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UNC-Chapel Hill GEOG 111 - Thunderstorms

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GEOG 111 1st Edition Lecture 31 Outline of Last Lecture I. Processes associated with freezing rain developmentII. Factors that control ice buildupIII. Weather features that produce big ice stormsOutline of Current Lecture I. Thunderstormsa. Characteristicsb. Developmentc. TypesCurrent LectureI. Thunderstormsa. Characteristicsi. Basic anatomy1. Warm air lifting up (buoyant because density is less than surroundings)a. Convection occurs in an unstable atmosphere2. Updraft beside downdrafta. Downdraft- falls and acceleratesi. Lots of precipitationii. Creates virga (evaporating precipitation droplets in dry air)  cooling near cloud base1. Instantaneously increases density in airb. Gust front -Leading edge of rain cooled air/separates two different air masses3. Air tends to converge around fronts/colliding/not readily mixinga. Warm air over cool airii. Heights range from 20,000 -80,000 feet1. Most are around 25,0002. What limits their growth?a. Inversion3. Thunderstorm severity (strong winds, hail, lightening strikes) correlates with the height of the storma. Have stronger updrafts that can break through the inversioniii. Thunderstorm movement is controlled by the large scale winds in the tropospheric column1. In high wind shear situations, thunderstorms can tilt downstream2. Winds aloft dictate speed and direction of movement of stormsiv. Why do anvil heads spread out much more to the east as opposed to the west?1. Winds are blowing west to eastThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Strong jet stream that prevents anything from going westwardb. Developmenti. The lifetime of a thunderstorm cell is only 1-2 hours, although some cells may linger in the dissipating state for several hoursii. Stages1. Begin as cumulus clouds a. A single updraft/thermal2. Mature stagea. Updraft and downdraftb. Lots of concentrated hydrometeorsi. Precipitation loading in the top part of the cloud1. Gets so heavy that the updraft can’t support it anymorea. Begin descent carrying air with them (creating the downdraft)c. Indicated by first lightningi. Associated with presence of updraft and downdraft 3. Dissipating stagea. Weak downdraftc. Types i. Air mass thunderstorms1. Most common in NC2. Random pattern of precipitation3. Multi-cellular pattern- typically multiple storms that develop4. Characteristicsa. In an unstable environmenti. Conditionally unstable higher upb. Thermals developing when sun is outi. Late afternoon and early evening occurrencec. Closer to surface… more variation in temperature between day and night5. Restricted to summertime monthsa. Warmest, most moistureb. Latent heat  sensible heat  buoyancyc. Under the Bermuda high regime6. Developmenta. Most thunderstorms are generated by the outflows from existing cellsi. Bottom of troposphere cools off1. Bottom of column is stage2. Storm dissipatesii. Squall line thunderstorms1. A line of thunderstorms2. An entity that has many thunderstorm cellsa. Exist in an organized fashionb. Once it develops, its behavior is very predictable3. Downdraft comes into the storm4. Strong winds higher up in the storm that descend to the bottom part of the storm, hit the ground and proceed to the front of the storm5. Creates a mass of rolling clouds moving in front of the storma. Lots of circular


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