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Uncharted Heat Index values

Posted at 7:53 AM on July 18, 2011 by Craig Edwards (11 Comments)
Filed under: Climate, Crops, Heat, Microclimates, dew point

Austin Schoen (left), Mark Schauer (center) and Tanner Schauer cool off on the Bumper Boats ride at Lilli Putt in Coon Rapids, Minn., on July 18, 2011. (MPR Photo/Nikki Tundel)

While we are calling this sweltering, oppressive atmosphere a Heat Wave, it equally worthy of being called a High Dew Point Warning. Yesterday afternoon and evening dew points, a very good indicator of the moisture in the atmosphere, were in the lower 80s over a large swath of southern Minnesota. It is very rare to observe sustained high dew points over a broad area this far north.

Dew point measurement can me impacted by the microclimate of the sensors location. We see dew points at their highest in southern Minnesota from mid July through about mid August. A number of us in the weather business believe that these seasonally high dew points are the results of the evapo-transpiration of the maturing corn corps across Iowa and southern Minnesota. Moisture is released back into the low levels of the atmosphere and we feel its affects.

A slight drop in dew points is seen for today. We may well see a few degrees of additional heat on the thermometer. That translates to Heat Index values of 105 to 115, in the shade, during the middle of the day. This is excessively sweltering when you add into the equation direct sunlight. Stay out of the sun today if you can. Unless you are standing in the lake.

Dogs and cats instinctly slow down in this weather. If your dog needs to have a walk, make it a quick trip early in the morning or in the evening. Provide plenty of water for pet during this sultry period.

Follow the advice from health officials with regard to your well being. Apply the number one rule; slow down. Dress in light colors with a brimmed hat.

Heat spell breaks a bit towards the end of the week. Just so you know; the climate records document the next seven to ten days as the warmest period during the calendar year.

The sensible temperature is about fifteen degrees warmer in the direct sunshine.

Think cool thoughts today.
CE

Comments (11)

Here's an interesting question. If higher dewpoints are the result of corn, will our dewpoints become lower if we end ethanol subsidies? One can hope!

Posted by Disco | July 18, 2011 10:01 AM

On July 18, 2011, there were 3 people stranded on an unknown desert island in the middle of Lake Minnetonka--a climatologist, a meteorologist, and a weatherman. They discovered a bottle and opened it, and out popped a jeanie. She granted them each one wish. So, the climatologist made a wish to be recording the advancing glaciers on cool Mount Shasta in California. And poof, he was gone. And the meteorologist made a wish to forecast the growth of pineapples in Hawaii. And poof, he was gone. So the weatherman thought for a moment, and then said to himself, "I really miss my buddies; I wish they were back here with me."

Posted by Mark | July 18, 2011 10:18 AM

I often hear people back home in DC-Maryland saying "it was 100 degrees and 100 percent humidity". From my observations this never happened at the same time, you can have a 100 daytime temp in the afternoon and 100% RH in the cooler morning hours. My question is, what is the highest dewpoint ever recorded?

Posted by Tom Heutte | July 18, 2011 10:34 AM

Uncharted or unchartered?

Posted by Anonymous Coward | July 18, 2011 10:40 AM

I found it interesting when looking at this make up baseball game with Cleveland. On April 22nd when the game was postponed, the high temperature was 45 degrees and there was about two tenths of an inch of rain in the Twin Cities.

Wish we could make this heat go POOF.
Craig

Posted by Craig | July 18, 2011 10:43 AM

Thanks anonymous! You are correct. My mistake.
Craig

Posted by Craig | July 18, 2011 10:50 AM

@Tom Heutte

I did a bit of searching last night on the world's highest dew point. It's not an easy record to find; there is a lot of conflicting information.

But the best I could find was at Dharan, Saudi Arabia, which once had a DP of 95 in 2003. This struck me as odd since it's a desert. I found another site listing Eritrea with a DP of 94.

http://www.usatoday.com/weather/resources/askjack/archives-weather-extremes.htm

- 90° at Appleton, Wisconsin at 5pm, July 13, 1995 (dry bulb temp 101)

http://www.accuweather.com/blogs/weathermatrix/story/34037/dew-points-near-record-levels-in-midwest.asp

There was a record low DP at Las Vegas of -22F set last month:

http://www.skyviewweather.com/2011/06/29/record-setting-dew-point-depression-at-las-vegas-yesterday/

Posted by Disco | July 18, 2011 11:51 AM

Thanks Disco. Dew points don't have a real long period of record, but lower 80s in our neck of the woods is exceptional.
CE

Posted by Craig | July 18, 2011 1:11 PM

Craig--last word of second paragraph should be "effects" (it's a noun, not the verb you used).

Posted by Bruce | July 18, 2011 1:30 PM

Thanks Bruce. A teachable moment.
Craig

Posted by Craig | July 18, 2011 2:16 PM