September 27, 2018

This Has Been One of the Eastern U.S.'s Muggiest Years on Record

This has been a miserable year in more ways than one. If it seems like the weather was especially stifling in the eastern United States this summer, now you have hard data to back up your months of complaining on Facebook. This has been one of the muggiest years on record in the eastern part of the country. Record warmth is one thing—we can sort of deal with the heat—but humidity is a clingy misery you just can't shake, and it was in deep supply this summer.

While relative humidity is a classic way to measure the amount of moisture in the air, it doesn't really tell us much since it's relative to the air temperature. Relative humidity goes down with the heat of the day and rises as the air cools off at night.

A better way to objectively measure how comfortable the humidity feels is to use the dew point, or the temperature at which the air would reach full saturation, or 100% relative humidity. Dew points below 60°F are generally considered comfortable. It's noticeably humid when the dew point reaches 65°F, putrid when it reaches 70°F, and unbearably muggy when the dew point climbs into the mid or upper 70s. The summertime dew point in Miami routinely reaches or exceeds 75°F.

So far this year, a number of major cities in the eastern United States have seen the most hours they've ever recorded with a dew point at or above 70°F. Cities that have seen their muggiest years on record stretch from Alabama to Massachusetts, including Montgomery, Charlotte, Washington-Dulles Airport, Scranton, Providence, and Boston.

Some cities have seen more than a thousand hours of dew points at or above putrid levels in 2018. Records at New York's JFK Airport stretch back to 1948. The previous record-high number of hours at or above 70°F was about 850 hours set in 1984. This year, the airport has recorded more than 1,200 hours with dew points at or above 70°F. It's a similar story at the airport in Charleston, West Virginia, where the previous record of around 850 hours set back in 1949 was eclipsed by this year's count of nearly 1,200 hours of putrid humidity.

A series of stubborn centers of high pressure were the driving forces behind this year's rancid summer. If you look back through my blog posts over the past couple of months—especially before the hurricanes—I sounded like a broken record talking about stifling humidity and the chance for flash flooding due to strong thunderstorms. (See also: "Oh, For Crying Out Loud, Please Not This Gross Weather Pattern Again.")
The GFS model's precipitable water forecast on the afternoon of July 31, 2018. | Source: Tropical Tidbits

The East Coast found itself stuck under the western side of a strong ridge of high pressure parked over the western Atlantic Ocean. This persistent southerly flow opened the conveyor belt for tropical air to flow north over the eastern part of the country for months on end. Not only has it been uncomfortable since the end of spring, but the relentless, excess moisture allowed thunderstorms to turn into water factories, leading to numerous flash flood emergencies across this region of the country.

(PS: I compiled this data using the Iowa Environmental Mesonet's awesome observation archives and their nifty tool that lets you plot the number of hours a station has seen a certain temperature or dew point over certain a period of time. If you're ever in a bar fight about how many hours the temperature in Buffalo was below zero in 2004, the IEM's got you covered.)

(PPS: The answer is 40 hours.)

[Top Image via Flickr user kandypics]

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I contribute to The Weather Network as a digital writer, and I've written for Forbes, the Washington Post's Capital Weather Gang, Popular Science, Mental Floss, and Gawker's The Vane. My latest book, The Skies Above, is now available. My first book, The Extreme Weather Survival Manual, arrived in October 2015.


  1. Thanks for sharing the new (to me) plotting tool! I've been using xmACIS for years but it is limited in some ways. More data can never hurt.

    1. The IEM's site is a treasure trove of resources. I love it.