July 1-10, 2001

On July 1 a strong cold front swept through the Midwest, producing a line of thunderstorms that extended from eastern New York back into eastern Illinois. As the front stalled south of the Ohio River on July 2, thunderstorms developed on the periphery of the cooler air in western Iowa and Minnesota. The dry weather was especially welcome in western Missouri, Iowa, Minnesota, and Wisconsin, areas which have received too much rain recently. However, showers and thunderstorms developed ahead of a warm front on July 3, producing moderate rainfall over parts of Iowa, Missouri, Illinois, and Indiana. This was the first significant rainfall in two weeks over parts of Illinois and Indiana, and came at an opportune time for corn and soybean development (Figure 5). Temperatures were well below normal for most of the central and northern Midwest during the first three days of July, due to the dominance of the Canadian high (Figure 6).

The week of July 4-10 was very dry in the northern tier states of the Midwest, and quite wet in a region of active weather arcing across the central and southern states of the region. Rain amounts were less than 0.25 inches across the north, while some places to the south received 2-4 inches (Figure 7). A narrow band passing through La Crosse, WI, received no measurable rain; in fact, La Crosse had experienced 19 consecutive days with no measurable rain, starting June 22. Most of eastern Illinois and Indiana received more than 200% of normal during the same period (Figure 8). The departures in Iowa, Minnesota, and Wisconsin exceeded an inch just for a single week (Figure 9), and, combined with previous dryness, that area began to have serious soil moisture shortages. A month earlier, these areas were saturated or under standing water. Ironically, the corn and soybeans that did make it through the wet period formed shallow roots, making them more susceptible to the incipient dry period. A quasi-stationary boundary to the south of the Midwest pushed back to the north on July 7 and 8, bringing the ring-of-fire convection to the central Midwest. Temperatures increased after the passage of a warm front on July 6, but it stalled short of the northeastern half of the region. The southeast Midwest was 3-5°F above normal, while the northeast Midwest was a few degrees below normal (Figure 10). Rain was spotty on the 7th and 8th, but some very strong mesoscale convective systems started rolling along the boundary from northern Nebraska, through central Iowa, into northern and eastern Illinois, the southern two-thirds of Indiana, and southward into much of Kentucky. From July 8 to 10, at least 3 separate mesoscale systems traveled on nearly the same trajectory (Figure 11, UIUC Department of Atmospheric Science).