Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather vary between 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.
Cyclone, also known as hurricane (in North America) or typhoon (in Asia and Oceania), is an organized rotating precipitation system packed with damaging winds and heavy rain, generally in a broad area. Cyclones typically form in tropical or subtropical regions, typically because of the sea temperatures which inhibits its development. But a special type of storms called extratropical cyclones can also happen outside the tropical regions during the fall and winter months. Effects include but not limited to: windstorm, very heavy rain which can lead to widespread flooding and mudslides, thunderstorms, and high waves.
It is never advised to travel in an area where a cyclone is expected to occur because of its potentially devastating aftermath. But if you are expected to be in an area where the cyclone hits, you are highly advised to seek shelter in a steady enough building.
The defining phenomenon in thunderstorms are lightnings and the associated thunder, but dangers include heavy rain, strong gusty wind and possibly hail. Most lightnings strike 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 lightnings 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 a few kilometres, which means you are too close to be safe.
Lightnings tend 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 in possible. Cars with enough steel form Faraday's cages and are thus safe, but avoid driving. Avoid anything connected to power lines, phone lines etc., as electricity induced by a lightning can travel far along these. Swimming or taking a shower is dangerous for the same reason.
In a semi-open area the safest position is at a distance about half the hight 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. Spread out, so that if somebody gets hurt, the others are unharmed and ready to help.
Surprisingly, fog is the most lethal kind of weather in some parts of the world, much because of traffic accidents. When driving a car into fog, limit the speed. 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).