Weather

Definition  The result of the atmosphere trying to balance temperature and humidity

The State of the Atmosphere  Air Pressure  Wind  Temperature  Amount of moisture in the air

Water Vapor   Water in air is in the form of a gas called water vapor   Water is also found in the atmosphere as clouds and fog   Estimated total of 14 million tons in the atmosphere

Evaporation   Changing of a liquid to a gas   Most evaporation occurs in oceans   Water also evaporates over lakes, rivers, puddles, and wet soil   Winds carry the water vapor

Transpiration   Water vapor changing back into liquid water droplets   Example: Breathing (seeing your breath)   Plants give off water vapor through leaves

Role of Water Vapor  Humidity: amount of water in the air Is dependent on temperature  Increase in temp results in an increase in humidity  Decrease in temp results in a decrease in humidity  When air is saturated it holds all the water vapor possible at that temperature  Figure 12-7 pg. 280

Water Vapor Continued  Relative Humidity: amount of water vapor air holds compared to what it can hold at a specific temperature.  Capacity is 100%, but usually water vapor may be 50%  Humidity increases as temperature increases  Humidity and comfort- Figure pg. 283

Dew Point   Temperature of air at which condensation takes place   Condensation- process of changing a gas to a liquid   This takes place when saturated air is cooled

Dew Point   Warm air holds more water vapor   Cold air holds less water vapor   Water vapor condenses, changes into liquid water   Ground cools faster, so condensation takes place causing dew

Dew Point

Clouds  Visible formations of small droplets of water or tiny crystals of ice.  Form from condensation in the atmosphere  Shape determined by how it formed

Steps to Cloud Formation 1. Air ascends (goes up) 2. Pressure decreases and temperature increases. 3. Air parcel cools to the dew pt. temperature. 4. Water condenses around small particles of dust, salt, and smoke.

Types of Clouds  Classified:  Height  Form

Height Classification Cirrus - high clouds, generally don’t produce precipitation.Cirrus - high clouds, generally don’t produce precipitation. Alto - middle clouds, grayish clouds, infrequent precipitation.Alto - middle clouds, grayish clouds, infrequent precipitation. Strato - low clouds, uniform layer covering much of the sky.Strato - low clouds, uniform layer covering much of the sky.

Cloud Forms Cumulus - puffy, white, cauliflower- likeCumulus - puffy, white, cauliflower- like Stratus - sheets or layersStratus - sheets or layers Cirrus - high, white, thin, featheryCirrus - high, white, thin, feathery Fair weather, with storm approachingFair weather, with storm approaching

Stratus

Cirrus

Cumulus

Combinations  Cirrostratus - indicates fair weather with rain in the forecast  Altostratus - produces intermittent precipitation.  Cumulus – fair weather  Cumulonimbus - heavy precipitation, lightning, thunder, hail  dark, dense, billowy  looks like huge towers with an anvil shape

Cirrostratus

Altostratus

Cumulus

Cumulonimbus

Precipitation   Conditions in the atmosphere vary from season to season   Precipitation is water that falls to Earth from clouds   May be a liquid or solid

Precipitation  Snow – falls when temperatures are below freezing  Rain – falls when temps are above freezing  Sleet – snow falls through a layer of warm air, melts and refreezes  Hail – freezes in layers around a particle of ice during thunderstorms

Effect of Cloud Cover  Clear skies - more heat reach’s earth’s surface leading to warmer temperatures.  Cloudy skies – sun reflected off clouds so less sun reaches earth’s surface leading to cooler temperatures.

Night Cloud Cover  Clear skies – heat from earth travels freely back to space resulting in cooler temperatures.  Cloudy skies – surface heat is trapped resulting in warmer temperatures.

Air Mass  Large body of air that has the same properties as the surface over which it develops.  Consists of the same temperature and same amount of moisture  Air masses are dependent on where they form

Types of Air Masses  P (polar)-cold  A (arctic)-coldest  m (maritime)-moist  T (tropical)-warm  E (equatorial)-warmest  c (continental)-dry

Potential Air Masses  cA – continental arctic  cP – continental polar  cT – continental tropical  mP – maritime polar  mT – maritime tropical

Fronts  Boundary between two masses  Identifies the leading edge of an advancing air mass  Cloudy and stormy  Travel east to west  Usually bring changes in weather

Warm Front  When a warm air mass advances on a cold air mass  Drizzly precipitation  Cirrus, cirrostratus, altostratus, stratus  After front passes temperatures warm-up  Slow clearing and warmer temperatures show that front has passed

Warm Front

Cold Front  When a cold air mass advances on a warm air mass  Fast moving, produces thunderstorms, heavy rain, or snow  Altocumulus, cumulonimbus  After front passes temperatures drop  Gusty winds are formed due to air pressure differences

Cold Front

Stationary Front  When neither a cold or warm air mass is advancing  Brings very little change in the weather

Occluded Front  When advancing cold front takes over a warm front and pushes warm air up.  Cool temperatures and lots of precipitation  Cloudy, rainy, or snowy

Front Symbols

Severe Weather  Thunderstorms with possible: hail, heavy rain, high winds etc  Tornadoes  Hurricanes  Snow storms

Thunderstorms  Forms in warm, moist air masses or at cold fronts  Atmosphere unstable  16 million occur each year worldwide  Results from cumulonimbus clouds

Accompanies T-Storms  Heavy rainfall – drops collide with others and grow larger  Electrically active  Thunder and lightning superheat, surrounding air (50,000 degrees F) air expands producing sound waves

Tornadoes  Violent whirling wind moving over land from SW to NE  Produces by severe thunderstorms  1% of storms  Differences in wind direction and speed create wind shear. When wind shear is tilted, rotation is produced.  Can reach speed of 500 km/hr

Tornadoes Continued  Nearly 800 reported annually  75% of all occur in the US in the spring and early summer  Tornado alley: TX, OK, KS, NE  Fugi intensity scale: F0 least damage, F5 most damage

Hurricanes  Large swirling, low pressure system that forms over tropical oceans  Wind speeds of at least 119 km/hr  Stages of development  Tropical disturbance  Tropical depression  Tropical storm  Hurricane

Hurricane Risks  Storm surge causes 90% of deaths  Heavy winds and low atmospheric pressure build up over ocean  Wall of water 1-8 m high and km long  Inland flooding

Summary  Clouds  Forms and heights  Air Masses  Classification  Fronts  Cold, warm, stationary, occluded  Sever Weather  Tornadoes, hurricanes. thunderstorms, etc.

Sources    r/hsweathr/index.html r/hsweathr/index.html r/hsweathr/index.html  phere/wind.html phere/wind.html phere/wind.html 