Download Meteorology Vocabulary

Meteorology Vocabulary
Advection fog - occurs when moist air passes over a cool surface by advection (wind) and is cooled.. It is
common as a warm front passes over an area with significant snow-pack. It is most common at sea when
moist air encounters cooler waters, including areas of cold water upwelling, such as San Francisco
Alberta clipper - fast moving low pressure area generally affecting central Canada and the Upper Midwest
and Great Lakes regions of the United States, precipitating a sudden temperature drop and sharp winds.
air mass - a huge body of air that has similar temperature, humidity, and air pressure at any given height
air pressure- the measure of the force with which air molecules push on a surface As an example, consider a
"unit area" of 1 square inch. At sea level, the weight of the air above this unit area would (on average) weigh
14.7 pounds! That means pressure applied by this air on the unit area would be 14.7 pounds per square inch.
Meteorologists use a metric unit for pressure called a millibar and the average pressure at sea level is 1013.25
millibars. = 1.0 Atm (atmospheres) = 101.3 kPa = 29.92 inches of Hg
albedo - the fraction of solar radiation that is reflected off the surface of an object
Beaufort wind scale – 0 = Calm, 6= Strong Breeze- Large branches in motion,12= hurricane
Blizzard - snowstorm characterized by strong sustained winds of at least 35 mph (56 km/h) and lasting for a
prolonged period of time—typically three hours or more
Chinook Winds -Snow eater foehn (dry downsloping wind) wind with warmth and lower humidity that
rapidly melt and evaporate snow.
cloud - a visible mass of water or ice particles suspended at a considerable altitude
cold front - forms when cold air moves under warm air which is less dense and pushes air up (produces
thunderstorms heavy rain or snow
condensation - the process of changing from a gaseous to a liquid or solid state
condensation nuclei - microscopic particles (such as dust or ice) on which water vapor condenses to form
cloud droplets
conduction - the transfer of thermal energy from one substance to another through direct contac
continental arctic - (cA) very cold, very dry air mass
continental polar - (cP) cold, dry air mass that forms over land
continental tropical - (cT) warm, dry air mass that forms over land
convection - the transfer of heat through a fluid (liquid or gas) caused by molecular motion
Coriolis effect -The way Earth's rotation makes winds in the Northern Hemisphere curve to the right and
winds in the Southern Hemisphere curve to the left
Cyclone -an area of low pressure around which the winds flow counterclockwise in the Northern Hemisphere
and clockwise in the Southern Hemisphere. often identifiable by a comma-shaped cloud mass.
dew point - temperature at which air is saturated and condensation begins
feeder bands - Feeder Bands. In tropical parlance, the lines or bands of thunderstorms that spiral into and
around the center of a tropical system. Also known as outer convective bands.
Foehn Winds - Warm and dry down-slope wind that occurs in the lee (downwind side) of a mountain range
and that warms by adiabatic compression as it moves toward a lower elevation.
freezing rain - raindrops that freeze after they hit the ground or other cold surfaces
front - the atmospheric phenomenon created at the boundary between two different air masses
graupel - also called soft hail, snow pellets or "Grail" is precipitation that forms when supercooled droplets of
water are collected and freeze on a falling snowflake, forming a 2–5 mm (0.079–0.197 in) ball of rime.
ground fog - is fog that obscures less than 60% of the sky and does not extend to the base of any overhead
clouds. However, the term is usually a synonym for radiation fog
hail - lumps or balls of ice that fall from cumulonimbus clouds formed from strong convection currents adding
layers of ice
heat index - an index that combines air temperature and relative humidity in an attempt to determine the
human-perceived equivalent temperature
high pressure - cool dense sinking air; associated with clear skies and calm weather
hydrometer - an instrument that measures the specific gravity (relative density) of liquids
hygrometer - an instrument used for measuring the moisture content in the atmosphere.
instability/ stability - refers to the ability of an air mass to resist vertical motion. A stable atmosphere makes
vertical movement difficult. In an unstable atmosphere, vertical air movements (such as in orographic lifting)
tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant
turbulence, extensive vertical clouds, and severe weather such as thunderstorms.
inversion - a deviation from the normal change of an atmospheric property with altitude. It almost always
refers to a "temperature inversion". An inversion can lead to pollution such as smog being trapped close to the
ground. Temperature inversion stops atmospheric convection.
Isobar – contours connecting locations which have the same pressure
Isotherm - contours connecting locations which have the same temperature
isotach - contours connecting locations which have the same wind speed
Isopleth – general term for contours with constant values
isotherm - line on a map connecting points equal temperature values
jet stream - a high-speed high-altitude airstream blowing from west to east near the top of the troposphere
lake effect snow – produced when a cold air mass moves across long expanses of warmer lake water,
land breeze – Especially at night, if the land becomes cooler than the adjacent sea surface temperature, the air
pressure over the water will be lower than that of the land, setting up a land breeze blowing from the land to
the sea.
Lenticular clouds - (Altocumulus lenticularis) are stationary lens-shaped cloud
low pressure - warm rising area that condenses and cools; associated with cloudy skies, precipitation, and
wind
maritime polar - (mP) cold, moist air mass that forms over cold oceans
maritime tropical - (mT) warm, moist air mass that is formed over water
microburst - A microburst is a small downdraft that moves in a way opposite of a tornado. Microbursts are
extremely hazardous to aircraft. Microbursts are found in strong thunderstorms .
Mountain Breezes - Wind impacted by differential cooling at night as the air becomes more dense
NEXRAD - a network of 160 high-resolution S-band Doppler weather radars operated by the National
Weather Service (NWS) Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988,
Doppler..
Nor’easter - a low pressure area that often passes just off the New England and southeast Canada Atlantic
coastline. Winds in the left-forward quadrant rotate onto land from the northeast.
Orographic clouds - occurs when an air mass is forced from a low elevation to a higher elevation as it moves
over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the
relative humidity to 100% and create clouds
Panhandle Hook - Fast moving low pressure area which generally affects the central provinces of Canada and
parts of the upper Midwest and Great Lakes region
pileus cloud - also called scarf cloud or cap cloud, is a small, horizontal, lenticular cloud that can appear
above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance.
polar front - boundary between the polar cell and the Ferrel cell in each hemisphere
precipitation - the falling to earth of any form of water (rain or snow or hail or sleet or mist)
pressure gradient - the amount of pressure change occurring over a given distance
radiation - energy that is radiated or transmitted in the form of rays or waves or particles
Radiation fog - formed by the cooling of land after sunset by thermal radiation in calm conditions with clear
sky.
rain guage - (also known as an udometer, pluviometer, or an ombrometer) is a type of instrument used by
meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a set period of
time.
rain shadow - a dry area on the lee side of a mountainous area (away from the wind). incoming warm and
moist air is drawn by the prevailing winds towards the top of the mountains, where it condenses and
precipitates before it crosses the top. The air, without much moisture left, advances behind the mountains
creating a drier side called the "rain shadow".
ridge - an elongated region of relatively high atmospheric pressure, the opposite of a trough.
Santa Ana Winds - Warm and dry wind - Low pressure to the South and high pressure to the North set up a
dry and adiabatically compressed wind from a higher elevation
saturated - being the most concentrated solution possible at a given temperature
scattering - the physical process in which particles are deflected haphazardly as a result of collisions
Sea Breezes – an onshore wind caused by the differential heating between land and water with air flowing
from higher pressure (water) to lower pressure (land)
sleet - partially melted snow (or a mixture of rain and snow)
specific humidity -the amount of water vapor in the air at a given time and place; expressed as the number of
grams of water vapor per kilogram of air.
station model – compressed graphical description of the weather a single location
stratosphere - the layer of the atmosphere that is above the troposphere and in which temperature increases as
altitude increases
tropopause - is the boundary between the troposphere and the stratosphere
troposphere - the layer of the atmosphere that contains life and weather; the temperature decreases as you go
up
weather - the condition of Earth's atmosphere at a particular time and place
westerlies - prevaling winds that blow from west to east between 30 degrees & 60degrees latitude in the
hemisphere
Upslope fog - forms when moist air is going up the slope of a mountain or hill which condenses into fog on
account of adiabatic cooling
UTC , GMT, Z – reference time zone centered at Greenwich, England
Valley Breezes - Wind impacted by movement toward higher elevations during the day with warming
resulting from more direct exposure to the sun
Virga - an observable streak or shaft of precipitation that falls from a cloud but evaporates or sublimes
before reaching the ground. Virga can cause varying weather effects, because as rain is changed from
liquid to vapor form, it removes heat from the air due to the high heat of vaporization of water. In some
instances, these pockets of colder air can descend rapidly, creating a dry microburst which can be
extremely hazardous to aviation.
weather watch – current conditions are favorable for hazardous weather. Be aware.
weather warning – developing weather hazard. Take action. Usually more local then watch.
weather advisory – less urgent statement which describes possible weather which may affect travel or cause
inconvenience
Watches and warnings may be given for hurricanes, tornadoes, severe thunderstorms, flash flood, winter
storm, ice storm, high wind
Windchill Temperature (WCT) index provides a formula for calculating the dangers from winter winds and
freezing temperatures. The index:
1)Calculates wind speed at an average height of 5 feet, the typical height of an adult human face, based on
readings from the national standard height of 33 feet, typical height of an anemometer
2)Is based on a human face model
3)Incorporates heat transfer theory: heat loss from the body to its surroundings, during cold and breezy/windy
days
4)Lowers the calm wind threshold to 3 mph
5)Uses a consistent standard for skin tissue resistance
6)Assumes no impact from the sun, i.e., clear night sky.