Above Normal Precipitation in Ohio River Valley
Precipitation during the third week of December was 125% to 400% of normal across the Ohio River Valley and into Michigan (Figure 1), with weekly totals in this region ranging from 1" to 3" (Figure 2). Much of this precipitation in the Ohio River Valley fell during the last two days of the week as a front stalled on December 20th and 21st (Figure 3), generating heavy rainfall across the Missouri bootheel, southern Illinois, Indiana, Ohio, and northern Kentucky (Figure 4). The heavy rainfall in this region created flash flooding and river flooding in portions of Indiana, with some rivers higher than they have been in 5 years or more after this event. A couple of locations saw the highest flood crests in over 20 years (report from NWS Indianapolis, IN). Several daily precipitation records were set throughout the week.
The storm event on December 20th and 21st not only brought heavy rainfall to the Midwest, but also severe weather, freezing rain, and snowfall. There were over 300 high wind reports associated with the December 20-21 event, with many reported within the Midwest. There were also a few scattered reports of tornadoes as well (Figure 5). For more information on the reported tornadoes in Kentucky, visit the summary from NWS Louisville, KY. There was also freezing rain across portions of central Missouri, central Illinois and into northern Indiana. Ice accumulation during the storm ranged from 0.10" to the highest totals of 0.50" in southwest Missouri (Figure 6) (report and data from NWS St. Louis, MO).
Weekly snowfall accumulations were greatest in northern Michigan, where 15" to 20" fell throughout the week (Figure 7). Other areas receiving at least 5" of snowfall during the week included northern Missouri, portions of Iowa, Wisconsin, Minnesota, and Michigan. The snow that fell across northern Missouri and Iowa occurred during the December 20th-21st event, where the greatest totals reached 8" to 10" in south central Iowa and north central Missouri (Figure 8). Weekly snowfall totals in northern Missouri and southern Iowa were 4" to 6" above normal, while the significant snowfall in northern Michigan was 8" to 16" above normal
(Figure 9). By the end of the week, snow depths of at least 12" was widespread across northern Minnesota, northern Wisconsin, and much of northern Michigan. The greatest snow depths of 24" to 30" were along Lake Superior in Minnesota (Figure 10). Quite a few daily snowfall records were set throughout the week, a majority of which occurred on December 15th and December 22nd.
North-South Split in Temperature Departures
The third week of December brought below normal temperatures to the upper Midwest, while southern portions of the region experienced above normal temperatures
(Figure 11). The largest temperature departures in the upper Midwest were in northern Minnesota, where average temperatures throughout the week were 10°F to 14°F below normal. On the other extreme, average temperatures across portions of southern Missouri, Kentucky, and southern Indiana were 6°F to 8°F above normal. There were several daily temperature records set throughout the week, many of which were record highs in southern states.