Meet the Computer Scientist You Should Thank For Your Smartphone’s Weather App

She was a key figure in the experiment that launched modern weather prediction, despite having no formal mathematical training

Each time you use your phone's weather app, you're indebted to a self-taught computer scientist named Klara von Neumann. (Anatolii Babii / Alamy )

A weather app is a nifty tool that predicts your meteorological future, calculated with the strength of radar, algorithms and satellites around the world. Today, computerized weather prediction—like moving pictures or flying by plane—is so commonplace that smartphone-users don’t give it a second thought. But at mid-century, the idea that you might be able to forecast the weather days or even weeks ahead was a tantalizing prospect.

One of the most important breakthroughs in weather forecasting took place in the spring of 1950, during an experiment at the U.S. Army’s Aberdeen Proving Ground in Maryland. For over a month straight, a team of scientists and computer operators worked tirelessly to do something meteorologists had been working toward for nearly a century: predict the weather mathematically. 

This was a long time before the MacBook Air. Scientists were using one of the first computers, a finicky, 150-foot machine called ENIAC that had been developed during the recent World War. One of the scientists, George Platzman, would later describe a complicated, 16-step process they repeated over and over: six steps for the ENIAC to run their calculations, and 10 steps to input instructions and record output on punch-cards. Minor errors forced them to redo hours—sometimes days—of work. In one tense moment, a computer operator’s thumb got caught in the machinery, temporarily halting operations.

But at the end of the month, the team had produced two groundbreaking 12-hour and four 24-hour forecasts (well, technically "hindcasts," as they used data from past storms). The New York Times hailed the project as a way to “lift the veil from previously undisclosed mysteries connected with the science of weather forecasting.” The benefits to agriculture, shipping, air travel and other industries “were obvious,” weather experts told the Times. The team's results proved that computer-based forecasting, the cornerstone of modern weather prediction, was possible.

A Weather Bureau memo proclaimed that “these men had made the first successful ... forecast on a computer.” They were mostly right. Except, it wasn’t just men. Numerous women played critical scientific roles in the experiment, for which they earned little to no credit at the time.

Two computer operators, Ruth Lichterman (left) and Marlyn Wescoff (right), wire the right side of the ENIAC with a new program in the pre-von Neumann era. (US Army, via Historic Computers Images of the ARL Technical Library)

The original ENIAC programmers—Jean Bartik, Betty Holberton, Kathleen Antonelli, Marlyn Meltzer, Ruth Teitelbaum, and Frances Spence—were all women who taught themselves how to program the vast machine. Most if not all of the computer operators working on the 1950 weather experiment (who were merely thanked in the paper’s acknowledgements for their “help in coding the problem for the ENIAC and for running the computations”) were also women.

Before the experiment even started, Norma Gilbarg, Ellen-Kristine Eliassen and Margaret Smagorinsky—the first female statistician hired by the Weather Bureau, who was married to meteorologist and experiment team-member Joseph Smagorinsky—spent hundreds of hours manually calculating equations the ENIAC would need to compute in the full experiment. Before she passed away in 2011, Smagorinsky recalled in an interview with science historian George Dyson: “It was a very tedious job. The three of us worked in a very small room, and we worked hard.” 

But perhaps the biggest single contribution came from a woman named Klara von Neumann.

Klara, known affectionately as Klari, was born into a wealthy Jewish family in Budapest, Hungary, in 1911. After World War I, in which Hungary allied with Austria to become one of the great European powers of the war, Klara attended an English boarding school and became a national figure skating champion. When she was a teenager, during Budapest’s roaring '20s, her father and grandfather threw parties and invited the top artists and thinkers of the day—including women.

Klara married young, divorced and remarried before the age of 25. In 1937, a Hungarian mathematician, John von Neumann, began to court her. Von Neumann was also married at the time, but his divorce was in progress (his first wife, Mariette, had fallen in love with the acclaimed physicist J.B. Horner Kuper, both of whom would become two of the first employees of Long Island’s Brookhaven National Laboratory). Within a year, John and Klara were married. 

John had a professorship at Princeton University, and, as the Nazis gained strength in Europe, Klara followed him to the U.S. Despite only having a high school education in algebra and trigonometry, she shared her new husband’s interest in numbers, and was able to secure a wartime job with Princeton’s Office of Population Research investigating population trends.

By this time John became one of the most famous scientists in the world as a member of the Manhattan Project, the now-notorious U.S. government research project dedicated to building the first atomic bomb. With his strong Hungarian accent and array of eccentricities—he once played a joke on Albert Einstein by offering him a ride to the train station and sending him off on the wrong train—he would later become the inspiration for Stanley Kubrick’s Dr. Strangelove. While Klara stayed behind, working full-time at Princeton, John moved out to Los Alamos, New Mexico, running the thousands of calculations needed to build the first of these weapons of mass destruction.

His work came to fatal fruition in 1945, when the U.S. dropped two atomic bombs on Japan, killing as many as 250,000 people. After the war, John decided to turn his mathematical brilliance toward more peaceful applications. He thought he could take the ENIAC—a powerful new computer that had been used for the first time to complete important calculations for a hydrogen bomb prototype—and use it to improve weather forecasting.

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A chart of the series of operations required to create the first weather forecasts, chronicled later by scientist George Platzman. (AMS Bulletin, ©American Meteorological Society. Used with permission.)

As John began to pursue this idea, getting in touch with top meteorologists in the U.S. and Norway, Klara came to visit him in Los Alamos. By this time, Klara had become quite mathematically adept through her work at Princeton.

“Long before [ENIAC] was finished, I became Johnny’s experimental rabbit,” she told Dyson. “It was lots and lots of fun. I learned how to translate algebraic equations into numerical forms, which in turn then have to be put into machine language in the order in which the machine has to calculate it, either in sequence or going round and round, until it has finished with one part of the problem, and then go on some definite which-a-way, whatever seems to be right for it to do next… The machine would have to be told the whole story, given all the instructions of what it was expected to do at once, and then be permitted to be on its own until it ran out of instructions.”

The work was challenging, especially compared to modern computer programming with its luxuries like built-in memory and operating systems. yet Klara said she found coding to be a “very amusing and rather intricate jigsaw puzzle.”

ENIAC was moved to Maryland in 1947, where, through an initiative led by John and Klara, it became one of the first stored-program computers. This meant the complicated sets of instructions telling the computer to perform various tasks could be stored in binary code on a memory device, rather than entered and re-entered manually. To install this new system, Klara trained five people who had worked on the Manhattan Project to program ENIAC. Up until then, no one but the von Neumanns and a young physicist named Nick Metropolis were well-versed in the ways of the computer.

For 32 days straight, they installed the new control system, checked the code, and ran ENIAC day and night. John wrote that Klara was “very run-down after the siege in Aberdeen, lost 15 pounds, and [had] a general physical check-up at the Princeton Hospital.” 

By the time a group of meteorologists—Platzman, Smagorinsky, Jule Charney, Ragnar Fjørtoft and John Freeman—came on the scene in early 1950, ENIAC had been operating in the new stored-program mode for over a year, which Platzman says “greatly simplified our work.” These scientists had spent the past few years developing equations to represent various dynamics in the atmosphere, which could be fed into the computer. In a letter, Charney wrote:

The atmosphere is a musical instrument on which one can play many tunes. High notes are sound waves, low notes are long inertial waves, and nature is a musician more of the Beethoven than the Chopin type.

ENIAC wasn’t perfect. It could only produce 400 multiplications per second, so slow that it produced rhythmic chugging noises. But after working around the clock for over a month, the team had six precious gems: two 12-hour and four 24-hour retrospective forecasts.

Not only were these the first computerized weather forecasts, but it was the first time scientists had ever succeeded in using a computer to conduct a physics experiment. It sparked a shift in academic thinking, shrinking the divide between “pure” mathematics and the use of math for meaningful, real-world applications. Platzman has since reflected that because “we live in an age when electronic miracles have become commonplace, we have grown immune to any sense of awe and astonishment” at things that were “literally unbelievable” just a few decades prior.

During these five weeks, Klara was a constant fixture. It was she who checked the final code for the experiment. She was involved with ENIAC from the ground up, and—according to letters and journal entries written by Charney, Platzman, and other team members—had a major leadership role in the Meteorology Project. In addition to leading the installation of the stored-program system, and training the scientists to code on ENIAC, she was in charge of hand-punching and managing each of the experiment’s 100,000 punch-cards, which served as ENIAC’s read/write memory. 

“When you have 100,000 cards, you have to make sure you don’t lose any of them,” says John Knox, who teaches his undergraduates at the University of Georgia about Klara’s contributions to meteorological computing. “If one of them falls out of order, the whole program is screwed up.”

For this difficult, highly technical work—which, Knox says, would surely earn her a co-authorship today—resulted in a merely a small “thanks” at the bottom of the team’s paper.  

Women computer scientists holding different parts of an early computer. From left to right: Patsy Simmers, holding ENIAC board; Gail Taylor, holding EDVAC board; Milly Beck, holding ORDVAC board; Norma Stec, holding BRLESC-I board. (US Army Photo, via Historic Computers Images of the ARL Technical Library)

In the 1940s, “it was sexier to be around the hardware than software,” says Knox. “You’ll see these pictures of [John] von Neumann and J. Robert Oppenheimer [head of the Manhattan Project] standing around computers and smiling and showing off. No one cared about software; it was ‘women’s work’ in a way, even though nothing would have worked without the software.” In regard to the Meteorology Project, Knox says, “It was like it was less important, like ‘Oh, this is just something Klara is punching’ I guess.”

By the late 1950s, companies like IBM, Raytheon and Texaco were hiring women for programming jobs, knowing that they were capable and adept. In fact, in Janet Abbate’s 2012 book Recoding Gender, she writes how women in the ’50s and ’60s “would have scoffed at the notion that programming would ever be considered a masculine occupation.” But as perspectives on the value of computers and programming evolved, the number of women hired for those roles shrank.

Klara, for her part, did little to no programming after the Meteorology Project. John was confined to a wheelchair in 1956 and succumbed to cancer a year later, thought to be due to his proximity to radiation during the Manhattan Project. Klara wrote the preface to his posthumous bookThe Computer and the Brain, which she presented to Yale College in 1957. In it, she briefly described her late husband’s contributions to the field of meteorology, writing that his “numerical calculations seemed to be helpful in opening entirely new vistas.”

She never acknowledged her own role. Yet without her, the experiment that set the stage for modern weather prediction would likely never have made it off the ground. So the next time you scroll through your weather app before deciding whether to don a raincoat—think of Klara, and her calculations that helped make it possible.


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