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Bob Henson | July 26, 2012 • We still have a few days to go before this torrid month ends, but July is already promising to go down as the hottest month ever recorded in a number of U.S. locations. (See the "Update" box at lower right for more details on how July turned out.)
One of the epicenters of this summer’s drought and heat is the St. Louis area. As of July 26, the city’s average temperature for the month (including both highs and lows) is a brutal 88.9°F. That’s well above the city’s warmest month since records began in 1874: July 1901, when the average was 87.4°F. A typical July (1981-2010) would average 80.0°F. Given continued heat in the forecast, it looks very likely that St. Louis will break this record.
The hot days in St. Louis this summer have been really hot. In fact, St. Louis has racked up 11 days at or above 105°F, the most recorded in any year. As for 100°F days, the city has had 16 this year—impressive, but still well short of the record 37 set in the Dust Bowl year of 1936.
In Detroit, July is currently averaging 79.6°F, compared to a typical 73.6°F. The city’s warmest July and warmest month on record were notched just last year, with 79.3°F. However, with a cool front pushing temperatures down this weekend, it’s likely that the Motor City will lose enough steam to keep the 2011 record safe.
Further west, Denver has a good chance of scoring the warmest month in its weather records, which go back to 1872. The champion thus far is July 1934, another Dust Bowl year, when the city’s monthly average was 77.8°F. As of the 26th, this July is averaging 79.0°F. As in St. Louis, Denver has also scored a record number of 105°F days this year: two. The only other times Denver has hit that value—its all-time high—were on July 20, 2005, and August 8, 1878.
The mid-Atlantic and Southeast haven’t been spared, although a few milder periods interspersed with heat waves have kept July just short of record territory in many cases. At Washington’s Reagan National Airport, this month is averaging 84.0°F thus far. That’s second only to July 2011 (84.5°F) among all months in D.C. weather annals, going back to 1871.
Update (August 9):NOAA's National Climatic Data Center has verified that July 2012 was the hottest month for the 48 contiguous states since national records began in 1895. The monthly average temperature was 77.6°F, 3.3°F above the 20th century average for July.
The last few days of a month can easily make or break a monthly record. Just one mild, rainy day that’s 15°F below normal can trim about 0.5°F from a monthly average. However, that’s unlikely to happen as July draws to a close across much of the drought-prone belt from the central Rockies to central Appalachians.
Indeed, the most dangerous aspect of heat waves like the current one is their relentlessness, when temperatures stay toasty day after day and night after night. On Wednesday, July 25, the low temperature in St. Louis was 86°F. That’s the warmest daily low in the city’s history, matching the record set on July 24, 1901.
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.