Marine Weather Flashcards
What is the primary source of the Earths weather?
the sun
Atmospheric pressure at sea level is equal to?
1013.25 millibars; 14.7lbs per square inch or 29.92 inches of mercury
What is used to predict the approach of a low pressure system?
barometer
A common unit of measurement for atmospheric pressure is?
inches
Prior to reading an aneroid barometer you should?
Tap the face lightly with your finger to bring the pointer to its true position
The most important information obtained from a barometer is?
The present reading of pressure combined with the changes in pressure observed in the recent past
The atmosphere in the vicinity of a high pressure is called?
Anticyclone
The wind circulation around a high pressure center in the Northern Hemisphere is?
Clockwise and moving outward from the high
Good weather is usually associated with?
A region of high barometric pressure
When low pressure area is approaching the weather generally?
worsens
a generally circular low pressure is called?
A cyclone
the wind direction around low pressure area in the Northern Hemisphere is?
Counterclockwise and inward
Weather systems in the middle latitudes generally travel from?
west to east
What is the wind pattern that has the most influence over North America?
the prevailing westerlies
A sea breeze is?
wind that blows towards an island or beach during the daytime
A local wind which occurs during the daytime and is caused by the different rates of warming of the land and water is a
sea breeze
A land breeze results from
a land mass cooling more quickly at night than an adjacent water area
Hail is a product of?
Violent convection found in thunderstorms
When a warm air mass overtakes and replaces a cold air mass the contact surface is called?
a warm front
what is typical of a warm front weather condition
steady precipitation
Barometric pressure should do what preceding an approaching warm front
steadily fall
When cold air displaces warm air you have a?
cold front
Whats associated with cold fronts?
A line of clouds, sharp changes in wind direction and squalls
A cold front moving in from the northwest can?
Produce thunderstorms, hail then rapid clearing
After a cold front passes what happens to barometric pressure?
Usually rises rapidly with clearing skies
Which move faster cold or warm fronts?
cold
When a cold air mass and warm air mass meet and there is no horizontal motion of either air masses it is called?
stationary front
an occluded front is usually caused by?
a cold front overtaking a warm front
A line on a weather chart connecting places which have the same barometric pressure is called?
An isobar
Pressure gradient is?
The measure of pressure differences over a horizontal distance
What enables you to estimate the bearing of a storm’s center?
Buys Ballot’s Law
When facing into the wind in the Northern Hemisphere the center of the low pressure lies?
to your right and behind you
Define relative humidity?
the ratio of the actual water vapor content to the current temperature of the air’s holding capability
The expression, the air is saturated means?
the relative humidity is 100%
The temperature at which the air is saturated with water vapor and below which condensation of water vapor will occur is referred to as the?
Dew Point
Fog forms when?
The air temperature is at or below the dew point
Fog is most commonly associated with?
a warm front at night
When warm moist air blows over a colder surface and is cooled below its dew point the result is?
Advection Fog
Frost smoke will occur when?
Extremely cold air from shore passes over warmer water
What is the classic thunderhead cloud?
Cumulonimbus
The wind speed and direction observed from a moving vessel is known as?
Apparent wind
In most cases the direction of apparent wind lies?
between the bow and the direction of true wind
Apparent wind can be zero only when?
True wind must be from dead astern and the wind speed must equal ships speed
A wind vane on a moving vessel shows?
Apparent wind
A weather forecast states that the wind will commence backing, in the Northern Hemisphere this means?
it would shift in a counterclockwise manner
A veering wind will change direction how in the Northern Hemisphere
clockwise manner
The USCG broadcasts weather reports on?
Channel 21A or 22A
A message warning of a hurricane will be prefaced by?
Pan-Pan (x3)
When do the highest frequency of tropical cyclones occur in the North Atlantic oceans?
August, September and October
When is the peak of hurricane season in the Western North Pacific?
July through October
Ocean swells originating from a typhoon can move ahead of it at speeds near?
50 knots
