A Few Clouds
Scattered clouds, with clear skies dominant. Cloud cover between 1/10
and 5/10.
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 4/10 and 6/10.
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 1/10. Clear is the nighttime
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 nighttime 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 10/10.
Cloudy with Clear
Breaks
The nighttime 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 Flurries
The cloud cover will be as described for "Cloudy", and the
precipitation light. The flurries will be short-lived and intermittent,
and will not amount to any significant accumulation on the ground. Visibility
will be reduced, but roadways will not generally be slippery.
Cloudy with Isolated
Flurries
The cloud cover will be as described for "Cloudy", and the
precipitation very light. The flurries will be brief and intermittent,
and will not amount to any significant accumulation on the ground. Visibility
will be reduced, but roadways will not generally be slippery.
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 Rain
or Snow Showers
The type of precipitation expected to fall can either be rain or snow
throughout the forecast period. The precipitation starts and stops.
No significant accumulations are expected. If the precipitation falls
as snow, visibility will be reduced and roadways can become slippery.
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 6/10 and 8/10.
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 dewpoint 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.
Drifting Snow
Created when winds lift snow from the surface and blow it to heights
less than 2 meters. No additional snow will be falling and visibility
will not generally be reduced, but roadways can still get slippery.
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.
Flurries
Intermittently falling snow, generally short-lived. Flurries are the
solid equivalent of "Rain Showers".
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 labeled
based on the temperature of the advancing air mass. For example, the
front would be labeled "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 (63-87 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. For related
information please see Relative Humidity and Humidex
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 kilometers
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
counterclockwise into the centre of the Low. The air will rise and cool
often resulting in clouds and precipitation.
Mainly Clear
The nighttime 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 occuring in the
early evening.
Mainly Cloudy
Mostly covered in clouds, possibly with brief periods of sunshine. Cloud
cover will be 9/10.
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
1/10 and 3/10.
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 occuring 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 occuring 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 grayish 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 10/10.
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 6/10 and 9/10.
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 is calculated at all times of the year but the humidex
is usually only given in the warmer months from May to September.
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 0/10 and 1/10.
Sunny with Cloudy
Periods
Mostly clear, with times when about half of the sky will be covered
in clouds. Cloud cover will be between 3/10 and 5/10.
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 nighttime 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. In Canada most
tornadoes occur in the Prairies and in Southern Ontario.
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 4/10 and 6/10.
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 favorable 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 (ie - 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 kilometers per hour.
