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Forecasting Notes
Climate
o An area’s long-term pattern of weather (30 years)
o
Controlled by latitude, elevation, nearby water, Ocean currents, topography, prevailing winds,
and vegetation
Weather
o It’s what’s happening outside now!
o
It’s a result of humidity, pressure, and condensation
o
Energy transfer: Energy transfer among sun, atmosphere & Earth’s surface produces weather
If more energy comes in than leaves, Earth’s temperature will increase
If more energy leaves than comes in, Earth’s temperature will decrease
Air Pressure: measured with a barometer
o Changes because of elevation, temperature, and humidity
o Isobar: a line that joins points with the same air pressure; lines closer together mean steeper
pressure gradient
Elevation: As elevation increases, the pressure decreases since there is less air around you
Temperature: As temperature increases, decreases because the molecules are
further apart.
 A warm air mass has low pressure & rises
 A cold air mass has high pressure & sinks
Warm air
rises
WINDS: Air flows from high pressure to low pressure, forming winds.
H= High pressure
L= Low pressure
Cold air
sinks
Winds (Continued)
o
Air over land cools faster & heats faster than air over water.
o
Sea breeze: when winds blow inland from the ocean, because a warm low pressure area is over
the land
o
Land breeze: when winds blow off the land to the ocean because a warm low pressure area is
over the ocean
Factors Affecting Winds: Coriolis effect
Hurricanes in the Northern Hemisphere rotate counterclockwise while hurricanes
in the Southern Hemisphere rotate clockwise.
Coriolis effect: the tendency of an object moving freely over Earth’s surface to curve away from its path
of travel, caused by E’s rotation.
and Jet Stream: a band of swiftly moving wind, moving from East to West, at the top of the troposphere,
unaffected by friction
Global Wind Patterns:
o
o
Intertropical convergence Zone(ITCZ): low-pressure zone near equator caused by warm, rising
air
Trade winds: 5-20° latitudes - warm & steady winds
o
o
Sub-Tropical highs: 20-35° latitudes - air usually sinks - very dry w/ little wind - deserts
Polar highs: high pressure regions near the poles (sinking air) - very dry
Seasonal Winds:
Summer: land hotter than ocean, so blows moist air inland
 Summer monsoon: winds and rain
Winter: ocean hotter than land, so blows dry air to sea
 Winter monsoon: winds and no rain
Temperature Maps
o are colored to show…
temperatures
o Isotherms:
lines that connect places with the
same temperature
Air Mass: A large body of air in the lower troposphere that has similar characteristics throughout
Temperature & humidity depend on origin and move with the air mass
Types of Air Masses
Continental polar (cP):
cold and dry
Maritime polar (mP):
cold and wet
Continental tropical (cT):
warm and dry
Maritime tropical (mT):
warm and wet
Fronts: boundary between two air masses
Cold Front: boundary between advancing cold air mass & a warmer air mass it is displacing
 Rising warm air usually produces precipitation if wet
 Air becomes colder after front passes
Warm Front: boundary between advancing hot air mass & a colder air mass it is displacing
 1st clouds days in advance, then RAIN
 Air becomes warmer after front passes
Occluded : when cold front ‘catches up’ to a warm front, producing clouds& precipitation
Stationary: when a front stops moving forward, producing clouds & precipitation – causes floods if
stationary too long
Locating a Front:
o Wind direction changes
o
Temperature changes sharply
o
Dew Point changes sharply
Forecasting:
 Computer models take current data & plug it into equations to predict weather
 Meteorologists take computer models & tweak them to fit their experience with local conditions
Trend Method: using past movement of a front & precipitation to predict future movement