Lesson 2-2 Weather Elements Part 2 of 2

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Lesson 2-2Weather ElementsPart 2 of 2
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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

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Current Weather Map
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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

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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

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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

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Key Factors in Wind and Atmospheric Motion

• Suns heat is main driver causing air to warm,
  become less dense and lift upwards
• Other atmospheric factors
• Air pressure gradients
• Temp changes of terrain
• Earths rotation about axis
• Coriolis Effect
• The result is wind currents that can and do
  change weather

Reproduced from NASA
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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

Reproduced from US Department of
Transportation/Federal Aviation Administration
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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
• wind patterns can take
• advantage of tailwinds

Courtesy of NASA
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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

Courtesy of NASA
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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

Courtesy of NASA
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Courtesy of NASA
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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

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Local and Surface Air Movement

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

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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

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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

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Terrain and Mountains

• 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
• 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 youll fly above the
  strong dangerous descending air

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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

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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?

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Climatic Provinces
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Normal Weather Patterns

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

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Normal Weather Patterns

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

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Normal Weather Patterns

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

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Normal Weather Patterns

• Semiarid Province
• 300-500 mile wide area west of subhumid province
  from Canada to Mexico
• Precipitation ranges from 12 to 25 inches
• Warm, dry air masses common in winter
• Hail frequent in spring and early summer
• The Great Valley of California is geographically
  separated from rest of province

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Normal Weather Patterns

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

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Normal Weather Patterns

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

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Normal Weather Patterns

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

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Next.

• Done weather elements
• Next aviation weather

Courtesy of NOAA/National Weather Service