When Paul Swift measures snow, he melts it and records how much liquid remains, which is included in overall precipitation amounts. Kyle Clayton photo.

Nearly every morning at 8 a.m. for the past 18 years Paul Swift has recorded weather observations, more than 6,500 total, for the National Weather Service. Today, Monday, April 30, is his last day. It begins, like all the other mornings, with precise measurements.

A metal box about the size of…