weather rain & drizzle- m ost common type of precipitation. freezing rain- drizzle from stratus...
TRANSCRIPT
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Weather
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• Rain & Drizzle- most common type of precipitation.
• Freezing Rain- drizzle from stratus clouds.
• Freezing Rain- raindrops freeze when they hit the ground.
• Sleet- raindrops that freeze before they hit the ground.
Waters 3 States Video 6:52
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• snow- as ice grows and merges into clouds they form snowflakes.
• hail- is the largest type of precipitation.
• Lumps or balls of ice that fall from cumulonimbus clouds in warm weather.
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Let’s take a look at the weather picture and why we have weather!
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What is Weather?• State of the atmosphere at a specific time and
place• Includes such conditions as air pressure, wind,
temperature, and moisture in the air• Temperature is a measure of air molecule
movement• Sun’s energy causes air molecules to move
rapidly; temperatures are high and it feels warm
• When less of the Sun’s energy reaches air molecules, they move less rapidly and it feels cold
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What is Weather?
• Energy is transferred between fast-moving molecules and slower-moving molecules• CONDUCTION – transfer of energy
when molecules collide• CONVECTION – occurs when warm air
rises and cool air sinks; it’s the transfer of heat, usually in liquids or gases
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If we were to pick one term to help explain why we have weather, what do you think would be a good word?
You might pick heat or sun….but another good choice would be
Convection
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After the atmosphere is warmed by radiation and conduction, the heat is transferred throughout the atmosphere by convection.• Since warmed
air has more space between the molecules, it’s less dense and rises
• Cooled air is more dense and tends to sink
• In general, air near the equator tends to rise and air near the poles tends to sink
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Take a look at this!
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Notice the band of clouds around the equator ?
This is the ITCZ or inter tropical convergence zone
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Why do you think there is this band of clouds near the equator?
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Did you figure it out?• Warm, moist air in the tropics
rises• Cold air can hold less moisture
than warm air• As the moist air rises, it
condenses and forms clouds!
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Now What?• Ok, so we know that the
weather moves around on these highways and that warm air rises and cold air sinks.
• But why is it sunny one day, and rainy the next?
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Let’s take another look at the weather map
• Notice that there are H’s and L’s on the map
• There are also blue lines with spikes and red lines with half circles
• Let’s take a closer look!
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AIR PRESSURE
• Air weight that varies over Earth’s surface• Warmer air is less dense and exerts
less pressure• Cooler air is more dense and exerts
more pressure
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High Pressure Areas• When cooler
air sinks and is warmed, the air can hold more moisture
• This usually means sunny skies
• Winds tend to move clockwise around a high
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Low Pressure Areas• When warm air rises
and is cooled, the air can not hold as much moisture
• Often, these areas are associated with precipitation and stormy weather
• Winds tend to move counter clockwise around the low
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So, if you see a big H on the weather map over the area you live, you can expect fair weather
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When you see a big L in your area, there will probably be stormy weather
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These highs and lows move or less along the jet stream and bring us our weather changes
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Humidity• The amount of water vapor in the air• Temperature affects how much moisture is in
the air - warmer air can hold more water vapor, tending to make it more humid
• Relative humidity – the amount of water vapor in the air compared to what it can hold at a specific temperature
• When air cools, it can’t hold as much water vapor, so the water vapor condenses to liquid or forms ice crystals
• Dew point – the temperature at which air is saturated and condensation forms
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Global Winds• Wind patterns, caused by convection currents combined
with the Coriolis effect, of Earth that affect the world’s weather• Near equator, very little wind and daily rain patterns
called the doldrums• Surface winds:
• Between equator and 30 degrees N and S latitude are steady trade winds
• Between 30 and 60 degrees N and S latitude, the westerlies blow in opposite direction from the trade winds.
• The polar easterlies blow from northeast to southwest near the north pole and from southeast to northwest near the south pole
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Global Winds
Equatorial doldrums
TRADEWINDS
TRADEWINDS
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The Weather Highways• The rotation of the
earth creates the Coriolis effect.
• The Coriolis effect causes the air and water to be deflected to the right north of the equator.
• This creates global weather highways
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The Westerlies• Because of our
latitude, most of our weather comes from the west
• Looking at the weather map, what type of weather might we expect?
• What type of weather might we expect in a few days?
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Fronts and Air Masses
• Because air and moisture move in the atmosphere, weather is constantly changing• Air pressure – measured by barometer
• An air mass is a large body of air whose temperature and moisture are fairly similar at
a given altitude; properties like the part of Earth’s surface over which it formed
• Fronts are boundaries separating different air masses – clouds, precipitation, and storms
occur at frontal boundaries• There are four different air masses that affect
the United States
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The Air Masses
• cP( continental polar) : cold, dry stable
• cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface
• mP( maritime polar) : cool, moist, unstable
• mT( maritime tropical) : warm, moist, unstable
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This map shows the air mass source regions and there paths
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Warm Fronts• A warm front
is warm air displacing cool air
• Shallow leading edge warm air must “overrun” cold air
• These are usually slow moving
Widespread precipitation develops!
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2. Warm Front: The zone where warm air is replacing colder air
• In U.S., warm fronts usually move from southwest to northeast
• Air gets more humid after a warm front moves through
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Cold Fronts
• Cold air advances into region of warm air
• Intensity of precipitation greater, but short lived
• Clearing conditions after front passes
• Usually approaches from W or NW
Temperature drops; narrow band of violent storms!
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1. Cold Front: The zone where cold air is replacing warmer air
• In U.S., cold fronts usually move from northwest to southeast
• Air gets drier after a cold front moves through
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Stationary Fronts
• Surface positions of the front do not move
• Often a region of clouds and precipitation
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3. Stationary Front: When either a cold or warm front stops moving
• When the front starts moving again it returns to either being a cold or warm front
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Occluded Fronts• Cold front
overtakes warm front
• Involves three air masses of different temperatures
• Often found close to the low
pressure center
Cloudy weather with precipitation!
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4. Occluded Front: Formed when a cold front overtakes a warm front
• This occurrence usually results in storms over an area
• In U.S., the colder air usually lies to the west
MENU
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Anemometer- A tool used to measure
wind speed in miles per hour.
Wind vane
· A tool used to measure wind direction.
· Sometimes referred to as a
wind-weather vane or a wind sock.
· Wind direction is described by the
direction from which the wind is blowing.
Thermometer - A tool used to measure air
temperature in degrees Fahrenheit or
Celsius.
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Sling Psychrometer- • A two-thermometer
instrument also referred
to as a wet-dry bulb used
to measure relative
humidity (the amount of
water vapor in the air).• Temperatures readings
are converted using a
relative humidity table.Weather Instruments Video 1 15:01
Weather Instruments Video 2 19:41
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Barometer- A tool used to
measure air pressure in
inches of mercury or
millibars (mb).
Rain gauge- A tool used for
measuring the amount of
precipitation in inches or
centimeters.
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MENU
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Reading a weather map
• ISOBAR= connects areas of equal pressure BAR comes from BARometric pressure
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Reading a weather map...
• Isotherm: Connects areas of equal temperature; therm means temperature
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Satellites
· Satellite images are used for seeing cloud
patterns and movements.
· For example, hurricane clouds and movement
can be observed using satellite images.
Radar
· Radar images can be used to detect cloud cover,
rainfall or storm location, intensity, and movement,
as well as the potential for severe weather (for
example, hurricanes or tornadoes).
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Severe Weather
• Thunderstorms occur inside warm, moist air masses and at fronts• Warm, moist air is forced rapidly
upward, where it cools and condenses
• Strong updrafts of warm air and sinking, rain-cooled air cause strong winds
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Lightning• Movement of air inside a storm
cloud causes parts of the cloud to become oppositely charged
• Current flows between the regions of opposite electrical charge, forming a lightning bolt
• Thunder – lightning superheats the air, causing it to expand rapidly and then contract, forming sound waves
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Tornado• Violent, whirling wind that moves in
a narrow path over land
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Blizzard• A winter storm with strong winds, cold
temperatures, and low visibility, that lasts more than three hours
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Hurricane• Large, swirling, low-pressure system
that forms over tropical oceans• Heat energy from moist air is
converted to wind that can reach speeds of 250 km/h
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Severe Weather Safety
• A National Weather Service WATCH means conditions are favorable for severe weather to develop
• A warning means that severe weather conditions already exist
• Meteorologists study and predict weather
• National Weather Service makes weather maps and issues watches and warnings