People have been trying to predict the weather for thousands of years. You’d think that by now we’d have it sorted out—yet open three different weather apps on your phone and you’ll probably find three slightly different forecasts. How hard can it be to get the weather right?

Pretty hard. Even weather experts agree that meteorology is “an art as much as a science.” Our instruments have come a very long way since the weather rock, and computer modeling allows us to capture and process huge quantities of data. Ultimately, though, a forecast comes down to one thing: the forecaster’s judgment.

Weather apps are like weather reports on TV, which never seem to match up, either. That’s because each app or station uses its own systems and formulas to predict the meteorological future.

Meteorologist Jeff Masters is the founder of Weather Underground. “You start with the same fundamental mathematical equations that govern the motion of the atmosphere,” he told The Virginian Pilot. “But the coding is different.”

Every forecaster starts with the same raw data, a “firehose” of information pouring in from satellites, radar, and weather stations around the world. From there, they have to decide how to process that data, and which variables will be relevant for any given situation.

No matter what channel you watch, site you visit, or app you download, you’re going to have to make room for a little error. Meteorologists call their forecasts “guidance,” not “the future.”

Some apps’ guidance hits the mark more often than others, but the best weather app for you depends on what you want.

The Weather Underground app (iOS, Android) is free and super-detailed. The Weather Channel (iOS, Android) is also free but focuses more on social media, allowing users to share weather updates with friends. Dark Sky ($3.99, iOS, Android) is hyperlocal and immediate, focused only on the present moment and the next few hours. For true weather nerds, there’s RadarCast Elite ($1.99, iOS), which offers high-definition radar imaging so you can watch that pressure system roll in.

[h/t The Virginian Pilot]