Historic. September in North Texas was not just very hot and very dry, but the hottest and driest on record by a country mile. Because detailed, long-standing climate statistics for Denton do not exist beyond the 1970’s, (although some people think 40 years is a long time), we’ll borrow from official records for DFW as well as Denton Enterprise Airport.
First, the numbers for Denton County. The average daily high for the month was 95.2; the average low was 71.6, deriving a day-night average temperature of 83.4 degrees, which was nearly 7 degrees warmer than the climatological norm. There were no 100-degree days in September, and only one day when we did not reach 93 or above; September 19th, when Denton Enterprise recorded a high of just 83 degrees.
Despite hot afternoons, Denton County cooled off into the 60’s more than a dozen mornings during September. From the, “You think it’s hot here,” department (to borrow from an old evangelist), DFW Airport never came close to the 60’s any morning in September, reporting an average low of 75.5 degrees. Despite bring only 23 miles north and 35 feet higher in elevation than DFW, Denton Enterprise was 4 degrees cooler than DFW at night, yet Denton’s average high of 95.2 was nearly identical to DFW’s average high of 95.5 degrees.
It’s a strong example of the “Urban Heat-Island” effect. The concrete, asphalt, glass and steel surrounding DFW soak up far more solar heat for nighttime release than the dirt, crops, grass and trees west of I-35 in general and west of Denton’s airport in particular. Although average temperatures here are warmer than they were 70 years ago, most of the increase has been due to warmer overnight lows, not hotter afternoon highs. Urban development, reservoirs (humidity) and 24/7 air conditioning are the three biggest contributors.
Using DFW climate records, (recorded at DFW International, Greater Southwest International and downtown Fort Worth), September 2019 exceeded all three monthly temperature records; “Average High” (95.2/2005), “Average Low” (74.1/1998), “Average Monthly” (83.7/2005). The top 10 monthly average records date from 2005 to 1911, with noticeable spikes in the 1930’s and 1950’s.
Rainfall, which was immeasurable at DFW in September was little better in Denton County. Three-hundredths was recorded over the 19th and 20th, while .09″ fell on the 23rd, for a monthly rainfall total of just 12/100ths of one inch; 2.55″ less than normal. Current rainfall for the year is just over 22 inches which is now more than 2 inches below normal. The U.S. Drought Monitor places southeast Denton County in the “abnormally dry” category for the first time this year. No severe weather was reported in Denton County during September.
Looking ahead, you can probably guess the rest. The Climate Prediction Center predicts October will be warmer and drier than normal throughout North Texas. That does not, however, preclude outbreaks of severe weather which are common during October.
Brad Barton is Chief Meteorologist of WBAP 820/570 KLIF/99.5 “The Wolf” and the Texas Rangers Baseball Club.