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”