A Few
Clouds
Scattered clouds, with clear skies dominant. Cloud cover between 5%
and 25%.
A Mix of
Sun and Clouds
At times there will be more clouds than sun, and at other times
there will be more sun than clouds. Cloud cover between 40% and 60%.
Air
Pressure (also known as atmospheric pressure)
Is the amount of force wielded on a surface by the weight of the air
above it. The unit for measuring air pressure worldwide is the
kilopascal.
Aurora
Borealis (also known as the Northern Lights)
Is the brilliant, glowing emission from the upper atmosphere over
middle and high latitudes, and centred around the earth's magnetic
poles. The Northern Lights are usually seen on clear winter nights
in an array of shapes and colours.
Barometric
Pressure
The pressure exerted by the weight of the column of air above a
given point, expressed in kilopascals. Generally speaking, when the
barometric pressure is high, the air is sinking, usually resulting
in fair weather. When the barometric pressure is low or falling, air
is rising, usually resulting in cloudy skies and precipitation.
Blood Rain
Rain mixed with red-coloured sand from the Sahara Desert in north
Africa. On windy days when the wind is blowing strongly from a
southerly direction, sand is carried over to the Maltese Islands and
beyond. If in also rains the sand comes down with the rain, hence
the term ‘blood rain’ since the Sahara Desert sand is reddish in
colour.
Clear
Skies will be almost totally clear, perhaps with a few small light
clouds visible. Cloud cover will be between 0% and 5%. Clear is the
night time term equivalent to "Sunny".
Clearing
Most of the sky will be covered in clouds, but you will see more and
more sunshine throughout the forecast period. It will take only a
portion of the period for the sky to become less than half covered
in clouds.
Climate
The prevailing or typical meteorological conditions and extremes of
any place or region.
Clear with
Cloudy Periods
The night time equivalent of "Sunny with Cloudy Periods".
Clouding
Over
Skies will be mostly clear, but more and more cloud cover will
develop throughout the forecast period. The sky will become
completely overcast before the end of the forecast period.
Cloud
An observable group of tiny water and/or ice particles in the
atmosphere.
Cloudy
No sunshine visible. Cloud cover will be more than 87%.
Cloudy with
Clear Breaks
The night time equivalent of "Cloudy with Sunny Breaks".
Cloudy with
Drizzle
The sky will be overcast and a heavy mist or very light continuous
rain is expected to fall. Your slow pulse wipers will be too fast in
clearing the windshield.
Cloudy with
Light Rain
The sky will be overcast and the precipitation will be strong enough
to get things wet in a short time. The rain will interfere with
outdoor activities. Puddles will form quickly and water may run down
the expressways, causing slippery road conditions. Precipitation
will persist throughout the forecast period.
Cloudy with
Periods of Rain
The sky will be overcast and the precipitation strong enough to get
things wet in a short time, but the rain may also stop for a short
period of time. The rain will interfere with outdoor activities. The
ground will get wet, puddles will form, but the precipitation will
be expected to cease for short periods of time over the forecast
period.
Cloudy with
Scattered Thundershowers
The sky will be cloudy, with some showers or light rain possible;
thunder and lightning will be associated with the precipitation. The
showers or rain may be heavy for short periods of time.
Cloudy with
Showers
The sky will be overcast and the strength of the precipitation will
be light. The showers will be intermittent, and will generally
interfere with outdoor activities. The ground will get wet.
Cloudy with
Sunny Breaks
A least half covered in clouds, but not totally cloudy. Cloud cover
will be between 60% and 80%.
Cloudy with
Thundershowers
The sky will become cloudy with a few showers or light rain
possible; thunder and lightning will be associated with the
precipitation. The showers or rain may be heavy for extended periods
of time.
Cloudy with
Thunderstorms
The sky will be cloudy, with showers or light rain possible; thunder
and lightning will be associated with the precipitation. The showers
or rain will be heavy for extended periods of time.
Coastal Fog
Fog will be expected to form near the shore line, and may cause
reduced visibility on roadways near the shore.
Cold Front
A front can best be described as the border between two different
air masses. A cold front is the leading edge of cooler or colder
air. It cuts into the space that is occupied by warmer air and
eventually replaces it with a cooler/colder Air Mass. This happens
as the cold air causes the warm air to rise up and over it. As the
warm air travels upwards, it begins to mix with the cold air aloft
and condenses to form clouds. You can usually expect scattered
showers and thunderstorms along the front as it approaches.
Cyclone
In the Northern Hemisphere, the closed counter-clockwise movement of
air referred to as a circulation - around a low pressure centre;
typically known as a low. Often this term is used in error to
describe a tornado.
Dew Point
The dew point is a measure of atmospheric moisture. It is the
temperature to which air must be cooled in order to reach saturation
(assuming that air pressure and moisture content are constant). As
the surface of the earth cools at night, warm moist air near the
ground is chilled and water vapour in the air condenses into
droplets on the grass and other objects. Dew is particularly heavy
on clear nights, when the earth cools rapidly. When a blanket of
cloud insulates the earth, the cooling rate is slower. The greater
the difference between the temperature and the dew point, the drier
the air.
Drizzle
Heavy mist or light, fine, continuous rain that will fall slowly,
reducing visibility somewhat more than light rain. Water droplets
will be between 0.2mm and 0.5mm in size. Drizzle can often be
confused with light rain, however drizzle's water droplets will be
smaller in size than those of rain.
Fog
A cloud with its base at the Earth's surface. Visibility is reduced
to less than 1 km.
Foggy
Fog is expected to form throughout the countryside, causing reduced
visibility over large areas. The fog will generally be slow in
breaking up, and may eventually result in a mixture of sun and
clouds as the fog lifts and breaks up. Foggy conditions may be
forecast after rain or showers overnight and into the early morning
hours.
Fog Patches
Some fog is expected to form, but will generally be restricted to
low lying areas. It may cause reduced visibility if encountered. Fog
patches generally break up through the first part of the morning if
they form overnight. They may be forecast after rain or showers at
any time of the day, but generally fog occurs late at night or in
the early morning hours.
Front
A front is the dividing line between two air masses that have
different densities and often different temperatures. A moving front
is labelled based on the temperature of the advancing air mass. For
example, the front would be labelled "cold" if it was colder air that
was advancing.
Funnel
Cloud
Is a cloud that reaches from the bottom of a towering cumulus or
cumulonimbus cloud. It is associated with a revolving column of air
that is NOT in touch with the ground (and therefore differs from a
tornado). A condensation funnel IS a tornado, NOT a funnel cloud, if
it meets one of the following criteria: it is in contact with the
ground or a debris cloud or dust whirl can be seen underneath it.
Gale
A forceful wind. A "gale warning" is issued winds are expected to
reach 34 to 47 knots (63 to 87 km/h) over the water.
Gradual
Clearing
Most of the sky will be covered in clouds, but you will see more and
more sunshine throughout the forecast period. It may take the entire
period for the sky to become less than half covered in clouds.
Gust
A sudden significant increase in, or rapid variation of wind speed.
Usually a gust lasts less than twenty seconds.
Hail
Frozen rain droplets created by the updrafts of convective
thunderstorms. Hail is generally associated with severe
thunderstorms.
Hazy
The sky will appear to be covered in a very light fog when viewed
off in the distance. Haze is created when fine dust particles
disperse through a portion of the atmosphere. It is generally not
noticeable when observed from directly above or below. Typically,
haze does not impair visibility to any great extent.
Heat Index
A calculation combining air temperature and relative humidity, given
in degrees Celsius. It represents the heating effect felt due to a
lack of body moisture evaporation, and gives the average person a
"feeling" for how hot and stuffy the air is. The Heat Index is
reported only during the summer months.
Heavy Rain
The sky will be overcast and the precipitation continuous, strong
enough to get things wet very quickly. There may be minor flooding
of storm drains and roadways if the precipitation continues for very
long. Heavy rain causes reduced visibility while driving.
High
Pressure Centre
Indicates an area of high pressure. In a high, air will slowly
descend and flow out in a clockwise direction at the ground.
Normally a high will bring mainly sunny skies to an area.
Humidity
Is a measure of the amount of water vapour content of the air.
Hurricane
Is a tropical storm with winds that can reach speeds of 64 knots
(117 km/h) up to 240 knots (414 km/h) that can be thousands of
square kilometres in size. These systems typically last several
days. In the North Atlantic, the hurricane season lasts from May to
November, however the bulk of the storms happen in August, September
and October. Even though the East Coast is the region of Canada most
frequented by hurricanes, these storms still average less than one
per year over the Atlantic Provinces and coastal waters. Other names
for hurricanes include typhoon and tropical cyclone.
Increasing Cloudiness
Skies will be mostly clear, but more and more cloud cover will
develop throughout the forecast period. It will not become
completely overcast before the end of the forecast period.
Jet Stream
Moderately strong winds grouped in a narrow stream in the
atmosphere, usually in reference to horizontal, high altitude winds.
The location and orientation of jet streams change from one day to
the next. Weather patterns (hot/cold, wet/dry) are influenced by the
position, strength and orientation of the jet stream (or jet
streams).
Lightning
Usually, any and all of the assorted forms of observable electrical
release created by thunderstorms.
Low
Pressure Centre
Indicates an area of low atmospheric pressure. In a low, air is
flowing counter clockwise into the centre of the Low. The air will
rise and cool often resulting in clouds and precipitation.
Mainly Clear
The night time equivalent of "Mainly Sunny".
Mainly
Clear with a Chance of Showers
The sky is expected to be less than half covered with clouds, but
there still may be brief periods of precipitation, generally
occurring in the early evening.
Mainly
Cloudy
Mostly covered in clouds, possibly with brief periods of sunshine.
Cloud cover will be more than 87%.
Mainly
Cloudy with a Few Showers
Cloud cover as for "Mainly Cloudy", with light precipitation of
short duration. The showers will be short-lived, but may interfere
with outdoor activity. The ground will get damp.
Mainly
Cloudy with Isolated Showers
Cloud cover as for "Mainly Cloudy", with very light precipitation of
short duration. The showers will be very short-lived and generally
will not interfere with any outdoor activity. You may get a bit
damp, but the shower will end quickly, and you will dry off almost
immediately.
Mainly
Cloudy with Scattered Showers
Cloud cover as for "Mainly Cloudy", with light precipitation of
short duration. The showers will come and go, and generally
interfere with outdoor activities. The ground will get wet.
Mainly
Sunny
Clear, with a small area of clouds visible. Cloud cover will be
between 10% and 30%.
Mainly
Sunny with a Chance of Showers
The sky is expected to be less than half covered with clouds, but
there still may be brief periods of precipitation, generally
occurring in the late afternoon.
Mainly
Sunny with a Chance of Thunderstorms
The sky is expected to be less than half covered with clouds, but
there still may be brief periods of showery precipitation with
thunder and lightning, generally occurring at the end of the
afternoon.
Meteorologist
An individual who studies meteorology. There are a variety of
disciplines that one can pursue within the field of meteorology.
Some of examples of the different types of meteorologists are:
research meteorologists, radar meteorologists, climatologists, or
operational meteorologists.
Meteorology
Is the study of the physics, chemistry and dynamics of the
atmosphere and the direct effects of the atmosphere on the Earth's
surface, the oceans and on life on Earth in general.
Mist
Is comprised of tiny water droplets hanging in the air which forms a
thin greyish blanket over the landscape. It causes a reduction in
visibility but not to the same degree that fog does.
Overcast
Totally covered with clouds, with clear skies not visible. Cloud
cover will be more than 87%.
Partial
Clearing
Most of the sky will be covered in clouds, but you will see more and
more sunshine throughout the forecast period. It will take longer
than the forecast period for the sky to become less than half
covered in clouds.
Partly
Cloudy
Clouds dominant, with little clear sky showing. Cloud cover will be
between 60% and 90%.
P.O.P.
(Probability of Precipitation)
The probability of precipitation does not predict when, where or how
much precipitation will occur. When a Weather Service issues a
forecast calling for rain, it is usually followed by a probability.
For example: " the chance of rain is 60%" Does this mean a) that it
will rain on 60% of the forecast area or b) that there is a 60%
chance of rain within the forecast area? Neither one! The expression
means that there is a 60% chance that any random place in the
forecast area, such as your home, will receive measurable rainfall.
Measurable rainfall means at least 0.2 mm of rain or the water
equivalent of snow.
Precipitation
Any and all forms of water, either in liquid or solid state, that
falls from clouds and reaches the ground. Deposits of dew, fog and
frost are not included in this category.
Rain
The sky will be overcast and the precipitation continuous, with
water droplets greater than 0.5mm in size. Things will get wet very
quickly. The rain will interfere with outdoor activities. Puddles
will form quickly, water will generally run down expressways, and
reduced visibility while driving may be a problem.
Rain
Showers
Intermittently falling rain, generally short-lived.
Relative
Humidity
Relative humidity is a percentage of water vapour per area at a
specific temperature. Relative humidity can be calculated using
various methods and instruments. It is a calculation to find out how
many grams of water vapour can be held at a given temperature.
Usually, the warmer the air the higher it's capacity for holding
water vapour. Each specific temperature has a holding limit for
water and the actual amount of water held in the air at the time of
measurement can be represented as a percentage.
For example, if a parcel of air at 20ºC has a limit or capacity of
16 grams of water vapour and 16 grams of water vapour is measured,
the air's holding capacity is at it's maximum, the relative humidity
(RH) of the air is said to be 100%. Take the same air with 8 grams
of water vapour and your RH is 50%.
Ridge
Defined as an extended area of fairly high atmospheric pressure.
Scirocco
wind
A warm moist wind blowing from the Southeast bringing high
temperatures combined with a high humidity.
Sky
Conditions
Brief remarks (usually only consisting of one to three words) that
describe the amount of cloud cover, the type of precipitation, the
intensity of precipitation, and conditions that affect visibility.
Smoke
Smoke is caused by forest fires or other human-related environmental
factors. Visibility will be reduced.
Squall
The rapid onset of strong winds with speeds increasing to at least
16 knots and sustained at 22 or more knots for a minimum of one
minute.
Sunny
Almost totally clear, with perhaps a few small light clouds visible.
Cloud cover will be between 0% and 10%.
Sunny with
Cloudy Periods
Mostly clear, with times when about half of the sky will be covered
in clouds. Cloud cover will be between 30% and 50%.
Temperature
Is the degree of hotness or coldness. Temperatures of the air are
influenced by the local landscape, such as the presence of bodies of
water. The air temperature is measured in degrees Celsius and is
rounded to the nearest degree. The daytime maximum and night time
minimum temperatures that a forecaster expects are often expressed
as a range. If the forecast issued covers a wide region, the highs
and lows are not going to be identical across all areas in that
region.
Thunder
Skies will be overcast or partly cloudy with the sound of thunder
detected, but no precipitation observed.
Thundershowers
Intermittent rain showers with thunder and lightning, generally
short-lived.
Tornado
Appears as a powerful, funnel-shaped wind current in the lower parts
of the atmosphere with winds that twist upwards at high speeds -
often spawning from severe thunderstorms. The tornado usually
emerges from the base of a cumulonimbus cloud. It usually has a
width of tens to hundreds of meters and can last only minutes to
several hours. Tornadoes occur in the United States more than any
other country.
Trough
An elongated area of low pressure.
Variable
Cloudiness
At times there will be more clouds than sun, and at other times
there will be more sun than clouds. Cloud cover will be between 40%
and 60%.
Variable
Cloudiness with a Chance of Thundershowers
The sky is expected to be at least half covered with clouds, with
some showers possible; thunder and lightning may be associated with
the showers. The showers may be quite heavy, but will be
short-lived.
Variable
Cloudiness with a Risk of Thundershowers
The sky is expected to be at least half covered with clouds, with a
very slight chance of some showers; thunder and lightning may be
associated with the showers. The showers may be heavy, but will be
short-lived.
Variable
Cloudiness with a Risk of Thunderstorms
The sky is expected to be at least half covered with clouds, with
some showers possible; thunder and lightning may be associated with
the showers. The showers may be very heavy and last for a long
period of time.
Warm Front
A front can best be described as the border between two different
air masses. A warm front is the leading edge of a milder or warmer
air mass. A warm front travels in such a way that it results in warm
air replacing colder air. This happens as the warm air rises up and
over the cold air below. As the warm air travels upwards, it begins
to mix with the cold air aloft and condenses to form clouds. You can
usually expect periods of rain or drizzle for many hours as the
front approaches.
Warning
Indicating that a particular weather hazard is either imminent or
has been reported. A warning indicates the need to take action to
protect life and property. Warnings are issued for heavy rains, heat
waves, severe thunderstorms and strong winds.
Watch
Indicating that a particular hazard is possible, i.e., that
conditions are more favourable than usual for its occurrence. A watch
is a recommendation for planning, preparation and increased
awareness (i.e. to be alert for changing weather, listen for further
information and think about what to do if danger materializes).
Waterspout
Is essentially a tornado happening over water. Often it refers to a
small, fairly weak revolving column of air over water underneath a
cumulonimbus or towering cumulus cloud.
Wind
The horizontal movement of air in relation to the earth's surface.
Wind direction tells where the wind is blowing from. For example, a
"north wind" is coming from the north and is blowing towards the
south. There are four components of wind that are measured:
direction, speed, character (i.e. - whether it's a gust or a squall)
and shifts.
Wind Chill
Calculated only in the winter, wind chill is a calculation combining
air temperature and wind speed, given in degrees Celsius. It
represents the cooling effect felt due to the loss of body heat,
caused by the strength of the wind.
Wind
Direction
Described using one of eight different compass directions, in 45
degree increments, and indicating the direction from which the wind
is coming.
Wind Speed
The average wind speed taken during an hourly five-minute window,
and given in kilometres per hour.
