Weather forecasting by computer has historical roots at the University of Pennsylvania. In the 1940s, physicist and amateur meteorologist John Mauchley and electrical engineering student J. Presper Eckert led a team that built the world's first electronic, large-scale, general-purpose computer. They unveiled it in February 1946 and called it ENIAC, for Electronic Numerical Integrator And Computer. ENIAC weighed 30 tons, had thousands of vacuum tubes and manual switches, and was 100 feet long and ten feet high. Parts of ENIAC still reside in the Moore Building on campus.

ENIAC was funded by the Army and was used mainly to calculate missile trajectories. But in the late 1940s, at Princeton, a mathematician named John Von Neumann and a meteorologist named Jule Charney had developed a primitive weather computer model. In 1950, they tested their model on ENIAC, achieving the first computer weather forecast. Yes, there were glitches - the computer was slow and broke down a lot. It took more than twenty-four hours just to forecast for tomorrow - in essence, the computer prediction moved slower than the actual weather!

But the results were accurate enough to convince the researchers that they were onto something. Just five years later, in 1955, the first operational numerical weather predictions were made on an IBM computer in a project jointly funded by the U.S. Weather Bureau and the military, launching Meteorology's computer age.