Thunderstorms and TornadoesLast Lecture:

We looked at severe weather events in the lower latitudes

Principal weather event is the formation and movement of Tropical Cyclones

Today:Today we will look at severe weather in the mid-latitudes

Most severe weather is related to thunderstorms• Significant convection and precipitation• Very strong winds• Produces thunder and lightning• Can also initiate tornados - most intense wind events on planet

Thunderstorms and TornadoesThunderstorms

Cells of local, intense convection resulting in the formation of cumulonimbus clouds, heavy rainfall, lightning and occasionally hail and tornados

Thunderstorms and TornadoesAir Mass Thunderstorms

Isolated storms generated by daytime heating of land surface

Convection Cell

Thunderstorms and TornadoesSevere Thunderstorms

Thunderstorms with high winds, hail and possibly tornados

Thunderstorms and TornadoesMesoscale Convective System

Long-lived, intense cluster of convection cellsMesoscale Convective Complexes

Large circular complex of thunderstorms active during the night

Thunderstorms and TornadoesSquall line

Line of severe thunderstorms and very strong winds

Thunderstorms and TornadoesDry line

Boundary between hot, dry air and warm, moist air, which tends to form squall line

Thunderstorms and TornadoesLightning

electrical discharge producing light from cloud to cloud or cloud to groundThunder

sound of rapid expansion & cooling of superheated air around a lightning bolt

Thunderstorms and TornadoesCharge Separation

Difference in charge between cloud top and bottom

Thunderstorms and TornadoesLightning stroke

Complex series of processes which produce electrical discharge between cloud and groundLeader

Channel of ionized air along which lightning stroke propagates

Thunderstorms and TornadoesTornado

Small, intense cyclonic storm characterized by a funnel descending from mesocyclone

Thunderstorms and TornadoesTornado Dynamics Wind Shear

Convection

Thunderstorms and TornadoesTornado Dynamics con’t. Mesocyclone

Tornado

Thunderstorms and TornadoesTornado Structure

Thunderstorms and TornadoesWeather Conditions during Formation

Cold front provides Wind Shear

Squall Line provides Convection

Thunderstorms and Tornadoes“Tornado Alley”

Region of the United States with high frequency of tornado occurrence

Thunderstorms and TornadoesFujita Scale

Measure of strength of tornado based upon severity of damage left behind

Thunderstorms and TornadoesDetection of Tornado Vortex Signature using Radar

Hook Echo