Thunderstorms, Tornadoes, and Hurricanes C.C. Hennon, UNC Asheville ATMS 103

Where are Thunderstorms common? C.C. Hennon, UNC Asheville Average number of days (per year) that a thunderstorm occurs (Fig 10.18) ATMS 103

Thunderstorms Common in the summer season Usually not part of a larger-scale weather system Short-lived, rarely severe Occur when a warm front and a cold front meet. Thunderstorms C.C. Hennon, UNC Asheville ATMS 103

Mature Stage Cumulus Stage Dissipating Stage Lightning, Thunder, Peak strength Clouds may reach 45-50,000 ft Cumulus Stage Updrafts dominate Precipitation begins to fall Dissipating Stage Downdrafts dominate C.C. Hennon, UNC Asheville ATMS 103

Stages of an Air Mass Thunderstorm C.C. Hennon, UNC Asheville ATMS 103

Severe Thunderstorms C.C. Hennon, UNC Asheville ATMS 103

A thunderstorm is a storm with thunder, lightning, and often heavy rain and strong winds. anatomy of a thunderstorm What is a Thunderstorm? C.C. Hennon, UNC Asheville ATMS 103

Structure of Severe Thunderstorms C.C. Hennon, UNC Asheville ATMS 103

Features of Severe Thunderstorms Cumulus clouds build up to form cumulonimbus clouds. Heavy rain or hail forms. C.C. Hennon, UNC Asheville ATMS 103

Features of Severe Thunderstorms Downburst A highly localized, very strong downdraft Hits ground and spreads out in a circular direction https://weather.com/tv/shows/weather- underground/video/inside-a- microburstMicroburst A downburst with winds only extending less than 4 km in any direction Winds can be as high as 150 kt. Extremely hazardous to Aircraft C.C. Hennon, UNC Asheville ATMS 103

Enhanced lift ends, plane pushed downward Strong headwind/lift Enhanced lift ends, plane pushed downward Strong tailwind stalls plane, crash ensues C.C. Hennon, UNC Asheville ATMS 103

Microburst produced increased lift initially Plane then experienced dramatic tailwind and decrease in lift Crash killed 136 / 167 Delta 191 Crash At DFW, 1985 C.C. Hennon, UNC Asheville ATMS 103

Supercell Thunderstorm C.C. Hennon, UNC Asheville ATMS 103

Thunderstorms Line of storms that form just ahead of a cold front or some distance ahead (100-300 km) Can be over 600 miles long C.C. Hennon, UNC Asheville ATMS 103

Lightning and Thunder C.C. Hennon, UNC Asheville ATMS 103

Thunder – Shock wave produced by lightning Lightning - An electrical discharge formed by charge separation within thunderstorms or between thunderstorms and the ground Thunder – Shock wave produced by lightning Lightning heats air to around 30,000 K Air expands very rapidly, creates loud noise Hurricane Matthew lightning C.C. Hennon, UNC Asheville ATMS 103

Lightning Characteristics Globally, about 100 flashes occur each second Most lightning (~80%) occurs between clouds. Only about 20% is between cloud and ground About 100 deaths/year in U.S. by lightning strikes (second most by a natural phenomena) Most in Florida Hazardous activities: golf, sailing, walking in open area Lightning Characteristics C.C. Hennon, UNC Asheville ATMS 103

Travels about 1100 ft./sec If lightning flash is 3 miles away, it will take about 9 seconds for thunder to be heard If lightning hits you, you will instantaneously hear thunder before vaporizing Thunder C.C. Hennon, UNC Asheville ATMS 103

C.C. Hennon, UNC Asheville ATMS 103

Net negative charge builds up near bottom of cloud This attracts net positive charge buildup from ground When charge separation is too great, lightning strike will occur C.C. Hennon, UNC Asheville ATMS 103

C.C. Hennon, UNC Asheville ATMS 103

Types of Lightning Cloud to cloud Cloud to ground Ball lightning Appears as a luminous sphere Cause unknown Sheet lightning Lightning inside of clouds, appears white Types of Lightning C.C. Hennon, UNC Asheville ATMS 103

wvlightning.com/types.shtml Ribbon Lightning Bead Lightning St. Elmo’s Fire? Sheet Lightning wvlightning.com/types.shtml C.C. Hennon, UNC Asheville ATMS 103

C.C. Hennon, UNC Asheville Ball lightning ATMS 103

Lightning Safety C.C. Hennon, UNC Asheville ATMS 103

Don’t talk on the telephone (cell OK) Don’t go for a walk Don’t go golfing Don’t talk on the telephone (cell OK) Don’t go for a walk Don’t find an isolated tree to stand under If your hair stands on end, lightning is about to strike Crouch down (don’t lay down) as low as possible Stay away from the bathroom and windows Cars are OK C.C. Hennon, UNC Asheville ATMS 103

Tornadoes Rapidly rotating, small-scale winds that form within severe thunderstorms Many different shapes; last anywhere from a few seconds to several hours --spinning ice skater C.C. Hennon, UNC Asheville ATMS 103

Have occurred in all 50 U. S. states, but rare in Western U. S Have occurred in all 50 U.S. states, but rare in Western U.S., Alaska, Hawaii Form during every month of the year, but 75% form during months of March – July Globally, U.S. has highest occurrence of tornadoes – WHY? Anatomy of a tornado Tornado Occurence C.C. Hennon, UNC Asheville ATMS 103

Top Number: Number of tornadoes over a 25-year period (1953-2004) Bottom Number: Average number per year per 10000 sq. km C.C. Hennon, UNC Asheville ATMS 103

Tornadic Winds and Classification Tornadoes are classified on the Fujita Scale F-0 : 65-85 mph F-1 : 86-110 mph F-2 : 111-135 F-3 : 136-165 F-4 : 166-200 F-5 : 200+ C.C. Hennon, UNC Asheville ATMS 103

F1 Tornado C.C. Hennon, UNC Asheville ATMS 103

F2 Tornado C.C. Hennon, UNC Asheville ATMS 103

F3 Tornado C.C. Hennon, UNC Asheville ATMS 103

F4 Tornado C.C. Hennon, UNC Asheville ATMS 103

F5 Tornado C.C. Hennon, UNC Asheville ATMS 103

Tornado Formation Updrafts in thunderstorms must rotate Called a mesocyclone As mesocyclone stretches vertically, its diameter shrinks and it spins faster Tornado forms within the mesocyclone and descends towards the surface (not understood why) If condensation occurs within funnel, a funnel cloud will be seen Tornado Formation C.C. Hennon, UNC Asheville ATMS 103

Observing Tornadoes First sign (visually) of a tornado is the appearance of a wall cloud Rotating cloud underneath the main cell C.C. Hennon, UNC Asheville ATMS 103 stormchasing.ca/_wsn/page11.html

Portable Radar Units (aka crazy people) C.C. Hennon, UNC Asheville ATMS 103

Tornado Watch – Conditions are favorable for tornado formation Tornado Watch – Conditions are favorable for tornado formation. Monitor local weather conditions and broadcasts Tornado Warning – Tornado and/or funnel cloud and/or hook echo has been spotted in the area Take cover immediately Warning For Tornadoes C.C. Hennon, UNC Asheville ATMS 103

Anatomy of a Tornadic Thunderstorm C.C. Hennon, UNC Asheville ATMS 103

Hurricanes A hurricane is a tropical storm with strong winds. C.C. Hennon, UNC Asheville ATMS 103

Eye The center of the storm is called the eye. It is calm and serene. No winds. Eye C.C. Hennon, UNC Asheville ATMS 103

Parts of a Hurricane anatomy of a hurricane C.C. Hennon, UNC Asheville ATMS 103

How a Hurricane Forms C.C. Hennon, UNC Asheville ATMS 103