Images (click to enlarge): U.S. heat index at 1 pm EDT, July 21, 2011, from Unisys; Heat index calculated from temperature and relative humidity (graph by CapitalClimate, table from National Weather Service)
6 PM Update: Added daily high temperatures to the table below. The Raleigh temperature tied the record set in 1952. Syracuse broke the record of 95° set in 1930 and 1933 by 6°.
A temperature of 98° and dewpoint of 76° (50% relative humidity) at Washington National at 5 pm produced a heat index of 114.
3 PM Update: The 97°/51% at Washington National raises the heat index to 112.
2:45 PM Update: This is the first time the temperature has ever reached 100° at Syracuse in July since records began at the current location in 1950. The temperature was 100° on August 9, 2001 and 101° on August 14, 2002.
Original Post
By 1 pm today, near-record heat coupled with high humidity to produce 100+ heat index values along most of the Southeast and Mid Atlantic coasts. In portions of the Carolinas and Virginia and northward into New York, heat indices were in the dangerous 105-110 range. Oppressive dewpoints of 70° or higher stretched from the Gulf Coast northward across the eastern Great Lakes into southern Canada and along nearly the entire East Coast. Here are some representative values of temperature, dewpoint, relative humidity, and heat index as of 2 pm EDT:
Location Temperature Dewpoint Relative Heat Daily
Humidity Index High
Washington Natl. 95 77 56 109 99
Washington Dulles 97 72 45 105 100
Baltimore BWI 98 74 46 109 100
Baltimore Downtown 101 75 44 114 103
Richmond 96 77 55 111 99
Raleigh 100 70 38 107 102
Philadelphia 96 74 49 107 98
Central Park NY 96 76 52 109 97
Albany NY 96 70 43 102 99
Poughkeepsie NY 96 73 48 105 98
Syracuse NY 100 73 42 110 101
Boston 97 70 42 103 97
Hartford 97 70 42 103 98
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