1. WEATHER

5. 5

6. Hydrologic Cycle 6

7. 7

8. Saturation and Dew Point
Saturated verses unsaturated air
At the dew-point temperature, air reaches saturation
temperature to which air must be cooled to (100% RH)
water on outside of drinking glass
ice on your car window
dew and fog 8

9. After Saturation Occurs the Air Must Release Extra Water as Fluid
Water forms on the outside of a cold glass as the cold
Air surrounding the glass chills the air to the Dew
Point Temperature
The resulting water
is not from the glass,
the water is from
condensation of
moisture in the air
around the glass 9

10. Lifting Condensation Level (LCL)
The altitude where the dew point is reached and clouds form
LCL / Cloud base = dew point altitude 10

11. In Nature Extra Moisture is Transformed to Water Droplets
Cold air next to the rain-soaked cliff is chilled
To The Dew Point Temperature & creates a
Misty Cloud
along a Rocky
Mountain slope
Air near the
Slope is 100%
Saturated 11

12. Measuring Relative Humidity
Sling psychrometer
Hair hygrometer 12

13. There are a number of ways in which clouds can form13

14. Convergence Convergence occurs
when large air masses meet & are forced to rise vertically by crowding of molecules.
This process is best seen at the ITCZ where the Trades Winds meet & rise to form towering clouds & heavy precipitation 14

15. Convectional Lifting
Anywhere air is warmer than its surrounding air, it will rise.
In this example an island heats more than the surrounding water and causes a massive cumulus cloud to form. 15

16. Convectional Lifting Over Florida
Warmer temperatures over the peninsula of
Florida, which is land, cause air to rise
compared to the cooler oceans nearby
Rising air in this
Shuttle Picture is
Shown by a
Cloud pattern
which generally
follows the shape
of the southern
Florida peninsula 16

17. Convectional Lifting in the Desert
Extremely high afternoon temperatures in late summer often leads to thunderstorms throughout the world’s arid regions.
Mojave Desert
The Grand Canyon in August 17

18. Orographic Lifting of Air
When air moving
Horizontally
Encounters a
Mountain it must
Rise over the crest
As it rises, it cools
To create clouds,
And most often
precipitation
Moisture
Lost
Dry
Air
Moist
Air
Run off NO Run off 18

19. WHY SO MUCH SEVERE WEATHER
OCCURS IN THE MIDWEST

20. CHANGES IN LATITUDE: WESTERLY WINDS WHERE WE LIVE; FLORIDA AND SOUTH TO
EQUATOR ARE THE TRADE WINDS FROM THE EAST. THE TRADE WINDS FROM NORTH
AND SOUTH OF THE EQUATOR MEET AND CAUSE UPLIFT. THE WEATHER NEAR THE
EQUATOR: LOTS OF RAIN AND NO WINDS.

21. Air Mass – an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any given latitude.
Source Regions – are regions where air masses originate. In order for a huge air mass to develop uniform characteristics, its source region should be generally flat and of uniform composition with light surface winds.

22. Classification
Air masses are grouped into four general categories according to their source region
Polar (P) are air masses that originate in polar latitudes
Tropical (T) are air masses that form in warm tropical regions
Maritime (m) are air masses that originate over water (moist in the lower layers)
Continental (c) are air masses with a source region over land (dry)

23. Air mass source regions and their paths.

24. Fronts
A front is a transition zone between two air masses of different densities. Since density differences are most often caused by temperature differences, fronts usually separate air masses with contrasting temperatures. Often they will also have contrasting humidities as well.

25. Cold Front
Represents a zone where cold, dry stable polar air is replacing warm moist unstable tropical air.
Drawn as solid blue line with the triangles along the front showing its direction of movement.

26. COLD FRONT
In the case of a cold front, a colder, denser air mass lifts the warm, moist air ahead of it. As the air rises, it cools and its moisture condenses to produce clouds and precipitation. Due to the steep slope of a cold front, vigorous rising motion is often produced, leading to the development of showers and occasionally severe thunderstorms.

27. Cold front

28. Warm Fronts
A warm front is a front that moves in such a way that warm air replaces cold air

29. WARM FRONT
In the case of a warm front, the warm, less dense air rises up and over the colder air ahead of the front. Again, the air cools as it rises and its moisture condenses to produce clouds and precipitation. Warm fronts have a gentler slope and generally move more slowly than cold fronts, so the rising motion along warm fronts is much more gradual. Precipitation that develops in advance of a surface warm front is typically steady and more widespread than precipitation associated with a cold front.

30. Warm Front

31. Although not a mountain range, masses of moving air
Create the same effect – Unlike mountains air masses
Can provide lifting in many different locations
Fronts can lift air
Which is stable,
Creating clouds
& large amounts
Of precipitation
As rain, snow,
Sleet or hail
Frontal Lifting of Air 31