1. Chapter 19

2.  Result of intense convection  Associated with heating Earth’s surface ◦ During spring, summer, and fall  Three-stage life cycle: ◦ Beginning stage– formation of cumulus cloud  Rapid heating during day, warm air rises  Cools, water vapor condenses, clouds form

3.  Clouds get bigger  Small-scale convection cells form  Draw in air from surroundings  Form winds at surface  Rapid vertical development ◦ 26,000 feet in 15 minutes; base 6 miles  Convection intensifies, creates strong winds

4.  Rising air creates strong updrafts  Causes water droplets/ice crystals to form ◦ Clump together to form precipitation  Height of cloud reaches 7 or more miles  Produces heavy precipitation  Known as a cumulonimbus cloud

5.  Mature phase ◦ Strong updrafts and downdrafts of wind intensify  Cause separation of lighter ice crystals at top  Heavier rain at lower part of cloud  Ice crystals become positively charged  Hail becomes negatively charged  Large electrical potential formed-released as lightning

6.  Electrical discharge of more that 100 million volts  Heats air to about 45,000° F  Cool air expands and creates thunder  Lightning can travel: ◦ Cloud-> cloud cloud-> ground cloud-> air ◦ All are potentially dangerous

7.  Dissipating stage ◦ Strong convection that formed the thunderstorm dissipates ◦ Decline in winds and rain ◦ Skies clear

8.  Spiraling column of air contacting the ground  Form at the base of thunderstorms ◦ When steep pressure gradient develops  Result of strong convection  Produce visible swirling air called funnel clouds  Composed of rapidly moving dust and debris

9.  Produce speeds up to 300 mph  Usually last only a few minutes ◦ Some up to 2 hours  Tornadoes over water form a water spout  Waterspouts and tornadoes move 30 to 75 mph

10.  Violent storm associated with large low- pressure system ◦ Also called a cyclone  Rotate counterclockwise in the Northern Hemisphere  Winds spiral inward  Form over the Atlantic Ocean near the equator

11.  Low pressure moves over ocean to the USA ◦ Picks up energy/moisture from warm water ◦ Called a tropical disturbance winds less than 20 mph  As it moves over warm ocean intensifies ◦ Becomes tropical depression- winds 21 to 39 mph

12.  Clouds thicken and rotate around the center ◦ Called tropical storm-winds 40 to 70 mph  When sustained winds reach 74 mph ◦ Called a hurricane in the Atlantic Ocean ◦ Winds greater than 250 mph ◦ Winds move inward and move counter- clockwise

13.  High winds cause pile up of water ahead ◦ Called a storm surge ◦ Can be as high as 16 feet  Intensity measured- Saffir-Simpson scale ◦ Measures pressure, wind speed, and storm surge ◦ Scale of 1 to 5- 5 highest intensity  In Pacific Ocean called a typhoon

14.  Three main steps: ◦ Gather current weather information ◦ Record information on charts and maps  Or either computer models ◦ Charts, maps, and computer models analyzed  Weather is predicted or forecasted

15.  Data gathered from almost 1,000 weather stations  Data is recorded each hour ◦ Surface air temp ◦ Barometric pressure ◦ Cloud cover ◦ Wind speed ◦ Dew point ◦ Precipitation ◦ Visibility ◦ Wind direction

16.  Plotted every three hours- coded form  Displayed on maps using station model ◦ Usually shows: ◦ Location of high- and low- pressure systems ◦ Temperatures ◦ Fronts ◦ Precipitation

17.  Surface temperature maps created using isotherms ◦ Lines that connect equal values of temperature  Can also be created using isobars ◦ Lines connecting value of equal pressure  Can be generated at different levels in the atmosphere  Refer to Pg. 394 in your textbook

18.  Divided into two categories: ◦ Long-term ◦ Short-term ◦ Short-term are reliable up to 6 hour ◦ Long- term– a few days, weeks, or months out  More difficult to make  Refer to Pg. 395 in your textbook

19.  Radar extremely successful over past 20 years ◦ Reflected radio waves off clouds and precipitation ◦ Locates poor weather ◦ Up-to-date radar images on Internet ◦ Can also differentiate forms of precipitation ◦ Predicts where snow/freezing rain may form

20.  Simple observations can also predict weather ◦ Low barometric air pressure-poor weather ◦ Rise in barometric pressure- good weather ◦ Type of clouds:  Cumulus- incoming thunderstorms  Stratocumulus- approaching warm front and precipitation  Clearing skies in winter- drop in temp