Weather is the state of the atmosphere at a given time and place. Most weather takes place in the troposphere, the lowest layer of the atmosphere.

Weather is described in a variety of ways by meteorologists, scientists who study and predict weather. Air temperature and pressure, the amount and type of precipitation, the strength and direction of wind, and the types of clouds are all described in a weather report.

Weather changes each day because the air in our atmosphere is always moving, redistributing energy from the Sun. In most places in the world, the type of weather events expected vary through the year as seasons change.† While weather can change rapidly, climate changes slowly, over decades or more, in response to changes in the factors that determine our climate.†

<a href="/earth/Atmosphere/clouds/kelvin_helmholtz.html&edu=elem&dev=">Kelvin-Helmholtz</a>
  clouds resemble breaking <a
  href="/earth/Water/ocean_waves.html&edu=elem&dev=">waves in
  the ocean</a>. They are usually the most developed near mountains or large
  hills. Wind deflected up and over a barrier, like a mountain, continues
  flowing through the air in a wavelike pattern. Complex <a
  and <a href="/earth/Water/condensation.html&edu=elem&dev=">condensation</a>
  patterns create the capped tops and cloudless troughs of the waves. This
  image was taken on February 9, 2003 in the morning in Boulder, Colorado.<p><small><em>       Courtesy of Roberta Johnson</em></small></p>Hurricane Alex, a <a
  3</a> storm at its strongest, traveled north along the east coast of North
  America in August 2004 causing <a
  strong <a href="/earth/Water/ocean_waves.html&edu=elem&dev=">waves</a>,
  and rip tides along the coast. <a
  form</a> in the tropics over warm ocean water and die down when they <a
  over land or out of the tropics. These storms are called hurricanes in the
  Atlantic and typhoons or tropical cyclones in other areas of the world.<p><small><em>      Courtesy of NOAA</em></small></p>A <a
  begins in a severe <a
  called a <a
  The wind coming into the storm starts to swirl and forms a funnel.
  The air in the funnel spins faster and faster and creates a very <a
  pressure</a> area which sucks more 
 This tornado was photographed in Carteret County, NC on June 7, 2004.<p><small><em>Courtesy of National Weather Service Forecast Office of Newport/Morehead City, NC</em></small></p>This photograph of a <a
  href="/earth/Atmosphere/clouds/cumulonimbus.html&edu=elem&dev=">cumulonimbus cloud</a> was taken on the <a
  href="/earth/grassland_eco.html&edu=elem&dev=">grasslands</a> of eastern Wyoming.
  Notice the <a
  href="/earth/Atmosphere/precipitation/rain.html&edu=elem&dev=">rain</a> and <a
  href="/earth/Atmosphere/precipitation/hail.html&edu=elem&dev=">hail</a> falling from this
  cloud! Cumulonimbus clouds form during <a
  href="/earth/Atmosphere/tstorm.html&edu=elem&dev=">thunderstorms</a>, when very warm, moist air rises into cold air. As this humid air rises, water vapor <a
  and forms huge <a
  clouds.<p><small><em>         Photo courtesy of <a href="">Gregory Thompson</a></em></small></p>The <a href="">EF-5</a> <a href="">tornado</a> that hit El Reno, Oklahoma on May 31st, 2013 was the widest ever recorded in the US, according to the National Weather Service in Norman Oklahoma. The tornado, which remained on the ground for 40 minutes and reached 2.6 miles across (4.2 km), took the lives of 18 people including storm chasers Tim Samaras, Paul Samaras and Carl Young.<p><small><em>Image courtesy of National Weather Service, Norman Oklahoma</em></small></p>Does Earth science matter?  The power outage experienced by residents in New York City on 10/30/2012 due to Hurricane Sandy demonstrates the interconnectedness of our society, and the power of the Earth system.  Every person should have an understanding of how the Earth system works so they can live better lives, protect those they love, and make wise choices.  Earth science education is critical!<p><small><em>Image courtesy of Hybirdd, licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license.</em></small></p>

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