Once used by seafarers to predict oncoming storms, this historical device responds to atmospheric fluctuations to forecast the weather! How to Predict the Weather: Clear liquid: Bright and clear weather. Cloudy liquid: Cloudy, possible thunderstorms & rain. Small dots in the liquid: Humid or foggy weather. Large flaky crystals: Cloudy skies, snow in winter. Threads of crystals at the top: Windy weather. Crystals at the bottom: Frost may be coming.