Water in the air has a large heatmass. So rain leaves a "shadow" in the infrared. Worse: it can make things invisible in infrared sometimes too. Rain/fog disto

Water in the air has a large heatmass. So rain leaves a "shadow" in the infrared. Worse: it can make things invisible in infrared sometimes too. Rain/fog distorts an image because there's droplets in the air that function as random lenses. This will affect infrared images just like it affects visible spectrum images. Only things with wavelengths larger than the droplets will be able to see through fog.