Most Humid Places in the U.S.

Why Iowa and Kentucky have humid climates

One of the women at my workplace was talking to me about the high humidity we've had this week. (The National Weather Service issued heat advisories several days because heat indexes were in the 102°-105° F. range. Heat index is a "feels-like" figure computed from heat and humidity readings.)

"Oh, it's hot and humid here in Kentucky," Miss K. assured me. "But this is nothing compared to Iowa! I've lived all over the U.S., and Iowa has the worst heat and humidity of anywhere! Oh my gosh, Iowa was even worse than New Orleans!"

I had never thought of Iowa as a place that rivaled New Orleans in heat and humidity, so I mentally filed her remark under "Odd things people have said to me about the Midwest".  (Also in that mental file: a customer's remark that it's downright rude how people in Kansas talk so fast.)

Later, I did a little research and found the following chart on NOAA's National Climatic Data website.

I wasn't too surprised that no cities in Iowa made the list of the top ten most humid cities in the U.S!  However, I'm sure that Iowa gets a full share of humidity. I don't doubt that Iowa becomes an uncomfortable place on summer days when it's very hot and very humid.

You see, Kentucky and Iowa are in the same climate zone. Both states lie entirely east of the 100th Meridian. You may remember from geography class that meridians are imaginary lines that run from the North Pole to the South Pole. The 100th Meridian cuts through the middle of North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas.

East of the 100th Meridian, we Kentuckians and Iowans (and the folks in various neighboring states) share a humid-continental climate. Our part of the U.S. is kept humid and rainy by the flow of warm, moist air northward from the Gulf of Mexico. West of the 100th Meridian, the climate is much dryer, and while summer temperatures can reach high levels, the average rainfall and humidity are much lower.

New Orleans is an entirely different climatic category. It has a humid subtropical climate, due to its location near the Gulf of Mexico.

Let's compare statistics from Weather Underground for July 2010, so far:

• At Witmer Park in Des Moines, Iowa, temps have averaged 76.1°F, and humidity has averaged 78.4%. 
• At the Christian County Weather Operations Center at Hopkinsville KY, temps have averaged 79.1°F and humidity has averaged 77%. 
• At the Louis Armstrong Airport near New Orleans, temperatures so far have averaged 81.0°F and --wow!-- humidity has averaged 85%.  

So, New Orleans wins both the high temps and the high humidity contest, so far in July 2010, for these three locations. I'm not shocked. Furthermore, it can't be denied that Des Moines has a much shorter summer than either New Orleans or Hopkinsville. I suspect that Miss K. was indulging in a bit of hyperbole or selective memory when she made that statement about Iowa's summers.