This article refers to meteorology. For the airborne base of the TV series Captain Scarlet and the Mysterons, see Cloudbase.

The cloud base (or the base of the cloud) is the lowest altitude of the visible portion of the cloud. It is traditionally expressed either in m or feet above mean sea level (or planetary surface), or as the corresponding pressure level in hectopascal (hPa, equivalent to millibar).

The height of the cloud base can be estimated from surface measurements of air temperature and humidity. Modern automated instruments to measure cloud base include specially designed laser systems called ceilometers.

The cloud base can be calculated by these simple steps:

1. Find the difference between Surface Temperature (°F) and Dew Point (°F)

2. Divide the difference by 4.4

3. Multiply the quotient by 1000

4. Add the product to the Field Elevation (ft)

In well-defined air masses, many (or even most) clouds may have a similar cloud base because this variable is largely controlled by the thermodynamic properties of that air mass, which are relatively homogeneous on a large spatial scale. This is not the case for the cloud tops, which can vary widely from cloud to cloud, as the depth of the cloud is determined by the strength of local convection.

Sidney K. "Sid" Meier (born February 24, 1954) is a Canadian-American programmer and designer of several popular strategy video games and simulation video games, most notably Civilization. Meier co-founded MicroProse in 1982 and is a Director of Creative Development for computer game developer Firaxis Games, which he co-founded with Jeff Briggs and Brian Reynolds in 1996. He has won several prestigious accolades for his contributions to the computer games industry.

Sid Meier was born in Sarnia, Ontario, Canada. He graduated from the University of Michigan.

Meier founded MicroProse together with Bill Stealey in 1982. MicroProse initially developed flight simulator video games, such as Silent Service and F-19 Stealth Fighter. In 1987, the company released Sid Meier's Pirates!, which also began a trend of placing Meier's name in the titles of his games. Meier later explained that the inclusion of his name was because of the dramatic departure in the design of Pirates! compared to the company's earlier games. Stealey decided that it would improve the company's branding, believing that it would make those who purchased the flight simulators more likely to play Pirates!. After the release of F-19 Stealth Fighter, Meier decided to focus on developing strategy games. He later said, "Everything I thought was cool about a flight simulator had gone into that game." Inspired by SimCity and Empire!, Meier created Railroad Tycoon and later the game series for which he is most widely recognized, Civilization, although he designed only the first installment. Meier eventually left MicroProse and in 1996 founded Firaxis Games along with veteran designer and gaming executive Jeff Briggs. Today Firaxis makes strategy games, many of which are follow-ups to Meier titles, such as Civilization V and Pirates!. In 1996 he was awarded US Patent 5,496,962 for a "System for Real-Time Music Composition and Synthesis" used in a product called "CPU Bach".