Coming off of what was an extremely tumultuous November in the Stateline, many folks understandably wondered with fear just what Mother Nature had up her sleeve in December. As a major relief to most, December's opened on an extremely tranquil note, and a relatively mild one at that.
Each of the month's first three days have posted above normal temperatures, a trend that's to continue for at least two more days, if not longer. Tuesday's high temperature of 44° is the warmest reading we've experienced since Thanksgiving Eve, and marks the eighth 40°+ high temperature in the past eleven days!
Many folks, however may contest the validity of the 44° high temperature reading, claiming to have seen higher figures on their car thermometers, the sign outside a local bank or pharmacy, or even at their home weather station. Personally, my car read 49° on my way into work this afternoon! But, more often than not, those readings are to be taken with a grain of salt.
There are many reasons for the frequent disparity between car/bank/home thermometers and the official thermometer readings to which we most frequently refer. Oftentimes, car and bank thermometers are placed in direct sunlight. Naturally, a thermometer struck directly by the sun's rays would warm more quickly than a thermometer placed in a shaded or protected area. Official thermometers like the one at the Chicago-Rockford International Airport are always shaded by a contraption called a Stevenson Box. This box, which serves as a shelter for thermometers and oftentimes other weather-related devices, including barometers, prevents direct sunlight from getting in from the outside, while still allowing air to circulate freely.
Secondly, many of the banks, homes, and cars with thermometers built in or nearby are dark in color. Those structures will absorb more heat than the Stevenson Box, which is always painted white, which will not absorb the heat nearly as efficiently.
Lastly, the bank, home, and car thermometers are often placed very near or on top of concrete or other pavement surfaces. Those surfaces also allow for additional heat absorption. By contrast, official thermometers, placed in Stevenson Boxes, are placed in open fields, far away from buildings or pavement, and are elevated between four and seven feet above the ground. This, too, ensures a more unbiased temperature reading.
A wind shift to the west-northwest Wednesday is to import slightly cooler air to the Stateline. However, generous sunshine is expected from start to finish, meaning a 40° temperature is likely for the third time in December's first four days. The drawback, however, will be the occasionally gusty breezes, which may reach speeds of up to 25 MPH at times.