GEOG 111 1st Edition Lecture 31 Outline of Last Lecture I Processes associated with freezing rain development II Factors that control ice buildup III Weather features that produce big ice storms Outline of Current Lecture I Thunderstorms a Characteristics b Development c Types Current Lecture I Thunderstorms a Characteristics i Basic anatomy 1 Warm air lifting up buoyant because density is less than surroundings a Convection occurs in an unstable atmosphere 2 Updraft beside downdraft a Downdraft falls and accelerates i Lots of precipitation ii Creates virga evaporating precipitation droplets in dry air cooling near cloud base 1 Instantaneously increases density in air b Gust front Leading edge of rain cooled air separates two different air masses 3 Air tends to converge around fronts colliding not readily mixing a Warm air over cool air ii Heights range from 20 000 80 000 feet 1 Most are around 25 000 2 What limits their growth a Inversion 3 Thunderstorm severity strong winds hail lightening strikes correlates with the height of the storm a Have stronger updrafts that can break through the inversion iii Thunderstorm movement is controlled by the large scale winds in the tropospheric column 1 In high wind shear situations thunderstorms can tilt downstream 2 Winds aloft dictate speed and direction of movement of storms iv Why do anvil heads spread out much more to the east as opposed to the west 1 Winds are blowing west to east These 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 westward b Development i The lifetime of a thunderstorm cell is only 1 2 hours although some cells may linger in the dissipating state for several hours ii Stages 1 Begin as cumulus clouds a A single updraft thermal 2 Mature stage a Updraft and downdraft b Lots of concentrated hydrometeors i Precipitation loading in the top part of the cloud 1 Gets so heavy that the updraft can t support it anymore a Begin descent carrying air with them creating the downdraft c Indicated by first lightning i Associated with presence of updraft and downdraft 3 Dissipating stage a Weak downdraft c Types i Air mass thunderstorms 1 Most common in NC 2 Random pattern of precipitation 3 Multi cellular pattern typically multiple storms that develop 4 Characteristics a In an unstable environment i Conditionally unstable higher up b Thermals developing when sun is out i Late afternoon and early evening occurrence c Closer to surface more variation in temperature between day and night 5 Restricted to summertime months a Warmest most moisture b Latent heat sensible heat buoyancy c Under the Bermuda high regime 6 Development a Most thunderstorms are generated by the outflows from existing cells i Bottom of troposphere cools off 1 Bottom of column is stage 2 Storm dissipates ii Squall line thunderstorms 1 A line of thunderstorms 2 An entity that has many thunderstorm cells a Exist in an organized fashion b Once it develops its behavior is very predictable 3 Downdraft comes into the storm 4 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 storm 5 Creates a mass of rolling clouds moving in front of the storm a Lots of circular motions
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