Rapid Temperature Swings

The final week of October was characterized by everything from summer-like warmth to winter-like cold. While the average temperatures were as much as 5°F above normal in eastern parts of Ohio and Kentucky, parts of western Iowa and Minnesota observed temperatures 5°F below normal (Figure 1). Both Kentucky and Ohio averaged temperatures at or above 3°F above normal, 3.4°F and 3.0°F, respectively. Meanwhile Minnesota had the largest temperature departure in the opposite direction, reporting an average statewide temperature of 4.3°F below normal for the week.

Minimum temperatures were record-setting during the final full week of October. Most of the region observed minimum temperatures 10-20°F above normal (Figure 2). It started October 24 west of the Mississippi River, where Des Moines reported a minimum temperature of 62°F, the warmest on record and 22°F above normal for that date. Manitowoc, Wisconsin, on the shore of Lake Michigan, reported a temperature of 55°F, the warmest on record for October 24 and 16°F above normal. By October 25, this warm air mass moved east, with minimum temperature records set in Greater Cleveland, Paducah, Kentucky, and Muskegon, Michigan. These locations all topped 60°F for overnight lows, which were 20°F or more above normal for all locations. On October 26, Lafayette, Indiana had a minimum temperature of 62°F, which was the warmest on record and 22°F above normal. On the same day, Toledo reported a minimum temperature of 63°F, which was also 22°F above normal. By October 27, minimum temperature records were still being set east of the Mississippi River, with much of the I-70 corridor ranging from 59°F in Urbana, Illinois to 62°F in Columbus, Ohio.

When it came to maximum temperatures, the most anomalous warmth was east of the Mississippi River. Daily maximum temperatures averaged 5-10°F above normal in most of Ohio, Indiana and Kentucky (Figure 3). Heading west, temperatures were at or just above normal in Illinois, near normal in most of Iowa, and trending below normal in northern Wisconsin and Minnesota. At the beginning of the period, most of the region saw near normal temperatures. Warmer temperatures only began cropping up on October 23, and were generally confined to Missouri and Iowa. On October 23, a record high temperature of 83°F was set in Vichy in central Missouri. By October 24, this warmth moved east, with record high maximum temperatures in Chicago, Milwaukee, and South Bend reaching the 80s, while Muskegon recorded a record high temperature of 77°F. This generally continued through the rest of the workweek, with a record high maximum of 78°F tied in Cleveland on October 27, and a record high of 79°F in Toledo on the same date. By October 29, temperatures were back to at or below normal.

Frightening Halloween Freeze

A major (and spooky) pattern change came just in time for Halloween. Temperatures were still well into the 70s late in the evening on October 27 for much of Ohio, Indiana, Illinois, and Kentucky, but by the next day, those same states struggled to top the mid-50s. A sharp cold front moved through the region October 27-28, which was then followed by another front that brought even colder air on Halloween. At their warmest, maximum temperatures were in the low-mid 60s in southeastern Kentucky on October 30, while simultaneously only reaching the upper 20s in Minnesota’s Arrowhead region. Maximum temperature departures were 10-20°F below normal on October 30, with much of Missouri up to 25°F below normal as cold air reached the far southern extremities of the region (Figure 4). By the morning of Halloween, temperatures had plummeted to as low as 17°F in Marquette, Michigan, the second coldest on record; 25°F in Indianapolis, also the second coldest on record; and 25°F in Evansville, the coldest minimum temperature ever recorded for the city on Halloween. Due to this, a large swath of the U.S., from Texas to the interior Northeast, experienced a freeze during the end of the period (Figure 5), and much of the Midwest actually reported a hard freeze as temperatures dropped below 28°F (Figure 6).

While the cold air itself was the talk of the town, much of the Great Lakes region actually had some snow on Halloween. The far northwestern section of Michigan’s Upper Peninsula, West Michigan, and Lake County, Minnesota all reported up to 8 inches of snow. The Twin Cities observed 2-4 inches, while metro areas further south, like Chicago and Cleveland, reported appreciable snowfall that triggered winter weather advisories. In Chicago, the local National Weather Service office received reports of thundersnow.

Minor Precipitation, Drought Persists

Thanks to a more amplified pattern than in previous weeks, healthy rains were noted in much of the region. The most significant rainfall totals were in a belt from the Twin Cities east through central Wisconsin and toward Lake Michigan, as well as further south in Missouri and along the Ohio River in Kentucky. Most states observed widespread 0.5-2 inches of rain for the period, but central Wisconsin, the Missouri Bootheel, and the Greater Kansas City area all received 3-5 inches of rain (Figure 7).

Kansas City, Missouri received most of its rain from a front that moved through the area October 23-25. This was when 2-3 inches of rain fell across the Kansas City Metro area (Figure 8). As a result, Kansas City went from straddling the edge of moderate-severe drought (D1-D2) drought to borderline abnormally dry-moderate drought (D0-D1). The Missouri Bootheel exited drought, and most of central Missouri, which was in extreme drought (D3), saw significant improvement.

This was not the case, however, in Iowa, where extreme drought persisted east of Des Moines. Improvement was noted in northwestern Iowa, where the region dropped from D1 to D0. The same occurred in Minnesota and Wisconsin, where vast stretches of each state exited drought classification. Much of Indiana, Kentucky, and Ohio observed removal of drought conditions as well (Figure 9).