Name________________________________
Block: __________
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
Air pressure
Condensation
Air Pressure: measured with a barometer.
o
Air pressure changes because of elevation,
temperature
humidity
o
Isobar: a line on a weather map that joins points with the same air pressure;
o
Lines closer together mean steeper pressure gradient, the winds are faster.
Elevation: As elevation increases, the pressure decreases since there is less air around you.
Temperature: As temperature increases, the pressure decreases because the molecules are
further apart.
 A warm air mass has low pressure & rises
 A cold air mass has high pressure & sinks
Winds: Air flows from high pressure to
low pressure, forming winds.
H= High pressure
L= Low pressure
Winds (Continued)
Warm air
rises
Cold air
sinks
o
o
o
o
Air over land cools faster & heats faster than air over water.
Sea breeze: when winds blow inland from the ocean, because a warm low pressure area is over the land
Land breeze: when winds blow off the land to the ocean because a warm low pressure area is over the ocean
Anemometer measures wind speed.
Factors effecting 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 the Earth’s rotation.
Jet Stream: a band of swiftly moving wind, moving East from the West, at the top of the troposphere, unaffected by
friction
Global Wind Patterns:
o Intertropical Convergence Zone (ITCZ), also known as the doldrums : low-pressure zone near equator caused by
warm, rising air
o Trade winds: 5-20° latitudes - warm & steady winds
o Subtropical highs: 20-35° latitudes - air usually sinks - very dry w/ little wind - deserts
o Polar highs: high pressure regions near the poles (sinking air) - very dry
Seasonal Winds:
Summer: land is hotter than ocean, so the wind blows moist air inland
Winter: ocean is hotter than land, so the wind blows dry air to sea
Isotherm: a line on a weather map that joins points with the same temperature
Temperature maps are colored to show temperature.
Air mass: A large body of air in the lower troposphere that has similar characteristics throughout. The temperature and
humidity of an air mass depends on the origin, and move with the air mass.
There are 4 types of air masses:
1. Continental polar (cP): cold and dry
2. Continental tropical (cT): warm and dry
3. Maritime polar (mP): cold and wet
4. Maritime tropical (mT): warm and wet
Front: A boundary between two air masses
Cold Front: boundary between advancing cold air mass and the warmer air mass that 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 that mass it is displacing
 1st clouds days in advance, then RAIN
 Air becomes warmer after front passes
Occluded front: when cold front ‘catches up’ to a warm front, producing clouds& precipitation
Stationary front: 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