Weather Air Masses

Vocab Weather – the conditions of the atmosphere at a particular time. Air mass – a large body of air throughout which temperature and moisture content are similar. Air moves from an area of high pressure to low pressure. Therefore, there is a general , worldwide movement of surface air from the poles toward the equator.

Air Masses Weather is the result of the movement of these large bodies of air, or air masses. Air masses are classified according to their source regions. The source regions for cold air masses are polar areas. The source regions for warm air masses are tropical areas. Air masses that form over the ocean are called maritime. Air masses that form over land are called continental. The combination of tropical or polar air and continental or maritime air results in air masses that have distinct characteristics.

Air Masses Source location Movement Weather cP Polar regions in Canada South-southeast Cold and dry mP Polar pacific; polar atlantic Southeast; southwest –south Cold and moist cT U.S. southwest North-northeast Warm and dry mT Tropical Pacific; tropical Altlantic Northeast; north-northwest Warm and moist

Fronts Cold front – the front edge of a moving mass of cold air that pushes beneath a warmer air mass like a wedge. Warm front – the front edge of advancing warm air mass that replaces colder air with warmer air. Stationary front – a front of air masses that moves either very slowly or not at all.

Find pictures for the following terms. Draw and label in your notes. Cold Front Warm Front Stationary front Occluded front What types of weather are the result of each kind of front?

Severe Weather Thunderstorms develop in three distinct stages: Cumulus stage – warm, moist air rises, and the water vapor within the air condenses to form a cumulus cloud. Mature stage – condensation continues as the cloud rises and becomes a dark cumulonimbus cloud. Heavy, torrential rain and hailstones may fall from the cloud. Updrafts continue, but strong downdrafts occur due to the precipitation pulling the air down with it. Dissipating stage – the strong downdrafts stop air currents from rising. The thunderstorm dissipates as the supply of water vapor decreases.

Severe Weather Lightning – during a thunderstorm, clouds discharge electricity in the form of lightning. The releases electricity heats the air, and the air expands rapidly and produces the loud noise known as thunder. The upper part of the cloud usually carries a positive charge and the lower part of the cloud carries a negative charge. Lightning is the result of equalizing the electrical charges. Essentially, electrons jump the “jump the gap”.

Severe Weather Hurricanes – a tropical storm that has strong wind speeds of more that 120 km/h that spiral in toward its intense low pressure center. A hurricane begins when warm, moist air over the ocean rises rapidly. When moisture in the rising warm air condenses, a large amount of energy in the form of latent heat is released. Latent heat – heat energy that is absorbed or released during a phase change.

Severe Weather Tornado – a destructive, rotating column of air that has very high wind speeds and that may be visible as a funnel-shaped cloud. A tornado forms when a thunderstorm meets high-altitude, horizontal winds. The winds cause the rising air in the thunderstorm to rotate. Why does “tornado alley” have so many tornadoes?

Classification of clouds Stratus clouds – clouds that have flat, uniform base and that begin to form at very low altitudes. These form when a layer of warm, moist air lies above a layer of cool air. When the overlying warm air cools, wide clouds appear.

Clouds Cumulus – low altitude, billowy clouds that commonly have a top that resembles cotton balls and a dark bottom. These occur when warm, moist air rises and cools.

Clouds Cirrus – Feathery clouds that are composed of ice crystals and that have the highest altitude of any cloud in the sky. These clouds form at altitudes above 6,000 m.

Forecasting Weather The data that weather stations collect are transferred onto weather maps. Weather maps allow meteorologists to understand current weather patterns and make predictions based on this information. Meteorologists use symbols to show weather conditions at the locations of weather stations. Our closest weather station is in Jackson, KY.

Weather maps Scientists use lines on weather maps to connect points of equal measurement. Isotherms – lines that connect equal points of temperature. Isobars – lines that connect equal points of atmospheric pressure. Closely spaced isobars indicate rapid change in pressure. What type of weather would you expect to experience with these conditions?

Weather Maps Most weather maps mark the location of fronts and areas of precipitation. Areas of precipitation are commonly marked by using colors of symbols. How have you seen precipitation marked on a map? Changes in fronts are associated with sharp changes in wind speed and direction, temperature, or humidity. What are the types of fronts and their associated symbols?

Weather Symbols

Weather Maps

Weather report analysis We will go outside to take down observations about our weather. Review the weather map for our forecast today and tomorrow. What conditions did you observe outside that relate to the weather map? What are your predictions for the weather tomorrow based on your observations and the weather map?