unit 2-5.docx

Midlatitude Severe Weather Thunderstoms Types Air mass thunderstorms Most common type Localized, short-lived Georgia: maritime, tropical: warm and humid Least destructive Occur within air masses Stages of thunderstorm development Developing, mature, dies out Developing stage: uplift (generated cloud), rapid upward growth Rises to base of tropapause Strong updraft Down draft is caused by precipitation--rain drags air down Mature stage: precipitation starts; downdrafts; most intense rain, wind, lightning Right before thunderstorm: advanced downdraft--chill (gust front) Dying stage No more uplift- Weak downdraft dominate rains and storm dies out HAIL FORMATION: Only with thunderstorms Updraft: ice pellet forms by moving down a little in the downdraft; gets caught by updraft and freezes more water on them; then eventually comes to the surface Occurs in mature stage with up and down drafts   Severe thunderstorms Characterized by High winds, large hail, tornadoes Meso-scale convective cluster--system of thunderstorms; Supercell--single, huge thunderstorms Squall lines-- along or ahead of cold fronts Potential for severe weather Low pressure cell Requirements High humidity through lower troposphere Uplift mechanism Wind shear (winds that are moving different directions at different levels)  Formation and requirements Patterns of occurrence mT air masses Florida (late afternoon and evening thundershowers are very common E slope Rocky Mountains (orgraphic lifting-- high level of lifting-->thus, lots of storms Tornadoes Associated with sever thunderstorm Rapidly rotating winds Most--cyclonic direction--Low Pressure Cell so spin counterclockwise in NH Travel about 30 mph Winds: 100-280mph Funnel is apparent because of condensation--because it is cool and spinning Winds are close to the same speeds for the first 1000 feet of the funnel. Tornado damage Sources of damage: High winds Abrupt pressure change   Requirements: Severe thunderstorm associates with: Squall line/supercell along cold front Often enhanced in great plains by dry line (Oklahoma/Kansas most tornadoes) Difference in latent heat: causes Hurricane landfall Spins off tornadoes (100-150mph winds) Vertical wind shear--includes rotation Strong updraft--strong jet stream support Occurrence US had the highest number of tornadoes; deal with tornadoes more often then anyone else on the planet Relatively large flat location from Rockies to Atlantic there is a clash between cP and ____mT____ Spring time: May and June Seasonal peak occurs late in season farther north Follows northward migration of jet stream Jet streams occur in polar front westerlies-- PFW is migrating north (jet stream is always with PFW)