Forecasting Weather
Forecasting Weather
• Now that Meteorologists understand the
factors that affect weather they must put all of
this together to create weather maps and to
determine weather patterns.
– Together weather maps and weather patterns are
very helpful in forecasting the weather.
Weather Maps
• Graphically show temperature, barometric
pressure, wind speed/direction, cloud cover
and relative humidity.
– Also shows:
• Air masses
• Fronts
• hazardous conditions
– Created by putting together data from thousands
of weather stations from all across the world.
Weather Map
Map Symbols
• Map symbols are used to help identify the
conditions reported from each weather
station.
Other Symbols
Weather Movement
• Weather moves from areas of high pressure
to areas of low pressure within air masses.
– A huge body of air that has similar temperature,
humidity and air pressure throughout it.
• Classified by two characteristics:
1.
2.
Temperature
humidity
• Warm or cold air masses depend on the temperature
of the region over which the air mass forms.
Air Masses
• 4 general air masses
1. Polar (P)
•
•
From the poles to 60° N or S latitude.
Very cold air mass.
2. Tropical (T)
•
•
From the equator to 25° N or S latitude.
Warm to hot air mass.
3. Continental (c)
•
•
Over any large land mass.
Dry air mass.
4. Marine (m)
•
•
Over any large body of water.
Wet air mass.
Combining Air Masses
1. Maritime Tropical (mT) – warm, humid air
masses that form over oceans near the tropics.
– Summer = hot and humid weather
– Winter = humid conditions that bring rain or snow.
2. Maritime Polar (mP) – cool, humid air masses
that form over the icy cold North Pacific and
North Atlantic oceans.
– Affect the West Coast more than the East Coast
•
Summer = cool, humid air brings fog, rain and cool
temperatures to the West Coast.
Combining Air Masses
3. Continental Tropical (cT) – Hot, dry air masses
that form only in the summer over dry areas of
the southwest and northern Mexico.
– Cover the smallest area of all air masses!
4. Continental Polar (cP) – cool to cold and dry air
masses that form over central and northern
Canada and Alaska.
– Winter = clear, cold and dry air to much of North
America.
•
Arctic Air Masses (A) – bring bitterly cold weather with
very low humidity.
–
Polar Vortex
North American Air Masses
Fronts
• An area where two air masses meet and tend to not
mix due to differences in temperature and density.
– Warm air masses = low densities and rise
– Cool air masses = higher densities and sink
• Colliding air masses often cause storms and
changeable weather.
• 4 Types:
1.
2.
3.
4.
Cold Front
Warm Front
Stationary Front
Occluded Front
Front Symbols
Types of Fronts
1. Cold Fronts – cold air masses meet and push
under a warm air mass.
– Violent storms occur followed by fair, cool
weather.
•
Cumulonimbus Clouds
Types of Fronts
2. Warm Fronts – warm air masses overtake a cold
air mass and moves over it.
– Rain is followed by hot, humid weather.
•
Cirrus clouds followed by stratus clouds.
Types of Fronts
3. Stationary Fronts – warm air mass meets a
cold air mass and no movement occurs
– Rain may fall for many days.
Types of Fronts
4. Occluded Front – A fast moving cold front
overtakes a warm front, lifts it quickly
causing large scale precipitation.
Understanding Weather Maps
X
cP
Understanding Weather Maps
1. What is the temperature in Pittsburgh? 78°F
2. What is the wind direction in NY City?
SE
3. What type of front is moving into X? Warm
–
What weather conditions should they be expecting?
Rain, hot & humid
4. What is the wind speed at X?
20
5. What type of air mass is moving into
Pittsburgh? cP – Continental Polar
Cyclones & Anticyclones
• Cyclones – areas of low pressure (L) that
contain rising warm air.
– Greek for “wheel”.
– Cooler air will move in and take the place of the
warm air causing air currents to spins
counterclockwise causes rainy, stormy weather.
• Anticyclones – high pressure centers (H) of
cold, dry air.
– Winds spiral clockwise causing clear, dry, fair
weather.
Cyclones & Anticyclones
Anticyclone
Cyclone
Hazardous Conditions
• Causes great human suffering and death.
– Responsible for sever damage to the environment,
infrastructure of cities and town and private
property.
• Types of Hazardous Conditions:
– Thunderstorms
– Hurricanes
– Tornadoes
– Winter Storms
Thunderstorms
• Thunderstorms form after severe heating of
Earth’s surface.
– Form within large cumulonimbus clouds when warm
air is forced upward at a cold front.
• Causes convection currents.
– Internal friction is created within these convection
currents causing electric charges in the clouds.
• Lightning is the discharge of the electric charges.
• Thunder is the sound that rapidly heated air, from lightning,
causes as it expands suddenly and explosively.
– Mechanical Energy
Tornadoes
• Develop in low, heavy cumulonimbus clouds
during spring and early summer often in late
afternoon.
– Rapidly whirling, funnel-shaped clouds that are short
lived and develop over land from severe
thunderstorms. Cyclone – counterclockwise rotation
• Over a lake or ocean = waterspout
• Occur ONLY in the United States
– The Great Plains has the greatest occurrence of
tornadoes and is called “tornado alley”.
Hurricanes
• A tropical storm that has winds of 119 km/hr or
higher and is about 600 km across.
– Develops over warm water as a low pressure area or
tropical disturbance.
• Gets its energy from the warm, humid air at the ocean’s
surface.
• Winds spiral inward, cyclone, toward the area of low
pressure.
– Lowest air pressure in a hurricane is found in the center, the eye.
• Storm Surge – the dome of water that is pushed
ashore where a hurricane lands.
– The cause of most damage and death!
Hurricane Categories
Winter Storms
• Snow falls when humid air cools below 0°C.
• Lake-Effect Snow is caused when land loses
heat faster than water and a dry, cold air mass
it picks up water vapor from the warmer
bodies of water.
– Oswego, NY is one of the snowiest cities in the
United States.
• Receives an average annual snowfall of over 200”.
Average Snowfall in New York