Glossary of Weather Terms
A Comprehensive Guide to Understanding Weather Phenomena
Weather Terms
ENSO (El Niño-Southern Oscillation)
ENSO refers to the periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean. It has two phases: El Niño (warmer than average sea surface temperatures) and La Niña (cooler than average sea surface temperatures). ENSO significantly impacts global weather patterns. In Australia, La Nina typically brings wetter conditions to the Eastern half of Australia and in El Nino, it typically brings drier conditions to the same area.
IOD (Indian Ocean Dipole)
IOD is an irregular oscillation of sea surface temperatures in the Indian Ocean. It has two phases: positive (warmer waters in the western Indian Ocean) and negative (warmer waters in the eastern Indian Ocean). The IOD influences the climate of surrounding regions, including Australia.
SAM (Southern Annular Mode)
SAM describes the north-south movement of the westerly wind belt that circles Antarctica, influencing weather patterns in the Southern Hemisphere, particularly in Australia, New Zealand, and South America.
MJO (Madden-Julian Oscillation)
MJO is an eastward-moving atmospheric disturbance that influences tropical weather patterns. It consists of an active phase (enhanced convection and rainfall) and a suppressed phase (reduced convection and rainfall) and impacts the timing and intensity of monsoons and cyclones.
Monsoon
A Monsoon is a seasonal wind pattern that can cause significant changes in precipitation. The most well-known monsoon occurs in South Asia, bringing heavy rainfall during the summer months. In Australia the Monsoon first effects Darwin around the Christmas period.
Equatorial Rossby Wave
Equatorial Rossby Waves are large-scale waves in the atmosphere that travel along the equator and influence tropical weather systems, such as cyclones and monsoons.
SST (Sea Surface Temperature)
SST refers to the temperature of the ocean’s surface. It is a crucial factor in weather and climate patterns, affecting phenomena like cyclones, ENSO, and monsoons.
Thunderstorm (Detailed)
A Thunderstorm is a weather phenomenon characterized by the presence of lightning and thunder, usually accompanied by heavy rain, strong winds, and sometimes hail. These storms often develop in warm, moist air masses and are driven by the rapid upward movement of this air into cooler regions of the atmosphere. This process, known as convection, leads to the formation of cumulonimbus clouds, which are the hallmark of thunderstorms.
Thunderstorms can vary greatly in intensity and size, ranging from small, short-lived storms to large, organized systems that can span hundreds of kilometers and last for several hours. There are three main stages in the life cycle of a thunderstorm:
- Cumulus Stage: This initial stage is marked by the rising of warm, moist air, which cools and condenses to form a cumulus cloud. As the updraft continues, the cloud grows vertically.
- Mature Stage: This is the most intense phase of the thunderstorm. The cloud reaches great heights, often exceeding 10 kilometers. Strong updrafts and downdrafts coexist, leading to heavy rainfall, lightning, thunder, and possibly hail. The downdrafts bring cool air and precipitation to the ground, sometimes causing gusty winds.
- Dissipating Stage: During this final stage, the downdrafts dominate, cutting off the supply of warm, moist air. The storm’s intensity decreases, leading to lighter rain and eventually the dissipation of the cloud.
Thunderstorms can produce a variety of hazardous weather conditions, including flash flooding, strong winds, hail, and tornadoes. They are most common in the spring and summer months when atmospheric conditions are favorable for their development.
Severe Thunderstorm
A Severe Thunderstorm is a more intense version of a thunderstorm, capable of producing large hail, flash flooding, damaging winds, and tornadoes.
Supercell
A Supercell is a highly organized and powerful thunderstorm with a rotating updraft called a mesocyclone. Supercells are the most likely to produce severe weather, including large hail, severe winds, and tornadoes.
Tornado
A Tornado is a violently rotating column of air that extends from a thunderstorm to the ground. Tornadoes can cause significant damage due to their intense winds. In Australia, lastest data indicates we see up to around 80 Tornadoes a year but the real amount is likely more. Most would go unreported.
Gustnado
A Gustnado is a small, weak tornado that forms along the gust front of a thunderstorm. Gustnadoes are typically short-lived and less intense than tornadoes.
Water Spout
A Water Spout is a tornado that forms over water. There are two types: fair-weather waterspouts, which form in light wind conditions, and tornadic waterspouts, which form from severe thunderstorms.
Dust Devil
A Dust Devil is a small, rapidly rotating column of air that forms over dry land and lifts dust and debris into the air. Dust devils are usually harmless, but larger ones can cause minor damage.
Land Spout
A Land Spout is a non-supercell tornado similar to a water spout but occurs over land. They are typically weaker and shorter-lived than supercell tornadoes.
Tropical Cyclone
A Tropical Cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and heavy rain. In Australia, tropical cyclones can cause significant damage to coastal areas, including flooding, wind damage, and storm surges. They typically form in the warm waters of the tropical regions and can impact the northern coasts of the country.
Tropical Low
A Tropical Low is a low-pressure system in the tropics that has the potential to develop into a tropical cyclone.
Cut off Low
A Cut off Low is a low-pressure system that becomes separated from the main atmospheric circulation, leading to prolonged periods of unsettled weather.
East Coast Low
An East Coast Low is a low-pressure system that forms off the east coast of Australia, often bringing heavy rain, strong winds, and coastal erosion.
Polar Vortex
The Polar Vortex is a large area of low pressure and cold air surrounding the Earth’s poles. It can influence winter weather patterns, leading to extreme cold outbreaks.
Blocking High
A Blocking High is a high-pressure system that remains stationary for an extended period, blocking the movement of other weather systems and often leading to prolonged periods of dry or settled weather.
Ridging
Ridging refers to an area of high pressure that extends from a high-pressure center. Ridging can lead to clear and calm weather conditions.
CAPE (Convective Available Potential Energy)
CAPE is a measure of the amount of energy available for convection. Higher CAPE values indicate a greater potential for severe thunderstorms.
CIN (Convective Inhibition)
CIN is a measure of the amount of energy that prevents convection. High CIN values can inhibit thunderstorm development.
Capping Inversion
Capping inversion (or simply CAP) occurs when a layer of warm air aloft prevents cooler air at the surface from rising. This inhibits convection and can suppress thunderstorm development, even when other conditions for severe weather are present. When the cap is strong, it acts as a lid on the atmosphere, limiting the vertical development of clouds and storms. However, if the cap weakens or is broken by sufficient heating or lifting mechanisms, it can lead to explosive thunderstorm development as the trapped energy is released.
Total Totals
Total Totals is an index used to assess the potential for severe weather based on temperature and humidity at different atmospheric levels.
SWEAT (Severe Weather Threat)
SWEAT is an index used to assess the potential for severe weather, including thunderstorms and tornadoes, based on temperature, humidity, and wind shear values.
Effective Inflow Layer (EIN)
The Effective Inflow Layer (EIN) refers to the layer in the atmosphere from which air parcels can effectively rise and contribute to convection. This layer is crucial in determining the potential for thunderstorm development and intensity. The characteristics of the effective inflow layer, including its depth and the amount of moisture it contains, can significantly influence the strength and behavior of storms. High-quality inflow layers often lead to more powerful and sustained convection, enhancing the risk of severe weather events such as thunderstorms and tornadoes.
Wind Shear
Wind Shear refers to the change in wind speed and direction with height. It is a critical factor in the development and organization of severe thunderstorms and tornadoes.
Vertical Wind Shear
Vertical Wind Shear is the change in wind speed and direction with height in the atmosphere. High vertical wind shear can enhance the development of severe weather.
Dew Point
The Dew Point is the temperature at which air becomes saturated with moisture, leading to condensation and the formation of dew, fog, or clouds.
Air Temperature
Air Temperature is the measure of the warmth or coldness of the air, typically recorded in degrees Celsius or Fahrenheit.
Wind Speed
Wind Speed is the measure of how fast the air is moving, typically recorded in kilometers per hour or miles per hour.
Humidity
Humidity is the amount of moisture in the air. High humidity can make the air feel warmer, while low humidity can make it feel cooler.
Feels Like
Feels Like is an index that combines air temperature, humidity, wind speed, and other factors to indicate how the temperature feels to the human body.
Wind Chill
Wind Chill is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of air. It can make cold temperatures feel even colder.
Urban Heat Index
The Urban Heat Index measures the elevated temperatures in urban areas caused by human activities and modifications of the natural environment, such as buildings, roads, and other infrastructure.