UIUC ATMS 100 - Ordinary Thunderstorms (4 pages)

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Ordinary Thunderstorms

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Ordinary Thunderstorms


Brief overview of thunderstorms, triggers, types of thunderstorms, and their development.

Lecture number:
Lecture Note
University of Illinois at Urbana, Champaign
Atms 100 - Introduction to Meteorology
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Lecture 21 Outline of Last Lecture I Review II Rising Air III Forced vs Buoyant Ascent IV Stability and Thunderstorm Development V Envrionmental Lapse Rate VI Dry Adiabatic Lapse Rate VII Moist Adiabatic Lapse Rate VIII Lapse Rates IX Lapes Rates and Soundings X Lifting Condensation Level LCL XI Level of Free Convection LFC XII Equilibrium Level EL XIII CAPE and CIN XIV Lifted Index XV Atmospheric Stability XVI Make Atmosphere more Stable XVII Make the Atmosphere More Unstable XVIII Stability and Thunderstorms Outline of Current Lecture XIX Thunderstorms ATMS 100 1st Edition XX Thunderstorm Ingredients Instability XXI Thunderstorm Ingredients Trigger XXII Trigger Front or Dryline XXIII Trigger Sea Breeze Lake Breeze XXIV Trigger Mountains XXV Thunderstorm Ingredients XXVI Severe Thunderstorms XXVII Types of Thunderstorms XXVIII Ordinary Thunderstorms XXIX Ordinary Thunderstorms Stage Development XXX Cumulus Stage XXXI Mature Stage XXXII Outflow XXXIII Dissipation Stage Current Lecture XXXIV Thunderstorms a tall vertically developed cloud that produces lightning and thunder i can t have thunder without lightning ii usually produce heavy precipitation b thunderstorm clouds are called cumulonimbus clouds XXXV Thunderstorm Ingredients Instability a all thunderstorms require instability i warm and humid air near the surface and or cold air aloft ii air can rise on its own due to buoyancy XXXVI Thunderstorm Ingredients Trigger a all thunderstorms require a trigger i something to make the air rise b What can make air rise i front or drylines ii sea breezes or lake breezes iii outflow boundaires gust fronts XXXVII Trigger Front or Dryline XXXVIII Trigger Sea Breeze Lake Breeze a cool air over water moves inland converges with warm air over land b warm air rises often forming thunderstorms XXXIX Trigger Mountains a atmosphere heats from ground up b air over mountain warmer than air around it and rises XL Thunderstorm Ingredients a severe thunderstorms also require vertical wind shear i recall that wind shear is a change in wind speed and direction with height ii help storms organize XLI Severe Thunderstorms a a severe thunderstorm contains any of the following i wind gusts at the surface greater than 50 knots 57 5 mph ii hail with diameter greater than 1 inch 1 roughly quarter sized iii tornado XLII Types of Thunderstorms a oridnary single cell thunderstorms ii usually not severe iii form in envrionments with weak vertical wind shear b multicell thunderstorms MCSs ii thunderstorm complexes iii form in environments with moderate vertical wind shear c supercell thunderstorms ii almost always severe iii produce nearly all intense tornadoes and hail larger than golfball sized iv form in envrionments with strong vertical wind shear d vertical wind shear most important factor in determining thunderstorm type XLIII Ordinary Thunderstorms a most common type of thunderstorm b usually not severe c last about an hour from formation to dissipation d generally develop in regions of weak wind shear ii often form in summer not near fronts Ordinary Thunderstorms Stage Development a cumulus stage b mature stage c dissipation stage XLV Cumulus Stage a warm air rises expands and cools b water vapor condenses and forms a cloud c the rising air is called updraft ii air rises due to buoyancy iii cannot have a thunderstorm without an updraft iv latent heat release condensation in updraft powers thunderstorm d as cloud gets deeper precipitation particles begin to form e fair weather cumulus clouds ii most amount to nothing but some can grow into thunderstorms XLVI Mature Stage a updraft may eventually reach tropopause ii tropopause is very stable inversion layer acts as lid on storm b air diverges outward when it reaches tropopause forms anvil cloud c top of updraft may penetrate into stratosphere ii called overshooting top d precipitation particles grow become heavy begin to fall into updraft ii falling precipiation drags air downward with it e some rain evaporates cooling air even more f when air is cooler than its surroundings it sinks ii this sinking air is called a downdraft iii precipitation is required to form a downdraft XLVII Outflow a when cold downdraft reaches ground it spreads out ii forms a pool of cold air beneath storm iii known as a cold pool or outflow b boundary between cold outflow and warm inflow is called gust front or outflow boundary c this is why temperature drops and wind increase just before a thunderstorm beings ii also why is it cooler just after a thunderstorm d convergence at outflow boundary may trigger new storms XLVIII Dissipation Stage a rain falls into updraft ii cools updraft drags rising air downward b updraft weakens replaced by downdraft XLIV c surging outflow cuts off supply of warm moist unstable air needed to feed updraft d updraft dissipates ii thunderstorm dominated by downdrafts and precipitation and quickly dissipates

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