1 March 30 2015 CH 10 Three requirements for thunderstorm o Moisture especially near surface o Instability o Source of vertical motion low front o Need vertical wind shear for severe storm Most severe storms are in Midwest Life of non severe thunderstorm 1 Cumulus stage a Updrafts only no precip reaches ground b Warmer in the middle 2 Mature stage a Anvil b Downdrafts eventually take over updrafts choke them off c When the downdraft reaches the ground it becomes gust front 3 Dissipating stage a All downdrafts b Orphan anvil is left April 3 2015 Multicell Storm 4 Lasts about an hour severe storm s top is higher than normal normal is 30K feet Requires stronger vertical wind shear Gust front triggers new storm That storm s updraft triggers new storm Can have several storms at different stages for many hours Tornado watches the atmospheric conditions are right for a tornado don t see any yet Severity depends on vertical wind shear instability Gust front is the outflow boundary o This is a density boundary between the storms cooler air and the surrounding warm air o New thunderstorms often occur along this o Shelf cloud arcus along the edge of the gust front o Roll cloud is behind the gust front Super downdraft of about ten mins wind can reach 100 MPH Microburst Dry type no rain Wet type in the rain o Difficult to see o Detectable on Doppler o Little warning time April 6 2015 Squall Line Continuous or broken line of thunderstorms 2 Prefrontal squall line thunderstorms ahead of advancing cold front due to upper air flow winds Severe squall line Bow Echo Tornados o Rear inflow jet carries strong winds from high alt down to the surface creating horizontal straight line winds o Derecho high winds extending horizontally for long distance bow echo Strong winds at the surface Sometimes left northern side will develop cyclonic rotation and produce tornado Meoscale convective complex Organized mass of multicell thunderstorms Warning for a given county when one is spotted take action Air rotating strongly about a vertical access Usually counterclockwise clockwise is weaker Most destructive ones form from supercell o Supercell large intense individual storm with rotating updraft Mesocyclone forms tornado o Overshooting top is formed by updrafts from mesocyclone When facing a tornado coming at you strongest winds are on your left Wall cloud local lowering of cloud base Multiple Vortex Tornado Suction swatch outside rotating counterclockwise Tornado center counterclockwise April 8 2015 Tornado days are worst in June tornados are worst at end of April o Worst in Oklahoma then Central Fl and central Indiana Fujita Tornado Intensity Scale he said we will not be tested on wind speeds F0 to F1 is weak F2 to F3 is strong F4 to F5 is violent o Theoretically this scale goes to F12 Conditions for supercells and tornados Front at the surface warm moist air Dry air above at 10K feet Trough aloft Jet stream or streak strong wind shear Step 1 o Spinning vortex tubes at the surface caused by wind shear Step 2 o Thunderstorm s strong updrafts carries the vortex tube into the thunderstorm which produces vertical rotation o Horizontal rotation turns vertical Hook echo represents a tornado spawning supercell on Doppler 3 Air convergence at surface is good for tornados What does wind shear have to do with it o Leads to horizontal rotation o Updraft leads to vertical rotation o Now we have mesocylcone cell o This is slow rotation we don t know how they get it to strong rotation tornado o Less than 10 of rotating super cells make tornados This is why we cant accurately predict Waterspouts AKA nonsupercell tornado A tornado that formed over water once over land it s called a tornado o Florida Keys have the most waterspouts in the US o A cloud with updrafts moves over an area of rotating winds Second most common cause of weather death o Most common is heat stroke Occur with heavy rain for extended period ground close to saturation more likely Almost half of all flash flood deaths occur in cars just two feet of rushing water can Formation Flash floods in low lying areas sweep away a car Hail No hail deaths in US plenty of animal death Costs 1B per year in the US Heaviest 1 67 LBS Worst in Colarado Nebraska Wyoming borders Largest volleyball size can hit earth at 100MPH Lightning Florida leads country in lightning specifically just North of Tampa Bay o Bc of sea breeze colliding causing thunderstorms 1000s degrees hot see flash instantly Heat of lightning produces shock wave of sound that moves at speed of sound thunder o 761 MPH 1 mile per 5 seconds Count time between lightning and thunder divide by 5 to get distance away A thunderstorm has pos charges at top neg in middle and bottom o Objects on earth have pos charge Bolt out of the blue lightning travelling away from the cloud turns downward and strikes earch Formation 1 Stepped leader from the cloud finds path of least resistance to an object 2 Pos charges reach up from earth s objects and meets the stepped leader 3 When they meet the return stroke brings pos charge into the cloud a We see the return stroke 4 April 13 205 Ch 11 Hurricanes Hurricane Galveston o Deadliest US disaster o 1900 8 12K people died Katrina o Costliest 125B in damage Training cells dropping lots of rain on a single point Need o Warm water greater than 78 deg F o Small wind shear o Reasonable distance from equator at least 5 deg of lat away preferably 10 Some coriolis force o Lots of humidity o Initial disturbance General process o Disorganized cluster of thunderstorms Rising air creates saturation and condensation Condensation to latent heat release to warming heat engine Lowers pressure o Air travels toward areas of lowest pressure Wind picks up moisture from ocean Energy source is warm ocean water o Pressure falls winds increase wind rotates Hurricanes form from areas of Tstorms Tropical easterly waves coming from Africa o Bad weather on eastern side Along ITCZ o Summertime shift North of equator providing instability Southern end of front of G of Mexico Types classifications of tropical cyclones cyclone is just a low pressure area wont be tested on wind speeds Trop Disturbance o Unorganized area of low pressure and showers No circular flow yet Trop Depression o Winds 20 34 kt up to 38mph o Have some circular motion o 35 63 kt visible center of rotation 39 73mph Trop Storm Hurricane o Winds at least 64 kt 74 mph 5 We don t fly into storms in pacific because they re moving away from us
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