Chapter 13 The Nature of Storms

Lesson 1 Thunderstorms

Think About It… During which months do we get the most damaging thunderstorms here in the Piedmont?

How do the major types of thunderstorms form? Focus Question… How do the major types of thunderstorms form?

Average Number of Thunderstorm Days Annually…

Types of Thunderstorms… Air Mass - Mountain Where… within one air mass over a mountain Why… warm air rises over a mountain, forming storm clouds! When… midafternoon http://web.mst.edu/~rogersda/umrcourses/ge301/press&siever12.3.png

Types of Thunderstorms… Air Mass - Sea-Breeze Where… coastal areas, esp. tropics/subtropics Why… temperature differences between land and sea create convection cells and updrafts When… summer http://apollo.lsc.vsc.edu/~wintelsw/MET1010LOL/web/notes/chapter11/ts_ingredients4summary.html

Types of Thunderstorms… http://apollo.lsc.vsc.edu/classes/met130/notes/chapter11/graphics/cf_xsect.jpg Types of Thunderstorms… Frontal - Cold Where… at the leading edge of a cold front Why… cold air pushes warm air rapidly up at the steep cold-front boundary When… anytime a cold front moves in!

Types of Thunderstorms… Frontal – Warm Where… at the leading edge of a warm front Why… warm air mass slides up over a cold air mass creating clouds When… if a warm front moves in with enough moisture and instability http://www.atmoz.org/img/warm-front.png

Thunderstorms in the Piedmont… Which types of thunderstorms do we experience here in the Piedmont? Frontal (warm and cold) Local Air Mass (in the summer) http://www2.journalnow.com/mgmedia/image/0/354/118602/severe-storms-cause-damage-across-region/

Stages of Development of a Thunderstorm… http://chiefio.wordpress.com/2010/12/28/ignore-the-day-at-your-peril/

NSSL – Q&A Thunderstorms… The National Severe Storm Laboratory is in Norman, OK. http://www.nssl.noaa.gov/primer/tstorm/tst_detecting.html

Severe Thunderstorms anvil Rain Free Base Precipitation http://ed101.bu.edu/StudentDoc/Archives/ED101fa06/mattwall/Extreme%20Weather.htm

How Lightning Forms … http://www.erh.noaa.gov/bgm/preparedness/swaw/ny/images/Light1.gif

Lightning… A giant spark of static electricity What is lightning? A giant spark of static electricity When does a lightning bolt form? When there is an electrical imbalance between clouds (-) and the ground (+) What is a stepped leader? An invisible channel of negatively charged air from a cloud http://i.imwx.com/web/multimedia/images/blog/stepped_lightning2.jpg

Lightning… 4. What is return stroke (positive streamer)? A channel of positively-charged ions from the ground 5. How hot is lightning? 30,000 degrees Celsius 6. What causes thunder? Super-heated air expanding and contracting http://www.eoearth.org/files/119701_119800/119773/Step5.jpg http://www.srh.noaa.gov/jetstream/lightning/images/lightning8.jpg

Lightning Damage… 7500 forest fires/year 300 injuries/ 93 deaths/year http://www.barransclass.com/phys1090/circus/JenkinsD/JenkinsD.html Lightning Damage… Describe the damage that lightning can do. 7500 forest fires/year 300 injuries/ 93 deaths/year Property damage Lightning-struck trees on the Blue Ridge Parkway http://www.sciencephoto.com/images/download_lo_res.html?id=670034119

Lightning Q&A and Safety… http://www.srh.noaa.gov/jetstream/lightning/lightning_faq.htm#10

Lesson 2 Severe Weather

Where is the safest place to be during a tornado? Think About It… Where is the safest place to be during a tornado?

How do tornados form and how are they classified? Focus Question… How do tornados form and how are they classified?

The Fury of the Wind… 1. What is a downburst? A violent downdraft concentrated in a local area 2. What are the two types of downbursts? macro- (big) and micro- (small) 3. Microbursts are deadly because they are harder to detect and prepare for.

Floods… 4. What are 3 conditions that cause floods to occur? Abundant moisture over a limited area. Rain falls faster than the ground can absorb it. Wind currents in the upper atmosphere are weak so that weather systems move slowly

The Flooding Mississippi River Slide show May 17, 2011… http://www.huffingtonpost.com/2011/05/12/mississippi-river-flooding-photos-2011_n_861204.html#s279672&title=Mississippi_River_Flooding

Tornados… A change in wind direction and speed creates a horizontal rotation. Strong updrafts tilt the rotating air to a vertical position. A tornado forms within the rotating winds. http://www.weatherwizkids.com/tornado_formation.jpg

Tornado Alley - The Midwest! A cP air mass from Canada meets a mT air mass from the Gulf of Mexico forming a supercell. A supercell is a giant, self-sustaining storm that can spawn tornados. http://midwestweather.net/archives/tornadoclimatology.htm

The Enhanced Fujita Scale…EF0 or EF1 - % of all tornados… 80 - Path… up to 3 miles - Wind Speed… 60-115 mph - Duration… 1 – 10 minutes Dr. Theodore Fujita http://0.tqn.com/d/weather/1/0/i/C/-/-/fujita2s_600.jpg

The Enhanced Fujita Scale…EF2 or EF3 - % of all tornados… 19 - Path… 15+ miles - Wind Speed… 110 - 165 mph - Duration… 20+ minutes

The Enhanced Fujita Scale…EF4 or EF5 - % of all tornados… 1 (Thankfully!) - Path… 50+ miles Wind Speed… 200+ mph Duration… 1+ hours http://thedailycap.com/alabama-tornado-2011

Tornado Safety… Move to a pre-designated shelter – to a basement if possible. Move to an interior room/hall, lowest floor, under sturdy furniture. Stay away from windows. Get out of vehicles! Don’t try to outrun a tornado. If outside, lie flat in a ditch or depression. Abandon a mobile home for a shelter.

Lesson 3 Tropical Storms

From which direction do the hurricanes which hit our east coast come? Think About It… From which direction do the hurricanes which hit our east coast come?

How does a hurricane form? Focus Question… How does a hurricane form?

Tropical Cyclones… Large, rotating, low pressure storm hurricanes A tropical cyclone can be described as a… Large, rotating, low pressure storm We call these storms… hurricanes 3. Tropical cyclones derive a tremendous amount of energy from… Warm, tropical oceans http://www.nhc.noaa.gov/HAW2/english/history.shtml

Fran, 1996, Cape Fear, NC Name was retired! Tropical Cyclones… Which direction do tropical cyclones turn in the northern hemisphere? Counterclockwise It is a low pressure system! Fran, 1996, Cape Fear, NC Name was retired!

Tropical Cyclones… As a hurricane strengthens, what do the following components do? Air pressure in eyewall– decreases Surface wind speeds – increase What are two basic conditions that tropical cyclones require to form? Lots of warm ocean water Disturbance to lift the air

Tropical Cyclones… the west! the prevailing westerlies http://www.srh.noaa.gov/shv/?n=hurricane_rita Tropical cyclones move steadily towards… the west! Which wind system moves across the USA and usually guides hurricanes out into the Atlantic Ocean? the prevailing westerlies Hurricane Rita – 2005, 3rd lowest pressure in Atlantic (897 mb), hit as cat. 3

Development of a Tropical Cyclone… Tropical Disturbance – a weak, low-pressure system – group of thunderstorms collect

Development of a Tropical Cyclone… http://www.uvs-model.com/WFE%20on%20tropical%20cyclone%20(Hurricane).htm Development of a Tropical Cyclone… Tropical Depression – a disturbance begins to rotate around the center of low pressure Katrina as a tropical depression

Development of a Tropical Cyclone… http://www.weatherstockphotography.com/ Development of a Tropical Cyclone… Tropical Storm – a depression is labeled a storm when the wind speeds reach 39 mph. Tropical Storm Dalila, July 2007

Development of a Tropical Cyclone… http://www.weatherstockphotography.com/ Development of a Tropical Cyclone… Tropical Hurricane – pressure drops and the wind speeds reach 74 mph Dean 2007 Katrina 2005 Ivan2006

Hurricane History… http://www.nhc.noaa.gov/HAW2/english/history.shtml#galveston

Anatomy of a Hurricane… http://apollo.lsc.vsc.edu/classes/met130/notes/chapter15/vertical_circ.html

Classifying Hurricanes… What scale is used to classify hurricanes? Saffir-Simpson What are the three characteristics of a hurricane described by the scale? Wind speed – how high? Air pressure – how low? Potential for damage – how much?! http://www.nhc.noaa.gov/sshws_table.shtml?large

Classifying Hurricanes… The Saffir-Simpson Scale… Categories 1 – 5 For a tropical storm to be considered a cat. 1 hurricane – 74 mph The category that does the most damage – 5 Wind speed of a cat 5? > 155 mph Three most powerful storms to hit USA? Florida Keys, 1935 Camille, 1969 Andrew, 1992 http://www.nhc.noaa.gov/pastint.shtml

Classifying Hurricanes… A hurricane runs out of energy When it moves over land When it moves over cold water http://backyard.weatherbug.com/profiles/blogs/the-south-central-texas-445

Hurricane Hazards… The strongest winds in a hurricane are in … The eye wall http://www.med.navy.mil/sites/nmcp/localarea/Weather/PublishingImages/def1.gif

Hurricane Hazards… What is a storm surge? When hurricane force winds drive a mound of ocean water towards coastal areas http://www.chathamemergency.org/images/storm%20surge%202.png

Flooding from Hurricane Fran Hurricane Hazards… What hurricane hazard is caused by great amounts of rain? floods Flooding from Hurricane Fran http://pubs.usgs.gov/of/1996/of96-499/text/PHOTOS.html

Hurricane Hazards… Which agency is responsible for tracking and forecasting hurricanes? The National Hurricane Center in Miami, FL at the FIU Campus (NOAA)

Recurring Weather – Review handout! Lesson 4 Recurring Weather – Review handout!