Temperature and Precipitation Anomalies.

The central and eastern Midwest became quite wet under the influence of an active weather pattern during April, and the Midwest experienced its 12th wettest April on record. Several states had a top 20 wettest precipitation rank, including Wisconsin (5th), Michigan (10th), Indiana (12th), Ohio (14th), and Illinois (19th). Rain totals exceeded 7 inches in southern Indiana, and were greater than 3.5 inches in most of the Midwest (Figure 1). The eastern Corn Belt and Ohio Valley reached 125% to 175% of normal precipitation, while the northern Great Lakes region had more than 200% of normal (Figure 2). Several snow storms swept through the upper Midwest during April, with totals of 10-20 inches not uncommon in Minnesota and Wisconsin (Figure 3). Temperatures were near or 2-4°F above normal in the southeastern two-thirds of the Midwest, and 2-4°F below normal in parts the northwest (Figure 4). Overall, April was the 36th warmest for the Midwest and 9th warmest in Kentucky. Concern for drought in the western Midwest has faded, and instead the effect of surplus rain on planting in the central and eastern Corn Belt has become a problem (Figure 5, CPC).

Extreme Events and Impacts.

April Fool's Snow Storm, April 1-2.
The snowstorm on April 1-2 brought 4-8 inches of snow to a broad area of Minnesota, and lighter amounts to surrounding areas (Figure 29). Four people died in Iowa and three died in Minnesota in weather-related traffic accidents. In the Minneapolis-St. Paul area alone, 45 people were injured in traffic accidents, and more than100 flights were cancelled. To the south, heavy rain occurred in northern Illinois, but the severity of the storms soon diminished as the onrushing cold front undercut the storms energy supply. Before the lake-effect ended several days later, Grand Rapids, MI, established the 2001-2002 snow season as its 2nd snowiest on record as of April 4.

April Heat Wave and Snow Melt Floods, April 15-18.
The heat wave in the Midwest was very unusual for the time of year. Chicago experienced a four day period with high temperatures of 85°F or higher from April 15 to April 18, setting records on all but the 17th. Minneapolis reached 91°F on April 15, the earliest maximum at or greater than 90°F in the observational record. Milwaukee officials reported an unseasonable heat related death; a man taking medications that reduce the ability of a body to cope with heat died after spending time outdoors and reaching a body temperature of 107.6°F. The heat wave set maximum records at first-order stations throughout the Midwest: 52 locations on April 15, 35 locations on April 16, 4 locations on April 17, and 14 locations on April 18. The effects of the heat wave were mostly positive for the people in the region, providing relief from a cold and dreary spring, moving the growing season forward in the natural world, and letting farmers get some field work done. Unfortunately, in northern Michigan and Wisconsin, the tremendous snow packs built up in February and March suddenly gave way to high temperatures and rain. Snow depths at the opening of the week exceeded 20 inches over the UP of Michigan (Figure 30a), and were reduced to zero by the end of the week (Figure 30b). A snow pack of 29 inches at Marquette melted away completely during the week, due to 1.5 inches of rain at the beginning of the period and temperatures reaching 83°F and 73°F on two consecutive days during the week. The snow melt and rain caused widespread flooding in the western UP of Michigan and northern Wisconsin. Ironwood, MI, was especially hard hit, with 50 people forced from their homes and many roads and highways flooded. The Black River rose more than 6 feet above flood stage before the equipment malfunctioned. A 10-foot section of a dam collapsed along Presque Isle River, leading to alerts regarding the possibility of dam failure; fortunately, the remainder of the dam held. Severe flooding continued in the UP of Michigan through the 24th, as more heavy rain fell on the already flooding rivers (Figure 31, USGS; black dots indicate record flow for the date). Gogebic County was declared a disaster area by the governor of Michigan, and federal disaster applications are pending.

The Severe Weather Season Begins in Earnest, April 18-24:
By the afternoon of the 18th thunderstorms had developed across the Midwest, producing one tornado north of Chicago in Illinois, five tornadoes in Iowa, and six tornadoes in Wisconsin, and many reports of large hail and damaging winds (Figure 32, SPC). The progress of the cool air moving southeast across the region could be followed by observing the severe storm reports. On April 19th severe thunderstorms occurred from southwestern Missouri, through the southern half of Illinois and Indiana, and over most of Ohio (Figure 33, SPC). The warm air returned at that point in advance of another approaching cold front on the 21st. Severe weather broke out in southern Illinois and surrounding areas at the southern end of the cold front, resulting in the first tornado death of the year in the U.S. at the unusually late data of April 21 (Figure 34, SPC). A tornado estimated to be F3 in strength hit Wayne County, Illinois, in the late afternoon, spreading damage along a 30 mile path and hospitalizing 42, including 13 critically injured. The death occurred in the collapse of a mobile home.

A strong low pressure system moving out of the Central Plains intersected with a strong cold front dropping out of Canada and brought another round of severe weather to the Midwest on April 24. Severe storms developed across the core of the Midwest (Figure 35, SPC), from Iowa southeastward into Kentucky. Several tornadoes were reported. Hail as large as 4.5 inches was observed in Palmyra, MO, and 3.5 inch hail was reported in Louisville, IL. The most significant storm of the day was a tornado that struck Carter and Butler counties in southeastern Missouri. The tornado was rated as an F4 on the Fujita scale at its worst state, had a track 38 miles long and up to 650 yards wide, and resulted in extensive destruction in several small towns in a rural area. The initial damage assessment reached $30 M, including the loss of trees in Mark Twain National Forest. The business core of the community of Poplar Bluff was flattened, along with at least 30 homes rated as totally destroyed. Fortunately, no one was killed, but at least 16 were hospitalized.

Severe Weather Outbreak, April 27-28.
During the evening hours between April 27 and 28, a substantial outbreak of severe weather took place in advance of an approaching cold front. Radar for this time indicates that a distribution of supercell thunderstorms develped, some along a frontal boundary in Missouri, Illinois, and Indiana, and some ahead of the front in the warm sector along the Ohio Valley (Figure 36, UI DAS). The severe weather was widely distributed, but the strongest tornadoes formed from southeastern Missouri through to eastern Kentucky (Figure 37, Storm Prediction Center). Severe weather continued through the 28th as the front moved through the region (Figure 38, SPC), but the worst severe weather occurred east of the region, including the F4 tornado in La Plata, MD.

The damage was accompanied by some fatalities. Near Marble Head, MO, a 12-year old was picked out of a house and hurled some 50 yards to his death by an F3 tornado. In southern Illinois, in Dongala, a woman was killed as she tried to escape the tornado by going from her mobile home to her car; an F3 removed her from the car. Several hundred structures were damaged or destroyed in these events. Another person in the town of Irvington, in western Kentucky, was also thrown a distance from a smashed mobile home and died. It is thought that the three deaths may be linked by a single tornado family traveling 100-miles and spawning tornadoes as the parent storm moved along. A pair of radar images of the tornado near Dongala, IL, shows both the hook echo reflecting from the rain droplets around the tornado (Figure 39a, Paducah NWSFO), and the strong reversal of wind direction as seen in a rotating storm from the Paducah radar site (Figure 39b, Paducah NWSFO). While the death toll was low, there were 20-40 hospitalizations reported with each of these three tornadoes. Warnings were excellent, but many of the injured were asleep as the storms approached. Others were injured in tornadoes in Indiana, Ohio, and in central and eastern Kentucky, but no other deaths were reported. The governor of Kentucky declared a state of emergency state-wide to deal with the widespread damage. Thousands also lost electrical service, and this took days to restore in the most damaged locations.

More Heavy, Wet Snow in the Northern Midwest, April 28.
To the north of the severe weather outbreak on April 28 in the Midwest, a different kind of weather calamity was taking place. A substantial amount of heavy wet snow fell in north-central Minnesota and Wisconsin (Figure 40). Snowfall amounts of 4-6 inches were common, but in some core areas, 10 inch snow falls were observed. An official cooperative observer actually recorded 20 inches of snow for the storm in Elcho, WI. This was confirmed with photographic evidence (Figure 41, Green Bay NWSFO), and with widespread reports of power outages affecting 57,000 customers in Minnesota and 25,000 customers in Wisconsin.