Question of the Day What are cyclones? What does “cyclone” mean to you? 119

Questions high low 1) Winds blow from _____ to ___. 2) Due to the Coriolis effect, winds in the N. Hemi. are deflected to the ____. 3) High pressure systems bring happy or lousy weather? 4) Low pressure systems bring happy or lousy weather? right Happy Lousy

Cyclone Low-pressure system Wind toward center Rotates counter- clockwise in N. Hemi. Warm, moist, less dense air rises Lousy weather: hurricanes, tornadoes

Anticyclone High-pressure Wind away center Rotates clockwise Cool, dry, dense air sinks Happy weather

Is a hurricane a high-pressure or low-pressure region?

1 3 2 4

In the N. Hemisphere, in which direction does surface wind circulate in a low-pressure air mass? 1) clockwise & toward the center 2) clockwise & away from the center 3) counterclockwise, toward center 4) counterclockwise, away from center

In the N. Hemisphere, in which direction does surface wind circulate in a high-pressure air mass? 1) clockwise & toward the center 2) clockwise & away from the center 3) counterclockwise, toward center 4) counterclockwise, away from center

Question of the Day What causes storms? High or Low Pressure System? Name That Front! A High or Low Pressure System? B C D ? ? 120

Storms Violent or severe disturbance of atmosphere Dangerous conditions Injuries, loss of life or property

Mid-Latitude Cyclones (Cyclonic Storms) Large low-pressure storm Brings much precipitation to U.S. Caused by movement of air along Polar Fronts - N. edge of Prevailing Westerlies

http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp29/animations/ch29/global_wind_circulation.swf

Life Cycle A. Polar Front - Stationary ● Opposite winds create eddies B. Cold & Warm Fronts develop ● Warm air starts to rise

C. Occluded Front ● Warm air completely above front D. Stationary Front ( → 1st stage) ● Warm air mixes with surrounding air

Classic Midlatitude Cyclone

Jet Stream moves cyclone W → E

The most likely location for heavy precipitation is at A, B, C or D?

Question of the Day How are hurricanes formed? Which way do prevailing winds blow between: 0º & 30º N? 30º N & 60º N? 60º N 30º N 0º 121

Hurricane (Tropical Cyclone) Also typhoon or tropical cyclone Large (100’s of miles wide) Strong (sustained winds 74 mph +) Lasts weeks

Birth Tropical waters in E. Atlantic, Gulf of Mexico or Caribbean Evaporating water condenses & provides energy (latent heat released)

Structure Large pressure gradient = strong winds Eye: calm, very low pressure @ center

Growth Tropical Depression: mild low-press. Tropical Storm: sustained winds > 39 mph Hurricane: winds > 74 mph

Saffir-Simpson Scale Classification by sustained wind speed

Official Season June 1 - Nov. 30

Typical Track Affected by N.E. then S.W. winds

Flooding from torrential rains Destruction High winds (>74 mph) Flooding from torrential rains Storm surge - 90% of all deaths from hurricanes Hurricane Katrina damage, New Orleans

Storm Surge Wall of water - low pressure, high winds

Death Loses strength over: 1. Cold ocean water - loses energy source of warm water 2. Land - friction + no water Becomes mid-latitude cyclone

Safety Listen to weather alerts! Evacuate area Move to higher ground Prepare survival kit Backup electric power

Question of the Day How are thunderstorms & tornadoes formed? Which is the fastest-moving front? 122

Heavy rainstorm with thunder, lightning Sometimes flash floods, hail, tornadoes Formed by rapidly moving cold front

Lightning & Thunder Friction in cloud results in electrical charges (+ -) Discharge = lightning Heated air expands explosively = thunder

Squall Line Thunderstorms along cold front

Supercell Giant thunderstorm w/ strong updrafts

Safety Listen to weather alerts! Seek indoor shelter Don’t touch electrical outlets or plumbing Stay in car Avoid high ground

Narrow (100-foot-wide) funnel of spiraling winds Most violent storm: winds 300+ mph Lasts minutes to an hour

Formation 2. U P D R A F T 1. Winds converge 3. Tornado Descends Tornado in Supercell

Formation Warm, moist air rises Air flows in & counter- clockwise

Occurences Usually forms over land, but also over water = waterspout

Most common in spring & summer Prime region - flat terrain, and clash of cP & mT air masses

Fujita Intensity Scale Classification by wind speed & damage

Safety Listen to weather alerts! Get indoors to strongest structure Lowest level or safest interior room Stay away from windows Open windows if time Cover body with coat or blanket

Question of the Day How is a weather map made? This station model shows all the key information needed to predict the weather. How many factors can you list? 124 A,B,C

Station Model Weather variables at a particular site.

Synoptic Map Summary of weather variables. Used to predict the weather.

ESRT p. 13

Air Temperature Recorded in ºF.

Present Weather Use symbols in box below

Visibility Greatest distance (miles) at which objects can be identified.

Dewpoint Temp. air is saturated if cooled. ºF.

Wind Direction (From!) Circle = head of an arrow.

Wind Speed Whole feather = 10 knots Half feather = 5 knots Total 1- 4

Cloud Cover % circle dark = % covered by clouds

Precipitation Inches over past 6 hours Liquid water equivalent

Barometric Pressure 3-digit code

Do what brings you closer to 1000 mb Barometric Pressure Cracking the Code (Converting to mb) Do what brings you closer to 1000 mb < 500, place 10 in front and decimal between last 2 digits. > 500, place 9 in front and decimal between last 2 digits.

Cracking the Code Coded 320 999 499 Decoded 1032.0 mb 999.9 mb 1049.9 mb

Barometric Trend What pressure did over past 3 hours Before the number + Pressure now higher than 3 hrs. ago - Pressure now lower than 3 hrs. ago

Add a decimal inside the number (mb rounded to nearest 1/10th) Barometric Trend Decoding the Number Add a decimal inside the number (mb rounded to nearest 1/10th)

After the number / Increasing \ Decreasing Stable Barometric Trend What pressure did over past 3 hours After the number / Increasing \ Decreasing Stable

This station model shows weather conditions at Massena, NY, 9 a. m This station model shows weather conditions at Massena, NY, 9 a.m. on a June day. What was the barometric pressure 3 hours earlier that day? 1) 997.1 mb 3) 1003.3 mb 2) 999.7 mb 4) 1009.1 mb

Draw a station model to indicate a temperature of 20º C, a dewpoint of 11º C, and clear skies. (Be sure the numbers are in the proper position!)

Question of the Day How can we use synoptic maps to predict the weather? How will temperature & barometric pressure change at X as this front passes? 125

How does station data become a weather map?

4 Principles of Weather Predictions 1. Air temp. increases ↑, air pressure decreases ↓ 2. Air temp. closer to dew point, chance of precip. increases ↑ 3. Greater air pressure gradient = greater wind speeds 4. Rapidly falling air press. → low press. system coming (lousy weather)

Where would the isobar for 1008.0 mb be drawn? Barometric Pressure Where would the isobar for 1008.0 mb be drawn?

Barometric Pressure

Where would the isotherm for 60º F be drawn? Temperature Where would the isotherm for 60º F be drawn?

Temperature

Barometric Pressure Temperature + Wind Direction Precipitation