Midwest Weekly Highlights - August 25-31, 2005

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Heavy Rain Misses Most of Drought-Affected Areas

In contrast to much of the summer, the last week of August was marked by heavy rain in a number of areas of the Midwest. Thunderstorms brought torrential rains to central and southern Missouri and western and central Minnesota the first part of the week, while the remnants of Hurricane Katrina brought rain to the southeastern portions of the Midwest at the end of the period. However, the rain this week managed to miss most of the area in extreme drought on the August 23 U.S. Drought Monitor (Figure 1). Precipitation this week was normal to much above across much of Missouri, western and central Minnesota, and in southern Illinois, the southern half of Indiana, Kentucky, and Ohio (Figure 2). Temperatures were generally near normal throughout the region, with some warmer areas noted across southern Missouri and the Michigan Upper Peninsula (Figure 3). Temperatures were 2°F to 3°F below normal across northwestern Minnesota.

Thunderstorms Bring Flooding

On August 25-26 a complex of thunderstorms brought several inches of rain to western and central Missouri (Figure 4), and record record rainfall amounts to western and central Minnesota (Figure 5), causing flash floods. By the morning of August 26 flash flood watches covered most of the southwestern half of Missouri (Figure 6). In Minnesota, many areas received between two and six inches of rain, and record daily rainfall amounts for August 26 were recorded at the Minneapolis-St. Paul (2.00 inches), St. Cloud (2.84 inches), New London (5.52 inches), Morris (1.73 inches), and Glenwood (5.00 inches). In Missouri the heavy rain reversed the dry regime that existed over much of the state during June in July. After a July that ranked in the top five driest, rainfall in August of eight to 11 inches was at near record or record levels at a number of locations in western and central Missouri.

A weak cold front slowly moving south through the region August 27-28 triggered thunderstorms across southern Illinois and Indiana. In northwestern Missouri, there were numerous reports of 1.75 inch hail from thunderstorms in association with an upper level disturbance.  The weak cold front that fired up the line of storms in Illinois and Indiana on August 27 later triggered scattered severe thunderstorms in Kentucky on August 28 producing some wind damage.

Katrina Soaks Ohio Valley

The first effects from Hurricane Katrina were felt in the southern Midwest soon after landfall on August 29 (Figure 7). Heavy rain developed from the Missouri bootheel across extreme southern Illinois and much of Kentucky as an upper air disturbance over the Great Lakes interacted with the outflow from Hurricane Katrina.  Flooding closed a number of highways in southern Kentucky. By the morning of August 30 Katrina, now weakened to a tropical storm, was located over western Tennessee (Figure 8). The rain shield with the storm spread northward into southeastern Illinois, the southern half of Indiana, and much of Ohio (Figure 9). Rainfall amounts in many Kentucky locations exceeded four to five inches. Louisville, KY set a new daily maximum rainfall record of 3.08 inches on August 30, breaking the old record of 2.35 inches in 1978. Indianapolis, IN received 2.16 inches of rain, breaking the old record of 1.29 inches in 1876. The path of Katrina is easily seen in a dot map of precipitation reports prepared by Rich Tinker of the Climate Prediction Center (Figure 10). Flash flooding was reported in Kentucky, Indiana, and Ohio.

On August 31 skies were clearing over most of the Midwest as the remnants of Katrina, now a tropical depression, moved into the northeastern U.S. A few scattered showers lingered in Ohio during the morning, and skies cleared from west to east during the day.

-SDH-