1. Weather Patterns & Forecasting

2. Pressure Systems
Weather- the conditions of the atmosphere at a certain place and time.
Weather is often associated with pressure systems
Air pressure is the weight of the molecules in the air

3. High Pressure Systems
High-pressure system- a large body of circulating air that has high pressure at it’s center and lower pressure on the outside.
Occurs when air masses move apart.
High-pressure air at the center sinks and moves toward low pressure areas.
Brings clear skies and “nice” weather
Winds rotate clockwise around high pressure
Symbol:

4. Low Pressure Systems
Low pressure system- a large body of circulating air that has low pressure at it’s center and higher pressure on the outside.
Occurs when air masses come together.
Air in the center of the system rises, and the water vapor in it condenses and forms clouds.
Bring cloudy skies and showers
Winds rotate counter-clockwise around low pressure
Symbol:

5. Air Masses
Air masses- large bodies of air that have specific temperature and moisture characteristics.
forms when a high pressure system stays in one area for a few days.
Changes in weather are caused by the movement and interaction of air masses.

6. Air Masses
4 kinds of Air masses:
Maritime (m)- originates over a body of water
Continental (c) -originates over land
Polar (P) -originates over a cold area
Tropical (T) -originates over a warm area
The characteristics of an air mass are determined by where it is formed.

7. Air Mass Combinations cP = continental polar = cool and dry
cT = continental tropical = warm and dry
mP = maritime polar = cool and wet
mT = maritime tropical = warm and wet

8. WRITING RESPONSE
If an air mass forms over land, what type of air mass is it? What words would you use to describe an air mass that formed over water near the equator?

9. WRITING RESPONSE
If an air mass forms over land, what type of air mass is it?
Air masses that form over land are called continental air masses
How would you describe an air mass that formed over water near the equator?
An air mass that formed over water and near the equator could be described as maritime tropical

10. Weather Fronts A weather front is the boundary between two air masses.
They occur where air masses come together
4 kinds of weather fronts:
Cold front
Warm front
Stationary front
Occluded front

11. Cold Fronts Cold air mass meets a warm air mass
Pushes the warm air up, lifting the clouds
Results in heavy rains or thunderstorms and cooler temperatures
Symbol:

12. Warm Fronts Warm air mass meets a cold air mass
Warm air rises above cold air and gradually replaces it
Results in clear weather and warmer temperatures
Symbol:

13. Cold & Warm Fronts
Cold Front
Warm Front

14. Stationary Fronts
Cold air mass meets a warm air mass, but there is not enough force for the warm air to be lifted
Results in days of cloudiness and constant rain
Symbol:

15. Occluded Fronts
Warm air mass gets caught above two cold air masses that converge
Results in large amounts of rain and cooler temperatures
Symbol:

16. Stationary & Occluded Fronts
Stationary Front
Occluded Front

17. WRITNG RESPONSE
What type of front is being modeled in the diagram? Justify your answer

18. WRITNG RESPONSE
What type of front is being modeled in the diagram? Justify your answer
The front being modeled by the diagram is a Cold front because a cold air mass is moving toward a warm air mass.

19. Weather Forecasting These measurements include:
Meteorology – the study of weather
Meteorologists( scientists who predict weather) measure weather variables before making a forecast.
A surface report describes a set of these weather measurements made on Earth’s surface.
These measurements include:
Temperature
Air pressure
Humidity
Precipitation
Wind speed and direction

20. Temperature
Temperature is the measure of the average kinetic energy of molecules in the air.
Molecules in warm air move faster than molecules in cooler air.
Thermometers are used to measure temperature.

21. Air Pressure
Air pressure is the measure of the force exerted by air molecules as they push down on objects—including you—with a force that we call the “barometric pressure.”
Air pressure decreases as altitude increases.
Barometers -respond to differences in air pressure

22. Humidity Humidity is the amount of water vapor in the air
When air is saturated, it holds the maximum amount of water vapor possible at that temperature.
Sling Psychrometers and Hygrometers are used to measure relative humidity.

23. Dew Point
When air near the ground becomes saturated, the water vapor condenses into a liquid and forms dew.
It the temperature is below 0C, ice crystals referred to as frost form.
The temperature at which saturation occurs is called the DEW POINT.

24. Measuring Precipitation
Rain is easy to measure—all you need is an “open tube with a ruler”—a RAIN GAUGE.
“Tipping bucket” rain gauges can measure rainfall outside and connect to show a display inside.

25. Measuring Precipitation
Measuring Snowfall-
Measuring how much snow falls is trickier than measuring rain, because wind can carry it away or pile it up in drifts.
Meter sticks or rulers in carefully selected locations are used to record how deep the snow lies.
Meteorologists may also melt snow to find its “water equivalent”—what it would have been had it fallen as rain.

26. Wind Direction and Speed
When air moves—”wind”—we feel both its direction and speed (force.)
Wind direction is measured with a “vane”—an arrow or other shape that points into the wind.
Speed is measured with an anemometer.
The faster the cups spin, the faster the wind.

27. Weather Conditions above the Surface
An upper –air report describes wind, temperature, and humidity conditions above Earth’s surface.
Weather balloons with an attached instrument package called a radiosonde are released into the atmosphere to measure weather conditions above the surface
Radiosondes contain:
Temperature sensor
Relative humidity sensor
Barometer
Radio transmitter
Battery
Parachute
String to attach to balloon

28. Weather Satellites & Radar
Weather satellites provide even larger views of weather systems
They provide weather information by measuring the radiation given off by Earth and by taking photographs.
Infrared Satellite images provide information about cloud temperature & height
Doppler radar- a special form of radar that can be used to detect precipitation and approximate wind speed.

29. This color-enhanced image shows a storm passing Des Moines, Iowa.
Heavier precipitation is shown by yellows and greens.

30. Here is a satellite image for the same time
Here is a satellite image for the same time. ”X” shows the area where the storm in the radar image was located X

31. Weather Maps
A station model displays many weather measurements for a specific location
It appears on weather maps.
The next set of slides will explain how to read one.

32. Temperature
Air temperature is shown in Fahrenheit degrees by the number to the upper left of the circle. 75

33. Pressure
Pressure—measured in mb (millibars)—is given by the number to the upper right of the circle
For example, suppose it’s mb
Only the 10s/1s/0.1s are shown—so it is represented as 194
Pressures below 1000 mb would start with high numbers, such as 964 for mb
194

34. Dew Point Temperature
The dew point temperature in Fahrenheit degrees is shown to the lower left of the circle. 57

35. Wind Direction and Speed
Wind direction is show by an “arrow” going into the circle. The example shows wind blowing from the lower right, so this is a southeast wind.
Each long “feather” represents 10 mph and each short “feather 5, so the wind speed is 25 mph.

36. Cloud Cover
The amount of the circle that is filled in indicates how much of the sky is covered by clouds.
It may range from “clear” (left) to “overcast” (right).

37. about 60%
no clouds
about 75%
about 10%
about 80%
about 25%
completely overcast
about 40%
sky obscured
about 50%

38. Present Weather
When rain, snow, or other forms of precipitation, lightning, and special weather conditions exist, these are shown by symbols to the left of the circle between air temperature and dew point temperature
thunderstorm

39. Samples of present weather symbols.
rain
fog *
snow
haze
slight rain showers ,
thunderstorm
drizzle .
ice or snow pellets
lightning

40. Try to interpret this station model
1. Temperature: 45 o F
2. Pressure: mb
3. Dew Point: 29 o F
4. Clouds: overcast
5. Wind: from southeast at
15 mph
6. Precipitation: light rain 2 1 6 4 3 5

41. Weather maps have isobars which are symbols made up of lines that connect places that have equal air pressure.

42. Isotherms – are lines that connect places that have the same temperature.

43. Fronts- are represented as lines with symbols on them.

44. Predicting The Weather
Modern weather forecasts are made with the help of computers.
Computer Models are detailed computer programs that solve a set of complex mathematical formulas. The formulas predict temperature, winds, precipitation, and types of clouds.