Correction to July 2011 Flight Training story
I made two errors in my “Hot, Humid, and Dangerous” column in the July 2011 issue of Flight Training Magazine, which includes a link to a page on this site about why humid air is lighter than dry air.
First, the date of the extremely hot and humid day at the Newton, Iowa, Municipal Airport that I used as an example of density altitude in the story was really July 14, 2010, not a month earlier as I said in the column I sent to Flight Training.
Second, I used an incorrect figure for the density altitude at 10 a.m. that day when the temperature was nine degrees cooler than at 2:15 p.m. I should have given the figure as 3,417 feet.
I’ve recalculated the other figures in the story and they are correct. My figure for what the density altitude would have been in the afternoon if the day had been dry used a dew point of 50 degrees instead of the 88-degree reported dew point.
I used figures from Newton, Iowa, for my story because that week was one of the most humid ever in the Midwest and Newton had recorded extremely high dew points.
Jesse Ferrell’s WeatherMatrix Blog from that week on the AccuWeather.com site is a good discussion of the high dew points. This was one of the sources that led me to use Newton for my exmples.
He notes that the 88-degree dew point at Newton that day was the highest he’d ever seen listed for the United States. On the other hand, he and others make the point that dew point observations aren’t as reliable as those from other weather sensors.