A local wind which blows up a slope heated by sunshine.
The horizontal transportation of air or atmospheric properties.
The mass density of air expressed as weight per unit volume.
An extensive body of air with uniform conditions of moisture and temperature
in the horizontal.
The ratio of the amount of solar radiation reflected by a body to the
amount incident on it, commonly expressed as a percentage.
An area of high atmospheric pressure which has a closed circulation
that is anticyclonic (clockwise) in the Northern Hemisphere.
A winter storm with winds exceeding 40 km/h, with visibility reduced by
falling or blowing snow to less than one kilometre, with high windchill values
and lasting for at least three hours. All regional definitions contain the same
wind speed and visibility criteria but differ in the required duration and temperature
A cat paw-like, ripple signature on water given by strong downdrafts or
outflow winds. A good indication of turbulence and wind shear.
Either (a) the height above the surface of the base of the lowest layer of
clouds or obscuring phenomena (i.e. smoke) that hides more than half of the
sky; (b) the vertical visibility into an obstruction to vision (i.e. fog).
A warm dry wind blowing down the slopes of the Rocky Mountains and
over the adjacent plains.
Clear air turbulence (CAT)
Turbulence in the free atmosphere not related to convective
activity. It can occur in cloud and is caused by wind shear.
The formation of a layer or mass of ice which is relatively transparent
because of its homogeneous structure and smaller number and size of air
spaces; synonymous with glaze.
The statistical collection of long-term (usually decades) weather conditions
at a point; may be expressed in a variety of ways.
The leading edge of an advancing cold air mass.
Atmospheric motions that are predominately vertical, resulting in the
vertical transport and mixing of atmospheric properties.
A condition that exists when the distribution of winds in a given area
is such that there is a net horizontal inflow of air into the area; the effect is to
A term descriptive of all convective clouds exhibiting vertical
An area of low atmospheric pressure which has a circulation that is
cyclonic (counterclockwise) in the Northern Hemisphere.
A decrease in the central pressure of a pressure system; usually applied
to a low. Indicates a development of the low.
An area in the atmosphere where winds converge along one axis
and diverge along another.Where the winds converge, the air is forced upward
and it is in these areas where deformation zones (or axes of deformation as they
are sometimes referred to) can produce clouds and precipitation.
Applied loosely: (a) any small-sized low pressure system; (b) an area
where the weather, wind, and air pressure show signs of cyclonic development;
(c) any deviation in flow or pressure that is associated with a disturbed state in
the weather; and (d) any individual circulatory system within the primary circulation
of the atmosphere.
A condition that exists when the distribution of winds in a given area is
such that there is a net horizontal outflow of air from the area.
A small scale downward current of air; observed on the lee side of large
objects that restrict the smooth flow of air or in or near precipitation areas
associated with cumuliform clouds.
An exceptionally strong downdraft beneath a thunderstorm usually
accompanied by a deluge of precipitation.
An increase in the central pressure of a pressure system; applied to a low.
Föhn wind (foehn wind)
A warm dry wind on the lee side of a mountain range,
whose temperature is increased as the wind descends down the slope. It is
created when air flows downhill from a high elevation, raising the temperature
by adiabatic compression.
A surface, interface or transition zone of discontinuity between two adjacent
air masses of different densities.
A scale used to rate the intensity of a tornado by examining the damage
caused by the tornado after it has passed over a man-made structure.
A tornado cloud or vortex cloud extending downward from the parent
cloud but not reaching the ground.
A sudden, rapid and brief increase in wind speed. In Canada, gusts are
reported when the highest peak speed is at least 5 knots higher than the
average wind and the highest peak speed is at least 15 knots.
The leading edge of the downdraft outflow ahead of a thunderstorm.
An area of high barometric pressure; a high pressure system.
An intense tropical weather system with a well defined circulation and
maximum sustained winds of 64 knots or higher. In the western Pacific, hurricanes
are called 'typhoons,' and similar storms in the Indian Ocean are called
Any deposit of ice forming on an object.
A state of the atmosphere where the vertical distribution of temperature
is such that a parcel displaced from its initial position will continue to ascend.
An increase of temperature with height - a reversal of the normal
decrease of temperature with height.
Equal or constant temperature with height.
A quasi-horizontal stream of wind concentrated within a narrow band;
generally located just below the tropopause.
Downslope gravitational flow of colder, denser air beneath the
warmer, lighter air. Also known as 'drainage wind' or 'mountain breeze'.
Strength can vary from gentle to extremely violent winds.
A unit of speed equal to one nautical mile per hour.
The rate of change of an atmospheric variable (usually temperature) with
Any stationary wave disturbance caused by a barrier in a fluid flow; also
called mountain wave or standing wave.
Any and all forms of visible electrical discharge produced by a thunderstorm.
An area of low barometric pressure; a low pressure system.
Airflow in the direction of the geographic meridians, i.e. southnorth
or north-south flow.
The science of the atmosphere.
The formation of a white or milky and opaque layer of ice that
demonstrates an appearance that is a composite of rime and clear icing.
A front that is no longer in contact with the surface.
Of, pertaining to, or caused by forced uplift of air over high ground.
A condition where air is flowing from the interior land area through
mountain passes, valleys and inlets onto the coastal areas; used most commonly
in winter when cold Arctic air spreads onto the coastal area and adjoining sea.
A condition when warm air overtakes or is lifted by colder denser air.
A small volume of air, small enough to contain uniform distribution of
meteorological properties, and large enough to remain relatively self-contained
and respond to all meteorological processes.
Usually associated with the spreading out of a downburst from a thunderstorm;
a strong, straight-line wind in advance of a thunderstorm that often
results in severe damage.
Any and all forms of water particles, whether liquid or solid, that fall
from the atmosphere and reach the surface.
A front that is stationary or nearly so; commonly called
An elongated area of relatively high atmospheric pressure; also called ridge
The formation of a white or milky and opaque granular deposit of ice
formed by the rapid freezing of supercooled water droplets.
The condition in the atmosphere where actual water vapour present is
the maximum possible at the existing temperature.
Precipitation from cumuliform cloud; characterized by suddenness of
beginning and ending, by rapid changes in intensity, and usually by rapid
changes in the appearance of the sky.
Essentially gusts of longer duration. In Canada, a squall is reported when
the wind increases by at least 15 knots over the average speed for a duration of
at least 2 minutes and the wind reaches a speed of at least 20 knots.
A non-frontal line or narrow band of active thunderstorms.
A state of the atmosphere where the vertical distribution of temperature
is such that a parcel will resist displacement from its initial position.
Term descriptive of clouds of extensive horizontal development; flat,
The atmospheric layer above the tropopause; characterized by slight
increase in temperature from base to top, very stable, low moisture content and
absence of cloud.
The downward motion of air over a large area resulting in dynamic
Liquid water at temperatures below freezing.
A local storm invariably produced by a cumulonimbus cloud, and
always accompanied by lightning and thunder.
A violently rotating column of air, shaped from a cumulonimbus cloud,
and nearly always observed as 'funnel-shaped;' other names are cyclone and
The transition zone between the troposphere and the stratosphere;
characterized by an abrupt change in lapse rate.
The portion of the earth's atmosphere from the surface to the
tropopause; characterized by decreasing temperature with height and
appreciable water vapour. Often referred to as the weather layer.
An elongated area of relatively low atmospheric pressure; also called
A trough of warm air aloft; related to occluded front.
Any irregular or disturbed flow in the atmosphere.
A localized upward current of air.
Any frontal zone which is not manifested at the surface.
Water or ice particles falling from a cloud, usually in wisps or streaks, and
evaporating completely before reaching the ground.
The trailing edge of retreating cold air.
The instantaneous conditions or short term changes of atmospheric
conditions at a point; as opposed to climate.
Air in motion relative to the earth's surface; normally horizontal motion.
The direction from which the wind is blowing.
Rate of wind movement expressed as distance per unit time.
The rate of change of wind direction and/or speed per unit distance;
conventionally expressed as vertical and horizontal wind shear.
A west wind; conventionally used to describe large-scale flow that is
neither cyclonic or anticyclonic; also called zonal flow.