Tuesday, February 28, 2012

Leap Day Weather History

Philadelphia has had 33 record Leap Days of weather -- daily observations go back to 1874 in Philadelphia.  Tomorrow marks the 34th Leap Day of recorded weather -- the ever-rare once-in-a-four year day that has been rather mundane historically with an exception or two.  More on those in a minute.

Here are the particulars for the day.  You can see the full list of Leap Days on the left.

1) The average high of the 33 Leap Days is 44.2 degrees, with the average low of 28.5.  For sake of comparison, the "smoothed" National Weather Service climate normals for tomorrow are 47 and 30, reflective of a smoothed average of temperatures that are typical for the end of February over the last three full decades.

2) We have picked up accumulating snow on three of the 33 days, just under ten percent of the time.  The most snow on any of the Leap Days is one inch in 1968, with the other two snowfall totals of just 0.3" in 1920 and 0.2" in 1960.

3) Record high for Leap Day is 69 in 1972, followed by a record low of 10 in 1884.  This is one of the noteworthy sets of data from Leap Day.  The old record high of 66 was from 1880, which means it and the record low are on consecutive "years" and the record low (10) is rather typical for record lows for late February and early March, which generally range between 5 and 10 over a ten day period surrounding Leap Day.

4) The record for most rainfall on any Leap Day was 1.03" in 1896.  It's rained more than a trace on eight of the 33 Leap Days.  Tomorrow will make it nine in 34.  The 1968 Leap Day was the second rainiest (as well as the snowiest) as temperatures hung out near freezing for the most part.

With tomorrow's rain (perhaps some sleet at the very front of the event), enjoy our bonus February day as the calendar tries to correct itself!