CU-Boulder ATOC 1050 - ATOCch18-24 (21 pages)

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ATOCch18-24



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ATOCch18-24

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Pages:
21
School:
University of Colorado at Boulder
Course:
Atoc 1050 - Weather and the Atmosphere
Weather and the Atmosphere Documents

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Chapter 18 Thunderstorms are Critical for redistribution of heat and moisture in the atmosphere Occur continuously Provide essential water and agricultural resources 2 4 billion property crop loss in US over past decade NWS requirements for a sever thunderstorm Hail with diameter of 1 inch or larger any thing smaller does not inflict damage Wind damage or gusts of 50knots 58mph or greater And or tornado Lightning occurs in all thunderstorms it is not used to differentiate between sever and non sever Four elements required for thunderstorm formation 1 Source of moisture 2 Conditionally unstable atmosphere 3 Mechanism to trigger updraft 4 Vertical wind shear Destructive thunderstorms develop most often in an environment characterized by large conditional instability and strong vertical wind shear Mechanisms for updraft of lifting include Frontal boundaries Daytime heating Differential heating of air over surfaces with different properties Leading edge of cool air outflow from a past thunderstorm The primary mechanism that triggers the updraft of an airmass thunderstorms is solar heating of the surface Non sever thunderstorms Often called airmass thunderstorms Typically form within an airmass not along a front Triggered by weak boundaries cool air outflow surface heating lifting along slopes Form during hot afternoons Winds do not change with height lifetime time is short about an hour Airmass thunderstorms grow vertically without significant tilt No vertical shear Symmetric anvil In mature stages downdraft falls into updraft cutting off the moisture source In the dissipation stage downdrafts dominate often producing a gust front outflow boundary 1 Anvil the flat top of a thunderstorm formed when updraft hits tropopasue Mammatus clouds often form at base of thunderstorm anvils Airmass thunderstorm would most likely form far away from any frontal boundaries around 4pm Airmass thunderstorms tend to occur in environments where the winds do not increase substantially with



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