Heart of 2018 Winter: A Wild Pattern of Ups and Downs in the Midwest
In many ways, the heart of 2018 winter that encompassed January and February was a wild ride of ups and downs in terms of both temperature and precipitation in the Midwest. While Chicago saw a significant increase in snowfall as compared to the prior year, it was mild weather and flooding rains that stole much of the headlines toward the end of the period in the Ohio Valley. There was plenty of significant weather to talk about, with a good deal of broken records as well.
A MUCH SNOWIER CHICAGO:
It was quite an active beginning to 2018, as January and February lived up to the billing in terms of cold and snow. This was certainly a large contrast to 2017, where wintry weather seemed like an afterthought. While a few periods of exceptionally mild weather moved in at times, the snow dominated the story.
To get an idea of how snowy the period was, we have to take it back to 2017. Snowfall in January and February was almost literally non-existent, with the pair of months seeing mere flakes and less than an inch of total snowfall for the entire period. Not only was this a rare occurrence, it was record-breaking. The warmth broke records as well. Fast forward to 2018 and an entirely different story unfolded.
An arctic airmass with staying power enveloped the entire northern half of the country to finish off the month of December, and the momentum from this would carry over into January. Right off the bat, it was bone-chilling. O’Hare Airport set a record for the lowest daytime high temperature on New Year’s Day, at a measly 1 degree above zero. Rockford not only set the record mark with a high of 1 degree below zero, it also tied a daily low temperature record set back in 1968 of -13 degrees. The first 6 days of January were bitter cold as a result, with an overall average temperature that fell below zero in Rockford, squeaking under at -0.9 degrees. That is overall, high and low!
New Year's Eve Map showing a deep trough over the entire eastern half of the United States and large cold anomalies at the 850 millibar level. End result was record-cold for the Midwest on New Year's Day - courtesy Unisys Weather
The pattern was cold enough, however, for the storm track to be south of the area. This lead to a fairly dry start to the month with less than an inch of snow recorded for that first week. The airmass moderated in the second week, even bringing a record high of 53 in Rockford on January 11th, besting the previous 50 degrees set in 1980. The respite was brief, as another arctic surge blasted the region again on the 12th with highs only in the teens and twenties. It also came with snow. A fairly wide and slow-moving Clipper system pushed through the area in these arctic temperatures, producing a long-duration snow event for Chicago. A storm that started in the late afternoon on the 14th, lasted over 24 hours, with snow persisting through the morning of the 16th. Totals were significant, though certainly not major, with anywhere from 3 to 6” of the white stuff once all was set and done.
The rest of January finished above normal in the temperature department, providing a nice long thaw for the area. However, February proved to be the most active month. It was right back into the cold as the calendar turned to the new month, but this time it also was accompanied by a snowier period. Most notable was a record-tying 9 straight calendar days of measurable snowfall of at least 0.1” or more at O’Hare Airport from the 3rd through the 11th.
The period was highlighted by the winter’s most significant snowstorm. It was a long, stretched out event that brought snowfall in waves over a span of 4 calendar days. First flakes began to fly with this event on February 8th, and heavy snow persisted at times into the 9th. Two more waves of moderate to heavy snow returned to the area on the morning of the 10th and again the night of the 11th. The result was well over a foot of snow for many in northern and central Illinois when all was said and done.
Many images of a major snow-maker: At times it snowed heavily, and overall it snowed often, spanning 4 calendar days - images courtesy Iowa State Mesonet
OHIO VALLEY FRIGID AS WELL
More consistent with the rest of the eastern United States, the period overall was warmer than normal in the Ohio Valley. This was able to occur courtesy of some exceptional mild stretches, even despite some brutal cold spurts. Much like Chicago, the first six days were the coldest, to the point of record-breaking. The morning of the 2nd saw record low temperatures for Indianapolis (-12 degrees, ties 1887), Cincinnati (-7, beating -3 in 1928), and Dayton (-13, beating -5 in 1898). Meanwhile, Columbus was unable to make it past the old record lowest high temperature on the same day, tying the record of 10 degrees set in 1928.
After the same mild stretch that graced Chicago, the snowiest day of the month came in on the 12th. This was one that was largely a rain event in the Windy City, but changed to snow on the back side of a cold front in the morning hours in the Ohio Valley. While not an overly impressive event, it was able to drop 2 – 4” of snow across Indiana and Ohio. The rest of January was able to turn milder past the 18th, with just minor snowfalls during the rest of the month and into February as well. As a result, January and February were once again well below normal for snowfall from Indy to Cincy. Columbus was the one exception, actually finishing above normal at 16.5” for the two months. This was courtesy of higher totals from the 18th storm, along with a daily snowfall record of 4.4” on February 7th.
A RAINY END CAUSES PROBLEMS
February continued cold for much of the Midwest, at least for the first half of the month. However, the pattern changed halfway through. After what was a cold and suppressed pattern early on, things flipped toward a perpetual ridge in the second half. It was a record-breaking anomaly, with a stark upper level pattern that drew in exceptional heat for a winter month with temperatures averaging up to 15 degrees above normal!
Warming, though still impressive, was limited over Chicago. Still, with a healthy snowpack courtesy of the snows from the beginning of February, there was plenty of snow and ice to melt. A record daily rainfall occurred on the 20th, and as a result of this combined with snowmelt, flooding became a problem for many in northern Illinois.
— Sandra Torres (@SandraTorresNBC) February 20, 2018
The Ohio Valley did not get nearly as much snowfall, but any frozen precipitation deficiency was significantly replaced by rain. The same mechanism that helped to transport all of the mild air enjoyed by the region, also brought copious amounts of moisture. It was also a stalled out and sluggish pattern that would be stubborn to move. As a result, many across the area were stuck under the “training” effect, simply meaning rain that tracks over the same area over long durations of time, typically leading to flooding problems.
The heaviest rain was experienced in Cincinnati. Not only did they break a record on the 24th for a one-day total of rain at 2.26” (besting the prior record of 1.37” in 2011), but they broke a multi-day February record as well. Between the 21st and 25th, the 5-day rainfall total added up to 5.28”. For perspective, the previous highest mark was 4.08”, set in 1963. Not surprisingly, flooding did result, especially in the hardest-hit areas over the southern half of the Ohio Valley.