Leap day. It is what we call February 29, the day added onto February every fourth year to keep the seasons from slowly drifting through time as the earth takes slightly longer than 365 days to revolve around the Sun. Leap day on occasion does impact climate statistics and this past winter was possibly one of those times.
Our recently completed winter was the 16th coldest on record, but the National Weather Service recently released a statement that this past winter was the 17th coldest on record. The difference? February 29, 1904. Including that day makes the winter of 1903-1904 average temperature 4.4 degrees. Without that day, the average temperature is 4.2 degrees. The winter of 2013-2014 that we just completed had an average of 4.3 degrees meaning that depending on if you include that leap day this winter’s ranking changes by one position. Is one statistic more accurate than the other?
Not necessarily, but leap day seems to get little respect, so I always include in all my analysis and most other researchers do as well.