134 Reasons Why Sticking A Weather Station In A Soy Field Might Not Be A Good Idea

With the recent heat event across the middle of the country, there have been countless stories about heat index values of over 120 degrees. I've mused in twitter about "corn effect" heat index values of 128, 130, or even higher. One of the most aggressive examples of this occurred in Moorhead, MN on Tuesday where the heat index topped out at 134 degrees during the peak heat of the day, thanks to a dew point of 88 combined with temperatures in the mid 90's.

Few probably realize that Moorhead's observation site is in the middle of a farm field ten miles outside of Moorhead proper.   The map below shows the twin cities of Fargo (left of graphic) and Moorhead (where the Google map "A" label is).   Residing about ten miles outside of the city is Moorhead's community airport (a municipal aviation airport such as the ones in Coatesville, Pottstown, Millville, etc.), sitting smack dab in the middle of a field of sugar beets, soy, and perhaps some corn for good measure.   I've been through this area a couple of times in my life -- the area is flat as a pancake, lacking trees, and heavily farmed.

The National Weather Service in Fargo provided a really good write up explaining the factors that lead to some suspicion in the high dew point values -- farming areas where heat index values are substantially higher than surrounding larger towns thanks to the transpiration of crops and wet ground.   Transpiration is the part of the water cycle on the plant side of the fence and essentially is the plant's way to cool itself as it releases water vapor through its cells.  Essentially, think a less stinky form of sweat.   I lifted the temperature comparison between Fargo's airport (a bit farther removed from agricultural influences) and Moorhead's airport data for Tuesday from the NWS in Fargo to show the comparison in data for the two sites.   The peak heat index for Fargo was 116 -- still oppressive -- but the top dew point for Fargo was five degrees lower than the top dew point in Moorhead (83 versus 88), with Fargo's dew point consistently several degrees lower than Moorhead's.

There are countless other examples of "corn effect" heat in these heat waves -- parts of Iowa and other parts of Minnesota had heat index values over 120 thanks to observation sites in the midst or near a farm field.   While some of the dew point values reached in the heat wave in the Midwest were legitimate -- the 82 in Minneapolis is a definite "legit" record since their airport is just about smack dab in the middle of the metropolitan area, the mid and upper 80's dew point values in some of the rural areas are likely enhanced thanks to what may be on someone's dinner plate, feeding trough, or gas tank (ethanol) in a few weeks.   There's no denying the heat or even the humidity in many locations but understanding should be taken when analyzing some of the more extreme data due to location and what surrounds it.

All I can ask is that tomorrow we don't get a dew point in the low 80's with any temperatures over 100...I don't think the region needs a repeat of July 1995 around here.