Week 1: May 1-7, 2023

Cool Temperatures to Kick Off May

The month of May started off with unseasonably cold temperatures, almost the entire Midwest, except Minnesota, observed temperatures that were at least 4°F below normal (Figure 1a). By the second half of the week, temperatures were back to late-spring ranges; most of the Midwest observed above-normal temperatures and far western Missouri’s average temperature was up to 12°F above normal (Figure 1b). Overall, though, average temperatures were primarily below normal in the east and close to normal or slightly above normal in the west (Figure 2). Maximum temperatures over the week had a more distinct split and reached up to 7°F above normal in the west and 12°F below normal in the north (Figure 3). Minimum temperatures were below normal throughout the southern Midwest and slightly above normal in the north (Figure 4). There were 35 maximum and 11 minimum high temperature records broken or tied this week, with the majority in Missouri (Figure 5a). Additionally, there were 13 minimum and 138 maximum low temperature records broken or tied this week, most occurred in the eastern Midwest (Figure 5b).

Rare May Snowstorm Continues

The abnormal, late-spring snowstorm that began last week continued into this week and piled more snow onto the already high totals. The surface low continued to spin over the eastern Great Lakes region, which produced heavy, wet snow over the UP, some lighter snow in eastern Wisconsin, and rain/mixed precipitation through northeastern Illinois and northern Indiana. The activity continued throughout the day on May 1st and started to slow by early afternoon on May 2nd; the following figures show the surface analysis and placement of the low along with radar reflectivity from 11am EDT on May 1st and 2nd (Figure 6a: WPC, Figure 6b: NCEI, Figure 7a: WPC, Figure 7b: NCEI). Herman in Baraga County, Michigan, won the prize for highest storm total after recording a whopping 52 inches. Almost the entire UP received at least 10 inches of snow from the storm and locally heavier totals were observed (Figure 8). Per the Marquette, MI National Weather Service office, this station set a new record for greatest one-day May snowfall east of the Mississippi River with 27 inches recorded on May 1st! Many other monthly records were set from this storm, along with 31 daily records broken or tied (Figure 9).

End of the Week Flooding and Severe Weather

Over the last few days of the week, conditions were prime in the Midwest for severe storms to develop along multiple present boundaries. A stalled frontal boundary in the upper Midwest caused some storms to fire up in Wisconsin, southern Minnesota, and Iowa on May 5th. More storms developed along an outflow boundary in eastern Nebraska overnight and moved into Iowa and Missouri early on May 6th. More severe storms developed in the evening on May 6th in southern Minnesota with four brief tornadoes between 6pm and 7pm EDT and some hail; only minor building damage was reported from these storms. Stronger cells began to develop later in the evening (Figure 10a, 5/6 8pm EDT, NCEI) in northern Missouri along the intersection of a dryline and frontal boundary (Figure 10b, 5/6 8pm EDT, WPC). Three brief tornadoes occurred in this area (two in Linn County, one in Grundy County), and minor building damage was reported. Hail with a four-inch diameter was reported in Harrison, Daviess, and Grundy counties in Missouri from these cells; steel buildings were damaged and cattle were injured.

Overnight, these cells continued to travel eastward and more storms developed throughout the region (Figure 11, 5/7 2am EDT, NCEI). A stronger, more organized system developed in Illinois and Indiana in the morning (Figure 12a, 5/7 4am EDT, NCEI) and moved south into Kentucky (Figure 12b, 5/7 8am EDT, NCEI). There were three tornadoes from this round of storms that occurred around the Louisville area; one was rated EF-1 and caused two injuries. This widespread, somewhat scattered activity continued throughout the day on May 7th with hail and some high wind gusts.

The severe threat started to ramp up again in the late afternoon. Another, more organized line of storms developed around 4pm EDT in southern Illinois and western Kentucky and strong cells popped up, yet again, in Iowa. By 7pm EDT, an EF-1 tornado occurred in Muscatine County, Iowa, and landspout-type tornadoes were occurring in Illinois (Figure 13, NCEI). Again, large hail (up to 2.75 inches in diameter) and strong winds were observed with these storms. More information on this event, including tornado tracks and photos, can be seen at the NWS Quad Cities page.

Another main threat associated with these storms was flash flooding. A stalled frontal boundary through Illinois caused nearly stationary storms to dump rain on areas in central and northern Illinois, as well as far southwestern Indiana and western Kentucky. CoCoRaHS reports from this storms system can be seen in Figure 14, with orange-red dots representing the highest totals, ranging from 2-5 inches. The highest CoCoRaHS total was 5.71 inches of rain in Chatham and the highest station measurement was 4.25 inches in Morrisonville (both in Christian County, Illinois).

Despite locally heavy totals, most of the Midwest received up to half an inch less precipitation than normal (Figure 15). Areas in Minnesota, Illinois, Wisconsin, Indiana, Michigan, and Ohio received slightly above normal precipitation totals. The UP received up to 4 inches more precipitation than normal, thanks to the unseasonable amount of snow.

Two Illinois Dust Storms

Strong, gusty winds and freshly plowed fields caused a dust storm near Springfield, Illinois on May 1st. Low visibility along I-55 led to a massive, 72-vehicle pileup, and closures along the interstate. Sadly, there were at least seven fatalities from this crash and dozens of others who were injured.

Another dust storm occurred just days later in northeastern Illinois, in the later hours on May 7th, as strong winds from an outflow boundary disturbed dry soil. This dust storm was not as destructive as the previous one, but because it happened at night, visibility was reduced to near-zero levels. Additionally, this dust storm happened in conjunction with other severe threats, which made for a dangerous night.

Streamflow and Drought Update

When compared to last week, streamflow conditions returned to near or above normal levels in Ohio and Indiana (Figure 16). Conditions in northern Wisconsin, eastern Michigan, and the UP significantly increased to much above normal or high, as a result of the abundance of snow. Conditions in eastern Iowa, southern Missouri, and southern Illinois became below or much below normal.

Comparing the May 2nd and April 25th Drought Monitors, a significant area of D0 (Abnormally Dry) has been added to central Illinois and far eastern Indiana (Figure 17). D0 has also been expanded to bridge the gap between the areas in Iowa and Missouri. The Moderate Drought (D1) has been expanded in Missouri and added in a small area along the border of Iowa and Missouri. Severe Drought conditions (D2) have been added in central Missouri as well and a very small area of Extreme Drought (D3) was added in the far western extent.

Now, looking at the May 9th and May 2nd Drought Monitors, portions of the Abnormally Dry (D0) area in Illinois, Indiana, and Iowa have been eliminated due to the recent convective precipitation (Figure 18). D0 has, however, been expanded to cover most of Missouri. Areas of D1 and D2 have also been expanded in central Missouri and an area of D3 has also been added.