Severe weather
Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life.
[5] Due to the effects of climate change, the frequency and intensity of some of the extreme weather events are increasing, for example, heatwaves and droughts.
[8] Organized severe weather occurs under the same conditions that generate ordinary thunderstorms: atmospheric moisture, lift (often from thermals), and instability.
[11] Significant severe is defined as hail 2 inches (51 mm) in diameter or larger, winds 75 mph (65 knots, 120 km/h) or more, or a tornado of strength EF2 or stronger.
[13] 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.
[18] 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.
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.
[27] While not generally as dangerous as "classic" tornadoes, waterspouts can overturn boats, and they can cause severe damage to larger ships.
Downbursts are created within thunderstorms by significantly rain-cooled air, which, upon reaching ground level, spreads out in all directions and produce strong winds.
[29] The heat burst is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking.
[39] Intense bow echoes responsible for widespread, extensive wind damage are called derechos, and move quickly over large territories.
[41] 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.
[42] Coastal regions usually take more serious wind damage than inland, due to rapid dissipation upon landfall, though heavy rain from their remnants may flood either.
A synoptic-scale extratropical storm along the upper East Coast of the United States and Atlantic Canada is called a Nor'easter.
Nor'easters can cause heavy rain or snow, either within their comma-head precipitation pattern or along their trailing cold or stationary front.
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.
[52] 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.
[53][54] Torching and fires in tree canopies encourage spotting, and dry ground fuels that surround a wildfire are especially vulnerable to ignition from firebrands.
[58] 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.
[59] The updrafts and downdrafts within cumulonimbus clouds cause water molecules to freeze and solidify, creating hailstones and other forms of solid precipitation.
[62] The largest hailstone in terms of maximum circumference and length ever recorded in the United States fell in 2003 in Aurora, Nebraska, USA.
[65] 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 be caused by extensive rainfall released by tropical cyclones of any strength or the sudden thawing effect of ice dams.
[76] Possible trench foot infections may also occur when personnel are exposed for extended periods of time within flooded areas.
[77] A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain or squalls.
[81] 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.
Conditions within blizzards often include large quantities of blowing snow and strong winds that may significantly reduce visibility.
The strong winds present in blizzards are capable of damaging plants and may cause power outages, frozen pipes, and cut off fuel lines.
[95] 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.
