August 2000
Temperature and Precipitation Anomalies.
August was close to average for the Midwest region as a whole, being the 51st wettest and 45th warmest out of 106 years. However, there was a distinct pattern of temperature anomalies (Figure 1). Missouri was affected for part of the month by the Southern Plains ridge and heat wave, and had its 14th warmest August, while temperatures gradually diminished to the north and east, where Ohio had its 20th coolest August. The first half of the month was near normal to below normal in temperature in the eastern Midwest, and slightly to more than 4F above normal in the western Midwest. Troughing over the Great Lakes and northeastern U.S. predominated, although occasionally lifting northward at times. Between the 16th and 21st, the troughing intensified, leaving the northern Midwest 3-6 Deg F below normal and only southern Missouri above normal. Finally, the pattern broke in the last ten days of the month, as the southwestern quadrant of the Midwest came under the influence of the intense Southern Plains ridge and heat wave. Temperatures in Missouri were 6-12 Deg F above normal, and the rest of the Midwest was considerably above normal with the exception of southeastern Ohio and far eastern Kentucky. Toward the end of the month, the state of Missouri issued a hot weather health advisory and then a heat warning, as heat index values exceeded 110 Deg F in Kansas City and St. Louis. One person died in Kansas City due to heat-related illness.
Precipitation was light over large portions of the western Midwest in August, and heavier in the north-central and south-central areas (Figure 2). Indiana had its 20th wettest August, due mainly to a recurrence of storms in southeastern Illinois and southwestern Indiana that dropped more than 7 inches of rain in these areas. Lesser but still above normal amounts of rain fell along a storm track extending through northern Missouri, southern Illinois and Indiana, and southern Ohio/northeastern Kentucky. Another active precipitation region was northern Minnesota, Wisconsin, and northeastern Michigan, which also received well above normal precipitation totals. However, the generally very dry areas such as west-central Minnesota, southern Iowa, southwestern Missouri, and northern Illinois missed most rain systems. The last ten days of the month were the driest period, with corresponding high temperatures to dry soil moisture rapidly throughout the region (Figure 3, Climate Prediction Center).
The month started off with extremely good corn and soybean quality ratings throughout the Midwest, and ended with a considerable erosion of these values. By the end of the month, topsoil moisture was short or very short over 49% of Missouri, 41% of Iowa, 35% of Minnesota, and 24% of Illinois. Correspondingly, corn and especially soybean quality ratings fell during August, although corn ratings stayed above 65% good to excellent and soybeans above 60% in all 9 Midwest states. Conditions were too wet in Illinois and Indiana just south of the central parts of each state, and parts of Wisconsin were also very wet for crops. On the other hand, much of Missouri, western and southern Iowa, southern Minnesota, and northern Illinois were too dry for crops. In many of these areas, though, corn is well ahead of normal seasonal stages, and will be drying down more quickly than normal due to the dry and warm conditions, so further damage to yields is unlikely. Therefore, it is expected that record production estimates for corn and soybeans made by the USDA will be somewhat reduced in the September report, but not to a great extent.
Several outbreaks of severe weather occurred during the first two weeks of August. On August 6, a huge mesoscale convective system raced through Illinois, Indiana, and Ohio, leaving behind a great deal of wind damage (Figure 4, Storm Prediction Center). In the Chicago area alone, more than 100,000 customers were left without power due to power line damage, and 77,000 of those experienced outages greater than 6 hours. Transformers at a power substation at O'Hare Airport were also damaged; combined with the wind storms, this led to substantial numbers of delayed and canceled flights. Among other locations, the area around Ashland, Ohio, was especially hard hit, with a microburst lifting roofs from houses, collapsing walls, destroying mobile homes, and downing trees and power lines. Severe storms occurred in the same area on the 8th and 9th as a strong cold front swept through the Midwest and brought drier weather. Large amounts of hail and wind damage to crops were reported in Wisconsin (Figure 5, Storm Prediction Center) and central Illinois. After a quiet week, another set of storms entered the region on August 14, passing through Minnesota and Wisconsin before dissipating (Figure 6, Storm Prediction Center). Unfortunately, a scout master was killed in north-central Minnesota by a tree falling on his tent during one of the windstorms. In addition, one person died and another was critically injured by lightning after an outdoor concert in northern Wisconsin as the same line of storms passed through that location.
Late in the month, a strong set of thunderstorms affected the northern Midwest on the evening of August 25-26 (Figure 7, Storm Prediction Center). The Minneapolis and Milwaukee metro areas suffered widespread damage, with winds exceeding 90 mph in places. Power outages and tree falls were common in both places, and in smaller cities in between. Lake Elmo Airport east of St. Paul had a number of private planes flipped on their parking area, and several hangers destroyed by straight-line winds of up to 100 mph. The winds and hail up to 1.75 inches in diameter also caused significant crop damage in Minnesota and Wisconsin. One person was injured by lightning, but otherwise there were no casualties reported. However, parts of Wisconsin and Illinois that did not need heavy rain received 2-4 inches of precipitation (Figure 8), keeping some fields in Wisconsin and southeastern Illinois too wet for good crop growth.