Donald Rumsfeld, a former secretary of defense, famously discussed how unknown factors impacted his decision-making during the run-up to the war in Iraq.

“There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know,” he told a 2002 press briefing. “But there are also unknown unknowns — the ones we don’t know we don’t know.”

He must have been a meteorologist in a previous career.

Meteorologists are constantly on the hot seat over their forecasts. When they are right, they get grief, and when they are wrong they get an equal amount of grief.

During World War II, meteorologists had a job with life-and-death consequences. Armed with pilot reports and stacks of maps recording barometric pressure, they were responsible for the safety and success of air, sea and land combat operations. They did the best they could and the war effort generally benefited as a result.

Since the 1960s, when they added satellites, such as Tiros and Nimbus, to their toolbox, meteorologists have been getting better at forecasting the weather. Later on, radar imaging allowed them to track storms as they moved across the landscape.

Computer modeling then allowed them to plug in variables to predict the weather hours, days or weeks into the future.

And still, their forecasts are subject to unknowns, both known and unknown.

As an example, it appears El Niño is taking the winter off. Last May, forecasters predicted the El Niño weather phenomenon would bring warmer, drier weather to the Pacific Northwest this winter.

An El Niño occurs every two to seven years when the ocean temperature at the equator increases. This in turn disrupts normal weather patterns and causes the Pacific Northwest to experience a warmer and drier winter than normal.

In October, forecasters put the odds of an El Niño showing up at 70-75 percent. By November they said the odds of its appearance were more than 80 percent.

Then, last month, forecasters said El Niño was a no-show, but the winter and spring would still be warmer than normal.

That’s because another phenomenon, the Madden-Julian Oscillation, showed up. It has dominated U.S. weather since October, according to the National Oceanic and Atmospheric Administration. That weather pattern rises up in the Indian Ocean and slowly moves eastward. It has both dry and wet phases.

We understand how difficult it is be a meteorologist and predict the weather. Even with state-of-the-art equipment, forecasts can be wrong.

As a former World War II weatherman once told us, “It’s better than it was back then, but not as good as it will be in the future.”

Farmers and ranchers depend on weather forecasts, both long- and short-term. They need the information to help them determine which crops to grow, when to do field work, when to spray pesticides and when to harvest crops.

In short, no industry is more dependent on weather forecasts than agriculture.

That’s why it’s important to remember that, even with the best tools available, meteorologists can be wrong. And the further into the future the forecast is, the less accurate it is likely to be.

To paraphrase Rumsfeld, the unknowns will get you every time.

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