In a recent post about New York's major heat waves, a key finding was that the nine-day heat wave of July 1977 had the distinction of being the hottest heat wave of seven days or longer. This was based on the average high temperature. However, when low temperatures are added to the equation a different story emerged.
It turns out that New York's seven-day heat wave of July 14-20, 2013 had the warmest average low of any lengthy heat wave - 79.0°. And although the average high during these days, 94.6°, put it in the middle of the pack, when it was averaged with the low temperature, the resulting mean temperature of 86.8° (the average of the high and low) made it the hottest of all the major heat waves. It bested a heat wave in August 1988 by 0.1 degree. And 1977? It fell to third.
|12 HOTTEST HEAT WAVES RANKED BY MEAN TEMPERATURE|
|(Heat Waves of 7 Days or More)|
|Year||Dates (# of Days)||High||Low||Mean|
|2013||July 14-20 (7)||94.6||79.0||86.8|
|1988||Aug 9-15 (7)||95.3||78.0||86.7|
|1977||July 13-21 (9)||97.1||75.6||86.4|
|1955||Aug 1-7 (7)||96.1||75.3||85.7|
|1944||Aug 10-17 (8)||96.6||74.0||85.3|
|1973||Aug 28 - Sept 4 (8)||95.4||75.0||85.2|
|1993||July 7-16 (10)||95.7||74.5||85.1|
|1983||July 12-18 (7)||95.0||74.9||85.0|
|2002||July 29 - Aug 5 (8)||94.0||75.5||84.8|
|2002||Aug 11-19 (9)||94.2||75.2||84.7|
|1953||Aug 24 - Sept 4 (12)*||95.4||73.9||84.7|
|1991||July 15-21 (7)||96.6||71.7||84.2|
|*Lengthiest on record|
Another striking characteristic of July 2013's heat wave was its relatively small diurnal variation - average high and low were 15.6 degrees apart. By comparison, most of the other heat waves among the twelve hottest had diurnal variations greater than twenty degrees. (1991's was the greatest, at nearly 25 degrees.) Meanwhile, the last two days of 2013's heat wave had diurnal variations of just 13 degree and 12 degrees (high/low of 96°/83° and 93°/81°).