The last month of the decade across the Midwest was abnormally warm with only brief shots of cold air. From Chicago to Columbus, average temperatures for the month were 6 – 8 degrees above normal thanks to mild air masses. This, in turn, led to a below average amount of snowfall for most except for Indianapolis, where a total of 7.6” accumulated (normal is 6.9"). Thanks to these milder temperatures, liquid precipitation fell below average in most areas, except for Cincinnati where precipitation came in around 3.58” with an average monthly amount of 3.37”.
Somewhat Cold and Snowy First half
The start of the month started off mild with high temperatures in the low 40s in Chicago while areas east saw highs in the upper 50s before a cold front swept through the area. This front triggered snow showers in the afternoon and evening on the 1st in Chicago resulting in a coating to an inch of snow. This front weakened as it moved across the Midwest on the 2nd and 3rd causing only coatings of snow and sleet from Indianapolis to Columbus. Cooler temperatures developed in the wake of this front on the 3rd with highs in the 30s to near 40 degrees with a round of snow showers in the afternoon and evening in Dayton and Columbus. Above average temperatures (3-5 degrees) continued from the 4th – 8th with mainly dry conditions except for a few rain showers in Cincinnati. In addition, strong winds on the 6th in Chicago produced waves as high as 8’ on Lake Michigan.
A warm front then pushed through the Midwest on the 9th, producing periods of rain amounting to 0.50”-1.00”, while highs were in the middle to upper 50s. A cold front ushered in much colder air on the 10th, sparking snow showers during the morning in Chicago and Indianapolis. Then during the evening on the 10th and into the 11th, a stronger cold front pushed through the Midwest. This generated up to 2” of snow in Chicago before it weakened as it moved east into Dayton and Cincinnati and eventually Columbus. A colder air mass stuck around on the 12th - 14th with lows in the 20s to lower 30s. These below freezing temperatures in conjunction with dense fog in Chicago, led to patchy ice on surfaces.
The coldest and snowiest stretch of the month was the 15th – 19th as multiple disturbances worked through the Midwest. The first system pushed in on the 15th with snowfall amounts around 0.5” in Chicago, while areas east like Indianapolis and Ohio observed totals in the 2-5” range. A second system on the 16th generated patchy ice from freezing rain and 2-4” of snow in Indianapolis. The third system was the weakest of the set with only coatings on the 17th and 18th. The bigger takeaway was the cold air, as lows plummeted to 8-14 degrees.
Warm Second half
High pressure systems dominated between the 19th and 26th allowing well above normal temperatures and dry conditions. During this stretch, temperatures rose as high 60 - 65 degrees, which is 20-25 degrees from normal! Chicago actually broke their high temperature record on the 26th with a reading of 56 degrees at Midnight! This was a historic warmth stretch, as it marked the 2nd warmest Christmas on record in Chicago and only the 9th time since 1871 where temperature readings were in the 50s for more than 5 days in a row. This mild weather came to a halt thanks to a cold front on the 27th - 28th, which produced some freezing drizzle in the Windy City. A soaking rain fell on the 29th before colder temperatures returned on the 30th - 31st with wind driven snow, sleet and freezing rain showers. The highest totals were in Chicago where many locations saw up to 2” of snow, while areas like Dayton and Columbus only observed scattered coatings. Thanks to this last batch of moisture before the calendar flipped to 2020, Chicago received enough precipitation to generate its 3rd wettest year on record!