Long ago, Admiral Sir Francis Beaufort of the British Navy developed a way to estimate wind speeds just by looking around him. It was originally developed by gauging waves at sea, but was later extended to include land effects.
Leaves rustling is about a 5-10 mph breeze. Thin branches move around 15 mph. When trees begin to sway, that's about a 20-25 mph breeze. When large tree branches move and umbrellas go inside-out, that's a 30 mph breeze. Large trees sway around 35 mph, and small branches start to break around 40 mph. Shingles will blow off roofs around 50 mph, and trees start toppling around 60 mph.
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