Lesson 2-2 Weather Elements Part 2 of 2

Lesson Overview   Types of air masses and fronts   Factors that impact air masses  Fronts   Wind and Atmospheric Motion   High- and low-pressure systems  Terrain factors that affect weather  Normal weather patterns Chapter 2, Lesson 2

Current Weather Map

Fronts – Quick Review   What color indicates a cold front? Warm front? Stationary front? Occluded Front?  Blue (triangle); Red (semicircle); Blue and Red (both triangle and semicircle); purple  How is a warm front defined?  The air is warmer than the air it is displacing  Which front has more potential violent weather? Why?  Cold Front. It moves faster, lifting warmer air and causing updrafts and condensation of moisture

Fronts – Quick Review   What three types of high clouds might you see hundreds of miles prior to the passing of a warm or cold front?  Cirrus, cirrostratus, cirrocumulus  Why does the air near the surface of a warm front remain foggy or hazy with low cloud buildup?  Because dust, pollution and other particulates are not lifted higher up as the warm air moves over the colder air  What do squall lines in a cold front represent?  Low pressure air cells in the warm air that meet with the higher pressure cells of the cold front, causing increased turbulence and cloud formation

Fronts – Quick Review   What direction do cold fronts normally take in the Northern Hemisphere?  Northwest to Southeast  What causes winds to shift right in the Northern Hemisphere? Why does it shift right?  The Coriolis Force. As the earth rotates, the surfaces nearer the equator move faster than surfaces nearer the poles.  What causes wind?  A low-pressure area next to as high pressure area  What is the difference between air currents and wind?  Currents go up and down; wind is horizontal

Key Factors in Wind and Atmospheric Motion  Sun’s heat is main driver causing air to warm, become less dense and lift upwards  Other atmospheric factors:  Air pressure gradients  Temp changes of terrain  Earth’s rotation about axis  Coriolis Effect  The result is wind currents that can and do change weather Chapter 2, Lesson 2 Reproduced from NASA

Wind Patterns  Anticyclonic circulation  Flow of air from high to low pressure, produces clockwise circulation  Cyclonic circulation  Flow of air around a low- pressure area, produces counterclockwise circulation Chapter 2, Lesson 2 Reproduced from US Department of Transportation/Federal Aviation Administration

High- and Low-Pressure Systems  High-pressure systems generally produce good weather  Low-pressure systems often bring in bad weather  Pilots who understand high- and low-pressure high- and low-pressure wind patterns can take wind patterns can take advantage of tailwinds advantage of tailwinds Chapter 2, Lesson 2 Courtesy of NASA

The Pressure Gradient  The atmosphere is a constantly changing “airscape” of high pressure and low pressure pockets of air  Air moves from the high pressure pockets to lower pressure pockets….the result is wind  The Pressure Gradient is the difference in pressure between high and low pressure pockets Chapter 2, Lesson 2 Courtesy of NASA

The Pressure Gradient  On weather maps lines called isobars show the magnitude of the pressure gradient  Isobars are drawn through points of equal sea-level atmospheric pressure  Similar to topographic lines on an orienteering map indicating the altitude of the terrain  Isobaric lines close together indicate a higher Pressure Gradient and usually higher wind speeds Chapter 2, Lesson 2 Courtesy of NASA

Chapter 2, Lesson 2 Courtesy of NASA

Local and Surface Air Movement  The general circulation of air is complicated by the irregular distribution of land and water areas  Different types of surfaces differ in the rate at which they absorb heat from the Sun and transfer heat to the atmosphere  In some regions local low-pressure areas form over hot land surfaces and over warmer water surfaces in the winter

Local and Surface Air Movement  Some surfaces give off or reflect a great amount of heat Sand Sand Rocks Rocks Plowed areas Plowed areas Barren land Barren land  Other surfaces tend to absord and retain heat Meadows Meadows Planted fields Planted fields Water Water

Local and Surface Air Movement  Rising air currents are encountered by aircraft flying over sand, rock, and other surfaces that give off considerable heat  Descending air currents are encountered over surfaces that retain heat

Terrain and Mountains  The presence of mountain ranges change the characteristics of a front  As air masses enter the United States the mountains cause them to rise   Upward slope pushes air up, water vapor cools, condenses into clouds, can rain or snow making air mass dryer   After reaching the peak, air descends on the leeward side, warms up; little rain/snow

 Think of the air reaching the peak and then descending on the leeward side  This air tends to break into eddies These eddies are descending and turbulent air These eddies are descending and turbulent air The stronger the wind rising up and over the peak, the greater the turbulence The stronger the wind rising up and over the peak, the greater the turbulence As a pilot, if you are coming towards the leeward side of a mountain, say from Denver heading west, make sure you have enough altitude between your plane and the mountain so you’ll fly above the strong dangerous descending air As a pilot, if you are coming towards the leeward side of a mountain, say from Denver heading west, make sure you have enough altitude between your plane and the mountain so you’ll fly above the strong dangerous descending air Terrain and Mountains

Terrain and Bodies of Water  Along many seacoasts there is a breeze from the sea during the day (sea breeze)  The land heats up more than water, warming the air and lowering the pressure  As the cooler moist air from the water comes onto land, it heats up, rises and causes water vapor to condense  Afternoon showers are quite common   Later in the day, as the land cools, the pressure over land increases causing the wind to shift back from land to sea (land breeze)   The clouds disappear as they turn back into water vapor

Terrain and Lake Effect Snow   Lake Effect Snow is the result of a cold air mass passing over a warmer body of large water like Lake Erie   Explain the process creating so much snow   Why is it only the southern or eastern sides of Lake Erie that get the lake effect snow and not the Canadian side?

Climatic Provinces

Normal Weather Patterns  Superhumid Province Lies along the north Pacific coast Lies along the north Pacific coast Precipitation from 30 to 150 inches per year Precipitation from 30 to 150 inches per year Temperatures are mild and summers dry Temperatures are mild and summers dry Cloudiest part of the country. Cloudiest part of the country.

Normal Weather Patterns  Humid Province Area east of a line from Texas Gulf Coast to Lake Superior Area east of a line from Texas Gulf Coast to Lake Superior 30 to 50 inches of rain annually 30 to 50 inches of rain annually Average temperature from 40 o F in north, 70 o F along the Gulf of Mexico, 75 o F in Florida Average temperature from 40 o F in north, 70 o F along the Gulf of Mexico, 75 o F in Florida Cold waves in winter, heat waves in summer Cold waves in winter, heat waves in summer Hurricanes are common Hurricanes are common

Normal Weather Patterns  Subhumid Province Belt miles wide just west of humid province Belt miles wide just west of humid province Average rainfall 18 to 30 inches Average rainfall 18 to 30 inches Cold in winter, hot in summer Cold in winter, hot in summer Quick and severe temperature changes Quick and severe temperature changes Tornadoes in most of southern part of this area Tornadoes in most of southern part of this area

Normal Weather Patterns  Semiarid Province mile wide area west of subhumid province from Canada to Mexico mile wide area west of subhumid province from Canada to Mexico Precipitation ranges from 12 to 25 inches Precipitation ranges from 12 to 25 inches Warm, dry air masses common in winter Warm, dry air masses common in winter Hail frequent in spring and early summer Hail frequent in spring and early summer The Great Valley of California is geographically separated from rest of province The Great Valley of California is geographically separated from rest of province

Normal Weather Patterns  Arid Province Includes parts of California, Texas, Arizona, New Mexico, Nevada and Utah Includes parts of California, Texas, Arizona, New Mexico, Nevada and Utah Less than 10 inches of rain annually Less than 10 inches of rain annually Hot and dry summers, winters above freezing Hot and dry summers, winters above freezing Clear dry air and plenty of sunshine Clear dry air and plenty of sunshine

Normal Weather Patterns  Hawaii Two major factors determine weather Two major factors determine weather Dramatic heights and contours of land areas Dramatic heights and contours of land areas Prevailing northeast trade winds Prevailing northeast trade winds Pleasant temperatures Pleasant temperatures Little distinctions between summer and winter Little distinctions between summer and winter

Normal Weather Patterns  Alaska Has several different kinds of weather Has several different kinds of weather No great extremes in southern part of state No great extremes in southern part of state Arctic slope lies in northern part of state Arctic slope lies in northern part of state Broad valley and low mountain ranges Broad valley and low mountain ranges Continental weather Continental weather Temperatures from -70 o F in winter to 90 o F in summer Temperatures from -70 o F in winter to 90 o F in summer

Next….  Done – weather elements  Next – aviation weather Chapter 2, Lesson 2 Courtesy of NOAA/National Weather Service