Lesson 2-2Lesson 2-2Weather ElementsWeather Elements

Part 2 of 2Part 2 of 2

Lesson OverviewLesson Overview

Types of air masses and fronts Factors that impact air masses FrontsFronts Wind and Atmospheric Motion High- and low-pressure systems Terrain factors that affect weatherTerrain factors that affect weather Normal weather patternsNormal weather patterns

Chapter 2, Lesson 2

Current Weather MapCurrent Weather Map

Fronts – Quick ReviewFronts – 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 ReviewFronts – 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 ReviewFronts – 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 Key Factors in Wind and Atmospheric MotionAtmospheric Motion

Sun’s heat is main driver causing Sun’s heat is main driver causing air to warm, become less dense air to warm, become less dense and lift upwardsand lift upwards

Other atmospheric factors:Other atmospheric factors: Air pressure gradientsAir pressure gradients Temp changes of terrainTemp changes of terrain Earth’s rotation about axisEarth’s rotation about axis Coriolis EffectCoriolis Effect

The result is wind currents that The result is wind currents that can and do change weathercan and do change weather

Chapter 2, Lesson 2 Reproduced from NASA

Wind PatternsWind Patterns AnticyclonicAnticyclonic circulation circulation

Flow of air from high to Flow of air from high to low pressure, produces low pressure, produces clockwise circulation clockwise circulation

CyclonicCyclonic circulation circulation Flow of air around a low-Flow of air around a low-

pressure area, produces pressure area, produces counterclockwise counterclockwise circulation circulation

Chapter 2, Lesson 2Reproduced from US Department of Transportation/Federal Aviation Administration

High- and Low-Pressure SystemsHigh- and Low-Pressure Systems

High-pressure systems generally produce good weatherHigh-pressure systems generally produce good weather Low-pressure systems often bring in bad weather Low-pressure systems often bring in bad weather Pilots who understand Pilots who understand

high- and low-pressure high- and low-pressure wind patterns can take wind patterns can take advantage of tailwindsadvantage of tailwinds

Chapter 2, Lesson 2 Courtesy of NASA

The Pressure GradientThe Pressure Gradient

The atmosphere is a constantly changing “airscape” of The atmosphere is a constantly changing “airscape” of high pressure and low pressure pockets of airhigh pressure and low pressure pockets of air

Air moves from the high pressure pockets to lower Air moves from the high pressure pockets to lower pressure pockets….the result is windpressure pockets….the result is wind

The The Pressure Gradient Pressure Gradient is the difference in pressure is the difference in pressure between high and low pressure pocketsbetween high and low pressure pockets

Chapter 2, Lesson 2 Courtesy of NASA

The Pressure GradientThe Pressure Gradient

On weather maps lines called isobars show the magnitude of the On weather maps lines called isobars show the magnitude of the pressure gradientpressure gradient

Isobars are drawn through points of equal sea-level atmospheric Isobars are drawn through points of equal sea-level atmospheric pressurepressure Similar to topographic lines on an orienteering map indicating the Similar to topographic lines on an orienteering map indicating the

altitude of the terrainaltitude of the terrain Isobaric lines close together indicate a higher Pressure Gradient and Isobaric lines close together indicate a higher Pressure Gradient and

usually higher wind speedsusually higher wind speeds

Chapter 2, Lesson 2 Courtesy of NASA

Chapter 2, Lesson 2 Courtesy of NASA

Local and Surface Air MovementLocal and Surface Air Movement

The general circulation of air is complicated by the The general circulation of air is complicated by the irregular distribution of land and water areasirregular distribution of land and water areas

Different types of surfaces differ in the rate at which Different types of surfaces differ in the rate at which they absorb heat from the Sun and transfer heat to the they absorb heat from the Sun and transfer heat to the atmosphereatmosphere

In some regions local low-pressure areas form over hot In some regions local low-pressure areas form over hot land surfaces and over warmer water surfaces in the land surfaces and over warmer water surfaces in the winterwinter

Local and Surface Air MovementLocal and Surface Air Movement

Some surfaces give off or reflect a great amount Some surfaces give off or reflect a great amount of heatof heat

• SandSand• RocksRocks• Plowed areasPlowed areas• Barren landBarren land

Other surfaces tend to absord and retain heatOther surfaces tend to absord and retain heat• MeadowsMeadows• Planted fieldsPlanted fields• WaterWater

Local and Surface Air MovementLocal and Surface Air Movement

Rising air currents are encountered by aircraft Rising air currents are encountered by aircraft flying over sand, rock, and other surfaces that give flying over sand, rock, and other surfaces that give off considerable heatoff considerable heat

Descending air currents are encountered over Descending air currents are encountered over surfaces that retain heatsurfaces that retain heat

Terrain and Mountains Terrain and Mountains

The presence of mountain ranges change the The presence of mountain ranges change the characteristics of a frontcharacteristics of a front

As air masses enter the United States the As air masses enter the United States the mountains cause them to risemountains 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 Think of the air reaching the peak and then descending on the leeward sidedescending on the leeward side

This air tends to break into eddiesThis air tends to break into eddies• These eddies are descending and turbulent airThese eddies are descending and turbulent air• The stronger the wind rising up and over the peak, the The stronger the wind rising up and over the peak, the

greater the turbulencegreater the turbulence• As a pilot, if you are coming towards the leeward side of As a pilot, if you are coming towards the leeward side of

a mountain, say from Denver heading west, make sure a mountain, say from Denver heading west, make sure you have enough altitude between your plane and the you have enough altitude between your plane and the mountain so you’ll fly above the strong dangerous mountain so you’ll fly above the strong dangerous descending airdescending air

Terrain and Mountains Terrain and Mountains

Terrain and Bodies of WaterTerrain and Bodies of Water

Along many seacoasts there is a breeze from the sea during the day (sea Along many seacoasts there is a breeze from the sea during the day (sea breeze)breeze) The land heats up more than water, warming the air and lowering the pressureThe 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 As the cooler moist air from the water comes onto land, it heats up, rises and causes

water vapor to condensewater vapor to condense Afternoon showers are quite commonAfternoon 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 SnowTerrain 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 ProvincesClimatic Provinces

Normal Weather PatternsNormal Weather Patterns

Superhumid ProvinceSuperhumid Province• Lies along the north Pacific coastLies along the north Pacific coast• Precipitation from 30 to 150 inches per yearPrecipitation from 30 to 150 inches per year• Temperatures are mild and summers dryTemperatures are mild and summers dry• Cloudiest part of the country.Cloudiest part of the country.

Normal Weather PatternsNormal Weather Patterns

Humid ProvinceHumid Province• Area east of a line from Texas Gulf Coast to Area east of a line from Texas Gulf Coast to

Lake SuperiorLake Superior• 30 to 50 inches of rain annually30 to 50 inches of rain annually• Average temperature from 40Average temperature from 40o o F in north, 70F in north, 70o o F F

along the Gulf of Mexico, 75along the Gulf of Mexico, 75o o F in FloridaF in Florida• Cold waves in winter, heat waves in summerCold waves in winter, heat waves in summer• Hurricanes are commonHurricanes are common

Normal Weather PatternsNormal Weather Patterns

Subhumid ProvinceSubhumid Province• Belt 300-500 miles wide just west of humid provinceBelt 300-500 miles wide just west of humid province• Average rainfall 18 to 30 inchesAverage rainfall 18 to 30 inches• Cold in winter, hot in summerCold in winter, hot in summer• Quick and severe temperature changesQuick and severe temperature changes• Tornadoes in most of southern part of this areaTornadoes in most of southern part of this area

Normal Weather PatternsNormal Weather Patterns

Semiarid ProvinceSemiarid Province• 300-500 mile wide area west of subhumid 300-500 mile wide area west of subhumid

province from Canada to Mexicoprovince from Canada to Mexico• Precipitation ranges from 12 to 25 inchesPrecipitation ranges from 12 to 25 inches• Warm, dry air masses common in winterWarm, dry air masses common in winter• Hail frequent in spring and early summerHail frequent in spring and early summer• The Great Valley of California is geographically The Great Valley of California is geographically

separated from rest of provinceseparated from rest of province

Normal Weather PatternsNormal Weather Patterns

Arid ProvinceArid Province• Includes parts of California, Texas, Arizona, Includes parts of California, Texas, Arizona,

New Mexico, Nevada and UtahNew Mexico, Nevada and Utah• Less than 10 inches of rain annuallyLess than 10 inches of rain annually• Hot and dry summers, winters above freezingHot and dry summers, winters above freezing• Clear dry air and plenty of sunshineClear dry air and plenty of sunshine

Normal Weather PatternsNormal Weather Patterns

HawaiiHawaii• Two major factors determine weatherTwo major factors determine weather

Dramatic heights and contours of land areasDramatic heights and contours of land areas Prevailing northeast trade windsPrevailing northeast trade winds

• Pleasant temperaturesPleasant temperatures• Little distinctions between summer and winterLittle distinctions between summer and winter

Normal Weather PatternsNormal Weather Patterns

AlaskaAlaska• Has several different kinds of weatherHas several different kinds of weather• No great extremes in southern part of stateNo great extremes in southern part of state• Arctic slope lies in northern part of stateArctic slope lies in northern part of state• Broad valley and low mountain rangesBroad valley and low mountain ranges

Continental weatherContinental weather Temperatures from -70Temperatures from -70o o F in winter to 90F in winter to 90o o F in summerF in summer

Next….Next….

Done – Done – weather elementsweather elements

Next – aviation weatherNext – aviation weather

Chapter 2, Lesson 2 Courtesy of NOAA/National Weather Service