UIUC ATMS 100 - Tornadoes (3 pages)

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Brief overview of tornadoes, where/how they form, their lifeycle, types, and safetey

Lecture number:
Lecture Note
University of Illinois at Urbana, Champaign
Atms 100 - Introduction to Meteorology
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Lecture 25 Outline of Last Lecture I What is a Supercell II Hook Echo III Supercell Structure IV Supercell Envrionments V Outbreak Summary VI Supercell Components VII Mesocyclone VIII Supercell Rotation IX Wall Cloud X Mammatus Clouds XI Forward Flank Downdraft XII Rear Flank Downdraft XIII Types of Supercells Outline of Current Lecture XIV Tornadoes XV Tornado Statistics XVI Where Do Tornadoes Form XVII Tornado Lifecycle XVIII Tornado Touchdown XIX The Role of Downdraft Idealization XX Multiple Vortex Tornadoes XXI Tornado Dissipation XXII Cyclic Tornadogenesis ATMS 100 1st Edition XXIII Non Supercell Tornadoes XXIV Tornado Intensity XXV Enhanced Fujita Scale XXVI EF Scale Well Constructed XXVII Tornado Destruction XXVIII Tornado Safety XXIX Places that are not Safe Places that are Current Lecture XXX Tornadoes a a violently rotating column of air in contact with the ground pendant from a cumuliform cloud b typically visible as a funnel cloud c occur in all 50 states though much more common in certain areas d winds can range from 40 mph 300 mph XXXI Tornado Statistics a average of 100 tornadoes reported in the US each year b average of 56 people killed and 975 injured by tornadoes each year c most tornadoes are short lived i last only for a minute or two ii some can last for up to an hour or longer XXXII Where Do Tornadoes Form i most likely form in supercell thunderstorms 1 about 1 4 of supercells produce tornadoes 2 virtually all strong and violent tornadoes F2 or greater form in supercells 3 look for hook echo indicating rotaton on radar ii Can occasionally form in squall lines MCSs 1 tend to be weak iii Essentially never form in ordinary thunderstorms 1 except for landsprouts and watersprouts XXXIII Tornado Lifecycle a Funnel Cloud forms b Rotation makes contact with ground i see dust or debris swirl ii mature stage tornado is typically largest most intense iii rope stage tornado weakens and dissipates XXXIV Tornado Touchdown a tornado touches down when circulation NOT funnel reaches the surface b look for rotating debris dust in ground beneath fnnel XXXV The Role of Downdraft Idealization a Rear flank downdraft transports circulation from aloft down to surface i downdraft can create additional rotation via tilting b rotating air converges and rises into updraft rotation amplifies rapidly via streching c relatively warm downdraft air more likely to rise in updraft XXXVI Multiple Vortex Tornadoes a strong tornadoes are often multiple vortex tornadoes i less intense tornadoes have rising air in center but central downdraft can form in strong tornadoes b downdraft in center breaks circulation into smaller vortices i wind field is complex must add tornado motion rotaton of tornado and rotation of suction vortices ii one house may be destroyed while house next door is not c smaller vortices rotate around center of tornado XXXVII Tornado Dissipation a liftetime ranges from minutes to an hour i not sure why some tornadoes last for a long time while others do not b funnel becomes deformed i winds blow in different direction aloft and near ground ii circulation forms a rope shape c cloud outflow air wraps around tornado i air is not as buoyant does not rise XXXVIII Cyclic Tornadogenesis a the same supercell can produce multiple tornadoes roughly parallel paths XXXIX Non Supercell Tornadoes a landspouts and waterspouts i pre existing circulation at surface stretched by updraft usually originates along wind shift line ii no downdraft or supercel required iii can occur in ordinary thunderstorms or MCSs iv usually less intense than supercell tornadoes but still dangerous XL Tornado Intensity a tornado winds are generally not mesaured directly b intensity determined by damage i depends on quality of construction ii did tornado hit anything c enhanced fujita EF scale accounts for quality of construction i original fujita F scale was not XLI EF Scale Well Constructed a EF0 Minor damage roof shingles missing tree limbs down b EF1 Moderate significant roof damage damge to doors windows c EF2 Considerable roofs torn off damage to exterior walls large trees snapped and uprooted mobile homes destroyed d EF3 Severe most walls one e EF4 Devastating Home completely leveled f EF5 Extreme Foundation wiped clean XLII Tornado Destruction a storm spotter can see tornado i tornadoes tough to see at night in rain in forested or hilly areas ii doppler radar is able to detect rotation within thunderstorm XLIII Tornado Safety a go to interior room on lowest floor of a study structure i basements preferred ii if on isn t available use closet or bathroom iii stay away from windows iv protect yourself from flying debris if possible XLIV Places that are not Safe a Places that are not safe i cars ii mobile homes iii highway overpasses iv Large Rooms

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