1. Weather

2. Precipitation 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

3. Precipitation
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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5. Let’s take a look at the weather picture and why we have weather!

6. 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

7. 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

8. You might pick heat or sun….but another good choice would be
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

9. 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

10. Take a look at this!

11. Notice the band of clouds around the equator ?
This is the ITCZ or inter tropical convergence zone

12. Why do you think there is this band of clouds near the equator?

13. 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!

14. 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?

15. 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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16. 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

17. 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

18. 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

19. So, if you see a big H on the weather map over the area you live, you can expect fair weather

20. When you see a big L in your area, there will probably be stormy weather

21. These highs and lows move or less along the jet stream and bring us our weather changes

22. 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

23. 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

24. Global Winds
TRADEWINDS
Equatorial doldrums
TRADEWINDS

25. 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

26. 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?

27. 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

28. 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

29. This map shows the air mass source regions and there paths

30. 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!

31. Warm Front
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

32. 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!

33. Cold Front
1. Cold Front: The zone where cold air is replacing warmer air
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In U.S., cold fronts usually move from northwest to southeast
Air gets drier after a cold front moves through

34. Stationary Fronts Surface positions of the front do not move
Often a region of clouds and precipitation

35. Stationary Front
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

36. 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!

37. Occluded Front
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

38. Weather Tools 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.

39. Weather Instruments Video 1 15:01 Weather Instruments Video 2 19:41
Weather Tools
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

40. Weather Tools
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.

41. Weather Map Symbols

42. MENU

43. Reading a weather map
ISOBAR= connects areas of equal pressure BAR comes from BARometric pressure

44. Reading a weather map...
Isotherm: Connects areas of equal temperature; therm means temperature

45. Satellites & Radar 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).

46. 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

47. 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

48. Tornado
Violent, whirling wind that moves in a narrow path over land

49. Blizzard
A winter storm with strong winds, cold temperatures, and low visibility, that lasts more than three hours

50. 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

51. 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