Weather-- deals with changes in the atmosphere

Weather is caused by unequal heat distribution in our atmosphere.

Atmospheric Composition]

--  The atmosphere is composed of a mixture of gases containing minute quantities of solid and liquid
    particles.

[Gas Composition by Volume]

78% nitrogen
21% oxygen
1%  other gases and substances

This composition remains relatively stable.

Nearly all the atmosphere is confined to a thin shell surrounding the Earth.    The atmosphere is stratified into layers, each having distinct properties.   Nearly all weather occurs in the lowest layer of the atmosphere (called the troposphere).

[Some Relationships or Tendencies in the Troposphere]

1.  As altitude increases, air pressure tends to decrease.

2.  As altitude increases, air temperature tends to decrease.

3.  Cooler air is capable of holding less moisture. (hence there is usually more precipitation in the higher elevations)

climate -- that characteristic "average weather" that prevails from season to season and year to year

We can use models to help us understand weather.

What chiefly determines weather conditions at a location?

1.  Temperature
2.  Humidity (percentage of moisture in the air)
3.  Air pressure

Air masses -- air residing over a large section of the earth's surface which takes on the
                      temperature and moisture characteristics of that surface

Air masses change local weather conditions as they move over the earth's surface.

How are air masses identified?

1.  By their source region
2.  By their temperatures relative to the surface which they move over.
3.  By their moisture characteristics.

Air mass movement is determined by the prevailing winds and upper air currents.
 

Major Air Masses Influencing the Continental U.S. 1.  Polar maritime -- cold, wet 2.  Polar continental -- cold, dry 3.  Tropical maritime -- warm, wet 4.  Tropical continental -- warm, dry

After moving from their source regions, air masses tend to move from west to east across the 
United States.

Air pressure -- the pressure of the air on the earth's surface

Air pressure tends to decrease as elevation increases.

Air temperature tends to decrease as elevation increases.
 
 
 

Highs -- high pressure --  tend to be fair weather systems. Winds around a high tend to blow in a clockwisefashion.  (anticyclonic) Winds tend to spiral outward from the center of a  high pressure area. Lows -- major storm areas of our latitudes (produce cloudy and sometimes stormy weather) Low pressure areas form along fronts. Lows at our latitude are sometimes called wave cyclones. Low pressure areas have cyclonic circulation in a counterclockwise direction and winds  spiral inward toward the center.

fronts -- boundaries between air masses where they come into contact

Because fronts are the battle grounds between contrasting air masses, abrupt weather changes
tend to occur across fronts.

Precipitation tends to occur at fronts as warm, moist air will condense and drop moisture when it hits
colder air.

Air masses tend not to mix together because of their density differences.  Cold air is denser than warm air.
 

cold front -- the boundary where cold air moves into and replaces warm air

 

warm front -- the boundary where warm air slowly replaces                       cold air

**  Changes in air pressure are important indicators of passing high and low pressure areas.

Surface weather maps use observations taken simultaneously at many locations.

The combined use of surface weather maps, satellite photographs, and doppler radar have led to increased
understanding of weather and improved weather forecasting.

**  Wind is a vector quantity which is measured using  terms of speed and the direction FROM which it
    is blowing.

All weather forecasts are described in terms of probabilities because of the complex
interrelationships of the elements making up weather.

Interpreting Weather Maps

**  The following map appeared at the weather channel website predicting weather
for August 1, 2001 AM.
 

Key to front symbols (bumps on front indicate its direction of motion) 1 = cold front 2 = warm front 3 = stationary front 4 = occluded front 5 = trough 6 = squall line 7 = dry line (we are only worried about knowing symbols for the 1st three fronts) H = high pressure L = low pressure

Based on the map above, what kind of weather would you expect for that time here?

Answer:   Note:  We are under the influence of a high on that Wednesday!

.TONIGHT...CLEAR.  AREAS OF DENSE VALLEY FOG FORMING AFTER MIDNIGHT.
LOW 50 TO 55. CALM WIND.
.WEDNESDAY...MOSTLY SUNNY WITH AREAS OF DENSE VALLEY FOG EARLY IN
THE MORNING. HIGH IN THE MID 80S. LIGHT AND VARIABLE WIND.
.WEDNESDAY NIGHT...MOSTLY CLEAR.  AREAS OF DENSE VALLEY FOG FORMING
AFTER MIDNIGHT. LOW 55 TO 60.
.THURSDAY...AREAS OF DENSE VALLEY FOG EARLY...THEN PARTLY SUNNY WITH
A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON. BREEZY. HIGH
IN THE UPPER 80S. CHANCE OF RAIN 30 PERCENT.

Many weather elements vary somewhat periodically with the time of day or the season.

exs.  (1.) It tends to be cooler at night than during the day.
        (2.) It tends to be cooler in Winter than in Summer.

**  Weather conditions show a tendency to remain similar from day to day.  Abrupt changes are the
exception rather than the rule.  Highs are large and tend to move and change slowly.

Highs and lows tend to move from west to east in the U.S.

Local atmospheric conditions are determined by prevailing weather systems.

[Factors Modifying Local Weather

1.  Daily and seasonal factors.
2.  Topographical features

    (a.) elevation -- increases in elevation tend to produce more cooler, wetter weather
    (b.) nearness to a large body of water --  increases precipitation and moderates temperature

3.  Human Activity -- we are adding gases like carbon dioxide to the atmosphere which is trapping
                                 the earth's heat and making the climate slowly get warmer

**  Sometimes it is possible to detect relationships between two or more weather elements.

**  Local weather measurements and their changes can be used to identify broad-scale weather
    systems and to track their movements.  These large scale movements and features can be
    plotted on a weather map.
 
 

Atmopsheric Effects and Human Activities

1.   Atmospheric oxygen is constantly replenished by plants in the process of photosynthesis.

2.   Dust from volcanic eruptions may pollute and cool the atmosphere by preventing incoming sunlight
      from entering/

3.  Greenhouse Effect -- Carbon dioxide, with methane and water vapor to a lesser extent,
                                         although found in small amounts in the atmosphere compared
                                         with nitrogen and oxygen, appears to have
                                         the effect of increasing atmospheric temperatures.

-- The increasing amounts of carbon dioxide in the atmosphere appears to be causing a global warming
 of the Earth's atmosphere.   This carbon dioxide is coming from increased burning of fossil fuels such
 as gasoline, coal, and oil.

-- This may be bad because it is changing sea levels and climate/rainfall patterns.
 

4.   Acid Rain

-- sulfur dioxide (also nitrogen oxides) from coal burning sources + rain = ACID RAIN
-- most of the acid rain damaging New York State comes from the midwest U.S.
-- Acid rain kills aquatic life, crumbles buildings, and has many other effects, etc.
 

5.  Ozone Layer Destruction in the Stratosphere

ozone -- is triatomic oxygen
 -- usually found at highest concentration at 20 km. altitude
 -- brings about a reduction of ultraviolet  rays associated with skin cancer
-- our use of chlorofluorocarbons (CFC's) is destroying the ozone layer

**  Lower level ozone from automobile emissions is a major pollutant however!
 

HAZARDOUS WEATHER

--  Weather, on certain occasions, can threaten life and property.
Steps can be taken to lessen the effects of hazardous weather.

--  The National Weather Service has developed a system of warnings to inform
the public of weather hazards.

weather watch -- the hazardous weather conditions described may occur

weather warning -- the hazardous conditions are either imminent or occurring

Some Types of Hazardous Weather Conditions

I.  Thunderstorms

--  May form along fronts, near mountain barriers, and within air masses when heating forces warm,
    humid air upward.

--  While thunderstorms are helpful to man because of the precipitation they bring, their frequency
    and potential for violence make them one of nature's great destroyers.

--  The major dangers from a thunderstorm are those of lightning and flash flooding.

[Some Lightning Safety Rules]

1.  Stay indoors and away from open doors and windows, stoves, metal pipes,
     sinks, plug-in electrical appliances, and telephones.

2.  Get inside an enclosed all metal vehicle.

3.  Get out of the water, off beaches, and off small boats.

**  Heavy thunderstorm precipitation can bring on sudden flooding.

[Some Flash Flood Safety Rules]

1.  Act quickly and seek higher ground.

2.  Get out of areas subject to flooding.

3.  Avoid areas already flooded.

4.  Do not attempt to cross a flowing stream by foot
    or vehicle.

Strong gusts (shear winds) occur directly beneath mature thunderstorm cells.  These straight line
winds can cause damage.

The rapid expansion of air due to intense heating during a lightning discharge produces thunder.

Hail can occur during severe thunderstorms.  It almost always accompanies tornadoes.

II.  Tornadoes -- violently rotating local winds associated with severe thunderstorms

Tornadoes normally strike suddenly, do not last
long, and can cause great death and destruction.

[Some Tornado Facts]

1.  Tornadoes are often observed as funnel shaped appendages to a thunderstorm cloud.

2.  They have occurred in every state, at all times of the year, but most often occur in the Midwest
    and South, in the Spring of the year, in the warm part of the day between noon and midnight.

3.  An appoaching tornado often has a roar like a freight train.

4.  Tornadoes do their destructive work primarily through their strong winds and through the
    impact of wind-borne missiles.

As the general conditions favorable for tornado formation are known, it is possible to forecast
their possible occurence.  The National Weather Service forecasts watches and warnings.

**  It is important to maintain a tornado watch on your own during any period of severe
    thunderstorm activity.

[Some Tornado Safety Rules]

1.  Your immediate action can save your life.

2.  Stay away from windows, doors, and outside walls.  Protect your head.

3.  Go to the cellar (basement) or to an interior part of the lowest building level -- closets,
    bathrooms, or interior halls.  Get under something sturdy.

4.  In large buildings, go to pre-designated shelter  areas or in the interior hallways on the lowest floors.

5.  If in a mobile home or vehicles, leave them and go to a substantial shelter.  If none is
    available, lie flat in the nearest ditch or culvert with your hands shielding your head.

III.)  Hurricanes -- gigantic whirling storms with high winds, torrential rains, and related
                             storm surges capable of causing widespread damage and destruction

[Some Facts About Hurricanes]

1.  Hurricanes tend to form over oceanic surfaces during the warmest part of the year.  Atlantic
    hurricanes are most likely to form between August and October.

2.  Mature hurricanes have a calm central region called an eye.  It is in the towering wall
    clouds surrounding the eye where winds and precipitation are greatest.

3.  As hurricanes approach and cross shorelines, they bring ashore mounds of water topped by
    wind-blown waves.  These storm surges are often 50 miles wide near the area where the eye makes
    landfall.  Storm surges can be 10, 15, or more feet above normal sea level.

4.  Most hurricane related deaths are due to storm surge flooding, although high winds and fresh
    water flooding take their toll.

[Hurricane Safety Rules]

1.  Hurricane watches are issued for coastal areas when there is a threat of hurricane conditions
    within 24 to 36 hours.  Hurricane warnings are issued when hurricane conditions are expected in
    24 hours or less.  Actions to protect property and life should begin immediately when a warning
    is issued.

2.  Persons living in low lying coastal areas which could be threatened by the storm surge should
     evacuate the threatened area.

3.  Anyone living in flood prone areas should seek refuge at higher elevations.

4.  People should be prepared for the effects of  high hurricane winds and flying debris.
     Board,  shutter, or tape windows.

5.  Non-perishable food, water, medicines, flashlights, and the like should be acquired and
     safely stored for emergency use.

6.  Stay indoors during the hurricane.

IV.  Winter Storms

Snow, low temperatures, wind, blizzard conditions and freezing rain or drizzle are components of
winter storms.  Singularly or in combination, they can be hazardous.

[Some Winter Storm Safety Rules]

1.  Prepare for winter storms by laying supplies of  food, heating fuel, batteries, medicines, or
    other necessities.

2.  Dress warmly, avoid travel, and do not overextend yourself.  (Heart attacks are a major
    cause of death during and after winter storms.)

3.  Wear multiple layers of protective clothing, scarves, mittens, and hoods.

4.  Avoid travel, but if stranded, stay in your vehicle, keep it ventilated, bundle up, stand
    watches, occasionally change positions, and do not panic.

**  The combined effect of wind as well as temperature affects the rate at which the body
    loses heat.  THe combined effect of temperature and wind is called wind chill.

Blizzard -- a severe storm condition in which low temperatures and strong winds bearing a
                 great amount of snow reduce visibility to the extent that travel is nearly
                 impossible

**  Persons stranded in vehicles during blizzards should not attempt to walk to shelter in open
    areas.

freezing rain -- precipitation that freezes when it hits exposed surfaces

**  Significant ice accumulation can cause slippery roads, down electrical wires, and snap tree
    branches.
**  Travel by foot or vehicle should be avoided  during an ice storm because of slippery surfaces
    and falling wires.

[Key Points]

1.  Heavy snowfalls can happen anytime during New York State's autumns, winters, and springs.
    People should be prepared to spend several days without fresh supplies of food, fuel, and
    medicines.

2.  Areas along the lee (eastward) sides of Lakes Erie and Ontario are subject to "lake-effect"
     snowstorms.  In these "snowbelts" several feet of snow can accumulate within hours with
    visibility near zero.  Residents and travelers  must be prepared for these local, sometimes
    sudden storms.

V.  Windstorms -- winds of at least 40 miles per hour for at least one hour

[Some Windstorm Safety Tips]

1.  Persons along coastal aras should be alert for possible severe shoreline erosion and flooding.

2.  Mobile home dwellers should securely anchor their residences, which are especially
    susceptible to wind damage.

VI.  Heat Waves -- periods of at least a day during the
      summer which are abnormally and uncomfortably hot (and usually humid)

**  Heat waves can result in heat exhaution and death.

**  The systems of the body must work hard to maintain normal body temperature under heat wave
    conditions.

[Some Heat Wave Safety Rules]

1.  Slow down
2.  Dress for summer
3.  Take in fewer calories
4.  Drink plenty of water
5.  Increase salt intake in accordance with personal needs
6.  Spend some time in a cooler environment, such as an air conditioned room, cellar, or cool bath if possible.