September 17-23, 2003
Midwest Weekly Highlights - September 17-23, 2003
Isabel Visits the Midwest
The week of September 17-23 was memorable for the rare event of a named tropical system reaching the Midwest. On its last advisory for the storm, the Tropical Prediction Center placed the center of Isabel just 30 miles northeast of Cleveland, along the Lake Erie coastline. Most of the week was less exciting, but much of the Midwest received average to above average rain for the period. Areas that were missed by rain last week in the dry Wisconsin/Minnesota border region received 2-3 inches of rain, while Isabel dropped similar amounts in eastern Ohio and far southeastern Michigan (Figure 1). Only eastern Wisconsin, most of Illinois, and southeastern Missouri received less than 50% of normal rain for the week (Figure 2). Temperatures were 1-3°F colder than normal in the southwestern Midwest, while reaching 3-6°F above normal in the northern Great Lakes area (Figure 3). The precipitation did help to lessen drought status in northwestern Wisconsin and parts of Missouri, but conditions in far northern and far southern Lower Michigan deteriorated in the US Drought Monitor (Figure 4, National Drought Mitigation Center).
Some Drought Relief Early
The Midwest entered a period of more active weather during the week, with two strong cold frontal passages sandwiched around the visit of Isabel to the Midwest. The first front entered the northern Midwest on the 17th, and substantial rains fell in the Minnesota/Wisconsin border region. Upper level support was limited to the northern Midwest, so the rain was concentrated north of Eau Claire, WI (Figure 5, NWS). The totals of 2-4 inches of rain were welcome as a down payment for soil moisture recharge, and did not impede agriculture significantly. The front was fairly dry to the south, but perhaps its most important role there was to help push the remnants of Isabel quickly eastward.
A Named Tropical Storm in the Midwest
Hurricane Isabel accelerated northwest across the Cape Hatteras coast of North Carolina in the early afternoon on September 18 (Figure 6, NOAA). By the end of the afternoon, the cloud shield of Isabel extended all the way to Indianapolis, as the cold front to the west barreled eastward to meet the storm (Figure 7, College of DuPage). Both Isabel and the cold front were quite active at this time, with the first rain bands of the storm reaching southeastern Ohio (Figure 8, College of DuPage). The path of Isabel bought it further west than originally expected; as it weakened, it was still able to dump 3-4 inches at a number of locations in eastern Ohio and southeastern Michigan (Figure 9, Climate Prediction Center). A few locations received more than 4 inches of rain in Ohio. There was some river flooding in Ohio and Kentucky, but no casualties were reported. The life of Isabel ended as a tropical depression about 30 miles northeast of Cleveland at 11 AM EDT on September 19.
One More Front
On the 21st, another strong cold front began to enter the Midwest. Precipitation generally remained less than an inch along its northern extent, but there were some significant thundershowers along the southern part of the front. Late on the 21st, a significant line of thunderstorms stretched from southwestern Missouri to Illinois (Figure 10, College of DuPage). These storms, fired up by solar heating, dropped 2-3 inches of rain on a band of Missouri running from southwest to northeast (as seen in the precipitation totals for the week, Figure 1). However, the frontal storms dried out, as low pressure center moved north-northeastward into the Midwest from the south and captured all the moisture. The low intersected the front in Indiana, and the Ohio Valley and Kentucky and locations to the north received substantial rains (Figure 11, College of DuPage). The front passed quickly, and the week ended under the dominance of a cool high pressure center from Canada, signaling the beginning of astronomical fall.