Air Masses and FrontsAir Masses and Fronts

CHAPTER 17-1CHAPTER 17-1

FRONTSFRONTS

A A FRONTFRONT is the boundary between two is the boundary between two different air massesdifferent air masses• Storms and changeable weather are Storms and changeable weather are

commoncommon• Differences in air pressure, temperature Differences in air pressure, temperature

and humidity are common with frontsand humidity are common with fronts• Four types of fronts are:Four types of fronts are:

•Cold•Warm

•Stationary•Occluded

COLD FRONTCOLD FRONT

A cold air mass replaces a warm air A cold air mass replaces a warm air massmass• Showers and Thunderstorms are Showers and Thunderstorms are

commoncommon• Cooler and drier air follows the frontCooler and drier air follows the front

WARM FRONTWARM FRONT

A warm air mass replaces a cold air A warm air mass replaces a cold air massmass• Steady precipitation for several hours or Steady precipitation for several hours or

daysdays• Weather tends to be warm and humidWeather tends to be warm and humid

STATIONARY FRONTSTATIONARY FRONT

A front that does not move or barely A front that does not move or barely movesmoves• Two air masses in a “standoff” with neither one Two air masses in a “standoff” with neither one

movingmoving• Periods of rain, drizzle and fog are commonPeriods of rain, drizzle and fog are common• Several days of clouds and precipitation are Several days of clouds and precipitation are

likelylikely• Temperatures remain constant and winds are Temperatures remain constant and winds are

gentlegentle

OCCLUDED FRONTOCCLUDED FRONT

Occurs when a warm air mass is Occurs when a warm air mass is caught between two cooler air caught between two cooler air massesmasses• Warm air is “cut off” from the groundWarm air is “cut off” from the ground• Periods of rain or snow are commonPeriods of rain or snow are common

warm

warm

FRONT SYMBOLSFRONT SYMBOLS

WEATHER MAP SYMBOLSWEATHER MAP SYMBOLS

ANTICYCLONESANTICYCLONES

High pressure centers of dry airHigh pressure centers of dry air• Usually called “HIGHS” Usually called “HIGHS” • Appears as an “H” on a weather mapAppears as an “H” on a weather map• Winds spin clockwise in N. HemisphereWinds spin clockwise in N. Hemisphere• Areas of sinking air in the centerAreas of sinking air in the center• Dry, clear weather is likelyDry, clear weather is likely

ANTICYCLONESANTICYCLONES

HIGH PRESSURE AREASHIGH PRESSURE AREAS

CYCLONESCYCLONES

Low pressure areasLow pressure areas• Usually called “LOWS”Usually called “LOWS”• Appears as an “L” on a weather mapAppears as an “L” on a weather map• Winds spin counterclockwise in N. HemisphereWinds spin counterclockwise in N. Hemisphere• Areas of warm, rising air in the centerAreas of warm, rising air in the center• Clouds and precipitation are likelyClouds and precipitation are likely

CYCLONESCYCLONES

LOW PRESSURE AREASLOW PRESSURE AREAS

REVIEW # 1REVIEW # 1

1) The air mass that forms over central Canada 1) The air mass that forms over central Canada is called_________is called_________

2) The front that brings rising temperatures and 2) The front that brings rising temperatures and steady rain is the ______frontsteady rain is the ______front

3) The air mass that is warm and humid is 3) The air mass that is warm and humid is called__________called__________ 4) The front that brings showers and cooler 4) The front that brings showers and cooler temperatures is called a ______fronttemperatures is called a ______front 5) The front that doesn’t move is called_______5) The front that doesn’t move is called_______ 6) An air mass that is warm and dry is called ? 6) An air mass that is warm and dry is called ? 7) Clear and dry weather is common to a _____7) Clear and dry weather is common to a _____

REVIEW # 2REVIEW # 2

1)1) What are the symbols used on a weather What are the symbols used on a weather map for the four types of fronts?map for the four types of fronts?

2)2) In what direction do LOWS spin?In what direction do LOWS spin?3)3) How many air masses are found in an How many air masses are found in an

OCCLUDED FRONT?OCCLUDED FRONT?4)4) What are the weather conditions does a What are the weather conditions does a

CYCLONE bring?CYCLONE bring?5)5) Air masses move across the U. S. from Air masses move across the U. S. from

________ to __________.________ to __________.6)6) What kind of air mass is outside today?What kind of air mass is outside today?

REVIEW # 3REVIEW # 3

1) Maritime means ________________.1) Maritime means ________________. 2) Tropical means________________.2) Tropical means________________. 3) Continental means_______________.3) Continental means_______________. 4) Polar means________________.4) Polar means________________. 5) Several days of clouds and precipitation 5) Several days of clouds and precipitation

would be likely with a _________ front.would be likely with a _________ front. 6) Which air mass forms over the Gulf of 6) Which air mass forms over the Gulf of

Mexico? ______Mexico? ______ 7) An “L” on a weather map is called ___.7) An “L” on a weather map is called ___.

REVIEW ANTICYCLONEREVIEW ANTICYCLONE

1) What direction does it spin in the northern1) What direction does it spin in the northern

hemisphere? ______________hemisphere? ______________

2) What kind of weather does it have? ________2) What kind of weather does it have? ________

___________.___________.

3) What is another name for this feature?_______3) What is another name for this feature?_______

_____________._____________.

REVIEW CYCLONEREVIEW CYCLONE

1) What direction does it spin in the northern1) What direction does it spin in the northern

hemisphere? ___________________.hemisphere? ___________________.

2) What kind of weather does it have?_________2) What kind of weather does it have?_________

______________.______________.

3) What is another name for this feature?_______3) What is another name for this feature?_______

__________________.__________________.