Week 4: February 22-28, 2023

Temperatures of Both Extremes

To close out the month, the northwestern Midwest observed anomalously low temperatures and the southeastern Midwest observed anomalously high temperatures; only a narrow band of the region had near-normal temperatures this week (Figure 1). As a whole, Kentucky had the largest positive temperature deviation from normal (10.9°F) and Minnesota had the largest negative deviation from normal (13°F). Both maximum and minimum temperature departures followed the same pattern (Figure 2, Figure 3). A handful of southern stations reported average mean temperatures in the top 10 warmest on record for the last week of February, while the northwest had multiple stations where this week was within the top 10 coldest on record (Figure 4).

February 22nd Winter Storm

The week started off with a strong surface low set up over Missouri on the afternoon of February 22nd (Figure 5). As this system moved eastward through the Midwest overnight and into the 23rd, temperatures to the north remained below freezing, supporting heavy snowfall and ice accumulations. This report from the NWS Office in Detroit/Pontiac, Michigan provides more detail about this storm, including ice and snowfall totals. Notable impacts from icing included downed powerlines and trees, resulting in widespread power outages. Further north, heavier snowfall totals were reported; Marquette County, Michigan recorded 20 inches of snow on February 23rd. While winter storm and blizzard warnings were in effect in the northern Midwest, severe thunderstorms were occurring in the southern Midwest. Kosciusko County, Indiana, reported 3.04 inches of precipitation on February 22nd. As a cold front pushed eastward with this surface low, hail with up to a 1-inch diameter occurred in central Illinois and the St. Louis area. Additionally, strong winds with gusts up to 70 mph were recorded along the system’s path in Missouri, Illinois, and Kentucky.

February 26th-27th Severe Weather

After a brief calm period, severe weather fired up again on February 26th in the Plains caused by an upper-level disturbance (Figure 6, 2/27, 1am EST). The quasi-linear convective system (QLCS) that developed began to enter the Midwest around 1am EST (Figure 7) and caused severe weather that is typical of these systems. Three weak tornadoes occurred around this time in far southwestern Missouri, along with numerous high wind reports throughout Missouri (Figure 8). As the system traversed the Midwest, widespread, heavy precipitation was observed, especially in a swath spanning from Iowa through southern Wisconsin/northern Illinois (Figure 9). Ozaukee County, Wisconsin received 2.31 inches of precipitation from this storm. (Figure 10) shows the surface analysis map at 10am EST, with the low situated over eastern Iowa and the warm front extended from Iowa through Kentucky. These two factors provided the forcing mechanism that caused weak tornadoes, up to 1-inch diameter hail, and strong, straight-line winds in Missouri, Illinois, Indiana, and Ohio (Figure 11). Throughout the afternoon, there were five tornadoes in Illinois, two in Indiana, and four in Ohio. Severe threats diminished in the evening, however, stratiform precipitation and some snow lingered in the northern Midwest through early morning on the 28th. Visit the following NWS offices in Chicago, Northern Indiana, and Wilmington, OH for more detail on these tornadoes and other threats.

Wet End to February

Looking at the week as a whole, most of the Midwest recorded over one inch of precipitation, with the highest totals (upwards of four inches) in northern Indiana (Figure 12). Resulting from this, this week was in the top 10 wettest last weeks of February on record for most stations, with a handful ranking this week as number one (Figure 13). Almost all of the accumulated snowfall this week occurred with the winter storm, but additional lower, accumulations resulted from the second storm (Figure 14). Overall, 145 snowfall records were broken or tied this week (Figure 15). The two rounds of heavy precipitation this week increased streamflow conditions to above and much above normal surrounding Lake Michigan (Figure 16). Below normal streamflows were observed along the Ohio River Valley and in eastern Michigan. Abnormally dry conditions (D0) were eliminated or downgraded in northeastern Missouri, Illinois, northwestern Indiana, Ohio, and southeastern Minnesota (Figure 17). Abnormally dry areas, and areas with Moderate (D1) and Severe Drought (D2) were largely downgraded in eastern Michigan. Seventy-seven percent of the Midwest was denoted as free of drought or dryness.