Ch. 3: Weather Patterns

Transcription

1 Ch. 3: Weather Patterns Sect. 1: Air Mass & Fronts Sect. 2: Storms Sect. 3: Predicting the Weather Sect. 4: Weather forecasters use advanced technologies

2 Ch. 3 Weather Fronts and Storms Objective(s) 7.E Explain the relationship between the movements of air masses; high and low pressure systems, and frontal boundaries to storms (including thunderstorms, hurricanes, and tornadoes) and other weather conditions that may result. 7.E Predict weather conditions and patterns based on information obtained from: Weather data collected from direct observations and measurement (wind speed and direction, air temperature, humidity and air pressure) Weather maps, satellites and radar Cloud shapes and types and associated elevation

3 Learners Objective(s) You will understand that storms are the result of interactions between moving air masses, high and low pressure systems and frontal boundaries. Essential Vocabulary -Air mass -Front -Pressure systems -Weather patterns *remaining vocabulary terms located at mrspruillscience.weebly.com

4 I. Sect. 3.1: Weather Changes as air masses move A. Air masses are large bodies of air Air mass is a large volume of air in which temperature, humidity and air pressure are nearly the same in different locations at the same altitude An air mass forms when the air over a large region of Earth sits in one place for many days Where Earth s surface is cold, the air becomes cold Where Earth s surface is wet, the air becomes moist As an air mass moves, it brings its temperature and moisture to new locations

5 B. Characteristics of an Air mass Air masses are classified by 2 characteristics 1. Humidity 2. Temperature A hot desert produces dry hot air masses, while cool ocean waters produce moist, cool air masses Each category name is made of two words one for moisture, one for temperature First word tells whether the air mass formed over water or dry land. The 2 nd word tells whether an air mass formed close to the equator (temperature)

6 The characteristics of an air mass depend on the temperatures and moisture content of the region over which the air mass formed. o Continental: air masses formed over land Air becomes dry as it loses its moisture to the dry land below it o Maritime: air masses formed on oceans or seas Air becomes moist as it gains water vapor from the water below it o Tropical: warm, air masses formed in the tropics Air becomes warm as it gains energy from the warm land or water o Polar: cold, air masses formed north or south of 50º latitude Air becomes cool as it loses energy to the cold land or water

7 The colder the air the higher the air pressure subsequently the hotter the air the lower the air pressure. Cold air more dense Hot air less dense Types of Air masses There are 4 major types of air masses that affect the weather of the U.S. o Maritime tropical - air mass that is moist and warm o Continental polar - air mass that is dry and cold o Maritime polar - air mass that is moist and cold o Continental tropical - air mass that is dry and warm

8 C. Movement of an Air Mass - 2 primary methods for air mass movement 1. Prevailing Westerlies Pushes air masses from west to east. 2. Jet streams Pushes fast moving air masses from west to east.

9 When air masses move to a new region, it carries along its characteristic moisture and temperature As the air moves over Earth s surface, the characteristics of the surface begin to change the air mass

10 D. Weather changes where air masses meet When a new air mass moves over your area, you can expect the weather to change Fronts are the boundary between two air masses. Storms & different types of weather phenomena occur along fronts. Air masses do not easily mix with each other due to the differences in 1. Density (Air pressure) 2. Temperature 3. Moisture content Weather near a front can differ from the weather inside the rest of an air mass Clouds can form in this rising air

11 Types of Fronts Cold front - a cold dense air mass that pushes warmer air upward Occurs when a fast moving cold air mass overtakes a slower moving warm air mass. o Can move into regions quickly o Often produce tall cumulonimbus clouds and precipitation o Brief, heavy storms are likely and after it, the air is cooler and often very clear

12 2. Warm front - warm air masses that push colder air upward Occurs when a fast moving warm air mass overtakes a slow moving cold air mass. o Produces cloud-covered skies high cirrus and stratus and low stratus clouds o Often brings many hours of steady rain or snow and as it passes the air is warmer

13 3. Stationary front - occur when air masses first meet or when a cold or warm front stops moving Occur when a cold and warm air mass meet but neither can move the other. A wide variety of weather can be found along a stationary front including clouds, prolonged precipitation, fog, and storms. o Produces clouds that cover the sky, sometimes for days at a time

14 4. Occluded front Occurs when a warm air mass is caught between 2 cooler air masses. A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass.

15 C. High-Pressure Systems Letter H represents high-pressure systems or highs Letter L represents low-pressure systems or lows Each center is the location of the highest or lowest pressure in a region At a high-pressure center, air sinks slowly down. As the air nears the ground, it spreads out toward areas of lower pressure High pressure system is formed when air moves all the way around a high-pressure system o Are often large and change slowly o When one stays in one location for long time, air mass may form warm or cold, moist or dry o Often brings clear skies and calm air or gentle breezes

16 F. Low-Pressure Systems Low-pressure system is a large weather system that surrounds a center of low pressure o It begins as air moves around and inward toward the lowest pressure and then up to higher altitudes o Rising air produces stormy weather o In the northern hemisphere, the air in a low-pressure system circles in a counterclockwise direction Pressure System Weather

17 II. Section 3.2 Low-pressure systems can become storms A. Hurricanes form over warm ocean water Near the equator, warm ocean water provides the energy that can turn a low-pressure center into a violent storm Tropical storm is a low-pressure system that starts near the equator and has winds that blow at 40mph or more Hurricane is a tropical low-pressure system with winds blowing at speeds of 74 mph or more o Are called typhoons or cyclones when they form over the Indian Ocean or the western Pacific Ocean

18 B. Formation of Hurricanes Energy from warm water is necessary for a lowpressure center to build into a tropical storm and then into a hurricane Tropical storms generally move westward with the trade winds As long as the storm stays over warm water it can grow bigger and more powerful Once the hurricane moves over land or cooler water, it loses its source of energy Eye at the center of a hurricane that is a small area of clear weather (about kilometers/10-30 miles in diameter) Anatomy of A Hurricane

19 C. Effects of Hurricanes In the space below, list several effects that a hurricane can have Lift cars Uproot trees Tear the roofs off buildings May produce tornadoes Can cause river banks to overflow and flood nearby areas Storm Surge Huge mass of ocean water. Sea levels rise several meters, backing up rivers and flooding the shore Can be destructive and deadly Above the storm How hurricanes are formed!!!

20 Stages of Hurricane Development 1. Stage 1: Tropical disturbance; mph 2. Stage 2: Tropical depression; mph 3. Stage 3: Tropical storm; mph 4. Stage 4: Hurricane; 74 mph The Saffir-Simpson scale Scale used to determine the severity of a hurricane. Category 1: wind speed mph; storm surge 4-5 feet. Category 2: wind speed mph; storm surge 6-8 feet. Category 3: wind speed mph; storm surge 9-12 feet. Category 4: wind speed mph; storm surge feet. Category 5: wind speed 155+ mph; storm surge 18+ feet Hurricane Katrina was a category 3 hurricane when it made landfall near New Orleans, La on August 29, 2008.» Costliest natural disaster» 6 th strongest to form, 3 rd strongest to make landfall» 1 of the 5 deadliest

21 Hurricanes Tropical cyclone (low pressure) that typically measures miles across with winds from mph. Comes from the West Indian word Huracan or big wind. Called Typhoons when formed in the Pacific Ocean; Chinese word, Táifēng or great wind. Hurricanes are named by the World Meteorological Organization. Guided or directed by the Trade winds. Can only form over water that is at least 80ºF. Typically forms during the months of late July to early October.

22 D. Winter Storms produce snow and ice Most severe winter storms in the US are part of lowpressure systems The systems that cause winter storms are formed when two air masses collide Blizzards Are blinding snowstorms with winds of at least 35 mph and low temperatures (usually below 20 degrees F) Occur in many parts of the northern and central US Wind and snow can knock down trees and power lines Water pipes can freeze

23 Lake-effect Snowstorms Heavy snow fall in the areas just east and south of the Great Lakes Cold air from the NW gains moisture and warmth as it passes over the Great Lakes Over cold land, the air cools again and releases the moisture as snow

24 Ice Storms o Cold rain freezes as it touches the ground and other surfaces with a heavy, smooth ice o Ice-covered roads become slippery and dangerous o Drivers may find it hard to steer and to stop their cars o Branches or even whole trees may break from the weight of ice o Falling branches can block roads, tear down power and telephone lines, etc o Damage from ice storms can sometimes shut down entire cities