Last warning: Exam 3 Monday, April 9: end of volcanoes, tsunami, and weather through tornadoes; review tomorrow, 5.15 PM, UPSTAIRS in Rm 223. Exam 4 is on the website (as always, only partially applicable) ANNOUCEMENTS

homework If you have not yet done the homework, you do have until 5 PM; be sure not to have any spaces in the URL (if you copy and paste, you might see %20recent -- the %20 has to go for the website to load). So:

A couple of clicker review Qs

A cold front means that 1.A cold air mass is moving into a warm air mass 2.A warm air mass is moving into a cold air mass 3.Two air masses are next to each other, but neither is really moving

Which hemisphere… 1.Northern 2.Southern

severe weather (the good stuff) defined as –thunderstorms –tornadoes –hurricanes –blizzards –heat waves –dust storms

thunderstorms we have an average of 40 of them per year; the high is central/southern Florida (>100/year) three critical conditions –water (vapor) in the lower atmosphere –change in temperature with altitude so that air cools rapidly –air moving rapidly upward to take warm, moist air up into the upper troposphere

1) moist air need moisture in upper atmosphere, so need it to come from lower atmosphere

2) temperature change if warm air cools slowly (or if there isn’t enough moisture) the forming cloud will evaporate as fast as it forms

3) updraft taking the moisture upward has to be a continuing process

so what actually happens? rising moisture in warm air condenses growing cumulus cloud becomes cumulonimbus stage lasts about 10 minutes some lightning, little/no rain, but precipitation forming Stage 1: developing stage (cumulus stage)

so what actually happens? mass of frozen precipitation becomes heavier than the cloud rising and falling masses of air Stage 2: mature stage stage lasts about 20 minutes (can be much longer) black or dark green cloud thunder/lightning/rain/ tornadoes

approximate altitude of the tropopause

so what actually happens? downdraft > updraft rain decreases Stage 3: dissipating stage lightning still a hazard cloud dissipates

Hail…. round or irregular pieces of ice concentric rings (This is in a person’s hand…)

Hailstone sizeSize (“)Updraft wind speed pea1/424 mph penny3/440 mph quarter149 mph walnut1 1/260 mph golf ball1 3/464 mph tennis ball2 1/277 mph baseball2 3/481 mph tea cup384 mph grapefruit498 mph

a.gov/science.htm If you would like to read more about lightning, go here:

Tornadoes… We hold the record here in the US –generally ~1200/yr –avg. 70 fatalities How do they form? –the classic answer: "warm moist Gulf [of Mexico] air meets cold Canadian air and dry air from the Rockies" -