September 2006
Midwest Overview - September, 2006
Cooler than Normal...Wetter than Normal
The month of September was cooler than normal for just about everyone in the Midwest. The monthly temperature departure map illustrates that the coolest areas this month were found across western Iowa, southern Illinois and Indiana, and much of Kentucky (Figure 1). Departures across these areas were generally 3-4°F below normal. Meanwhile, cooler than normal temperatures, though warmer than the aforementioned areas, were found across Wisconsin, Michigan, and Minnesota, where departures were 0.5-1.5°F below normal. Across the central parts of the Midwest, departures were generally 1-1.5°F below normal for the month. As it turns out, the month of September was the first month below average for Rochester, MN, since December 2005. The average temperature in September at Rochester, MN was 58.9°F, which was 1.1°F below normal. Further south, Jackson, KY recorded their coolest September on record (since 1981), with an average temperature of 63.4°F, some 4.5°F below normal.
Precipitation for September was well above average across southern Illinois, much of Kentucky, portions of Ohio, and extreme western Minnesota. These areas received over 5 inches of rain this month (Figure 2), which is some 175 to 200% of normal for September. The south-side of Chicago also received abundant rainfall, about 150% of normal for September, during a few very isolated but important rain events (Figure 3). Due to numerous heavy rainfall events, Evansville, IN recorded their 2nd wettest September on record, of 8.75", which is 5.76" above normal. Moreover, the entire state of Kentucky ranked as the 2nd wettest September on record. The dry spots of the month were found across northern Wisconsin and northeastern Minnesota, where drought conditions continue, and across western and central Illinois southward into Missouri. These locations experienced generally less than 50% of normal precipitation for the month.
Slow Start...Wild Ending
September started out fairly wet and cool. The weekly precipitation map ending on the 7th shows that many areas of the Midwest experienced decent rains (Figure 4). The exception was Rockford, IL, where over 5 inches of rain fell in less than 3 hours, resulting in extreme flash flooding; an event not likely to return for another 100 years. Thereafter, cool autumn weather filtered into the Midwest, holding daytime maximum temperatures to less than 70°F over a good portion of the Midwest on the 13th (Figure 5). Another cold front swept through the region on the 16th, resulting in the development of numerous showers and thunderstorms, some of which became severe (Figure 6). The Minneapolis, MN area was particularly hard hit, as a tornado descended on Rogers, MN, north of the metropolitan area, late on the 16th. The tornado spun down quickly before high-resolution Doppler radar was able to detect rotation. Sadly, the tornado killed a young girl who was seeking shelter at a neighbor's house during the event. Finally, in the final stretch of the month, a powerful low pressure system (Figure 7) spun across the Midwest, and resulted in the development of tornadic thunderstorms on the 22nd (Figure 8). The storms produced an F-4 tornado which struck Crosstown, MO, which was the strongest September tornado to hit the Paducah NWS coverage area since 1880. Elsewhere, additional tornadic storms developed near Chicago, prompting tornado warnings for the City of Chicago, which was last done on August 1, 2003. The tornado threat then transitioned into a very heavy rainfall event across Kentucky and southern Illinois and Indiana, where at least 10 persons died on account of flooding-related incidents. When all was said and done, some locations received in excess of 13 inches of rain from this event, which is more than one-fourth of the annual average rainfall.
Kruk