Did you know that your morning cup of coffee can help you predict rain? It’s a trick used by backpackers that can come in handy you’re shooting outdoors without Internet: pour a cup of coffee and carefully watch the bubbles. Backpacker Magazine writes,
If the bubbles amass in the center, you’re in a high-pressure system, which is making the coffee’s surface convex (higher in the middle). Since bubbles are mostly air, they migrate to the highest point. It’s going to be a beautiful day. If the bubbles form a ring around the sides of the mug, you’re in a low-pressure system, making the surface concave. Rain is likely. Note: It has to be strong, brewed coffee to have enough oil to work, and the mug must have straight sides.
To make new bubbles, simply give your coffee a good stir.