.

Survival Guide:

• Avoid areas of certain death if lightning strikes. These include any natural or man made peaks, promontories, ridges and exposed cliff trails.

• Avoid areas that have been previously struck.

• Don't make yourself an inviting target by staying out in open country.

• Do not seek shelter under a solitary tree or a small grove of trees.

• Don't hole up in a small cave or mine opening that can act as a "spark gap" if lightning strikes nearby.

• Stay back from open water as discharges can travel along the surface to you.

• Avoid damp areas and natural drainages as they conduct ground currents.

[EDIT: Material added 3/7/13]

Analysis of direct strike lightning survivors shows a correlation between wearing hooded rain gear and reduced body absorption of the lightning charge. This reduction is attributed to a phenomenon known as a "flashover" where the charge travels in an arc around the victim through / over the victim's clothing. If the impedance of slick rain gear is less than the impedance of the victim's body (which can occur, especially if the rain gear is moist or wet) and the victim is wearing the rain gear's hood, he/she may experience a flashover rather than a direct body strike.

[End EDIT]

When you are overtaken by a severe thunderstorm, your safest place in that electrical storm is in a vehicle. Considering that you probably don't have one nearby when you are out riding, some other practical options include:

• Get down and away from exposed peaks and promontories.

• Take shelter in a building, if possible, but avoid isolated sheds or small structures in open areas that may be inviting targets.

• If in the woods, take shelter under shorter trees, staying as far away as possible from the taller trees or any tree that appears to have been struck before.

• If in open country, move to lower lying areas, remembering to stay clear of damp zones and drainages.

• Spread the group out to minimize the risk of multiple casualties.

• Stay clear of metal objects; wire fences, metal pipes or rails, equipment, etc. Remove metal tools that you may be packing and place them away from you.

• Unsaddle your horses and remove metal bits and bridles. If you choose to secure your horses, tie them to short trees and spread them out; close enough that they can see each other, but far enough apart to prevent multiple casualties. DO NOT tie horses to metal tie posts or railings during a thunderstorm. You will need the saddle pad or blanket for your own protection!

• Assume a semi-crouched position on your toes, hands folded and off the ground, feet close together. Crouch on your saddle blanket or pad, driest side up. This posture and use of the blanket or pad will help protect you from dangerous surface discharges.

• Realize that the horses may bolt, either due to getting frightened by the thunder or shocked from ground currents. Consider your own survival first. Mother Nature will take care of the horses. Wait for lightning activity to subside before rounding up your mounts. To attempt to do so during a severe series of lightning strikes is not only foolish, but probably futile.

First Aid:

If caught near a lightning strike, remember another strike could occur in about one minute. Don't leave your safe position. The group leader should "roll call" everyone to determine that everybody is OK.

If someone is down, unless he/she took a direct hit, he/she is probably only stunned. Don't everybody rush over to the victim and become mass casualties in the next strike. Someone should check the victim for breathing and circulation. If the heart or respiratory system is stunned, artificial respiration or CPR may be necessary until the victim recovers. (In severe cases, CPR may be required until medical intervention is available.)

Those appearing stunned or slightly disoriented should be watched for additional complications.

Never forget that until the cloud moves on, there is a significant possibility of one or more additional strikes. There are several documented instances where numerous people were killed while attending to a single lightning strike victim. While the lightning activity is continuing, the group's highest priority must be to prevent additional casualties.

Anyone taking a direct hit on a ridge, peak or promontory is probably dead. Upstrokes are 100% fatal. While you should not assume the person is dead, you must weigh the potentially grave risk to you or your party if anyone leaves a safe position to investigate while local lightning activity persists.

Getting Regrouped:

Wait for the storm's intensity to pass before getting the group reorganized to ride on. Continue to watch the weather. If the clouds appear to rise and break up, you are probably in good shape. If not, you may be caught in a series of storm cells in which case you should be particularly observant and be prepared to take all necessary precautions again.

Remember, most lightning fatalities are preventable! By being aware of changing weather, not placing yourself in a dangerous area when the storm closes in, and by taking proper action if you are overrun by severe lightning activity, you will probably not become another lightning strike statistic.

How do the experts know where lightning strikes occur, whether they are upstrokes or downstrokes, and that upstrokes are 100% fatal?

Every lightning strike in the United States is recorded by the Bureau of Land Management's Automatic Lightning Detection System, or "ALDS". ALDS consists of a network of sensors, satellite links and computers and can pinpoint the exact time and location of every lightning strike with 500 foot accuracy. ALDS can also determine the type of lightning strike, whether upstroke or downstroke, and plot the information on a map.

How much activity does ALDS record? According to the California Department of Forestry and Fire Protection, on an active day they will receive data of over 4,000 ground strikes in California alone!

It is early in the afternoon on a humid, August day. You and a couple of friends are riding out of a narrow, steep canyon up toward higher flat ground. The trail is narrow and you are about halfway through a one hour climb as you begin to notice the clouds, which were hardly present in the morning, becoming quite heavy and appearing to slowly roll or "boil". You have also noticed the wind pick up erratically and the air temperature feels cooler to you.

1. What are the probable short term weather conditions?

2. What hazards can you expect?

3. What is your best course of action?
   
   Note: This canyon scenario can be applied to any steep, narrow valley.

1. You are likely in for a severe thunderstorm. The "boiling" action of the clouds indicates updraft currents which could not only trigger electrical discharges (lightning), but condensation patterns which often result in huge drops of rain and hail.

2. Having started this segment of your trip from down in the canyon, you probably didn't "read" the signs of impending bad weather. (Of course, you wouldn't have placed yourself in this predicament if you had a more complete view of the sky, right?) As a result, you are caught in a bottleneck.

   Continuing to ride up the rim of the canyon and onto the mesa makes you a likely target for a lightning strike, and wind conditions near the rim could be quite severe. Depending on how well the canyon drains, the base of the canyon, while relatively safe from lightning, is going to catch a great deal of runoff and some flooding may result.

3. Based on my visualization of this scenario, I would suggest to the group that we head back down the trail. If the accumulated clouds start to collect down into the canyon opening, I would execute this plan with some sense of urgency as lightning strikes into the canyon would now be even more likely.

   It would probably not be safe to go to the bottom of the canyon due to potential rising water. We would need to look for locations somewhat higher than the canyon floor, some distance away from jagged, outcropping rock formations and isolated or very tall trees (lightning targets), and clear of washes and dry stream beds which could quickly become swollen with runoff.

   We would plan on getting wet and having to cope with frightened horses since lightning striking anywhere inside the canyon will be extremely noisy and may also result in some pretty incredible corona discharges across soil and rock formations. There may also be tree explosions. Accordingly, I would suggest reasonably spacing the horses apart, not so much so that they want to fight with their riders to get close to the other horses, but far enough apart to prevent a frightened horse from spinning, colliding with another and causing a runaway situation. (Whether to stay mounted or dismount and hold the horses would be based on the skill of the riders and the practicality of the terrain.)

   Unless forced out by water, we would hold our position until it is clear that the storm has passed, whereupon we could complete our journey.

As in most of these situations, there is often more than one solution, the practicality of each choice often dictated by the skill of the riders present and the tolerance of the horses for the conditions being experienced. If your solution differs from the one offered, but takes into account the hazards present in the scenario, you are probably on the right track!