On July 19, 2011, the sensor at the Moorhead Municipal airport was reporting a dew point of 88 degrees. Many of us in the weather community did not give much credence to the reading as that sensor gives calculated dew point temperatures three to five degrees higher than Hector Int’l no matter the time of year (and it still does, no matter what the vegetation type if any, time of day, month or season).
That day out of curiosity, I drove to the Moorhead airport, took a reading using an old fashioned sling psychrometer, which was used for years to measure relative humidity and dew point based on the cooling of a thermometer by evaporative cooling. I came up with an 83 degree reading on two tests, which was what the Fargo airport was reporting. Yet, in the end that 88 degree reading, which surprised many of us, was used as a new state record for Minnesota.
I put that record in this context; although Roger Maris’ record of 61 homers in a season has technically been broken, it was done so by questionable means. I think Roger Maris holds the true record and a humidity sensor that reads high consistently, in all seasons, perhaps should have as asterisk next to its record
Tuesday evening, the automatic sensor at the Moorhead Airport reported a dew point temperature of 88 degrees. This was prematurely reported by a number of local and national media as a new state record.
It was premature because the quality of the reading must be evaluated before it can be proclaimed a record, and it appears that the reading had a few problems. We went out to the site on Wednesday and found the sensor surrounded by moisture-producing corn, sugar beets, and very tall clover without a buffer as is required. Also, the field had standing water all around which doubtlessly added greatly to the humidity and would not be considered representative of the surrounding countryside as a whole.
Finally, the sensor at Fargo’s Hector Airport was simultaneously registering a dew point of 83 which, although very high, was five degrees lower than the Moorhead reading. Just like when track and field records do not count if they are wind aided, this dew point record will also fail to qualify as a record.
A couple of links you may want to read:
Hottest Place on Earth?
Unreliable Dew Points
We have all heard the old saying “it’s not the heat, it’s the humidity”, you may have even said that these past few days, but what you really should be saying is “it’s not the heat, but the dew point”. Relative Humidity is exactly that, relative and is directly correlated to the air temperature.
Instead, you feel uncomfortable base on the amount of water vapor in the air, which is not what relative humidity is measuring. The past few days the relative humidity has dropped to around 50-60% during the afternoon when the heat indexes were at the highest point of the day.
A better way to know what your comfort level will be is to watch the dew point and remember that dew points in the 40s you’ll be feeling great, in the 50s, you’re still comfortable, moving through the 60s, most feel slightly uncomfortable, but when the dew points are in the 70s (the case the past few days) no matter what the temperature, nearly everyone is uncomfortable and the word sultry will probably come to mind.