1. Monitoring the Weather
Air Pressure: the highs and lows
Fronts: cold and warm
Weather Symbols
Clouds
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2. highs and lows
highs and lows
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3. Hand twist H L highs and lows
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4. “Rules” for Highs and Lows
High and low refer to air pressure
High pressure area is relatively high compared to surrounding air
Low pressure area is relatively low compared to surrounding air
Highs
Fair weather
Clockwise rotation of sinking air (in Northern Hemisphere)
Generally track toward the east and southeast
Lows
Stormy weather
Counterclockwise rotation of rising air (in Northern Hemisphere)
Generally track toward the east and northeast
Lows tracking across the northern U.S. or southern Canada produce less moisture than lows tracking across the southern U.S.
Weather to the west and north – usually cold
Weather to the south and east – usually warm
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5. highs and lows
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7. Weather Systems & Weather Maps
A. clockwise and outward flow from a high-pressure system.
B. counterclockwise and inward into a low-pressure system.
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8. Weather Symbols
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12. Pressure Systems 2 Types
High Pressure
Systems or
“Anticyclones”
Low Pressure
Systems or
“Cyclones”
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More of this next week…..

13. Weather Systems & Weather Maps
Air Masses
Huge volume of air covering hundreds of thousands of square kilometers
Horizontally relatively uniform in characteristics
Temperature
Humidity
Gathers characteristics from its source region
Cold, dry air masses form at higher latitudes over continents
Cold, humid air masses form at higher latitudes over maritime surfaces
Warm, dry air masses form over continents in subtropical regions
Warm, humid air masses form near the equator or in the subtropics over maritime surfaces
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14. Weather Systems & Weather Maps
Air Masses
Polar air masses are colder in winter, milder in summer
Tropical air masses have less seasonal variation, due to nearly uniform sunlight duration and intensity
Air masses modify as they move away from source region
Taking on the characteristics of the area passing over
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15. Fronts
Warm Front
Cold Front
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16. Weather Systems & Weather Maps
Fronts are 3-dimensional
Where the front intersects the Earth surface is shown with the front symbol on the map.
Warm front clouds and precipitation occur over a wide band
May occur hours or longer
Usually light precipitation
Cold front clouds and precipitation occur over a narrow band,
May occur over minutes to hours
May be very heavy precipitation
Wind directions are different on the two sides of a front
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17. Weather Systems & Weather Maps
Some fronts have no clouds or precipitation
Passage indicated by wind shift, temperature/humidity changes
Fronts anchored to lows on a weather map
Counterclockwise flow brings contrasting air masses together to form fronts
Thunderstorms/severe weather often occur in the warm, humid air mass located between the cold and warm fronts
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18. Weather Systems & Weather Maps
In coastal areas
Lake/sea breezes may lower summer temperatures
May push km (6 -30 miles) inland from the coast/shore
Heavy lake-effect snow on Great Lakes or Great Salt Lake
Late fall and winter
Downwind (eastern and southern shores)
Central US
Most common location of tornadoes in the spring
Thunderstorms
Common in FL, western High Plains and eastern slopes of the Rockies
Rare along Pacific Coast and in HI
Tropical storms and hurricanes impact Atlantic and Gulf coasts
Mostly August through October
Rare on West Coast
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19. Describing the State of the Atmosphere
Maximum Temperature
Usually occurs in early to mid-afternoon
Minimum temperature
Usually occurs around sunrise
Dewpoint (frost point)
Temperature when air is cooled, at constant pressure, so it is saturated with water vapor; dew (frost) forms
Relative humidity
Percentage/ratio of actual water vapor concentration of air vs water vapor concentration if air was saturated
Relative humidity changes through the day as temperature varies
Generally highest around sunrise and lowest when warmest
Precipitation amounts
General rule: 10 in. of snow = 1 in. of precipitation
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