- Climate is what we expect. Weather is what we get. – Attributed to Mark Twain
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. Types of severe weather vary depending on latitude, altitude, 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 storm.
Travelers are highly 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 own life may be at risk!
Perhaps 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 may be 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, 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, either by watching the local TV station or using 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 always universal. 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.
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 & cruises may be delayed or even cancelled. 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 widespread 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 to give updates on your expected arrival time and alternative arrangements.
A cyclone, also known as a hurricane (in North America) or typhoon (in Asia and Oceania), is an organized rotating precipitation system packed with damaging winds and heavy rain. Unlike a tornado which usually inflicts damage only along a narrow path, a cyclone is generally spread out over a broad area; they can be hundreds of miles wide. Effects include but are not limited to: windstorm, very heavy rain which can lead to widespread flooding and mudslides, thunderstorms, and high waves. Flights and any methods to get out of the affected area will certainly be impeded.
This section covers only the dangers of cyclones for travelers on land. However, cyclones are also a major hazard at sea as that is where they form and get their energy from; 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, and visitors should know about those systems; see our destination articles for details. On the map, "RSMC" indicates a Regional Specialized Meteorological Center, the people responsible for such warnings.
Travelers should check the weather forecast for their destination before and during travel to be aware of any forthcoming weather risk, especially in cyclone season. Typically they show the future track of any incoming storm, in which you are advised to plan ahead or evacuate as soon as possible if it will affect your area. It is never advised to travel in an area where a cyclone is expected to occur because of its potentially devastating aftermath.
Regardless of the expected severity of the storm, obey warnings and commands from local authorities regarding what to do and where to evacuate; riding it out will likely result in loss of life, in which case even search and rescue may not risk themselves rescuing anyone trapped until the storm passes. If you are caught when a cyclone hits, you are strongly advised to seek shelter in a steady enough building and stay indoors until it is all over. 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.
While tropical cyclones are the most commonly heard, 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). Power outages are very likely when strong wind strikes, as tree branches can fall down and hit cars, houses, and electric lines; prolonged outages are not uncommon, it can last for days if the outage is widespread.
Cyclones can cause serious power outages as objects are flying and trees are falling, taking down power lines and causing widespread blackout that can take days before it is restored. 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 more widespread the outage is. Even evacuation shelters may be prone to outages 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. 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.
The defining phenomenon in thunderstorms are lightning and the associated thunder, but dangers include heavy rain, strong gusty wind and possibly hail. Most lightning strikes from inside or between clouds, but some hit the ground, causing fires, electrical damage etc.
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 even in the Arctic.
You can estimate the distance to the lightning by knowing that while you see the lightning instantly, the sound travels a kilometre in three seconds. This is not too much help though: you can usually hear the thunder only within a few kilometres, which means you are too close to be safe.
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. 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.
A hail is solid balls of ice falling during a thunderstorm, whose size can range from a benign pea-size to a devastating golf ball-size that can shatter a car's windshield! Bring all people and your car to any indoor space (your house or a garage) to avoid harm and hurt, and get away from windows or openings when hail hits.
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 is potentially deadly, especially for those with breathing problems. Some cities have taken drastic measures to combat smog in recent years, such as outlawing coal powered heating or drastically reducing the number of cars allowed to drive (even-numbered license plates one day and odd-numbered plates the other day, for example). Indeed, several cities once notorious for smog have now greatly reduced or all but eliminated it, but 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.
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.
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, 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 -10°C will feel like -20°C.
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.