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Weather and Storms Bell Work 1. What makes the prevailing winds in the Ferrel Cell unique compared to those in the Polar and Hadley Cells? 2. Carrboro, NC is at ~35°N latitude. a) What is the prevailing winds and wind direction here? b) Within what pressure cell do we lie and are we near a low or a high pressure region? 1. Meteorology - the study of atmospheric phenomena 2. Weather - the condition of the atmosphere at a certain time & place 3. Climate - Long term weather for an area averaged over many years. Weather Instruments Barometer• measures air pressure: rise of mercury in a tube ↑ as pressure on mercury in a bath ↑. Thermometermeasures temperature by using a liquid that expands or shrinks as it is heated or cooled, moving up or down in a tube. Windsockmeasures wind direction Anemometermeasures wind speed: wind pushes on cups causing them to spin and a dial attached to generator shows speed of wind. Station Model: A symbolic summary of the weather data for a location Isobars- lines that connect points of equal pressure Bell Work Look at the station model shown: 1. What is the temperature (in F)? 2. What is the dew point temperature? 3. What is the wind speed and direction? 4. Are there any clouds in the sky? Bell Work • Begin work on the FORECASTING THE WEATHER worksheet. • Notebook quiz at 3:05 Bell Work Get an Earth Science textbook & read pages 561–563 (Weather in North America) Answer the following in your notebook: 1. What is the source & type of air mass that is responsible for lake effect snowstorms in Rochester? 2. What is the source & type of air mass that is responsible for a nor’easter? 3. What is the source & type of air mass that can lead to an Indian Summer? When finished you can begin work on the NOAA Weather Map Analysis project. Get out your NOAA Weather Map Bell Work Analysis handouts In the map on the right: 1. What type of front is shown just south of A? 2. How will the temperature at A change tomorrow? 3. How was the temperature at B changing yesterday? A B Bell Work Get out your notebook for notes today On a sheet of paper answer the following: 1. What is the difference between dew point temperature and surface air temperature? 2. What causes a high pressure system and what type of weather can it lead to? 3. What causes a low pressure system and what type of weather can it lead to? Put your name on the sheet and leave at the top of your desk Thunderstorms - brief, heavy storms w/ rain, strong winds, lightning & thunder Thunder- the sound made by the expansion of air as it heats up Lightning- an electric discharge that takes place water/ice particles in clouds lose or gain an electric charge Conditions necessary for a thunderstorm to occur: 1. Moisture in the lower atmosphere 2. Warm air that is rising 3. Unstable atmosphere (e.g. changing rapidly) Stages of a Thunderstorm 1) Developing stage warm air rises carrying moisture (up-drafts). Forms tall cumulus clouds. No rain but lightning can occur. Stages of a Thunderstorm 2) Mature stage precipitation falls rapidly to earth causing downdrafts. Winds, heavy rain, hail, lightning and tornadoes can occur Stages of a Thunderstorm 3) Dissipation Stage: Downdrafts become, greater than updraft and storm loses energy Severity of storm depends on balance of updraft (rising hot air) and downdrafts (rain/hail) Weak updraft & weak Downdraft: Single-cell storm – Typical summer afternoon storm Strong updraft & weak Downdraft: Multi-cell storm Potential for flash flooding Weak updraft and strong Downburst: Microburst - violent local thunderstorm Strong updraft and strong downdraft: Supercell - A self-sustaining, powerful storm with tornadoes and rain/hail Thunderstorm Classification 1. Air-mass thunderstorms: unequal heating WITHIN an air mass a) Sea Breeze Thunderstorm Cooler, heavier air moves inland & forces warmer, lighter air up b) Orographic Uplift Thunderstorm Air rises due to topography of Earth’s surface 2. Frontal thunderstorms: a) Advancing cold front - Form lines of severe storms. Occur during winter to spring transition b) Advancing warm fronts • Less likely to produce thunderstorms Bell Work 1.How is the updraft stage of a thunderstorm different from the down draft stage? 2.How does the balance of the updraft and the down draft affect the severity of the storm (give 2 examples)? Tornado: Destructive, rotating column of air Winds up to 300 mph 2 air masses collide - warm air spirals up • Cold, dry, highpressure air from northwest • Warm, moist, low-pressure air from southeast Tornado Classification: • Enhanced Fujita Scale (EF0 to EF5) • Ranks based on wind speed, duration, and path of destruction. • EF0: Weak tornado • EF5: Strongest tornado “Tornado Alley”: Midwestern US states where cP air masses meet mT air masses. Tornado Watch A tornado is possible 1) Be ready to act if changes to warning Tornado Warnings A tornado has been sighted with winds ≥ 58 mph, hail & lightening 1) Take shelter right away – stay inside 2) Stay away from windows Path and Strength of Tornadoes 2011 in NC Tropical Cyclones • Rotating, low-pressure storms • Formed over warm ocean in late summer Tropical depression: winds ≤ 38 mph Tropical storm: winds 39 to 73 mph Hurricane/typhoon: winds ≥ 74 mph Hurricanes 1. 2. An intense, rotating oceanic weather system with winds of 74 mph or greater Occurs with rain, thunder, and lightning 3. 4. Forms and intensifies over tropical oceanic regions (i.e. near the equator). Moves into temperate latitudes (i.e. North Carolina). 5. 6. 7. 8. Begin as low pressure system off Africa Move into the Atlantic ocean where they grow and intensify. Hot air near equator meets a low pressure system → hot air rises up, cools, then sinks → creates a convection current The Coriolis effect causes the winds to curve to the right north of equator Hurricane winds: spiral counter-clockwise in the northern hemisphere towards a low pressure Eye: calm center of the storm Eyewall: wall of storms around the eye with strongest winds Classification of Hurricanes: Saffir-Simpson scale (1 to 5), based on wind speed, air pressure and potential for damage 1: weakest hurricane 5: strongest hurricane Hurricane watch - hurricane conditions possible within 36 hours Hurricane warning - hurricane force winds expected within 24 hours. Tsunami Waves created by the displacement of a large amount of water. Caused by: • • • • • Tsunami Earthquakes Volcanic eruptions Underwater explosions Landslides Meteorite & comet impacts in the ocean Tidal Surges 1. The onshore rush of sea water caused by the high winds that accompany a hurricane. 2. Also known as “storm surge” Tidal Surges 3. Geography of land affects strength of the surge: shallow & narrow inlets will have larger storm surges. Nor’easter (Northeastern storm) 1. A large storm with winds that rotate from the northeast. 2. Causes coastal flooding and erosion, high winds, and heavy precipitation (blizzards inland & rain at coast) Bell Work 1. How are Nor’easters and hurricanes different? 2. How are Nor’easters and hurricanes the same? 3. How could tides and geographic features affect a storm surge?