Weather Glossary

Explore commonly used weather terms.

A

Absolute Humidity

Absolute humidity

Absolute humidity is the total amount of water vapor present in a given volume of air, expressed in grams per cubic meter.

Air Humidity

Air humidity

Air humidity refers to the amount of water vapor present in the atmosphere, influencing weather patterns and comfort levels.

Air temperature

Air temperature is the measure of how hot or cold the air is at a specific location, typically recorded at 1.5 meters above ground level, and expressed in degrees Celsius or Fahrenheit.

Artificial Intelligence

Artificial intelligence

Artificial intelligence is a branch of computer science focused on developing systems that replicate human cognitive functions—such as learning, problem-solving, and decision-making—by enabling machines to analyze data, recognize patterns, and make autonomous decisions, driving innovation across various industries.

B

Buildup Index

Buildup index

The buildup index is the total amount of fuel available for consumption in the duff and larger fuels. It represents the cumulative effect of drying on these heavier fuel layers.

C

Celsius

The Celsius scale is a temperature measurement system where the freezing point of water is defined as 0°C, while the boiling point is 100°C under standard atmospheric pressure.

Chernozem

Chernozem refers to soil with a deep brown or black color, typically due to a high organic matter content, such as decomposed plant and animal material.

Climate models

Climate models are complex mathematical representations of the Earth's climate system, used to understand past climate patterns and predict future changes.

Cloudburst

A cloudburst is a very intense and localized rainfall event, typically occurring over a short period.

Coriolis Effect

The Coriolis effect

The Coriolis effect is the phenomenon where moving objects appear to curve due to Earth's rotation, with a rightward deflection in the Northern Hemisphere and a leftward deflection in the Southern Hemisphere.

Cyclone

A cyclone is a large-scale air mass that rotates around a central low-pressure area, typically bringing strong winds (119 km/h or more), heavy rainfall, and stormy weather conditions.

D

Dew point

The dew point is the temperature at which air, due to its humidity and temperature, becomes saturated and can no longer hold all its water vapor, resulting in condensation as dew, fog, or precipitation.

Drizzle

Drizzle is a type of rain consisting of very small, scattered droplets with a diameter of less than 0.5 millimeters.

Drought

Drought is a prolonged period of below-average precipitation, leading to water shortages that impact ecosystems, agriculture, communities, and economies.

Drought Code

Drought code

The drought code is an index that represents the average moisture content of deep, compact, organic layers, and large logs. It indicates the long-term drying effects on heavier fuels.

Dry Bulb Temperature

Dry bulb temperature

The dry-bulb temperature is the air temperature measured by a standard thermometer, representing the ambient air temperature without considering the effect of moisture.

Duff Moisture Code

Duff moisture code

The duff moisture code is a rating that shows the moisture level of the middle layer of decomposing material on the forest floor, and how likely it is for fires to smolder and burn deeper into the ground.

Dunkelflaute

Dunkelflaute is a meteorological phenomenon characterized by prolonged periods of low wind and little to no sunlight, leading to a significant drop in wind and solar power generation.

E

Evapotranspiration

Evapotranspiration is the combined process of water evaporation from soil and other surfaces and transpiration from plants, transferring moisture from the Earth's surface to the atmosphere.

F

Fahrenheit

Fahrenheit (°F) is a temperature scale where water freezes at 32°F and boils at 212°F under standard atmospheric pressure, with the interval between these points divided into 180 equal degrees.

Ferrel Cells

Ferrel cells

Ferrel cells describe an atmospheric circulation pattern that occurs between approximately 30° and 60° latitude in both hemispheres and they play a crucial role in the transfer of energy between the tropics and the poles, influencing weather patterns and climates in the mid-latitudes.

Fine Fuel Moisture Code

Fine fuel moisture code

The fine fuel moisture code is a numerical rating that indicates the moisture content of small, dead fuels like leaves, twigs, and litter, and from there, the relative ease of ignition and flammability of those fuels.

Fire Weather Index

Fire weather index

The fire weather index is a numerical rating of fire intensity based on weather conditions such as temperature, humidity, wind speed, and precipitation, used to assess wildfire risk.

Flood

A flood is an overflow of water, often caused by excessive rainfall, rapid snowmelt, storm surges, or the failure of dams, resulting in temporary or prolonged submersion of areas that are not typically underwater.

Fog

Fog is a dense collection of tiny water droplets or ice crystals suspended in the air near the ground, reducing visibility to less than 1,000 metres.

G

Global Atmospheric Circulation

Global atmospheric circulation

Global atmospheric circulation is the large-scale movement of air driven by the unequal heating of the Earth's surface due to its axial tilt, creating distinct pressure zones and wind patterns which distribute heat and moisture across the planet.

Global Forecast System

Global forecast system

The Global Forecast System (GFS) is a numerical weather prediction model that runs four times a day, and it processes data from satellites, weather stations, and other sources to generate weather forecasts.

Growing Degree Days

Growing degree days

Growing degree days is a measure of heat accumulation used to predict plant and insect development, calculated based on daily temperature thresholds.

H

Hadley Cells

Hadley cells

Hadley cells describe an atmospheric circulation of air near the equator where warm, humid air rises near the equator and moves toward the subtropics, where it descends as cooler, drier air where it starts moving back toward the equator.

Heat Stress in Plants

Heat stress in plants

Heat stress in plants occurs when air temperatures exceed their optimal range, disrupting biological processes, reducing growth, and potentially causing damage or death.

Hurricane

A hurricane is a rotating tropical cyclone with sustained winds of at least 74 mph (119 km/h), a well-defined eye, and the potential to cause severe damage through strong winds, heavy rain, storm surges, and flooding.

Hyperlocal Weather

Hyperlocal weather

Hyperlocal weather refers to weather data and forecasts that focus on a very small, precisely defined geographic area, often at the scale of a neighborhood, city block, or even a single street.

I

Initial Spread Index

Initial spread index

The Initial Spread Index is a rating that combines the effects of wind and fine fuel moisture on the expected rate of the initial spread of fire shortly after ignition.

J

K

Kelvin

The Kelvin (K) scale is an absolute temperature scale that begins at absolute zero—the theoretical point where all molecular motion ceases.

L

M

Microclimate

A microclimate is a small, localized atmospheric zone with distinct weather conditions differing from the surrounding climates, created by variations in topography, vegetation, bodies of water, or human-made structures.

N

Numerical Weather Prediction

Numerical weather prediction

Numerical weather prediction is the process of using mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions and physical laws governing atmospheric motion.

O

P

Pesticide Drift

Pesticide drift

Pesticide drift refers to the unintended movement of agricultural chemicals, including pesticides, herbicides, fungicides, and insecticides, from their intended application site to surrounding areas due to environmental factors such as wind, evaporation, and improper spraying techniques.

Polar Cells

Polar cells

Polar cells are atmospheric circulation patterns found near the poles, characterized by the movement of cold, dense air from the poles toward lower latitudes, influencing the frigid climates of these regions.

Q

R

Relative Humidity

Relative humidity

Relative humidity is the ratio, expressed as a percentage, of the current amount of water vapor in the air to the maximum amount of water vapor the air can hold at that specific temperature and pressure.

S

T

Temperature Inversion

Temperature inversion

A temperature inversion happens when cooler air is trapped beneath warmer air, preventing the normal circulation of air.

U

Urban Heat Island

Urban heat island

The urban heat island effect describes higher near-surface air temperatures in urban areas compared to surrounding rural areas, primarily caused by reduced vegetation, usage of heat-absorbing materials, and man-caused heat.

V

W

Wet Bulb Temperature

Wet bulb temperature

Wet bulb temperature is the lowest temperature air can reach by evaporating water, which cools the air until it is fully saturated with moisture.