Week 1: April 1-7, 2023

Overview

March’s active end was counteracted by a slightly calmer first week of April. Above-normal temperatures were observed throughout most of the Midwest, while the north still recorded below-normal temperatures. Far western Minnesota observed temperatures up to 15°F below normal (Figure 1). Maximum and minimum temperatures followed similar patterns (Figure 2), but below-normal minimum temperatures dipped a bit further south (Figure 3). There were 117 high maximum and 78 high minimum temperature records broken or tied this week, primarily in the southern Midwest (Figure 4). Much of the observed precipitation resulted from the March 31 – April 1 storm. Michigan and northeastern Wisconsin received the most above-normal precipitation totals this week. Missouri, Iowa, and southwestern Minnesota received below-normal precipitation (Figure 5). There were 179 precipitation records that were broken or tied this week (Figure 6). All snowfall remained in the northern tier of the Midwest this week as parts of Minnesota and the Upper Peninsula received over 750 percent of normal snowfall (Figure 7). As a result, 41 daily snowfall records were broken or tied (Figure 8).

Tail End of March 31st System

The widespread storm system that affected the entire Midwest in some capacity on March 31st still remained in the area through April 1st. As shown in the surface analysis map, the main low remained over the Great Lakes region at 2am EDT on April 1st (Figure 9a, WPC). Radar imagery indicated that the line of severe storms extended from central Ohio through Kentucky, ahead of the frontal boundary, and heavy snow with blizzard conditions continued to the north of the low (Figure 9b, NCEI). Severe storms exited the region around 5am EDT, while the northern snow lingered through 12pm EDT. There were seven preliminary tornado reports in Ohio. One tornado in Auglaize County caused seven injuries. Numerous preliminary high wind reports also occurred throughout Ohio; Lorain County Airport in Ohio recorded a 70-mph gust around 2am EDT. The presence of another frontal boundary and small surface low around Lake Erie sparked pop-up storms throughout the afternoon in northern Ohio and southeastern Michigan. A preliminary report even indicated that a brief, EF-0 tornado touched down in Monroe County, Michigan. An 82-mph wind gust was also observed near Oregon, Ohio. The passage of the cold fronts and the zonal upper-level flow contributed to cooler, calmer weather for the next few days.

Warm Temperatures for Many; More Severe Weather

As high pressure settled over the Midwest (Figure 10a, 4/4 8am EDT, Alicia Bentley), a warm front moved northeast through the area over the morning of April 4th which brought warm temperatures to most of the region (Figure 10b, 4/4 8am EDT, WPC). While a high-pressure system was present in most of the Midwest, a deep, upper-level trough was situated over the Rockies. This trough moved northeast throughout the day and the low pressure entered the western Midwest by the afternoon. There were three rounds of storms throughout the day on April 4th.

Morning Storms

The first round of severe storms affected eastern Iowa and northern Illinois. This area, along with most of the Midwest, was in a warm and moist airmass due to the warm front passage. Supercell development could be seen in the sequence of radar imagery from 9:30am EDT through 11:30 EDT (Figure 11a, Figure 11b, Figure 11c, NCEI). High reflectivity values (red/pink) indicated a strong hail core. Strong downdrafts brought extremely large hail and strong wind gusts to the surface; a four-inch diameter hailstone was seen in Davenport, IA around 10:45am EDT and a gust of 90-mph was recorded at the Quad-City Airport. Three brief tornadoes touched down in the morning; the first caused EF-1 damage in Rock Island, IL, the second caused EF-2 damage in Colona, IL, and the third caused EF-2 damage in Geneseo, IL. This supercell tracked northeast through Illinois and into the Chicago metro area in the afternoon (Figure 12, 4/4 3pm EDT) and then through central Michigan before dissipating in the evening hours. Numerous other large hail and high wind gusts were reported with this round of storms, and caused extensive damage to trees and infrastructure.

Evening Storms

As the first round of storms was dying down, more cells started popping up in central Missouri in the late afternoon. Daytime heating helped overcome the present capping inversion as plenty of instability and wind shear fueled these storms. This supercell tracked northeast from Missouri through central Illinois and eventually dissipated near the Chicago area; at the same time, a cold front began to move eastward through central Iowa, which provided proper forcing for a line of storms to form and span through Wisconsin (Figure 13, 4/4 11pm EDT, WPC). Radar imagery between 8pm EDT and 10pm EDT showed the development of both these storms and the severity was indicated by high reflectivity values (Figure 14a, Figure 14b, Figure 14c, NCEI). Again, the environment was conducive for very large hail and strong winds, and most notably, one EF-3 tornado touched down in Fulton County, IL, and traveled 20.9 miles northeast (Figure 15, NWS Central Illinois).

Overnight Storms into April 5th

Another line of storms began to develop along the strong cold front in Missouri just after midnight EDT. This line strengthened throughout the morning and spanned from Missouri through southern Wisconsin by 7am EDT (Figure 16, NCEI). While some hail was observed with this quasi-linear convective system (QLCS), the main threat was strong wind gusts and heavy downpours. One brief, EF-0 tornado touched down in Montgomery County, IN. This system traversed through the entire region, but decreased in intensity and became primarily rain in the evening hours.

Please view storm reports fromApril 4th andApril 5th for a listing of all threats. See the storm summary pages from the National Weather Service offices in the Quad Cities, Chicago, Central Illinois, and Indianapolis for more in-depth analysis and photos from this event.

Return to Cooler Temperatures

After the passage of the cold front, high pressure set in and conditions returned to cool, dry, and relatively clear for the remainder of the week.

Drought and Streamflow Update

When compared to last week, areas of Moderate Drought (D1) were removed in northern Minnesota and eastern Michigan, but was added in eastern Missouri (Figure 17). Abnormally Dry conditions (D0) were decreased in eastern Michigan, but were expanded in northern Minnesota and eastern Missouri. Streamflow conditions returned to near normal levels in the central and southern Midwest, for the most part, but became much above normal in the northern Midwest because of the enhanced precipitation (Figure 18).