Severe weather is the generic term for any dangerous weather phenomenon with the potential to cause damage, serious social disruption, or loss of human life. Severe weather can occur anywhere in the world, and there are different types of it, which can depend on geography, topography, and atmospheric conditions. High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, tornadoes, waterspouts, and cyclones. Regional and seasonal severe weather phenomena include blizzards, snowstorms, ice storms, and dust storms.
Travelers are strongly advised to be aware of any risk of severe weather affecting their area as they may affect any travel plans. Attractions may be closed, transportation will likely be impeded, and even your life may be at risk!
|“||Climate is what we expect. Weather is what we get.||”|
—Attributed to Mark Twain
The best advice for travelers is to first research the climate of your destination; if any risk of severe weather is the norm for the time period that you travel, you are advised to prepare for unpredictability regarding the weather. The predicted weather on your travel plan may only come out at the earliest 2 weeks before your travel and becomes more accurate only as the day gets closer, so you should plan ahead while at the same time be flexible, especially on where to go and what to wear.
As weather can change somewhat on a day-to-day or even hour-to-hour basis, check the weather forecast for your destination before and during your travel to be aware of any forthcoming weather threats on your destination, using either local TV and radio or your smartphone app. While television weather forecasts may be shown in different languages, their weather symbols (those that indicate for example sunny, rainy, or partly cloudy weather) are usually comprehensible. There are also radio stations which just transmit weather forecasts; Canada and USA reserve seven frequencies (162.4 to 162.55MHz in 0.025MHz steps) for weather radio, there's also one channel reserved on marine VHF radio for marine weather.
The rest of the world uses Celsius and millimeter as their temperature and precipitation intensity, respectively, while the USA uses Fahrenheit and inches. See the above chart for a rough conversion of the temperature between the two measurement systems. One inch of precipitation equals to 25mm (2.5cm) of liquid in the rain gauge, higher amounts mean that more rain is falling and severe weather may be happening. Many weather forecasts also use the overly complicated unit "liters per square meter", which they seem to think sounds more intuitive than "millimeter", but the two units are exactly the same with the former just being a roundabout way to express the latter. Marine and aeronautical forecasts are likely to use nautical miles per hour (knots) and will report conditions (such as rough seas for mariners) to suit their specific target audience.
If a severe weather does exist in the area that you wish to travel, you are highly suggested to have a change of travel plan; if a blizzard is occurring at the ski resort that you wished to go, you should go to an alternative resort, or perhaps go to the beaches or downtown if the weather there is better. If it does or will happen to where you are right now, obey all commands and warnings from local authorities; do not risk yourself by disregarding any threats.
Getting in and out of the area will be difficult because of severe weather: roads may be closed, flights or cruises may be delayed or even cancelled. Trains are sometimes the last thing still running, but when overhead wires have been hit and cut by trees and no Diesel locomotive is available, there is little the railway can do. Check your transportation provider regarding any alternative arrangements, compensation or rebooking. Keep your composure when interacting with them as weather is always beyond their control and they would have got the same complaints from other travelers that are stuck with you. Contact any people you will meet or the hotels you'll stay at your destination or your workplace and someone at your departure point to give updates on your expected arrival time and alternative arrangements.
A cyclone, also known as a hurricane (in the Americas) or typhoon (in Asia and Oceania), is an organized rotating precipitation system packed with damaging winds and heavy rain. Effects include but are not limited to: windstorm, very heavy rain which can lead to widespread flooding and mudslides, thunderstorms, and high waves. They occur mainly in tropical and subtropical regions.
Unlike a tornado which inflicts damage only along a narrow path, a cyclone is generally spread out over a broad area; they can be hundreds of miles wide. Cyclones form around low pressure areas and the winds spiral into those. They are usually doughnut-shaped, a circular band of high winds and heavy rain around a relatively calm center called the eye of the storm. An observer near the center of the storm's path sees two intense blasts of wind and rain separated by a calm period in the eye. Out toward the edge, there is only one blast of wind and rain but it may last longer.
This section covers only the dangers of cyclones for travellers on land. However, cyclones are also a major hazard at sea as that is where they usually develop; see our article Cruising on small craft for basic advice and consult specialist publications for more detailed advice.
Areas where cyclones are common often have good warning systems; typically they show the approximate intensity and the predicted future track of any incoming storm. Forecasts are not exact, but they are almost always good enough to provide a few days warning of major storms.
Once such a storm hits it is usually difficult or impossible to get out of the affected area; certainly neither planes nor boats can be used safely and other transport will be impeded. For most travellers, the best course is to heed weather warnings and leave before it hits. Alternately, take shelter and wait it out, then be prepared to deal with chaos in the aftermath of the storm.
|Tropical depression||≤ 62||≤ 38|
|Category 5||≥ 252||≥ 157||catastrophic|
The classification systems in different regions vary, and scientists have proposed several alternatives, but the systems in current use are all similar. The table shows the Saffir-Simpson scale used by the US weather service. Categories 3 and higher are described as "major hurricanes" in the US, while categories 4 and 5 are called "super-typhoons" in the Pacific.
Category 5 hurricanes are rare in the Atlantic (Zone 1 on the map). For storms that make landfall as cat 5, the last one in the US was Hurricane Andrew in 1992 and, as of mid-2017, there have been only three anywhere in the region in the 21st century. In the Pacific, cat 5 storms are more common. The Philippines has had two in this decade; Typhoon Bopha hit Mindanao in 2012 and Haiyan devastated the Eastern Visayas in 2013.
Regardless of the expected severity of the storm, obey warnings and commands from local authorities regarding what to do and whether, when, where and how to evacuate. A misjudged attempt to ride out a storm is dangerous, perhaps fatal. In these situations local residents, local government and the professional forecasters will all likely have both more experience and better information than a traveller, so take their advice!
If you are unable to evacuate, you are strongly advised to seek shelter in a sturdy building and stay indoors until it is all over. Even search and rescue may not risk themselves rescuing anyone trapped until the storm passes. In tropical or subtropical regions where cyclones can frequently form, the buildings are often designed to withstand high winds; for example they may have strong shutters which can be closed when a storm is expected. Still, stay away from windows—the cyclone may pick up pieces of gravel or other projectiles which can do real damage even when buildings are designed for the wind. In a house, get underground or cover yourself in a bathtub with sheets or blankets so that you are not blown away. In a high-rise, an interior stairwell on a lower floor may be the safest place in the building. But of course, follow the advice of local authorities above all else.
Cyclones can cause serious power outages as objects are flying and trees are falling, taking down power lines and causing blackouts that may be quite widespread and in some cases can last for several days. Weather forecasts would usually include wind speeds especially if its threat is imminent; winds that are generally 35mph (50km/h, 14m/s) or above have the potential to take down some trees; the higher the speed and the larger the cyclone, the higher and more widespread the threat is. Even evacuation shelters are prone though the building may not be structurally damaged; a damaged power pole can cause outages within the electricity network that utilizes the pole.
In case of a power outage threat, stock up with non-perishable meals that you do not need to cool in the fridge and can last for days. Take a look at the article on camping food for suggestions. Have a cellphone with you and use it only if you need to call help; if you have a car, bring a car charger and fill up with enough fuel.
If power is off, turn off and unplug all devices that use the electricity grid as it may be damaged by a power surge when electricity comes back on (and some devices may get overheated if forgotten). Do not touch the affected power lines. It is really helpful to stay at the evacuation center (if one is set up near your neighborhood) or government service offices as they have the highest priority to have power back on; they also have some spare rations for emergency.
While tropical cyclones are the most common, there is also a special type of storm called an extratropical cyclone which can happen outside the tropical regions or during the fall and winter months; these can sometimes cause great damage when they hit areas that are not prepared for them. The main concern would be the wind that can still reach cyclone speed in addition to the rainstorm or snowstorm (blizzard).
There are also polar vortexes which form near the poles and sometimes move into populated areas. These do not have the extremely high winds of tropical cyclones — cold air lacks the energy for that — but they may still be very unpleasant with high winds and lots of snow.
The defining phenomenon in thunderstorms are lightning and the associated thunder, but dangers include heavy rain, strong gusty wind and possibly hail. While most lightning strikes from inside or between clouds, some does hit the ground and causes a wide range of effects from electric damage to fires and death of persons hit.
Thunderstorms result from rapid upward movement of warm, moist air, which form very high (even more than 20 km) cumulonimbus clouds. They are common in tropical regions during the rainy season, but can occur around the globe depending on the season of the respective regions. If you see a towering cauliflower-like cloud in the distance, it is an imminent sign of a thunderstorm brewing or currently occurring (from nearby, the shape is masked).
Lightning tends to hit the highest object towering from the ground, so avoid hill tops and open areas and do not seek shelter under a high or lone tree. Get indoors if possible or crouch down on the ground if there's no shelter. Cars with enough steel (many modern ones are mostly plastic) form Faraday cages and are thus safe, but avoid driving if possible. Avoid anything connected to power lines, phone lines etc., as electricity induced by a lightning strike can travel far along these. Swimming or taking a shower is dangerous for the same reason.
During a storm, unplug your electronic devices to avoid risk of having them fried by a lightning-induced power surge. If you plan to spend a lot of time in a high-risk area, get a surge protector. These are reasonably cheap devices that go between your computer or other valuable device and the wall socket; they do not give perfect protection, but they do greatly reduce risk.
In a semi-open area the safest position is at a distance about half the height from a tree or other high object – if the lightning strikes here, it will hit that object instead of you; the strong sound, electricity spread in the ground and pieces flying from the hit object are still dangerous. Parts of the lightning can even bounce off to people in the vicinity. Keep your feet together so that electricity in the ground does not travel between them through you. Spread out, so that if somebody gets hurt, the others are unharmed and ready to help.
Hail is solid balls of ice falling during a thunderstorm. Hailstorms are not very common but are a risk in some areas such as the Canadian Prairies. In mid-latitudes and tropical regions, they typically occur in spring or transition from wet to dry season.
In most storms, the hailstones are about the size of a pea; being bombarded with these can be quite unpleasant but is not really dangerous. Some storms have larger stones, golf ball-size or more, and these are definitely dangerous; they can shatter a car's windshield or knock a person unconscious!
If there is a threat of hail, bring all people, pets, and your car to an indoor space (your house or a garage) to avoid harm and hurt, and get away from windows or openings when hail hits.
- Main article: Tornado safety
In a few parts of the world, especially in the United States, thunderstorms can also spawn tornadoes, which are spinning columns of air that sucks everything it blows inward and upward. They can have winds up to hurricane-force speeds (more than 100mph/160kph) and travel along a swath of area. These typically lasts up to an hour at most, but often comes with little warning especially for those unaware. They have been known to down trees and power lines, and even hoist a house from its foundation!
Tornado typically occurs in spring especially in mid-latitude countries. Large and organized weather systems that span across multiple states can spawn a tornado outbreak; which are multiple tornadoes forming within a wide area.
Spotting a tornado is easy at daytime but dangerously difficult at night. If you see a funnel coming down from a dark cloud or debris & dirt flying high, it is a good sign that a tornado is about to happen at that very spot. Hail, especially of larger size, usually precedes a brewing tornado. If you can't spot any of them at night, watch the weather forecast on TV or listen on the radio. In some localities, sirens warn of an incoming tornado in the immediate area from which you must seek shelter immediately. Fleeing a tornado by motorcar can be tough because heavy rains may blind drivers from seeing a tornado and its direction of travel.
Fog and smog
Surprisingly, fog is the most lethal kind of weather in some parts of the world, mostly because of traffic accidents. When driving a car in fog, go slow. If fog is very thick, you might need to wait it out. With a boat, mooring in a safe place is the best option, but if that is not possible you have to quickly note your position and keep track of your movement, especially if you do not have a GPS. Remember your fog signals, avoid shipping lanes and choose a route that is safe in these circumstances. With a GPS, remember it does not show other vessels, even a radar shows only some of them.
Smog is the combination of air pollution and fog that can occur in big cities, especially those with poor environmental protection, and also sometimes in suburban or rural areas near heavily-polluting factories, electric plants and refineries. Specific geographic features and environmental conditions, such as inversion (a warm layer of air sitting atop a cold layer of air and thus "blocking" all air beneath it from rising) may make certain places especially prone to smog. Smog at its best will only reduce visibility and grays the sky; at worst it can disrupt your breathing system and can cause death as you breathe pollutants into your body. If the smog is especially severe or you have breathing problems, it is unwise to get out and travel; if you have to, wear an N95 mask or an extra piece of clothing to cover your nose and mouth. Look out for weather advisories in the media or out and about. While some places have taken drastic measures to combat smog in recent years with positive results, in places like China, Mexico City or Los Angeles, smog is still a major problem.
Intense rain with insufficient areas to absorb the water can result in flash floods. In the US the National Insurance Flood Program defines it as “rapid flooding of low-lying areas in less than six hours, which is caused by intense rainfall”.
Flash floods often occur where the soil is too dry to quickly start absorbing water, where the topography forces the water into narrow valleys, and where wetlands have been drained and streams walled. In some areas quite moderate rain much upstream can cause a flash flood with little warning.
Another source of flash floods is volcanic activity under a glacier, which will melt extreme amounts of ice. If the water is contained by an ice barrier, even billions of tons of water may suddenly get loose. Similar outburst can occur without volcanic activity, when barriers of ice lakes break for other reasons. Such jökulhlaups are recurring events in Iceland, destroying roads and bridges on their way to the sea (mostly in uninhabited areas).
Like in the case of a tsunami, immediately try to get to high ground when there is a flash flood warning. Try to keep a flotation device near you. When the flash flood strikes, don’t try to walk or swim — the current is stronger than you and as little as 6 inches (15 cm) of rapidly moving water can knock you down (not to mention items from trash cans to branches that may be carried by the water).
Driving is also a bad idea; two feet (60 cm) is enough to sweep your vehicle away; even less is enough to make steering impossible and probably also to stall the engine. If you see a large strip of standing water on the road in front of you, do not pass through it, as you might not know if it's deep enough to stall your car and strong enough to sweep you away. You’re actually more of a sitting duck if you’re in a car and the water is rising. Open the car door if you can. If the water level is high enough to block the door, you'll have to roll down a window or break it to escape.
In areas where flash flood can be expected, avoid camping near streams and rivers (including wadis, dry riverbeds), which obviously are where most of the water will go, causing flooding. Be especially careful with canyons, from where it is difficult to escape and where flash floods often really are worthy of their name.
Heatwaves are abnormally high temperatures for a period of a couple of days. They can cause discomfort and health risk, even to those that are seemingly prepared.
Though a general definition of heatwave is when temperatures that are about 27°C (80°F) or above, its effect can be dramatically different depending on humidity, which affects the temperature that one feels on its skin. A person experiencing a dry heatwave may begin to feel discomfort when it is 32°C (90°F), but with the same temperature in a 75% humidity, one will feel like it is 43°C (109°F)!
Avoid strenuous activities outside, especially during the afternoon when the temperature is the hottest. Drink lots of fluid as that will cool you down while at the same time replacing the fluids in your body exerted by the heat. Do not wear any dark clothing, as it absorbs heat and will make your body lose fluid even quicker. It is a good idea to stay much of the time somewhere indoors where cooling systems are usually found, or go to a park and sit under a tree to avoid the sun; if you choose to enjoy the sun instead, wear a sunscreen or preferably lightweight sport fabrics, sunglasses, and a wide-brimmed hat to protect your head.
Do not leave children and pets in your car as the inside car temperature can rise quicker than the outside, and can soon be outright dangerous. Children and elderly people are especially prone to heat related illness, from cramps to heatstroke; you should regularly check how they feel, and go for emergency treatment as soon as the symptoms show up.
Cold weather is an issue in winter sports, in wintertime in temperate areas, when visiting high mountains – even by driving over mountain passes – and year round in the Arctic and Antarctic. Cold weather is part of everyday life for the residents of these areas and for visits in the cities the cold is rarely a threat.
Some preparations, like having adequate clothes, will make your visit much more comfortable, will let you stay outside for longer times, and may allow you to enjoy even quite severe circumstances. When venturing out on the countryside or out in the wilderness, or even driving along less busy roads, neglecting basic precautions can mean risking your life.
In places like Finnish Lapland a nice sunny day at -10°C may turn into a night at -25°C (+14 to -13°F), which means much more clothing will be needed. In mountainous areas even more extreme changes are common. This means you should be aware of possible changes at least when returning to your base will take substantial time (do not count on taxis if you are returning when everybody else is). If there is wind, the cold may find its way through your clothing and windchill will add to the cold, such that at 10 m/s (22,5 mph), -10°C (+15°F) will feel like -20°C (-5°F).
In temperatures near or below freezing, snowfall is usually possible. Snowfall or blowing snow can severely limit the visibility, like dense fog or worse. Snow and ice can hide dangers, such as clefts in the rock, and make a lake look like a field. While frozen lakes and rivers are often used for transport, weak ice is a severe risk. Snowfall can also severely hamper orientation. Without anything to guide them, humans have a natural tendency to walk in circles as their strides are slightly longer on one side. In heavy snow, this can make you totally lost and you'd be surprised to hear how many people died of exhaustion or exposure just a few kilometers from safety. A compass will help avoid this, just make sure you know the direction to a safe area you cannot miss (near the poles, note the difference between magnetic and geographic north). A map can of course allow more flexible options. A GPS may feel even better, but take care about it not dying from exhausted batteries, moisture or cold – a compass still makes a good backup.
Air pollution is a nuisance in some large cities, worsened when air is dry and stagnant. Pollution in cities tends to build up during weekdays, hitting a maximum before the weekend. Geography often worsens air pollution problems. Many cities lie inside a valley of some sort. If warm air sits atop colder air (inversion), the polluted air cannot move out and accumulates. Cities increasingly take measures to combat air pollution, including limiting the use of automobiles or restricting heating with wood or coal.
Visitors with asthma or other medical conditions might be affected even by mild air pollution.
When pollution gets severe, people might be advised to stay indoors.
Cities might restrict driving and electricity consumption during periods of high air pollution. In some cities, there might be cheaper or entirely free public transit tickets on "smog days" to entice people out of their cars or give an option when driving is forbidden.