This morning most of Western Wisconsin had clear sky conditions under high pressure. Light or calm winds.
Using MesoWest to look at the temperatures there are dramatic variations, some reporting by AWOS or DNR calibrated stations, and some by private individuals, which as we all know may not have the megabucks to install top notch equipment or have it calibrated. Nonetheless, most of those stations have in the past been reporting reasonable temps, and thus not entirely suspect.
https://mesowest.utah.edu/cgi-bin/droman/mesomap.cgi?lat=44.86668&lon=-91.48800&radius=25&rawsflag=290&site=KEAU&unit=0&time=LOCAL&product=&year1=&month1=&day1=00&hour1=00&currTimeChecked=This morning I had -9 on almost all of my thermometers, both electronic and mercury column.
A neighbor 1.5 miles to my east, down in a wee bit of a valley had -15 and -18 on some good 'quality' thermometers, too.
Around Eau Claire temps ranged from -7 to -19 all within a few miles of each other. To my south about 40 miles, at Black River Falls airport, the temperature was -25 and a mile or two to the east, -28.
I don't understand, other than radiation cooling, how the temperatures can vary that much, especially within a few miles. In the past I would have offered the explanation of bad equipment or observer bias wanting to be a bit dramatic and having the hottest or coldest temperatures. A couple decades ago when small radio stations were still independent, one station on the east side of Eau Claire near the lake was always, without exception, dramatically colder than any other reporting station, by as much as 10 to 15 degrees. Engineers who worked there were hams and said that they'd see the same numbers on the readouts as was being reported, and when car thermometers became standard (the epitome of quality, I'm sure) the temps were very close when one would drive by the station.
Is it all just radiation cooling? If so, why would one open area be dramatically colder than another?
Is it a myth that cold air 'drains' into the lower areas?
This has been so noticeable the last few days that it has prompted me to wonder about the reason behind it. As I mentioned observer bias and cheap advertising quality thermometers were my explanation in the past but now I'm wondering if this phenomenon is real.
Thanks for any thoughts or science.
Dale