The Hottest “Feeling” Place in the World?

LJWorld.com weblogs Lawrence Weather Watch

Posted by Alex Harrington June 25, 2009 at 8:53 a.m.

Believe it or not, parts of the American Midwest see some of the hottest temperatures in the world during summer months. While the actual temperature may not be all that impressive — 100°F is commonly reached all over the world — the Midwest humidity can make it feel much, much worse.

We often talk about the “dewpoint” when the humidity really cranks up.

A dewpoint is a measure of moisture. The more moisture there is in the atmosphere, the harder your body has to work in order to stay cool. Your body really sweats once the dewpoint starts to get above 60°F. Once the dewpoint gets above 70°F, you might need the air conditioner in order to stay cool. Dewpoints in the 60’s and low-70’s are common throughout the world; when it gets above 80°F, then a different can of worms is opened.

Dewpoints near and above 80°F are not too often reached around the world, even in the tropics. Such dewpoints can be readily touched when you have a lot of moisture evaporating—turning into water vapor—into the atmosphere. Parts of the Midwest are havens for this steam-bath potential.

By June and July, not only are rivers giving off lots of water vapor, but so are new plants, too: young plants, like the soybeans, corn and alfalfa, give off tremendous amounts of water vapor (sometimes more so than many of the established flora and fauna of the tropical rainforests). If you add high soil moisture content (from heavy spring rains) to the mix, then you have all the ingredients for near 80°F+ dewpoints. This is often the case right here in Northeast Kansas.

Northeast Kansas, Northern Missouri, Eastern Nebraska, Southern Minnesota, all of Iowa, Southwest Wisconsin and much of Illinois, all share in the potential for near 80°F+ dewpoints because of the combo of rivers, lakes and lots and lots of perspiring crops. It’s really the crops that do the trick in pushing that dewpoint towards 80°F. June and July are usually the worst of this combo. By the time we hit August, many crops mature. Maturing crops do not give off quite as much water to the atmosphere. So, by August, we usually see those dewpoints cap off in the low-to-mid 70’s, at best.

What does all of this mean? It means you do not have to live in the tropical rainforest to “feel” the highest humidity you can get. Factor in a hot Northeast Kansas sun, and actual temperatures near 100°F, you have a potentially lethal heat index pushing 110-120°F+; if those actual temperatures are combined with dewpoints pushing 80°F.

All of the ingredients are in place this June and July for near 80°F dewpoints to continue to be realized in and close Northeast Kansas. This means with each heat wave for the next few weeks, we have the potential for seeing heat index values topping 110°F. We will likely have to wait now until August before this dangerous potential wanes. Get ready for a hot, no doubt humid, summer in Northeast Kansas.

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Irish (Leslie Swearingen) says…

I had no idea that plants perspire. Thanks. I am leaning a lot from these blogs.
June 25, 2009 at 11:41 a.m.
49aharrington6 (anonymous) says…

@Irish,

"Transpire" would be the proper term, but for all intensive purposes they give off water vapor; like sweat in a gaseous form. The real meteorological/climatological term for plants giving off water vapor is "evapotranspiration". Stay cool!

Best,

Alex
June 25, 2009 at 12:25 p.m.
BrianR (anonymous) says…

It certaily is yucky out there.
June 25, 2009 at 12:43 p.m.
labmonkey (anonymous) says…

Irish-

Walk near or into a cornfield. You will notice it feels much hotter than away from it.

Plants do transpire. The evaporation of water vapor from the leaves of a tree creates the vacuum that pulls the water from the root system all the way to the top of the tree (30-50 ft here, hundreds of feet when you talk about a redwood).
June 25, 2009 at 12:55 p.m.
kthxbi (anonymous) says…

thanks Alex. That was interesting. I knew of of my complaining could be justified by science.
June 25, 2009 at 1:39 p.m.
The_Original_Bob (anonymous) says…

"Walk near or into a cornfield. You will notice it feels much hotter than away from it."

Oh, hell yes. I'm pretty sure getting irrigation rig tires unstuck in the middle of corn fields while I was in high school influenced my decision to goto college. Hell on earth in the cornfields.
June 25, 2009 at 1:45 p.m.
blindrabbit (anonymous) says…

It's hot and humid here alright; but say it's close to the worst is stretching it a bit. I'll take a day here anytime for those in Vietnam, Philippines, Houston, Florida, D.C., etc., etc., etc.

At least here, you know it does not last too long, a few days at most.
June 25, 2009 at 1:59 p.m.
firemedic301 (anonymous) says…

I agree Mr_Nancy, when I was in Iraq the hottest temp I saw was 134 degrees. But no plants or water made for no humidity. When I came home for leave in July 06 I lost 5 pounds in 3 days just from sweating.
June 25, 2009 at 3:33 p.m.
pdecell (Paul Decelles) says…

I just got back from the Rockies and this heat is horrible compared to 60 - 70 F low humidity etc in CO.

Help! Who thought up this place any way?
June 25, 2009 at 3:45 p.m.
49aharrington6 (anonymous) says…

Good thing about the high amount of moisture in the air right now is that it is actually helping to slow down the day's temperature rise. It takes more energy to heat up a humid airmass (and cool it off); so, that is why our highs may actually end up closer to 95°F, with a heat index of 105-110°F, versus 100°F, with a heat index pushing 115°F. We'll see just how a few more hours of sun will impact the temperature rise and subsequent heat index values by early evening...
June 25, 2009 at 3:45 p.m.
49aharrington6 (anonymous) says…

@Multidisciplinary,

You are right about some spots in Vietnam and the Philippines. I recall hearing about a dewpoint near 90°F once somewhere in Southeast Asia (which may be close the world record). I am not sure what the heat index was at that time.

There are even local places in Iraq that draw water from the sea to water plants. Desert air (dry, of course) can reach temperatures of 115-120°F, easily. That air, combined with high humidity near growing zones, can produce unbelievable heat index values well above 130°F.

Still, Midwest heat and humidity can be a real beast.

For all those interested, here is a heat index calculator:

http://www.hpc.ncep.noaa.gov/html/hea...

I know Matt posted the math code, but this calculator will do it for you.

Stay cool all,

Alex
June 25, 2009 at 3:53 p.m.