Severe weather travel safety guide

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.

Travellers 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!

General precaution
The best advice for travellers 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 travellers 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.

Severe thunderstorms can be assessed in three different categories. These are “approaching severe”, “severe”, and “significantly severe”.

Approaching severe is defined as hail between 1⁄2 to 1 inch (13 to 25 mm) diameter or winds between 50 and 58 M.P.H. (50 knots, 80–93 km/h). In the United States, such storms will usually warrant a Significant Weather Alert.

Severe is defined as hail 1 to 2 inches (25 to 51 mm) diameter, winds 58 to 75 miles per hour (93 to 121 km/h), or an F1 tornado.

Significant severe is defined as hail 2 inches (51 mm) in diameter or larger, winds 75 M.P.H. (65 knots, 120 km/h) or more, or a tornado of strength EF2 or stronger.

Both severe and significant severe events warrant a severe thunderstorm warning from the United States National Weather Service (excludes flash floods), the Environment Canada, the Australian Bureau of Meteorology, or the Meteorological Service of New Zealand if the event occurs in those countries. If a tornado is occurring (a tornado has been seen by spotters) or is imminent (Doppler weather radar has observed strong rotation in a storm, indicating an incipient tornado), the severe thunderstorm warning will be superseded by a tornado warning in the United States and Canada.

A severe weather outbreak is typically considered to be when ten or more tornadoes, some of which will likely be long-tracked and violent, and many large hail or damaging wind reports occur within one or more consecutive days. Severity is also dependent on the size of the geographic area affected, whether it covers hundreds or thousands of square kilometers.

High winds
High winds are known to cause damage, depending upon their strength.

Wind speeds as low as 23 knots (43 km/h) may lead to power outages when tree branches fall and disrupt power lines. Some species of trees are more vulnerable to winds. Trees with shallow roots are more prone to uproot, and brittle trees such as eucalyptus, sea hibiscus, and avocado are more prone to branch damage.

Wind gusts may cause poorly designed suspension bridges to sway. When wind gusts harmonize with the frequency of the swaying bridge, the bridge may fail as occurred with the Tacoma Narrows Bridge in 1940.

Hurricane-force winds, caused by individual thunderstorms, thunderstorm complexes, derechos, tornadoes, extratropical cyclones, or tropical cyclones can destroy mobile homes and structurally damage buildings with foundations. Winds of this strength due to downslope winds off terrain have been known to shatter windows and sandblast paint from cars.

Once winds exceed 135 knots (250 km/h) within strong tropical cyclones and tornadoes, homes completely collapse, and significant damage is done to larger buildings. Total destruction to man-made structures occurs when winds reach 175 knots (324 km/h). The Saffir–Simpson scale for cyclones and Enhanced Fujita scale (TORRO scale in Europe) for tornados were developed to help estimate wind speed from the damage they cause.

A dangerous rotating column of air in contact with both the surface of the earth and the base of a cumulonimbus cloud (thundercloud) or a cumulus cloud, in rare cases. Tornadoes come in many sizes but typically form a visible condensation funnel whose narrowest end reaches the earth and surrounded by a cloud of debris and dust.

Tornadoes’ wind speeds generally average between 40 miles per hour (64 km/h) and 110 miles per hour (180 km/h). They are approximately 250 feet (76 m) across and travel a few miles (kilometers) before dissipating. Some attain wind speeds in excess of 300 miles per hour (480 km/h), may stretch more than two miles (3.2 km) across, and maintain contact with the ground for dozens of miles (more than 100 km).

Tornadoes, despite being one of the most destructive weather phenomena, are generally short-lived. A long-lived tornado generally lasts no more than an hour, but some have been known to last for 2 hours or longer (for example, the Tri-State Tornado). Due to their relatively short duration, less information is known about the development and formation of tornadoes.

In some places, particularly in the Great Plains region of the United States, you can get tornadoes in a thunderstorm. Tornadoes are extreme winds that spin in a small area, and blow everything near them inward and upward. Tornadoes typically come with little warning, and they are powerful enough to destroy houses.

Tornadoes are easy to spot during the day but harder to spot during the night. However, if you notice a funnel reaching downward from a dark cloud or you see objects flying, you are probably about to see a tornado. Also, hail often occurs before a tornado. If you know there is a high chance of tornadoes but it is nighttime and you can’t see any, follow the weather forecasts on TV or radio. Sometimes, sirens will give warning of a tornado in the vicinity, in which case you need to seek shelter immediately. The best places to be when inside are in interior rooms (such as hallways or windowless basements) with as few doors as possible and no windows and as few large pieces of furniture as possible, such as dressers, bookshelves, or credenzas, as these may fall on you. Note that no room is entirely safe as tornadoes have the power to rip off roofs and in some cases floors. If outside, get inside as quickly as possible, driving to the nearest viable option if necessary, avoid trees, loose items (like farming equipment), bridges/overpasses, and – most importantly – the tornado itself. Due to the heavy rains that occur during a thunderstorm, and therefore when tornadoes are around, getting away from a tornado by driving can be difficult. If outside when debris and objects get thrown around, get down in the nearest ditch or gully, covering your head with your hands; if in a car, park the car, remain seated, and keep all parts of you below the windows with your head covered.

Downburst and derecho
Downbursts are created within thunderstorms by significantly rain-cooled air, which, upon reaching ground level, spreads out in all directions and produce strong winds. Unlike winds in a tornado, winds in a downburst are not rotational but are directed outwards from the point where they strike land or water.

“Dry downbursts” are associated with thunderstorms with very little precipitation, while wet downbursts are generated by thunderstorms with large amounts of rainfall. Microbursts are very small downbursts with winds that extend up to 2.5 miles (4 km) from their source, while macrobursts are large-scale downbursts with winds that extend in excess of 2.5 miles (4 km). The heat burst is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking. Heat bursts generate significantly higher temperatures due to the lack of rain-cooled air in their formation. Derechos are longer, usually stronger, forms of downburst winds characterized by straight-lined windstorms.

Downbursts create vertical wind shear or microbursts, which are dangerous to aviation. These convective downbursts can produce damaging winds, lasting 5 to 30 minutes, with wind speeds as high as 168 mph (75 m/s), and cause tornado-like damage on the ground. Downbursts also occur much more frequently than tornadoes, with ten downburst damage reports for every one tornado.

Squall line
A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front. The squall line typically contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes or waterspouts. Severe weather in the form of strong straight-line winds can be expected in areas where the squall line forms a bow echo, in the farthest portion of the bow. Tornadoes can be found along waves within a line echo wave pattern (LEWP) where mesoscale low-pressure areas are present. Intense bow echoes responsible for widespread, extensive wind damage are called derechos, and move quickly over large territories. A wake low or a mesoscale low-pressure area forms behind the rain shield (a high pressure system under the rain canopy) of a mature squall line and is sometimes associated with a heat burst.

Squall lines often cause severe straight-line wind damage, and most non-tornadic wind damage is caused from squall lines. Although the primary danger from squall lines is straight-line winds, some squall lines also contain weak tornadoes.

Tropical cyclone
Very high winds can be caused by mature tropical cyclones (called hurricanes in the United States and Canada and typhoons in eastern Asia). A tropical cyclone’s heavy surf created by such winds may cause harm to marine life either close to or upon the surface of the water, such as coral reefs. Coastal regions may receive significant damage from a tropical cyclone while inland regions are relatively safe from the strong winds, due to their rapid dissipation over land. However, severe flooding can occur even far inland because of high amounts of rain from tropical cyclones and their remnants.

Waterspouts are generally defined as tornadoes or non-supercell tornadoes that develop over bodies of water.

Waterspouts typically do not do much damage because they occur over open water, but they are capable of traveling over land. Vegetation, weakly constructed buildings, and other infrastructure may be damaged or destroyed by waterspouts. Waterspouts do not generally last long over terrestrial environments as the friction produced easily dissipates the winds. Strong horizontal winds disturbe the vortex, causing waterspouts to dissipate, While not generally as dangerous as “classic” tornadoes, waterspouts can overturn boats, and they can cause severe damage to larger ships.

Strong extratropical cyclones
Severe local windstorms in Europe that develop from winds off the North Atlantic. These windstorms are commonly associated with the destructive extratropical cyclones and their low pressure frontal systems. European windstorms occur mainly in the seasons of autumn and winter.

A synoptic-scale extratropical storm along the East Coast of the United States and Atlantic Canada is called a Nor’easter. They are so named because their winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada. More specifically, it describes a low-pressure area whose center of rotation is just off the East Coast and whose leading winds in the left forward quadrant rotate onto land from the northeast. Nor’easters may cause coastal flooding, coastal erosion, and hurricane-force winds.

Thunderstorms are storms with 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.

A sometimes dangerous occurrence in a thunderstorm is hail. Hail occurs when solid balls of ice (hailstones) fall to the ground during a thunderstorm; while hail is not usually dangerous due to its small size, hailstones can sometimes reach the size of golf balls, and if they reach this size they can shatter car windshields and knock people unconscious. When there is a threat of hail, get yourself and all of your belongings indoors as soon as possible, and do not go near windows or openings while inside that indoor space.

Flash floods
Sometimes, large amounts of rain occur within short amounts of time, causing floods that rise very quickly. These can be extremely dangerous and are called flash floods. As a general rule, if weather forecasts predict very heavy rains in the near future, or a flash flood has already started, get to high ground as soon as possible. Also, avoid camping in narrow canyons during the times of the year when heavy rainstorms or thunderstorms are likely, since these can flood very quickly.

Dust storm
An unusual form of windstorm that is characterized by the existence of large quantities of sand and dust particles carried by the wind. Dust storms frequently develop during periods of droughts, or over arid and semi-arid regions.

Dust storms have numerous hazards and are capable of causing deaths. Visibility may be reduced dramatically, so risks of vehicle and aircraft crashes are possible. Additionally, the particulates may reduce oxygen intake by the lungs, potentially resulting in suffocation. Damage can also be inflicted upon the eyes due to abrasion.

Dust storms can many issues for agricultural industries as well. Soil erosion is one of the most common hazards and decreases arable lands. Dust and sand particles can cause severe weathering of buildings and rock formations. Nearby bodies of water may be polluted by settling dust and sand, killing aquatic organisms. Decrease in exposure to sunlight can affect plant growth, as well as decrease in infrared radiation may cause decreased temperatures.

The most common cause of wildfires varies throughout the world. In the United States, Canada, and Northwest China, lightning is the major source of ignition. In other parts of the world, human involvement is a major contributor. For instance, in Mexico, Central America, South America, Africa, Southeast Asia, Fiji, and New Zealand, wildfires can be attributed to human activities such as animal husbandry, agriculture, and land-conversion burning. Human carelessness is a major cause of wildfires in China and in the Mediterranean Basin. In Australia, the source of wildfires can be traced to both lightning strikes and human activities such as machinery sparks and cast-away cigarette butts.” Wildfires have a rapid forward rate of spread (FROS) when burning through dense, uninterrupted fuels. They can move as fast as 10.8 kilometers per hour (6.7 mph) in forests and 22 kilometers per hour (14 mph) in grasslands. Wildfires can advance tangential to the main front to form a flanking front, or burn in the opposite direction of the main front by backing.

Wildfires may also spread by jumping or spotting as winds and vertical convection columns carry firebrands (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as firebreaks. Torching and fires in tree canopies encourage spotting, and dry ground fuels that surround a wildfire are especially vulnerable to ignition from firebrands. Spotting can create spot fires as hot embers and firebrands ignite fuels downwind from the fire. In Australian bushfires, spot fires are known to occur as far as 10 kilometers (6 mi) from the fire front. Since the mid-1980s, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season in the Western United States.

Any form of thunderstorm that produces precipitating hailstones is known as a hailstorm. Hailstorms are generally capable of developing in any geographic area where thunderclouds (cumulonimbus) are present, although they are most frequent in tropical and monsoon regions. The updrafts and downdrafts within cumulonimbus clouds cause water molecules to freeze and solidify, creating hailstones and other forms of solid precipitation. Due to their larger density, these hailstones become heavy enough to overcome the density of the cloud and fall towards the ground. The downdrafts in cumulonimbus clouds can also cause increases in the speed of the falling hailstones. The term “hailstorm” is usually used to describe the existence of significant quantities or size of hailstones.

Hailstones can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and crops. Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 12th century in Wellesbourne, Britain. The largest hailstone in terms of maximum circumference and length ever recorded in the United States fell in 2003 in Aurora, Nebraska, USA. The hailstone had a diameter of 7 inches (18 cm) and a circumference of 18.75 inches (47.6 cm).

Heavy rainfall and flooding
Heavy rainfall can lead to a number of hazards, most of which are floods or hazards resulting from floods. Flooding is the inundation of areas that are not normally under water. It is typically divided into three classes: River flooding, which relates to rivers rising outside their normals banks; flash flooding, which is the process where a landscape, often in urban and arid environments, is subjected to rapid floods; and coastal flooding, which can be caused by strong winds from tropical or non-tropical cyclones. Meteorologically, excessive rains occur within a plume of air with high amounts of moisture (also known as an atmospheric river) which is directed around an upper level cold-core low or a tropical cyclone. Flash flooding can frequently occur in slow-moving thunderstorms and are usually caused by the heavy liquid precipitation that accompanies it. Flash floods are most common in dense populated urban environments, where less plants and bodies of water are presented to absorb and contain the extra water. Flash flooding can be hazardous to small infrastructure, such as bridges, and weakly constructed buildings. Plants and crops in agricultural areas can be destroyed and devastated by the force of raging water. Automobiles parked within experiencing areas can also be displaced. Soil erosion can occur as well, exposing risks of landslide phenomena. Like all forms of flooding phenomenon, flash flooding can also spread and produce waterborne and insect-borne diseases cause by microorganisms. Flash flooding can be caused by extensive rainfall released by tropical cyclones of any strength or the sudden thawing effect of ice dams.

Seasonal wind shifts lead to long-lasting wet seasons which produce the bulk of annual precipitation in areas such as Southeast Asia, Australia, Western Africa, eastern South America, Mexico, and the Philippines. Widespread flooding occurs if rainfall is excessive, which can lead to landslides and mudflows in mountainous areas. Floods cause rivers to exceed their capacity with nearby buildings becoming submerged. Flooding may be exacerbated if there are fires during the previous dry season. This may cause soils which are sandy or composed of loam to become hydrophobic and repel water.

Government organizations help their residents deal with wet-season floods though floodplain mapping and information on erosion control. Mapping is conducted to help determine areas that may be more prone to flooding. Erosion control instructions are provided through outreach over the telephone or the internet.

Flood waters that occur during monsoon seasons can often host numerous protozoa, bacterial, and viral microorganisms. Mosquitoes and flies will lay their eggs within the contaminated bodies of water. These disease agents may cause infections of foodborne and waterborne diseases. Diseases associated with exposure to flood waters include malaria, cholera, typhoid, hepatitis A, and the common cold. Possible trenchfoot infections may also occur when personnel are exposed for extended periods of time within flooded areas.

Tropical cyclone
A tropical cyclone is a storm system characterized by a low-pressure center and numerous thunderstorms that produce strong winds and flooding rain. A tropical cyclone feeds on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. Tropical cyclones may produce torrential rain, high waves, and damaging storm surge. Heavy rains produce significant inland flooding. Storm surges may produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline.

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, but there are also extratropical cyclones that occur far from the equator, often as remnants of a tropical cyclone.

Cyclone wind speeds vary from tropical storm winds to category 5 storms, which can have winds above 170 miles per hour (76 m/s). Generally, cyclones lose energy once they hit land, but they can still cause great damage along coastlines and, in some cases, inland areas. Cyclones form in the oceans and usually travel west until they reach land.

Although cyclones take an enormous toll in lives and personal property, they are also important factors in the precipitation regimes of areas they affect. They bring much-needed precipitation to otherwise dry regions. Areas in their path can receive a year’s worth of rainfall from a tropical cyclone passage. Tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth’s troposphere.

Severe winter weather

Heavy snowfall
When extratropical cyclones deposit heavy, wet snow with a snow-water equivalent (SWE) ratio of between 6:1 and 12:1 and a weight in excess of 10 pounds per square foot (~50 kg/m2) piles onto trees or electricity lines, significant damage may occur on a scale usually associated with strong tropical cyclones. An avalanche can occur with a sudden thermal or mechanical impact on snow that has accumulated on a mountain, which causes the snow to rush downhill suddenly. Preceding an avalanche is a phenomenon known as an avalanche wind caused by the approaching avalanche itself, which adds to its destructive potential. Large amounts of snow which accumulate on top of man-made structures can lead to structural failure. During snowmelt, acidic precipitation which previously fell in the snow pack is released and harms marine life.

Lake-effect snow is produced in the winter in the shape of one or more elongated bands. This occurs when cold winds move across long expanses of warmer lake water, providing energy and picking up water vapor which freezes and is deposited on the lee shores. For more information on this effect see the main article.

Conditions within blizzards often include large quantities of blowing snow and strong winds which may significantly reduce visibility. Reduced viability of personnel on foot may result in extended exposure to the blizzard and increase the chance of becoming lost. The strong winds associated with blizzards create wind chill that can result in frostbites and hypothermia. The strong winds present in blizzards are capable of damaging plants and may cause power outages, frozen pipes, and cut off fuel lines.

Strong extratropical cyclones
The precipitation pattern of Nor’easters is similar to other mature extratropical storms. Nor’easters can cause heavy rain or snow, either within their comma-head precipitation pattern or along their trailing cold or stationary front. Nor’easters can occur at any time of the year but are mostly known for their presence in the winter season. Severe European windstorms are often characterized by heavy precipitation as well.

Ice storm
Ice storms are also known as a Silver storm, referring to the color of the freezing precipitation. Ice storms are caused by liquid precipitation which freezes upon cold surfaces and leads to the gradual development of a thickening layer of ice. The accumulations of ice during the storm can be extremely destructive. Trees and vegetation can be destroyed and in turn may bring down power lines, causing the loss of heat and communication lines. Roofs of buildings and automobiles may be severely damaged. Gas pipes can become frozen or even damaged causing gas leaks. Avalanches may develop due to the extra weight of the ice present. Visibility can be reduced dramatically. The aftermath of an ice storm may result in severe flooding due to sudden thawing, with large quantities of displaced water, especially near lakes, rivers, and bodies of water.

Cold weather
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 sunny day at -10°C may turn into -25°C (+14 to -13°F) at night, 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.

When driving in a white-out (blizzard-like conditions with minuscule visibility), drive slower than the posted speed limit, but not too slow as to cause vehicles behind you from hitting you. In most places the roads will have some form of marker to follow. In daytime, use full headlights to make you visible for meeting traffic, in dark or dusk fog lights or low beam are much better, as the falling snow is not what you want to see. Do not pull over and park your car on the shoulder unless it is your last resort, as it can be hit by other traffic or snowploughs. Instead drive until you find a safer exit, such as to a small village. The best option for white-out conditions is to not go out at all, but if you are caught in this scenario the best chances of survival are much like that of high fog.

Heat and drought

Another form of severe weather is drought, which is a prolonged period of persistently dry weather (that is, absence of precipitation). Although droughts do not develop or progress as quickly as other forms of severe weather, their effects can be just as deadly; in fact, droughts are classified and measured based upon these effects. Droughts have a variety of severe effects; they can cause crops to fail, and they can severely deplete water resources, sometimes interfering with human life. A drought in the 1930s known as the Dust Bowl affected 50 million acres of farmland in the central United States. In economic terms, they can cost many billions of dollars: a drought in the United States in 1988 caused over $40 billion in losses, exceeding the economic totals of Hurricane Andrew, the Great Flood of 1993, and the 1989 Loma Prieta earthquake. In addition to the other severe effects, the dry conditions caused by droughts also significantly increase the risk of wildfires.

Heat waves
Although official definitions vary, a heat wave is generally defined as a prolonged period with excessive heat. Although heat waves do not cause as much economic damage as other types of severe weather, they are extremely dangerous to humans and animals: according to the United States National Weather Service, the average total number of heat-related fatalities each year is higher than the combined total fatalities for floods, tornadoes, lightning strikes, and hurricanes. In Australia, heat waves cause more fatalities than any other type of severe weather. As in droughts, plants can also be severely affected by heat waves (which are often accompanied by dry conditions) can cause plants to lose their moisture and die. Heat waves are often more severe when combined with high humidity.

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, and the average temperatures for a particular place. A person experiencing a dry heatwave may begin to feel discomfort when it is 32°C (90°F), but at the same temperature and 75% humidity, 90°F will feel like 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.

Air pollution
Air pollution, including smog, is a nuisance in some large cities, worsened when air is dry and stagnant. Visitors with asthma or other medical conditions might be affected even by mild air pollution, and when it gets severe, it’s unhealthy for everyone. In case of severe smog or an existing medical condition, it is unwise to get out and travel; if you have to, wear an N95 mask. Look out for weather advisories, and for long-term stays, consider buying an air filter.

Surprisingly, fog is the most lethal kind of weather in some parts of the world. The deaths are usually caused by traffic accidents that become much more likely when visibility is reduced. In the same way, fog can be lethal in places where you must find your way or watch your step, for instance mountain environments. Fog is most common in the early morning just before sunrise, though there are places where fog is most common during other parts of the day. When driving a car in fog, go slow. If fog is very thick, you might need to wait it out. Sometimes there is fog only in valleys or by bodies of water; when driving downhill visibility can be abruptly reduced unless you are alert.

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. GPS does not show other vessels; even a radar shows only some of them.