1. Weather Water in the Atmosphere Water Cycle—know it Absolute Humidity
Measure of the amount of water vapor in the air (mL)
Amount of humidity depends on temp
Warm air can hold more water than cold air
Relative Humidity- % of water vapor in air compared to how much (the max)
it can hold at a certain temp
How “full” the air is with water vapor
This % changes when
Water vapor enters the air
Temperature changes
Saturated- when the air has the most moisture it can
possibly hold at the temperature on that day
Dewpoint- the temperature at which air is full saturated and
condensation occurs
This occurs when relative humidity is 100%
When the dewpoint is LOWER than air temp., condensation WILL NOT happen
When the dewpoint is EQUAL to the air temp., condensation happens

2. Weather
Relative Humidity and Dew Point are measured using a sling psychrometer
Two thermometers
Wet bulb-covered in moist cloth
Dry bulb
Psychrometer is “slung”, wet bulb temperature drops due to cooling caused by evaporation
High relative humidity = slow evaporation, little change in wet bulb temp
Low relative humidity = fast evaporation, large change in wet bulb temp
After data is gathered, use dry bulb temp and wet bulb depression, and tables to find RH and DP

3. Weather
How to use sling psychrometer

4. Weather Clouds Dew point- temperature at which condensation begins
Clouds form when water vapor in air condenses to form liquid water or ice crystals
Dew point- temperature at which condensation begins
Two conditions required for condensation to occur and clouds to form
Cooling of the air- below freezing = ice , above freezing = water
Presence of particles- water needs a surface on to condense, such as salt, dust or smoke, grass, window panes
Dew – liq. Water that condenses from air onto cooler surface
Frost – ice deposited on a surface that is below freezing
Types of clouds- based on shape and altitude
Cirrus – wispy, feathery, high altitudes, made of ice crystals, indicate fair weather
Cumulus – fluffy, round, low level, short = fair weather, towering = storm
Cirrocumulus-cotton ball, storm on its way
Stratus – flat layers, low level, cover all or most of the sky, dull, grey color
Alto- means “high” but are medium level
Nimbo – produces rain or snow
FOG- clouds that form near the ground, caused by ground cooling at night after a humid day

5. Weather

6. Weather Precipitation
Precipitation- any form of water that falls from clouds and reaches Earth’s surface; ex. Rain, sleet, freezing rain, snow, and hail
Warm climate- precip. almost always = rain
Colder climate – precip. might be snow or ice
Rain- drops of water, most common type of
precipitation, 0.5mm
Drizzle – smaller drops
Mist- smaller than drizzle
Rain Gauge- open ended tube that collects rain, ruler or
gauge read to determine how much rain has fallen
Freezing Rain- rain drops that fall as liquid but freeze
upon contact with a surface,
air temp = above 0oC, ground temp = below ooC
Snow – water vapor in a cloud is directly converted to ice
air temp = below 0oC, ground temp = below ooC
Hail – round pellet of ice larger than 5mm, layers of ice inside due to
being carried up and down with in cumulonimbus clouds
air temp = at or above 0oC, ground temp = above, at or below ooC
Sleet – start as falling rain drops but freeze on way down,
smaller than 5mm
air temp = at or below 0oC, ground temp = above, at or below ooC

7. Weather
Air Masses
Air mass- huge body of air in the lower atmosphere that has similar temperature, humidity and air pressure at any given temperature
Four major types
Maritime tropical
Continental tropical
Maritime polar
Continental polar
Polar = north of 500N
or south of 50oS

8. Weather Air masses moved by:
Prevailing westerlies-push air masses from west to east
Jetstream-found within prevailing westerlies, bands of high speed winds ~10 km above earth’s surface
Fronts:
Fronts- the boundary between where air masses meet
Storms and changeable weather often develop along fronts

9. Weather Types of Fronts: Cold Fronts- Warm fronts Arrive quickly
Abrupt weather changes
Forms when a faster moving cold
air mass pushes under a slower
moving warm air mass, forcing the
warm air to rise
Denser cold air slides under the lighter warm air, warm air pushed upward
Thunderheads can form as the moisture in the warm air mass rises, cools, and condenses. As the front moves through, cool, fair weather is likely to follow
Warm fronts
Arrive slowly
Forms when a moist, fast moving,
warm air mass slides up and over a
slower cold air mass
As the warm air mass rises, it condenses
into a broad area of clouds. If the air
mass contains moisture, it can bring gentle rain or light snow, followed by warmer, more humid, milder weather

10. Weather Occluded fronts Stationary Warm air mass caught
between two cooler air
masses
Denser cool air masses move
under the less dense arm air
mass and pushes the warm
air upward
Warm air mass is cut off, may cool causing water to condense producing clouds and maybe rain
Temperature near ground becomes cooler as warm air mass is occluded or “cut off”
Can bring strong winds and heavy precipitation
Stationary
Warm and cold air mass meet
Neither moves
Water vapor in warm air mass condenses
into rain, snow, fog or clouds
If front stalls, there may be many days of
clouds and precipitation

11. Weather Cyclones and Anticyclones
Circled L on weather map stands for “low” & indicates area of low pressure
Cyclone-Winds spiral in toward center, counterclockwise (when viewed from above)
Warm air at center rises, air pressure decreases
Air cools, condenses forming clouds and precipitation.
Circled H on weather map stands for “high” & indicates area of high pressure
Anticyclone- winds spiral outward from center, clockwise (when viewed from above)
Cool air moves downward from higher in troposphere, cool air warms so relative humidity drops
Dry clear weather

12. Weather Storms Storm- violent disturbance in the atmosphere
Sudden changes in pressure yielding rapid air movements
Winter Storms
All year round most precipitation starts in clouds as snow, if air is colder than 0oC all the way to the ground, precip will fall as snow
Lake effect snow-
1.) land near lakes cools faster than water
2.) cold dry air mass moves across lake picking up water vapor and heat
3.) air mass reaches other side of lake, rises and cools forming clouds and precip—snow
Buffalo and Rochester, NY
Effect of snow
Blockage of roads
People trapped in homes
Damage of crops
Burst pipes
Safety
Find shelter from wind
Cover exposed parts of body
Keep car engine running only if
exhaust pip is clear

13. Weather Storms Thunderstorms
Small storm, precipitation, thunder and lightning
Can form over land or water
Thunderhead-cumulonimbus cloud that creates
thunderstorm
Form on hot humid afternoons and evenings
or when warm air is forced up during cold front
Heavy rain and sometimes hail can be expected
Within thunderhead, there are strong updrafts
and downdrafts (strong upward and downward winds)
Most occur during spring and summer in southern states or on
western plains
Lightning-sudden spark or electrical discharge due to the
positive and negative electrical charges built up between different
parts of clouds or between clouds and the ground
Thunder- caused by the super heating of the air by lightning
Air expands explosively, thunder = sound of explosion, you see lightning
before you hear thunder because speed of light is much greater than the
speed of sound
Damage:
Heavy rains cause flooding, lightning can cause fires or damage trees
Safety
Avoid places where lightning may strike and objects that conduct electricity
Go inside, if stuck outside, find a low area away from trees, fences and poles, stay away from water
Avoid touching telephones, electrical appliances or plumbing fixtures

14. Weather Hurricanes Starts as Tropical storm (disturbance)
Lasts longer than other storms (a week or more)
Powered by warm ocean water
600 km across
Winds 119km/h or more
Formation
Begins as a low pressure area over warm water
Warm, humid air rises and forms clouds
Winds spiral inward toward the area of low pressure
Winds strongest in narrow band around the storms center
Eyewall= ring of clouds around center which encloses the quiet eye
Winds get stronger as eye approaches, weather changes quickly when eye arrives to calm conditions, after eye passes storm resumes but wind blows opposite direction
Damage
High waves
Storm surge-”dome” of water that sweeps across the coast where hurricane lands-washes away beaches, destroying buildings, eroding land
Safety
Watch = hurricane conditions possible w/in 36 hours vs. warning hurricane conditions expected w/in 24 hours
Evacuate- move away temporarily
If you hear a hurricane warning and are told to evacuate, leave the area immediately

15. Weather
Tornadoes
Rapidly whirling, funnel-shaped cloud that reaches down from a thunderstorm to touch Earth’s surface
Water spout- tornado that occurs over a lake or ocean
Few hundred meters across
Wind speeds as high as 500km/h
Develop in thick cumulonimbus clouds, same as thunderstorms
Often occur in spring and early summer when ground is warm
Great Plain where most tornadoes occur
Warm humid air mass moves north from Gulf of Mexico into great plains and a cold dry air mass moves south from Canada-cold air mass causes warm air to rise rapidly
Squall line- line of thunderstorms, can produce 10 or more tornadoes
Damage
Strong winds cause damage and flying debris
Fujita scale- ranking of tornado based on damage
they cause
Safety
Move to basement or storm shelter
Stay away from windows
Watch = possible vs. warning =tornado has been
seen

16. Weather Meteorologist- scientists who study and predict weather Maps
Make observations and collect/analyze data using maps, charts, computers and other tech to prepare weather reports
Tech and tools = balloons, satellites, radar, surface instruments
Maps
Isobars-lines joining places on the map
that have the same air pressure
Isotherms- line joining places that
have the same temperature
**these work the same way that
contour lines worked on the topographic
map
Maps in newspapers are simplified versions of maps produced by National Weather Service
Standard symbols on weather maps show
fronts, areas of high/low pressure, types of
precipitation and temperature (oF)
Limits of Forecasts
Butterfly effect- a small change in the weather today can mean a larger change in the weather a week later
Name based on scientist suggestion that even the flapping of a butterfly’s wings causes a tiny disturbance in the atmosphere which may lead to a larger disturbance (storm)

17. Weather Newspaper Weather Map
The symbols on this map show fronts, high- and low-pressure areas, the high and low temperature readings for different cities, and precipitation. The color bands indicate different temperature ranges.

18. Weather Station models-
The tables below show what various weather symbols represent.

19. Weather