Weather

Weather and Atmospheric Water

• Air temperature causes differences in pressure so that convection cells form.
• Air rising in a convection cell may cool enough to reach its dew point and form clouds or precipitation if the humidity is high enough.
• Clouds or fog may form if warmer air meets a colder ground surface. Air temperature and humidity also determine what sorts of clouds and precipitation form.
• These factors play a role in creating a pleasant or uncomfortable day, such as when it might be warm and dry or hot and humid.

Changing Weather

• An air mass takes on the temperature and humidity characteristics of the location where it originates. Air masses meet at a front.
• Stationary fronts become trapped in place and the weather they bring may last for many days.
• At a cold front, a cold air mass takes the place of a warm air mass and forces the warm air upwards.
• The opposite occurs at a warm front, except that the warm air slips above the cold air mass.
• In an occluded front, a warm front is overtaken by a cold front, which creates variable weather.

Storms

• Thunderstorms arise in warm weather when updrafts form cumulonimbus clouds that rain and hail.
• Lightning and thunder result when positive and negative electrical charges in different parts of the cloud and on the ground attempt to equalize.
• Tornadoes form most commonly from thunderstorms. Although they are shorter in duration and affect a smaller area than other severe storms, they do an enormous amount of damage where they strike.
• Cyclones of all sorts are large and damaging; they include nor'easters and hurricanes.
• Heat waves kill more people each year than any type of storm and mostly form in regions beneath an unusually high pressure zone.

Weather Forecasting

• Weather forecasts are more accurate than ever before. Older instruments and data collection methods such as radiosondes and weather balloons are still used.
• These techniques have now been joined by satellites and computers to create much more detailed and accurate forecasts.
• Still, forecasts are often wrong, particularly those that predict the weather for several days.
• Meteorologists are working hard to improve weather forecasts one to two weeks in advance of potentially hazardous weather.