What Causes Our Daily Weather To Change Change

What Causes Our Daily Weather To Change? Change in our weather is a result of a change in air masses.

What Is An Air Mass? An air mass is a large body of air in the lower troposphere that has similar characteristics throughout. An air mass can be several thousand kilometers in diameter and several kilometers high The temperature and humidity are nearly uniform throughout The temperature and humidity depend on where the air mass originates.

Where Do Air Masses Originate? Air masses originate in source regions. Source regions have flat, uniform composition and light winds.

How Are Air Masses Classified? The temperature of each air mass depends on whether the air mass originates in an arctic, polar, or tropical source region. The humidity depends on whether the air mass originates over land ( continental ) or over water ( maritime ). Air masses are classified by temperature and humidity.

Air Mass Classification Air Mass Maritime Tropical Maritime Polar Continental Tropical Continental Arctic Symbol m. T m. P c. T c. A Temperature & Humidity Where Air Mass Forms Area of the Country that is Impacted Warm and Wet Low latitudes over water Southwest and Southeast U. S. Cold and Wet Cold and Dry Warm and Dry High latitudes over water High latitudes over land Low latitudes over land Very Cold and Dry High latitudes over land Northeast and Northwest U. S. Midwest to Eastern U. S. Southwest U. S. Northern U. S. in winter

m. P – West Coast • Tends to be unstable • Heavy rains as cool moist air flows over mountains along west coast • m. P is modified by time it reaches interior of US, though is milder that c. P • (how? ? ? )

m. P – East Coast • Not as common as west coast m. P • Colder than west coast m. P • Usually brought onshore by high pressure to the north of us and/or low pressure to the south moving up the coast.

Maritime Tropical Air Mass West Coast • Brings showers and thunderstorms East Coast • Summer - Brings showers and thunderstorms • Winter – snow or heavy rain

Continental Tropical Air Mass – Summer only

Continental Polar Air Mass

Types of Air Masses

Global Source Regions For Air Masses

Stability of an Airmass Changes to the stability of an air mass can result from temperature differences between an air mass and the surface The stability of an air mass may be shown using a third letter: "k“ = un-stable or "w“ = stable

Air Mass Source Region – Practice Quiz Continental 1. Arctic 4. Maritime 3. Polar Maritime 6. Tropical Maritime Polar Continental 2. Polar 5. Maritime Polar Continental 8. Tropical 7. Maritime Tropical

Weather Patterns • Weather patterns are caused by the movement of air masses and what happens when different air masses collide. • Front – boundary between two air masses. • Air masses meet but do not mix. Front Poor Air Mass Great Air Mass The boundary line between the offensive and defensive lines would be a front.

Name Formation Warm Occluded Weather • Wind, heavy rain • Thunderstorms • Altocumulus • Cumulonimbus • Lightning • Colder air after front passes Cold Stationary Clouds Air masses stop moving • Cirrus • Cirrostratus • Altostratus • Nimbostratus • Clouds then gentle, steady rain arriving before the front • Cirrus • Cirrostratus • Altostratus • Nimbostratus • Steady rain for days along front if stationary too long • Cumulus • Cumulonimbus • Strong winds and heavy rains Symbol

Fronts Cold Front: boundary between advancing cold air mass & a warmer air mass it is displacing Rising warm air usually produces precipitation if wet Air becomes colder after front passes

Fronts Warm Front: boundary between advancing hot air mass & a colder air mass it is displacing 1 st clouds days in advance, then RAIN Air becomes warmer after front passes

Fronts Occluded Front: when cold front ‘catches up’ to a warm front, producing clouds & precipitation

Fronts Stationary front: when a front stops moving forward, producing clouds & precipitation – causes floods if stationary too long

The Life Cycle Of A Cyclone (Low Pressure System) • The United States often experiences weather due to the boundary between the cold air masses of the Polar Easterlies and the warm air masses of the Prevailing Westerlies. This arrangement results in a weather conditions called a Traveling Cyclone. • The formation of a cyclone is called "cyclogenesis". Cyclones form in areas of low pressure.

The Life Cycle Of A Cyclone (Low Pressure System) • The process begins when two air masses of different densities and temperatures move in opposite directions along a polar front resulting in a large temperature gradient.

The Life Cycle Of A Cyclone (Low Pressure System) • Cyclones are the result of instability forming along the polar front, resulting in a wave developing between the cold and warm air masses. The fronts are separated, and the warm front begins to move north as the cold front begins to move south

The Life Cycle Of A Cyclone (Low Pressure System) • The pressure at the center of the cyclone continues to get lower as the cyclone continues to form. Clouds ahead of the warm front begin to precipitate over a large area of surface, and clouds along the cold front begin to precipitate over a narrow stretch [along the cold front]. As the pressure is lowered, wind speeds increase.

The Life Cycle Of A Cyclone ( Low Pressure System) • The cold front continues to move eastward, speeding to overtake and undercut the warm front. This is called occlusion. It is at this point which the cyclone is at its peak. The area of the warm sector is decreasing.

The Life Cycle Of A Cyclone (Low Pressure System) • By the time the cold front completes occlusion with the warm front, the air in the warm sector is lifted upward as the cold air replaces it at the surface. The system is stabilizing.

Weather Forecasting Satellites Radiosondes Surface observations

Station Model

Surface Weather Map

Locating a Front Wind direction changes Temperature changes sharply Dew Point changes sharply

Forecasting Computer models take current data & plug it into equations to predict weather Meteorologists take computer models & tweak them to fit their experience with local conditions

Forecasting Trend Method: using past movement of a front & precipitation to predict future movement

Practice reading a weather map