Weather Instruments These are the instruments that measure the primary weather variables in our atmosphere Barometer Rain gauge Thermometer Anemometer Sling psychrometer

Most sudden changes in the weather are a result of Air Masses An air mass is defined as: a large parcel of air that has taken on the characteristics of the surface over which it has been sitting When an air mass sits over a surface of the earth It can acquire 2 primary properties 1. temperature 2. moisture content How many possible combinations of air masses could you have using only these 2 variables?

1.warm and moist 2. warm and dry 3. cold and moist 4. cold and dry What type of surface would these air masses form over?

Cold air mass

cP mT cT

The leading edge of an air mass is called a FRONT The symbols point in the direction the air is moving

COLD FRONT COLD air mass advances on a WARM air mass, pushing forward into the warm air

WARM FRONT WARM air mass advances on a COLD air mass. Since the cold air is more dense, the warm air mass is forced to rise as it pushes forward

OCCLUDED FRONT TWO cold fronts approaching each other are separated by a warm air mass As the two cold fronts near each other, the warm front is pushed up over the cold front and off the ground

Stationary Front A warm air mass and a cold air mass are adjacent to each other, but do not move

Front The leading edge of an air mass is called a: Here is a surface map showing a cold front that has just moved through the midwest

cold front side view The following things usually happen as a cold front approaches and moves past a location: cold front side view A rapid increase in cloud cover, usually tall cumulous or cumulonimbus type 2. A rise in the wind velocity, and shift in direction from south to north 3. Brief heavy precipitation or thunderstorm possible 4. A rapid fall in pressure, followed by a gradual rise 5. A sharp drop in temperature Notice the high angled slope or pitch

Simulation at high speed

Warm front side view 4. A gradual increase in temperature The following weather changes usually occur as a warm front approaches 1. A steady drop in pressure 2. Cirrus clouds are first indication of approaching warm front 3. A gradual increase in clouds until entire sky is covered 4. A gradual increase in temperature 5. Long term light to moderate precipitation 6. A shift in the winds from north to south

A warm front is a much gentler slope or pitch Changes in the weather Occur much more slowly