1. Thunderstorms
Chp 13.1

2. Types of thunderstorms
Orographic thunderstorms
air that is forced up by a mountain or hillside
As air strikes the windward side, it is uplifted and cooled.
Windward slopes of mountains tend to be the rainy sides
the leeward side is dry.
Dry climates found in the "rain shadow" of tall mountain systems

3. the result of localized convection in an unstable air mass.
a relatively weak thunderstorm that usually does not last much longer than an hour, moves slowly and does not produce severe weather
a garden variety thunderstorm.
Air mass thunderstorms tend to occur within a maritime tropical air mass
The main threats from an air mass thunderstorm are lightning and brief heavy rain.
air mass thunderstorms tend to occur in the afternoon hours because of uplifting produced from heat of the sun.

4. occur along the boundaries of weather fronts (e.g. cold front).
An intense line of thunderstorms that forms right along or just ahead of a cold front is called a squall line.
Severe thunderstorms, supercells, and/or tornadoes can form

5. Stages of Development

6. Cumulus stage Starts with a cumulus cloud. Heating by the sun
Air starts to rise vertically upward
The cloud will continue to grow as long as warm air below it continues to rise.

7. Mature Stage
When the cumulus cloud becomes very large, the water in it become large and heavy.
Raindrops start to fall through the cloud
cool dry air starts to enter the cloud.
Because cool air is heavier than warm air, it starts to descend in the cloud (known as a downdraft).
The downdraft pulls the heavy water downward, making rain.
This cloud has become a cumulonimbus cloud because it has an updraft, a downdraft, and rain.
Lightning and thunder start to occur, as well as heavy rain.
The cumulonimbus is now a thunderstorm cell.

8. Dissipating Stage
After about 30 minutes, the thunderstorm begins to dissipate.
This occurs when the downdrafts in the cloud begins to dominate over the updraft.
Since warm moist air can no longer rise, cloud droplets can no longer form.
The storm dies out with light rain as the cloud disappears from bottom to top.
The whole process takes about one hour for an ordinary thunderstorm

9. Assignment
P. 333 # 1 - 5

10. Severe Weather
Section 13.2

11. Supercells
responsible for producing tornadoes, large hail and other dangerous winds
warm, humid air in the lower atmosphere, colder air aloft and something to give the air near the ground an upward shove.
needs strong winds coming from different directions at different altitudes high above the ground
can last for hours,
Some supercells produce little rain, others, downpours that can cause flash floods.
Supercells are most common on the Great Plains, but also occur in other parts of the USA.
supercells can be detected using the National Weather Service's Doppler weather radar.
allow forecasters to peek inside a supercell and look for a Tornado Vortex Signature, or TVS.

13. Lightning Lightning strikes about 100 times every second.
Lightning is an electric current.
many small bits of ice (frozen raindrops) bump into each other as they move around in the air.
All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges.
The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud.
Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud.
The grounds electrical charge concentrates around anything that sticks up, such as mountains, people, or single trees.
The charge coming up from these points eventually connects with a charge reaching down from the clouds and - zap - lightning strikes!

16. 54,000 degrees Fahrenheit. That is six times hotter than the surface of the sun
Thunder is caused by lightning.
When a lightning bolt travels from the cloud to the ground it actually opens up a little hole in the air, called a channel.
Once then light is gone the air collapses back in and creates a sound wave that we hear as thunder.
The reason we see lightning before we hear thunder is because light travels faster than sound!

17. Next time you see a storm, count the number of seconds between when you see the lightning and hear the thunder.
Take the number of seconds and divide by 5 and that will tell you how far away the storm is in miles.
For example: If you counted 10 seconds between the lightning and the thunder, the lightning is 2 miles away!

18. Lightning Safety IF YOU’RE OUTDOORS:
Keep an eye at the sky. Look for darkening skies, flashes of lightning, or increasing winds.
Lightning often proceeds rain, so don’t wait for the rain to begin.
If you hear the sound of thunder, go to a safe place immediately.
The best place to go is a sturdy building or a car, but make sure the windows in the car are shut.
Avoid sheds, picnic areas, baseball dugouts and bleachers. If there is no shelter around you, stay away from trees.
Crouch down in the open area, keeping twice as far away from a tree as far as it is tall.
Put your feet together and place your hands over your ears to minimize hearing damage from thunder.
If you’re with a group of people stay about 15 feet from each other.
Stay out of water, because it’s a great conductor of electricity. Swimming, wading, snorkeling and scuba diving are not safe.
Also, don’t stand in puddles and avoid metal.
Stay away from clotheslines, fences, and drop your backpacks because they often have metal on them.
If you’re playing an outdoor activity, wait at least 30 minutes after the last observed lightning strike or thunder..

19. IF YOU’RE INDOORS:
Avoid water. It’s a great conductor of electricity, so do not take a shower, wash your hands, wash dishes or do laundry.
Do not use a corded telephone. Lightning may strike exterior phone lines.
Do not use electric equipment like computers and appliances during a storm.
Stay away from windows and doors and stay off porches

20. Types of Precipitation
Rain
growing cloud droplets become too heavy to remain in the cloud
fall toward the surface as rain.
can also begin as ice crystals that collect each other to form large snowflakes.
As the falling snow passes through the freezing level into warmer air, the flakes melt and collapse into rain drops.

21. Hail a large frozen raindrop produced by intense thunderstorms,
snow and rain can coexist in the central updraft.
As the snowflakes fall, liquid water freezes onto them forming ice pellets that will continue to grow as more and more droplets are accumulated.
Upon reaching the bottom of the cloud, some of the ice pellets are carried by the updraft back up to the top of the storm.
As the ice pellets once again fall through the cloud, another layer of ice is added and the hail stone grows even larger.
Typically the stronger the updraft, the more times a hail stone repeats this cycle and consequently, the larger it grows.
Once the hail stone becomes too heavy to be supported by the updraft, it falls out of the cloud toward the surface.
The hail stone reaches the ground as ice since it is not in the warm air below the thunderstorm long enough to melt before reaching the ground.

22. Freezing Rain
rain that becomes supercooled and freezes upon impact with cold surfaces.
Freezing rain is most commonly found in a narrow band on the cold side of a warm front, where surface temperatures are at or just below freezing.

23. Freezing rain develops as falling snow encounters a layer of warm air deep enough for the snow to completely melt and become rain.
As the rain continues to fall, it passes through a thin layer of cold air just above the surface and cools to a temperature below freezing.
However, the drops themselves do not freeze,
a phenomena called supercooling (or forming "supercooled drops").
When the supercooled drops strike the frozen ground (power lines, or tree branches), they instantly freeze, forming a thin film of ice, hence freezing rain.

24. Severe Storms
Formation of hail based on amount of updraft

25. Tornadoes
A violent, whirling column of air in contact with the ground.
Extreme pressure gradient between the center and outer portions cause the rotation and winds.
Classification
Fujita scale
Developed in 1971 by T. Theodore Fujita of the University of Chicago

26. FUJITA SCALE
DERIVED EF SCALE
OPERATIONAL EF SCALE
F Number
Fastest 1/4-mile (mph)
3 Second Gust (mph)
EF Number
40-72
45-78
65-85 1
73-112
79-117
86-109
86-110 2 3 4 5
Over 200

27. Tornado Alley

28. Killer tornadoes

31. Iowa Tornado Data

32. Iowa Tornadoes by Month 1980 - 2009

34. Iowa

37. Injuries & Death

38. 2009 Data

41. Greensburg, KS

45. Parkersburg, IA

48. Hurricanes Tropical cyclone Large, rotating, low-pressure storms
Thrive on the energy from warm tropical oceans
Originate along the ITCZ
Require abundant supply of very warm ocean water
Some sort of disturbance to lift the warm air and keep it rising

49. Stages Tropical waves Tropical depressions Hurricane
Minimum winds of 74 mph sustained
Eye – calm center of the storm
Eyewall – strongest winds of the hurricane
Storm surge
is the onshore rush of sea or lake water caused by the high winds associated with a landfalling cyclone and secondarily by the low pressure of the storm.

50. Saffir-Simpson hurricane scale

51. Hurricane Season

60. Naming Hurricanes
The practice of naming hurricanes solely after women came to an end in 1978 when men's and women's names were included in the Eastern North Pacific storm lists. In 1979, male and female names were included in lists for the Atlantic and Gulf of Mexico.
If all names are used then the Greek alphabet is used.
only time that there is a change is if a storm is so deadly or costly that the future use of its name on a different storm would be inappropriate for obvious reasons of sensitivity. If that occurs, then at an annual meeting by the committee (called primarily to discuss many other issues) the offending name is stricken from the list and another name is selected to replace it.
There is an exception to the retirement rule, however. Before 1979, when the first permanent six-year storm name list began, some storm names were simply not used anymore. For example, in 1966, "Fern" was substituted for "Frieda," and no reason was cited.

61. Retired Names 1954 Carol Hazel 1955 Connie Diane Ione Janet 1956 1957
1956 
1957
Audrey
1958 
1959 
1960
Donna
1961
Carla
Hattie
1962 
1963
Flora
1964 Cleo Dora Hilda
1965 Betsy
1966 Inez
1967
Beulah
1968 Edna
1969
Camille
1970
Celia
1971 
1972
Agnes
1973 
1974
Carmen
Fifi
1975 Eloise
1976 
1977
Anita
1978 
1979
David
Frederic
1980
Allen
1981 
1982 
1983
Alicia
1984 
1985 Elena Gloria
1986 
1987 
1988
Gilbert Joan
1989 Hugo
1990
Diana
Klaus
1991 Bob
1992
Andrew
1993 
1994 
1995
Luis
Marilyn
Opal
Roxanne
1996
Cesar
Fran
Hortense
1997 
1998
Georges
Mitch
1999
Floyd
Lenny
2000
Keith
2001
Allison
Iris
Michelle
2002
Isidore
Lili
2003
Fabian
Isabel
Juan
2004
Charley
Frances
Ivan
Jeanne
2005
Dennis
Katrina
Rita
Stan
Wilma
2006 
2007
Dean
Felix
Noel
2008
Gustav
Ike
Paloma
2009

62. Hurricane Names
2008
2009
2010
2011
2012
2013
Arthur Bertha Cristobal Dolly Edouard Fay Gustav Hanna Ike Josephine Kyle Laura Marco Nana Omar Paloma Rene Sally Teddy Vicky Wilfred
Ana Bill Claudette Danny Erika Fred Grace Henri Ida Joaquin Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda
Alex Bonnie Colin Danielle Earl Fiona Gaston Hermine Igor Julia Karl Lisa Matthew Nicole Otto Paula Richard Shary Tomas Virginie Walter
Arlene Bret Cindy Don Emily Franklin Gert Harvey Irene Jose Katia Lee Maria Nate Ophelia Philippe Rina Sean Tammy Vince Whitney
Alberto Beryl Chris Debby Ernesto Florence Gordon Helene Isaac Joyce Kirk Leslie Michael Nadine Oscar Patty Rafael Sandy Tony Valerie William
Andrea Barry Chantal Dorian Erin Fernand Gabrielle Humberto Ingrid Jerry Karen Lorenzo Melissa Nestor Olga Pablo Rebekah Sebastien Tanya Van Wendy

63. Atlantic Names – Pronunciation Guide
2010
2011
2012
2013
2014
2015
Alex Bonnie Colin Danielle Earl Fiona Gaston Hermine Igor Julia Karl Lisa Matthew Nicole Otto Paula Richard Shary Tomas Virginie Walter
Arlene Bret Cindy Don Emily Franklin Gert Harvey Irene Jose Katia Lee Maria Nate Ophelia Philippe Rina Sean Tammy Vince Whitney
Alberto Beryl Chris Debby Ernesto Florence Gordon Helene Isaac Joyce Kirk Leslie Michael Nadine Oscar Patty Rafael Sandy Tony Valerie William
Andrea Barry Chantal Dorian Erin Fernand Gabrielle Humberto Ingrid Jerry Karen Lorenzo Melissa Nestor Olga Pablo Rebekah Sebastien Tanya Van Wendy
Arthur Bertha Cristobal Dolly Edouard Fay Gonzalo Hanna Isaias Josephine Kyle Laura Marco Nana Omar Paulette Rene Sally Teddy Vicky Wilfred
Ana Bill Claudette Danny Erika Fred Grace Henri Ida Joaquin Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda