Weather

Meteorology Meteorology is the study of processes that govern the Earth’s atmosphere. Meteorology helps make weather predictions possible

Air Masses An air mass is a large body of air in the lower troposphere that has similar characteristics throughout. –Can be 1000s of kilometers in diameter and several kilometers high. –Temperature and humidity are nearly uniform throughout an air mass. –As air masses travel, they take with it the temperature and humidity of there place of origin.

Types of Air Masses

Continental Arctic (cA) –Originates in the arctic regions. –Air becomes extremely cold. –It will warm as it moves southward, but still brings waves of cold. –Very dry. VERY COLD AND DRY

Types of Air Masses Continental Polar (cP) –Originate over inland regions of Alaska and Canada –Warmer than cA air masses, but still cold. –Cause brilliantly sunny, cold winter days. –Very cold in dry, but can create precipitation in some areas. If is passes over that Great Lakes causes lake- effect snow COLD AND DRY

Types of Air Masses Maritime Polar (mP) –Originate over the ocean in high latitudes –Can be cold and damp. –Not as cold as cP air because oceans are waremer than land. –If mP air cools to dew point fog, clouds, and precipitation occurs –Causes Nor’easters COOL AND MOIST

Types of Air Masses Maritime Tropical (mT) –Originates over a warm tropical ocean. –Acquires both warmth and moisture. –Bring heat and humidity to Midwestern and Eastern United States  cause thunderstorms. WARM AND MOIST

Types of Air Masses Continental Tropical (cT) –Originate over deserts and are hot and dry. –Sometime starts as a mT air masses but dries out as it passes over mountains. –cT air masses produce large heat waves (exceed 100°F) HOT AND DRY

Fronts A front is a boundary that separates opposing air masses. –Most common at mid-latitudes where southward moving polar air masses and northward-moving tropical air masses meet. –Air masses may differ in temperature, humidity or both. Less dense air is forced to rise over the denser air mass. Usually bring precipitation (air cools as it rises)

Fronts

Kinds of Fronts

Cold Front The boundary between an advancing cold air mass and the warmer air mass it is displacing. –Cold air slides under warm air and forces it upward. –If warm air is moist, will produce clouds and sometimes short-lived, violent storms.

Cold Front

Warm Front Warm air mass overtakes a cold air and rises above it because it is less dense. –Produces a long line of clouds and heavy precipitation over a large area

Occluded Front Fast-moving cold front overtakes warm front, lifting warm air off the ground. Then the cold front connects with cold air that forms under warm air, completely cutting off warm air from the ground.

Stationary Front 2 air masses meet but move parallel to the front between them - The front stays where it is. Warm air still rises over denser, colder air. Produces weather like that seen in warm front.

Mid-Latitude Low Fronts are usually connected to a mid- latitiude low pressure systems.

Weather and Low Pressure Systems If a low pressure system: –Passes south of you: No fronts will move over you. May experience steady snow or rain. –Passes to north of you (heading east): Clouds and steady snow or rain form. When the warm front passes, the temperature warms, winds shift, and skies clear. Air is humid – showery precipitation. As the cold front approaches it is preceded by scattered showers and thunderstorms As the cold front passes, the temperature drops, winds shift and the ski clears.

Weather and High Pressure Systems High pressure do not form at a front, but within a single air mass. High pressure areas are associated with fair weather. Air is sinking, so skies are clear. Days may be hot, and night may be cold (no clouds to stop Earth from losing heat)