Check the forecast, then keep checking
Weather shapes almost every outdoor decision: what to wear, what to carry, which route to take, and when to turn back. The National Park Service's hiking safety page for Great Smoky Mountains National Park asks hikers to check the current forecast and be prepared for quickly changing conditions. Its backcountry camping page is blunter: weather can change quickly, especially in the mountains, so expect any weather, including extreme temperatures, lightning, rain and wind.
Read the forecast for the place you are going, not the nearest town, because a valley and a ridge a few miles apart can have very different days. On the water, use the marine forecast; the paddling guide covers that side. The rest of this guide is about the three weather hazards that most often turn an ordinary trip into an emergency on land: lightning, rising water and cold.
Lightning: the scale of it
The National Weather Service, which is part of NOAA, runs the federal lightning safety programme. Its lightning page gives the scale: lightning strikes the United States about 25 million times a year, and kills about 20 people in the United States in an average year, with hundreds more severely injured. Most lightning happens in summer, but the Weather Service stresses that people can be struck at any time of year.
Many people treat lightning as bad luck, something that either happens or does not. The Weather Service's guidance treats it as a risk that can be reduced, mostly by where you are when a storm arrives. That makes it a planning problem as much as a weather problem.
No safe place outside
The Weather Service's lightning tips begin with one sentence in capital letters: no place outside is safe when thunderstorms are in the area. The second point follows from it. If you can hear thunder, lightning is close enough to strike you.
The rule needs no calculation and no estimate of distance. If thunder is audible, the response is the same: move to safe shelter immediately.
The core rule
When you hear thunder, go to safe shelter at once, and stay there for at least 30 minutes after the last thunder you hear. Both parts come from the National Weather Service's lightning tips.
What counts as shelter
The Weather Service names two kinds of safe shelter: a substantial building with electricity or plumbing, or an enclosed, metal-topped vehicle with the windows up. Anything that is neither of those does not meet the Weather Service's description of safe shelter, and its last-resort list below names isolated trees and cliff or rock overhangs as places never to shelter. Once inside a building, it also advises staying away from corded phones, electrical equipment, plumbing, windows and doors, and off porches.
For hikers and paddlers this is a hard rule, because on most trails and lakes the nearest safe shelter is the car at the trailhead or a building at the launch. That is why lightning safety outdoors is mainly about timing: being near shelter, or off exposed ground and water, before a storm arrives, rather than finding shelter after it does.
If you are caught out
Sometimes a storm arrives with no safe shelter anywhere nearby. The Weather Service lists actions that may reduce your risk in that case. It calls them last-resort tips: they lower the risk but do not make you safe. Paraphrased, they are:
- Get off elevated ground, such as hills, ridges and peaks, at once.
- Never lie flat on the ground.
- Never shelter under an isolated tree.
- Never use a cliff or rocky overhang for shelter.
- Get out of and away from ponds, lakes and other bodies of water immediately.
- Stay away from objects that conduct electricity, such as wire fences and power lines.
For paddlers, the water point is the one to act on early: head for shore at the first sign of a building storm, not at the first thunder, because a canoe in the middle of a lake may be a long way from land.
Flash floods and rising water
Thunderstorms bring a second hazard that kills more people than lightning. The Weather Service's flood safety page says that each year more deaths occur from flooding than from any other hazard related to thunderstorms. Over half of flood drownings happen when a vehicle is driven into flood water; the next largest share happens when people walk into or near it.
The page gives figures that explain why. Six inches of fast-moving flood water can knock over an adult. Twelve inches of rushing water can carry away most cars, and two feet can carry away trucks and SUVs. It also warns never to drive around barriers across a flooded road, because the road under the water may have collapsed. Its conclusion is the source of the familiar slogan: it is never safe to drive or walk into flood water. Turn around; do not drown.
Outdoors, flash floods are a reason to look at the terrain as well as the sky. The Park Service's backcountry page asks visitors to research hazards before a trip, naming flash floods among them, and to have a plan for what to do if they meet one. The Great Smoky Mountains page adds that heavy rain can swell streams quickly, and the hiking guide covers crossing decisions.
Cold, wet and wind
Not every dangerous day looks dramatic. Rain, wind and falling temperatures can wear a person down slowly. The Weather Service's cold weather page describes hypothermia as the body losing heat faster than it can produce it, and notes that frostbite most often affects uncovered skin and the hands and feet. The Great Smoky Mountains page warns that cool, wet and windy weather can cause hypothermia even in summer.
The defence is in the pack before the weather turns: the extra layers, rain shell, hat and gloves from the ten essentials, put on early. Wind adds to the chill, so a sheltered spot to add layers and eat can make a large difference. If someone in the group starts shivering hard, stumbling or making poor decisions, treat it as a reason to stop, warm up and head out.
Building weather into the plan
The sources in this guide point to a few planning habits:
- Read the forecast for the exact area, the evening before and again on the morning of the trip.
- Know where the nearest safe lightning shelter is on your route; for many trails, it is your vehicle.
- Plan exposed stretches, such as ridges, summits and open water, for times when storms are least likely in the forecast, and be ready to skip them.
- Know which streams and low crossings on your route could rise in rain, and where you would wait.
- Agree in advance that thunder means turning back to shelter, and that nobody has to argue for it.
- Carry layers for the coldest, wettest version of the day, not the forecast high.
Example: a storm on the ridge
Worked example
This is an illustration and describes no real people or place. A pair of hikers plan a ridge walk on a summer day with a chance of afternoon thunderstorms in the forecast.
- They plan to be on the exposed ridge only in the morning, with a lower route back through the valley.
- Clouds build earlier than forecast. They hear distant thunder while still on the ridge.
- They do not wait to see how close it is. They leave the ridge at once by the nearest safe descent, staying away from isolated trees and rock overhangs.
- Rain starts on the way down. They put on rain gear and keep moving towards the trailhead.
- At the car, they close the doors and windows and wait until 30 minutes after the last thunder before driving out, avoiding a low crossing that is starting to flood.