While Hot, This Heat Wave Not Unprecedented
It was a hot Sunday with temperatures in the 90's for a second consecutive day. Today's 95 degree high in Philadelphia tied a record high from 1999 and records were set in York (96) and Georgetown, DE (95). Temperatures were generally about the same as yesterday but dewpoints were slightly lower, resulting in heat index values around 100 as opposed to yesterday's 105. Yeah, it's still a hot one regardless but I'm trying to show any "relief" that there may be, even if it is fickle.Some of you have opined to me that the first heat wave of 2008 is rather early and/or unusual compared to past years. While the first heat wave of the year is early compared to "average" (which is early July) there have been several instances where the heat has been as bad if not worse at an earlier time of the year than the first full weekend of June.
Going back to 1874 there have been 25 days on or before June 8th where the thermometer hit or exceeded 95 degrees in Philadelphia, most recently done on April 18th, 2002. These occurrences tend to be rather infrequent, with the non global warming years of 1895 and 1899 accounting for five of the 25 occurrences all-time by themselves.
One of the most impressive early season heat wave occurred in between June 2nd and June 7th, 1925. The high on each of those days was 96 or higher, including back to back 100 degree readings on June 5th and 6th. Those 100 degree readings are the earliest in Philadelphia history. June 1925 ended up being the second warmest June since 1872 in Philadelphia and featured a total of 11 90 degree high temperatures.
Another impressive early season heat wave was between May 18th and 20th, 1962. Temperatures all three days were 94 and higher, including the earliest 96 degree high in Philadelphia recorded annals on the 19th.
Heat waves have happened as early as April around here, with 1976 and 2002 featuring recorded setting warmth during the middle of the month, including a 94 in April 1976 and a 95 degree reading in April 2002.
The most impressive early season heat waves belong to May 1991, with a record 12 90 degree days occurring during that particular May. A nine day heat wave at the end of May and beginning of June included two 95 degree highs, a 96, and two 97's for high temperatures, all of which are present record high temperatures in Philadelphia.
What is, however, a bit unusual about the heat is the sudden arrival. With no 90 degree reading to Philadelphia's credit before Saturday, the first 90 degree reading this year has been among the hottest of all "first 90's" since 1872. The fuel added to the fire is the fact we haven't flirted with 90 since mid-April plus we are three weeks removed from some of the coolest weather we have seen in May in several years in Philadelphia. Going from cool to sauna in very little time does not allow for much adjustment by the body and continued heat only exacerbates the problem.
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