The Weather Builders

Moisture, Pressure & Temperature Control the Air

These three physical properties, pressure, temperature and humidity, are basic weather builders, determining by themselves and by their interaction how air is going to behave. Changes in moisture, pressure and [...]

Atmospheric pressure

The atmospheric pressure is the force exerted on any point of Earth’s surface by the weight of the column of air above it. Air molecules have volume, weight, mass and [...]


When heat enters a substance, energy comes into it as well. That energy can be used to increase the rate of movement (kinetic energy) of the molecules, which would cause [...]


Life in the planet is possible because of the presence of water. Air contains moisture, that is, water vapor, which absorbs energy very well and prevents Earth’s heat from escaping [...]

Air Masses (upper level)

Knowing about air masses provides interesting information about the kind of weather to expect. An air mass can be defined as a large body of air that has relatively uniform characteristics, [...]

Types of Air Masses

According to the source region, air masses are classified as: P – Polar Air Masses, originated in polar latitudes, located pole-ward of 60 degrees north and south. T – Tropical Air Masses, [...]

Pressure Systems (upper level)

Air pressure is a measure (in millibars) of the force exerted by air on every point of Earth’s surface. The concept of pressure system refers to a region of the [...]

Basic concepts

Pressure system: “individual cyclonic-scale feature of atmospheric circulation commonly used to denote either a high or a low, less commonly a ridge or trough”. Cyclone - also named as depression, or [...]

Internal dynamic of highs and lows

Air rotates around highs in an anticyclonic (clockwise in the Northern Hemisphere) direction while spiraling outward from the high pressure center. Such spreading out of the air is known as [...]

Semipermanent Highs and Lows

They are areas of high pressure (anticyclones) and low pressure (cyclones) that tend to persist at a particular latitude belt throughout the year, averaged over long periods of time. Semi-permanent [...]

Creation of fronts

A front is the relatively sudden transition zone between air masses. Fronts are not permanent features; they form and intensify in a process known as frontogenesis. The arrival of a new [...]

Troughs & Ridges

A ridge is an axis or line of high atmospheric pressure, depicted on a weather map as a rise in an isobar; a system of nearly parallel isobars, approximately u-shaped, [...]

Airflow Patterns (general circulation of winds aloft)

The air moving above the rotating Earth is called wind. There are surface winds and "planetary winds aloft", the latter of which is part of the Earth's general circulation of [...]

Circulation Cells

Back in the 1680s, Edmond Halley (1656-1742), discovered the key element of the planet’s global circulation: warm air near the equator rises, it flows out toward the poles at high [...]

Coriolis Force

It is an apparent force, due to the rotation of the Earth, which acts normal to, and to the right of the velocity of a moving particle in the Northern [...]

Prevailing Westerlies

The Westerlies are global-scale, dominant mid-latitude winds that blow from the subtropical high pressure belt toward the polar front. They come from the west, which characterize the mid-latitudes both north [...]

Jet Stream

The jet stream is a flat tubular quasi-horizontal current of air, generally near the tropopause, whose axis is along a line of maximum speed and which is characterized by strong [...]

Ocean Currents

An ocean current can be defined as a horizontal movement of seawater at the ocean's surface. Ocean currents are driven by the circulation of wind above surface waters. The surface layer [...]