1. Humidity  Capacity of air is primarily a function of temperature  Relative Humidity (RH) = (actual water vapor content) x 100 (max. water vapor capacity of the air)  Heated air becomes lower in RH because denominator gets larger  Cooled air becomes higher in RH

2. Saturation vs Air Temperature The actual amount of Water air can hold changes With air temperature Air at 104 F can hold 3 times As much water as 68 F air ! (47 grams vs only 15 grams) Air at 68 F can hold 4 times As much water as air at 0 F (15 grams vs only 4 grams) 32 F 68 F 104 F 4 grams 15 grams 47 grams

3. Forms of Condensation and Precipitation Chapter 5 Meteorology

4. Clouds, Fogs, Snow and Sleet  Clouds: visible aggregate of minute droplets of water, or tiny crystals of ice or a mixture of both  Indicate what’s going on in atmosphere  For any form of condensation to occur the air must be saturated  There generally must be a surface on which water vapor can condense

5. Clouds, Fogs, Snow and Sleet  Cloud Condensation Nuclei: tiny particles that serve as surfaces for which water vapor condenses  Includes dust, smoke and salt particles  If nuclei are absent the relative humidity needs to be well above 100% in order to produce cloud droplets

6. Growth of Clouds  Hygroscopic (water seeking) Nuclei:  Particles that are effective sites for condensation  Items that quickly absorb moisture when exposed to humid air and become stale  Byproduct of combustion (forest fires, automobiles, coal burning furnaces)  Hydrophobic (water repelling) Nuclei:  Water will only form if relative humidity reaches 100%  Major sources of Nuclei  Dust storms, volcanic eruptions, pollen

7. Cloud Condensation Nuclei

8. Cloud Formation

9. Types of Clouds  Identify Ten Major Types  Where located: High, Medium, Low  Picture  EMAIL TO ME: saderks@bluevalleyk12.orgsaderks@bluevalleyk12.org  With you and your partners name on it.

10. Cloud Classification  Cirrus:  High, white and thin; “curl,” “filament”  Separated and detached, form delicate veil-like patches; extended wispy fibers; feathery appearance.  Cumulus  Globular individual cloud masses. Flat base and appear as rising domes or towers (cauliflower)  Stratus  Clouds are best described as sheets or layers that over much or all of the sky  No distinct individual units

11. Cloud Classification: High Clouds 6000m (20,000ft) base  High clouds: low temperatures, ice crystals, small quantities of water vapor  Cirrus (Ci)  Thin delicate fibrous ice-crystal clouds (mare’s tails)  Cirrostratus (Cs)  Thin sheets of white ice-crystal clouds that give sky a milky look  Cirrocumulus (Cc)  Thin, white ice crystal clouds  Least common

12. Cirrus

13. Cirrostratus

14. Cirrocumulus

15. Cloud Classification: Middle Clouds 2000 – 6000m  Altocumulus (Ac)  White to gray clouds often made up of separate globules  “Sheep back”  Altostratus (As)  Stratified veil of clouds that are generally thin and may produces very light precipitation  Can produce a bright spot in the sky (not a halo)  Seen with warm fronts

16. Altocumulus

17. Altostratus

18. Cloud Classification: Low Clouds below 2000m (6500 ft)  Stratus (St)  Low uniform layer resembling fog, but not resting on the ground  Leads to drizzles  Stratocumulus (Sc)  Soft gray clouds in globular patches or rolls  May form continuous clouds  Nimbostratus (Ns): Nimbus: “rain cloud”, Stratus: “to cover with a layer  Form during stable conditions  Amorphus layer of dark gray clouds  Chief precipitation producing clouds (light to moderatecontinuous rain)

19. Stratus

20. Stratocumulous

21. Nimbostratus

22. Cloud Classification: Cloud of Vertical Development  Clouds that span more than one height  Associated with unstable air  Cumulus (Cu): Fair Weather clouds  Dense billowy clouds often characterized by flat base  Seen on clear days with unequal surface heating  Cumulonimbus (Cb)  Towering cloud, “anvil head”  Thunder, lightening, hail, tornadoes

23. Cumulus

24. Cumulonimbus

25. Lifecycle of Cumulonimbus

26. Cloud Varieties  Uncinus: “hook shaped,” streaks of cirrus clouds, look like commas  Cirrusuncinus: bad weather is coming  Fractus: stratus/cumulus are broken  Mammatus: rounded protuberances on their bottom surfaces  Associated with stormy weather and cumulonimbus clouds  Lenticular: lens-shaped  Found in rugged or mountainous topography

27. Uncinus

28. Fractus

29. Mammatus

30. Lenticular

31. Types of Fog  Fog: cloud with base near the ground  Physically no difference between a fog and a cloud; appearance and structure the same  Difference is method and place of formation  Fog results from cooling or by addition of enough water vapor to cause saturation  Atmospheric Hazard:  Light – reduces visibility (2 to 3 km, 1 to 2 miles)  Dense – cut to a few dozen meters or less

32. Types of Fog  Radiation Fog: results from radiation cooling of the ground and adjacent air  A nighttime phenomenon requiring clear skies and a fairly high relative humidity  Thickest in valleys  Dissipates within one to three hours of sunrise, fog evaporates from the bottom up

33. Radiation Fog

35. Types of Fog  Advection Fog: when warm and moist air blown over a cold surface, it becomes chilled by contact and to a certain extent, by mixing with the cold air  If cooling is sufficient, fog will form air moving horizontally  Are a consequence of air giving up heat to the surface below during horizontal movement  Winds up to 6 to 18mph required (turbulence facilitates cooling through a thicker layer of air but it also carries fog higher)  Thicker than radiation

36. Advection Fog

40. Types of Fog  Upslope Fog: created when relative humidity moves up a gradual sloping or up the steep slope of a mountain  Because of upward movement air expands and cools adiabatically  If dew point is reached, an extensive layer of fog may form

41. Upslope Fog

43. Formation of Fog  Steam Fog: when cool air moves over warm water; enough moisture may evaporate from the water surface to saturate the air immediately above  As rising water vapor meets the cold air, it condenses and rises  Common over lakes and rivers on clear crisp mornings in the fall

45. Formation of Fog  Frontal Fog: When frontal wedging occurs, warm air is lifted over colder air  If the resulting clouds yield rain and the cold air below is near dew point, enough rain can evaporate to produce fog  Results in a continuous zone of condenses water droplets reaching from the ground up through clouds

46. Dew  Condensation of water vapor on objects that have radiated sufficient heat to lower their temperature below dew point  May form on some surfaces but not others

47. White Frost  Forms when the dew point of air is below freezing  Not frozen dew  Gas to a Solid (deposition

48. Frost

49. Types of Precipitation Atmospheric Pressure A Crash Course Chapter 5 and 6

50. Precipitation Formation  Why do some clouds produce precipitation and other just float overhead?  Cloud Droplets are very tiny in comparison to rain droplets  For precipitation to occur cloud droplets must grow in volume by roughly 1 million time

51. Collision – Coalescence Process  Warm clouds are those having temperatures greater than 0 °C throughout.  The largest droplet (collector drop) falls through a warm cloud and overtakes some of the smaller droplets because of its greater terminal velocity

52. Collision – Coalescence Process  A collector drop collides with only some of the droplets in its path. The likelihood of a collision depends on both the size of the collector and its size relative to the droplets below.  If the collector drop is much larger than those below, the percentage of collisions will be low.

53. Collision-Coalescence  The tropics are the ideal environment for the C-C process.  Very humid and relatively clean so fewer condensation nuclei exists  In these areas, large cumulonimbus clouds form and within those clouds the larger drops quickly gather smaller droplets to generate the warm afternoon showers associated with tropical climates

54. Bergeron Process  A cloud at a temperature of -10 o C (14 o F) has ice crystals that are surrounded by liquid droplets  Supersaturated clouds contain more water vapor than “regular” clouds.  Ice Crystals collect more water than they lose through sublimation  Evaporation of water droplets provides a water source of water vapor to feed the growth of ice crystals

55. Bergeron Process  As the ice crystals descend they enlarge as they intercept cloud drops that freeze on them  B.P. produces precipitation throughout the year in the middle latitudes (if the clouds are cold enough).  The type of precipitation that reaches the ground depends on the temperature profile in the lower atmosphere.

56. Bergeron Process

57. RAIN  Rain is precipitation arriving at the surface in the form of liquid drops, usually between 0.5 and 5 mm.  Episodic precipitation from rapidly developing cumuliform clouds is called showers and can occur as either rain or snow.

58. RAIN  In Mid-latitudes precipitation leaves cold cloud as snow, if temperatures are higher than freezing precipitation will become rain near the surface

60. SNOW  Snow results from the growth of ice crystals through deposition, riming, and aggregation.  Ice crystals in clouds can have a wide variety of shapes, including six-sided plates, columns, solid or hollow needles, and complex dendrites with numerous long, narrow extensions.

61. SNOW  As precipitation leaves cold clouds, the temperature must remain below freezing at or near the surface

63. SLEET  Sleet (above) occurs as rain falling from a cloud, passes through a cold layer, and freezes into ice pellets. This is most common along warm fronts.

64. FREEZING RAIN (GLAZE)  Freezing rain begins when a light rain or drizzle of supercooled drops falls through air with a temperature at or slightly below 0 °C.  When the raindrops hit the surface, they form a thin film of water, but only for a moment.  Soon afterward the water freezes to form a coating of ice.

66. Formation of Sleet

68. Global average annual precipitation.

70. HAIL  Hail consists of ice pellets formed in roughly concentric layers.  Formed from updrafts that carry a particle into the colder reaches of a cloud, and the liquid water coating the ice freezes.  When the stone exits the updraft and falls, it becomes wet from its collisions with liquid droplets.  The hailstone can be captured once again by an updraft, and the coating of water freezes

71. HAIL FORMATION