What are “traces” of precipitation?

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Dear Tom,
What are “traces” of precipitation?
— Alecia Condral
Dear Alecia,
Liquid precipitation (and the water content of frozen precipitation like snow) is measured in hundredths (0.01) of an inch. “Trace” amounts are defined as less than half that amount (0.005 inches). The depth of frozen precipitation like snow is measured in tenths (0.1) of an inch and trace amounts are defined as less than half that amount (0.05 inches). When very light precipitation occurs (a sprinkle or minor snow flurries), a weather observer determines if the measured total equals or exceeds the trace amount.
The water content of snow or other frozen precipitation is determined by collecting snow in a rain gauge, melting it and then measuring it as if it had fallen as rain. Precipitation is defined as liquid or frozen particles that fall to the ground; dew and frost are not precipitation.

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