August 4, 2008 – Oppressive Weather

The last few days have been off the charts as far as uncomfortable weather is concerned.

Here’s a screen capture from the Weather Underground showing the conditions on Sunday afternoon – the temperature is not unusual, but the 0 mph wind with a 81 degree dewpoint is off the charts.  I tried to look up the highest all-time dewpoint in Iowa as I can not remember it ever over 80 before. I didn’t find the Iowa record, but I did find the highest dewpoint in 102 years in Minnesota was 81. I’m assuming it wouldn’t be much different in Iowa because southern Minnesota is practically Iowa as far as landscape and crops.

Here’s the chart that lists human comfort and dewpoints:

Dew Point    Human Perception
>75°F              Extremely uncomfortable, oppressive
70 – 74°F        Very humid, quite uncomfortable
65 – 69°F        Somewhat uncomfortable for most people at upper edge
60 – 64°F        OK for most, but all perceive the humidity at upper edge
55 – 59°F        Comfortable
50 – 54°F        Very comfortable
<49°F             A bit dry for some

Many people wonder why the Midwest can be more humid than the coasts and tropics – how exactly does warm, moist gulf air increase in moisture after traveling 1,000 miles?  The answer is corn.  At this time of year, corn transpires enormous quantities of water through its leaves.  Even in the weather forecaster discussion, the evapotranspiration of corn is factored into the weather forecast during the height of evapotranspiration season.

I’ve been working in the basement the last few days, adding insulation to the sill plates and under the floor below an unheated basement room.

one year ago…”Gourd Tunnel”

3 thoughts on “August 4, 2008 – Oppressive Weather

  1. Did you know that corn is also an important source of oxygen? You may be surprised to know that, at this time of year, the average acre of corn produces enough oxygen to meet the respiratory needs of 131.5 people. That means approximately 22,677 acres of corn will sustain Iowa’s entire population. Given that the average size of an Iowa farm is approximately 356 acres, it takes fewer than 64 average-size family farms (or one humongous corporate farm) to keep Iowans breathing. Isn’t that a-maize-ing?

  2. By the way, here in Casa Grande, Arizona, the dew point is a “very comfortable” 50°F. The temperature is 107°F, but with a 9 mph wind, it feels much cooler. The humidity is only 22%, perhaps because we are surrounded by cotton, which apparently does not evapotranspirate as much as corn. The barometer is falling….[CRASH]. Sorry, old radio joke.

  3. Interesting… and “evapotranspiration” is such a great word! As today is what I would consider a “nice” day I just checked to compare and the dew point is back down to a comfortable 56F.

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