Extratropical cyclone in the context of "Cyclogenesis"

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwealth usage), snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor (reaching 100% relative humidity), so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation; their water vapor does not condense sufficiently to precipitate, so fog and mist do not fall. (Such a non-precipitating combination is a colloid.) Two processes, possibly acting together, can lead to air becoming saturated with water vapor: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers.

Moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed by the low temperature into clouds and rain. This process is typically active when freezing rain occurs. A stationary front is often present near the area of freezing rain and serves as the focus for forcing moist air to rise. Provided there is necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely nimbostratus and cumulonimbus if significant precipitation is involved. Eventually, the cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow is possible within a cyclone's comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation occurs within the tropics and is caused by convection.

Weather refers to the state of the Earth's atmosphere at a specific place and time, typically described in terms of temperature, humidity, cloud cover, and stability. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature, precipitation, and other atmospheric conditions, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, "weather" is generally understood to mean the weather of Earth.

Weather is driven by air pressure, temperature, and moisture differences between one place and another. These differences can occur due to the Sun's angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley cell, the Ferrel cell, the polar cell, and the jet stream. Weather systems in the middle latitudes, such as extratropical cyclones, are caused by instabilities of the jet streamflow. Because Earth's axis is tilted relative to its orbital plane (called the ecliptic), sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C (−40 °F to 104 °F) annually. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by Earth, thus influencing long-term climate and global climate change.

The middle latitudes, also called the mid-latitudes (sometimes spelled midlatitudes) or moderate latitudes, are spatial regions on either hemisphere of Earth, located between the Tropic of Cancer (latitude 23°26′09.3″) and the Arctic Circle (66°33′50.7″) in the Northern Hemisphere and between the Tropic of Capricorn (-23°26′09.3″) and the Antarctic Circle (-66°33′50.7″) in the Southern Hemisphere. They include Earth's subtropical and temperate zones, which lie between the two tropics and the polar circles. Weather fronts and extratropical cyclones are usually found in this area, as well as occasional tropical cyclones or subtropical cyclones, which have traveled from their areas of formation closer to the Equator.

The prevailing winds in the middle latitudes are often very strong. These parts of the world also see a wide variety of fast-changing weather as cold air masses from the poles and warm air masses from the tropics constantly push up and down over them against each other, sometimes alternating within hours of each other, especially in the roaring forties (latitudes between 40° and 50° in both hemispheres), even though the winds on the Northern Hemisphere are not as strong as in the Southern Hemisphere, due to the large landmasses of North America, Europe and Asia.

A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (/ˈhʌrɪkən, -keɪn/), typhoon (/taɪˈfuːn/), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon is the same thing which occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more.

Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, cyclones rarely form within 5° of the equator. South Atlantic tropical cyclones are very rare due to consistently strong wind shear and a weak Intertropical Convergence Zone. In contrast, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea.

Hurricane Sandy (unofficially referred to as Superstorm Sandy) was an extremely large and devastating tropical cyclone which ravaged the Caribbean and the coastal Mid-Atlantic region of the United States in late October 2012. It was the largest Atlantic hurricane on record as measured by diameter, with tropical-storm-force winds spanning 1,150 miles (1,850 km). The storm inflicted nearly US$70 billion in damage (equivalent to $96 billion in 2024), and killed 254 people in eight countries, from the Caribbean to Canada. The eighteenth named storm, tenth hurricane, and second major hurricane of the 2012 Atlantic hurricane season, Sandy was a Category 3 storm at its peak intensity when it made landfall in Cuba, though most of the damage it caused was after it became a Category 1-equivalent extratropical cyclone off the coast of the Northeastern United States.

Sandy developed from a tropical wave in the western Caribbean Sea on October 22, quickly strengthened, and was upgraded to Tropical Storm Sandy six hours later. Sandy moved slowly northward toward the Greater Antilles and gradually intensified. On October 24, Sandy became a hurricane, made landfall near Kingston, Jamaica, re-emerged a few hours later into the Caribbean Sea and strengthened into a Category 2 hurricane. On October 25, Sandy hit Cuba as a Category 3 hurricane, then weakened to a Category 1 hurricane. Early on October 26, Sandy moved through the Bahamas. On October 27, Sandy briefly weakened to a tropical storm and then strengthened back to a Category 1 hurricane. Early on October 29, Sandy curved west-northwest (the "left turn" or "left hook") and then moved ashore near Brigantine, New Jersey, just to the northeast of Atlantic City, as a post-tropical cyclone with hurricane-force winds. Sandy continued drifting inland for another few days while gradually weakening, until it was absorbed by another approaching extratropical storm on November 2.

Thundersnow, also known as a winter thunderstorm or a thundersnow storm, is a thunderstorm in which snow falls as the primary precipitation instead of rain. It is considered a rare phenomenon. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone. Thermodynamically, it is not different from any other type of thunderstorm, but the top of the cumulonimbus cloud is usually quite low. In addition to snow, graupel or hail may fall as well. The heavy snowfall tends to muffle the sound of the thunder so that it sounds more like a low rumble than the loud, sharp bang that is heard during regular thunderstorms.

Thundersnow can occur during a normal snowstorm that sustains strong vertical mixing which allows for favorable conditions for lightning and thunder to occur. It can also occur from the lake effect or ocean effect thunderstorm which is produced by cold air passing over relatively warm water; this effect commonly produces snow squalls over the Great Lakes.

Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of life. These vary depending on the latitude, altitude, topography, and atmospheric conditions. High winds, hail, excessive precipitation, and wildfires are forms and effects, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones. Regional and seasonal phenomena include blizzards, snowstorms, ice storms, and duststorms.

Severe weather is one type of extreme weather, which includes unexpected, unusual, severe, or unseasonal weather and is by definition rare for that location or time of the year. 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.