Sniff the Air
Smell the air. Prior to a storm it's possible to smell the scent of ozone, a sweet odor, being carried to lower altitudes. Meanwhile, during a low pressure system and rain, molecules from decomposing plant matter are released from the surfaces they've attached to, such as soils, and often smell like compost, which can also indicate rain.
20 Surprising Ways to Predict the WeatherFrom coffee cups to crickets, discover these unusual weather predictors