1. AMS Weather Studies Introduction to Atmospheric Science, 4th Edition
Chapter 1
Monitoring the Weather
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2. Case-in-Point
There have been monumental advances in monitoring of weather
Case-in-point – the blizzard of 1888
A similar storm in December 2000
Still lacked data on sea surface temperatures – overestimated snowfall
Today, though not exact, we are much better at monitoring and forecasting weather
Satellites
Radiosondes
Surface observations
The Blizzard of 1888
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3. Driving Question
What are some basic characteristics of the atmosphere and weather?
This chapter will introduce and describe some of the tools and basic understandings that will guide your investigation of the atmosphere
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4. Weather and Climate
Weather is the state of the atmosphere at some place and time
Described with quantitative variables
Temperature, humidity, cloudiness, precipitation, wind speed, wind direction
Meteorology is the study of the atmosphere and the processes that cause weather
Climate is weather conditions at some locality averaged over a specified time period
Climate is an average of the weather, figured over the last 30-years and updated every decade
A locale’s climate also includes weather extremes
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5. Sources of Weather Information
Television
The Weather Channel and local newscasts
Radio
NOAA Weather Radio
Continuous broadcasts repeated every minutes
Interrupted with warnings
and watches
The Internet
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6. Weather Systems and Weather Maps
Weather info received via TV,
radio, or the Internet includes
Weather maps
National
Regional
Satellite/radar images
Data on current/past
conditions
Weather forecasts
Short-term
24 – 48 hours
Long-term
Up to 7 days or longer
Automated Surface Observing System (ASOS)
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7. Pressure Systems 2 Types
High Pressure
Systems, or
“Anticyclones”
Low Pressure
“Cyclones”
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8. Pressure Systems, Continued
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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9. Pressure Systems, Continued High and Low Pressure Centers
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Arrows indicate surface horizontal winds

10. Air Masses Huge volume of air covering 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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11. Fronts
Warm Front
Cold Front
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© American Meteorological Society

12. Characteristics of Air Masses & Fronts
Polar air masses are colder in winter, and 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
Starts taking on the characteristics of the area it is passing over
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, and may occur over 1 to 2 days
Usually light precipitation
Cold front clouds and precipitation occur over a narrow band, and may occur over minutes to hours
May be very heavy precipitation
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13. Characteristics of Air Masses & Fronts, Continued
Wind directions are different on the two sides of a front
Some fronts have no clouds or precipitation.
Passage indicated by wind shift, and temperature/humidity changes
In summer, temperature can be nearly the same on both sides of a cold front
Difference will be humidity
Fronts are 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 front
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14. Other Weather Characteristics
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 U.S.
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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15. Describing the State of the Atmosphere What do Forecasters Tell Us?
Maximum Temperature
Usually occurs in early to mid-afternoon
Minimum temperature
Usually occurs around sunrise
Dewpoint (frost point)
The temperature at which air must be cooled at constant pressure to become saturated with water vapor and for dew (or frost) to form
Relative humidity
A percentage; the ratio of the actual concentration of the water vapor component of air compared to the concentration the air would have if saturated with water vapor
Relative humidity will change throughout the day as the temperature varies
Generally highest around sunrise and lowest when warmest
Precipitation amounts
General rule – 10” of snow = 1” of precipitation
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16. Describing the State of the Atmosphere What do Forecasters Tell Us
Describing the State of the Atmosphere What do Forecasters Tell Us? (Continued)
Air Pressure
And its tendency (rising or falling)
Falling may indicate approaching
cold front
Wind direction and speed
Wind direction is the direction wind
is blowing from
Example; a west wind is blowing from the west, toward the east
Sky cover
Fraction of the sky covered in clouds
NWS Weather watch – issued when hazardous weather is considered possible
NWS Weather warning – issued when hazardous weather is imminent or actually taking place
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17. Weather Satellite Imagery
Two major types of satellite orbits
Geostationary
High orbits
36,000 km (22,300 miles) high
Orbits planet at same rate as Earth’s rotation and in same eastward direction
Currently 2 of these provide a complete view of much of N. America and adjacent oceans to latitudes of about 60 degrees
Positioned over equator at 750 W longitude, 1350 W longitude
Polar orbiting
Low orbits
km (~ miles) high
Provides overlapping north-south strips of images
Passes over the same point twice every 24 hours
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18. Orbit of a Geostationary Satellite
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19. Orbit of a Polar-Orbiting Satellite
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20. Weather Satellite Imagery
Visible
Black and white photograph of the planet
Only available during daylight hours
Highly reflective surfaces appear bright white and less reflective surfaces are darker
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21. Weather Satellite Imagery
Infrared
Available anytime, not just during daylight
Provides temperature comparison of features within image
Whiter = colder
Higher cloud tops appear whiter, because they are colder
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22. Weather Satellite Imagery
Water vapor imagery
Enables tracking of plumes of moisture
Shades of white = increasing moisture
Upper-level clouds appear milky to bright white
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23. Weather Radar Complements satellite surveillance
Doppler radar detects movement
Excellent tool to forecast tornadoes
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24. Combination of Images
Composite of IR and Radar
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25. Sky Watching
You can determine much about the weather by watching the sky
Clouds are aggregates of tiny water droplets, ice crystals, or some combination of both
A cloud in contact with the ground is fog
Cloud forms:
Stratiform clouds are sheet-like clouds formed in horizontal layers
Form where air ascends gradually over a broad region
Cumuliform clouds are puffy, like cotton balls
More vigorous ascent of air over a smaller area
Under the right conditions can build vertically into a cumulonimbus (thunderstorm) cloud
The appearance of high, wispy, feather-like clouds (composed of ice) in the western sky is often the first sign of an approaching warm front
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26. Cloud Forms
These high thin cirrus clouds appear fibrous because they are composed of mostly tiny ice crystals
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27. Cloud Forms
These relatively low clouds are composed of tiny water droplets and have more sharply defined edges than ice-crystal clouds
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28. Fog, stratus clouds in contact with the ground, reduces visibility
Cloud Forms
Fog, stratus clouds in contact with the ground, reduces visibility
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29. Cloud Forms
Fair weather cumulus clouds are most common during the warmest time of day and then vaporize after sunset
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30. Cloud Forms Clouds of vertical development
Merging and vertically-growing cumulus clouds
Can become Cumulonimbus clouds
Nimbo, nimbus prefix or suffix = rain producing
These clouds always produce lightning and sometimes heavy rain, hail, or strong and gusty surface winds
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31. Cloud Forms
Clouds may move in different directions at different altitudes
Indicates horizontal wind shifts with altitude
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