Secrets
of the Saint-Lawrence - Marine Weather Guide
A to Z
Air mass
A large volume of air with uniform properties of temperature
and moisture. Air masses extend over thousands of square kilometres.
Breaker
A swell wave that has broken into foam.
Chop
Irregular motion of waves, in which it is difficult, if not impossible,
to find one's bearings. Creates a confused sea. Produced on top of rip
by wind blowing against the current.
Deep water
Water depths more than one-half the wavelength of a wave.
Fog
Minute water droplets suspended in the air that reduce visibility
to less than one nautical mile. Fog is cloud on the ground.
Front
The line of separation between 2 air masses with different temperatures
and moisture levels. A warm front is a mass of warm air displacing a mass
of cold air, and vice versa.
Haze
Same phenomenon as fog, except that visibility is equal to or greater
than 1 nautical mile.
High
A region of high pressure. Air flows outwards and clockwise around
high pressure areas. A high is usually associated with good weather.
Isobar
Line on a weather map joining points of equal pressure.
Low
A region of low pressure. Winds flow counterclockwise around the low
centre. A low pressure centre is usually a storm centre accompanied by
precipitation and strong winds.
Main cabin
On a ship or pleasure boat, the main room in which the crew
gathers to plan routes and manoeuvres.
Millibar
A unit used to measure barometric pressure.
Northwest gyre
Slow gyrating motion of sea water. In the Gulf of St Lawrence, this
counterclockwise motion may extend over 200 kilometres. The gyre's axis
is located in the Northwestern part of the Gulf, between Anticosti and
Pointe-des-Monts. Its speed is almost imperceptible: slightly more than
0.10 knot. 23
Radiocopy
Transcription of a message received by radio, or name of the computer
system by means of which such messages are transcribed automatically or
are pre-recorded. Radiocopy is an exclusive Weatheradio Weathercopy service.
Radiograms
A message transmitted by radio, in particular by Weatheradio or Coast
Guard radio.
Ridge
An elongated area of high pressure, associated with a high.
Rip
Turbulence on the sea's surface that results when 2 currents
meet.
Sea
Combined wind waves and swell. Cross sea -Confused sea formed
when one train of waves moves at an angle to other groups of waves. The
sea becomes steep, with short, sharp wave crests. When cross seas combine
with an underlying tidal current, the sea surface becomes especially confused
and hazardous. Also known as cross swell. Choppy sea -Short, sharp,
breaking waves. Typically caused by the reflection effect.
Breaking sea -Unstable sea resulting from steep, breaking or near-breaking
waves.
Significant wave
height
Average height of the highest 33 % of all the waves present.
Squall
A brief, violent windstorm, often accompanied by rain or snow.
Squalls are generally associated with cumulonimbus clouds. If they accompany
a fast-moving cold front, they may be of longer
duration.
Strong winds
By convention, combination of forces 4, 5 and 6 on the Beaufort
Scale to indicate sustained wind speeds in the range of 20 to 33 knots.
Trough
An elongated area of low pressure, associated with a low, often
produces a wind shift and showery weather.
Wave steepness
Slope of a wave that may not exceed 14 %. Beyond that point, the
crest will break and the wave will tumble.
Weatheradio
This is the name of Environment Canada's weather information
broadcast network. The network has transmitters in every region. Mariners
interested in listening to this network need a receiver which can be purchased
from electronic equipment dealers. Many portable models are available.
Weatheradio signals warnings of severe weather automatically to
receivers equipped with special alarm devices for that purpose.
Zephyr
A soft, warm and gentle breeze. For the Ancients, this was the West
wind. |
