Friday, May 31, 2013

May 90's And Summer's Performance

Today marks the third 90 degree day of the year -- as  many as we picked up in 2011 and 2009.  However, the two years had vastly different totals for 90 degree days.

Going back to 1998, we've averaged just under two 90 degree days before the end of May and 28 90 degree days for the entire year.  Extra 90 degree days early in the year can help (1991 picked up 12, which is a record for May) boost your yearly total but having a monthly total that's relatively close to normal doesn't have much of a bearing one way or the other on the summer as a whole.

Two cases in point -- 2004 and 2010 -- both had two 90 degree days but 2004 only had seven more 90 degree days for the entire summer, while 2010 was just getting started on its record setting total of 55.

Overall May temperatures (the whole month) in recent years do have a bit of a correlation to warmer than average summer temperatures.  Going back to 1980, years that finished among the top 15 warmest in May in Philadelphia's record have correlated to significant warmth in summer at a 66% clip (six years since 1980 feature top 15 warmth during the month of May, four were at least 1.5 degrees above average for the whole of summer).  This year will feature an above average final temperature but it will not likely be top 15 warm.