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Camping in the Boundary Waters and Quetico

5.) Explain the saying "Red sails in morning, sailor take warning. Red sails at night, sailors delight."

If the sun is setting (W) and it's rays are filtered through high, thin clouds (or atmospheric dust) in an otherwise clear atmosphere, the effect is a deep red tinge. That means that there are no major clouds (weather systems) to the west to block out the sun for several hundred miles. No bad weather is expected during the night.
If, at sunrise, there are high, thin clouds that cause the red, then this often is the leading edge of an approaching weather system. (Low pressure system overriding a high pressure system.) This approaching weather system may include high winds, gales, and heavy rain or snow, none of which a sailor would like.