September 1-7, 2005
Midwest Weekly Highlights - September 1-7, 2005
September Starts Out Dry
The first week of September was very dry across the central and southern Midwest, with most active weather limited to the northern part of the region. Through the morning of September 7, significant precipitation had been limited to central and southern Minnesota and parts of adjacent states (Figure 1). More than two inches of rain fell over two swaths through Minnesota corresponding to areas of convection along a stalled frontal boundary during September 3-4 and 5-7, reaching more than 300% of the weekly normal (Figure 2). More rain fell across Minnesota, Wisconsin, and Michigan on the last day of the period during the 24-hour period ending on the morning of the 8th, so this precipitation will be included in next week's totals for the most part. Temperatures this week were 2-5°F above normal in the Great Lakes region, but 1-2°F below normal in the Ohio Valley (Figure 3). Areas south of Minnesota and Wisconsin displayed an interesting pattern of well above normal maximum temperatures and near normal minimum temperatures due to the clear, sunny, and dry conditions. This dry week, added to several weeks of dry weather previously, caused the ongoing drought situation to intensify once again in northern Illinois, southern Wisconsin, and northern Indiana, and in the areas of Minnesota, Wisconsin, and Michigan near Lake Superior (Figure 4, National Drought Mitigation Center).
Severe Storms in Minnesota
On September 3, a warm front advanced northward through Minnesota and stalled near the Minneapolis - St. Paul metro area. A series of intense thunderstorm moved from west to east, then turning southeastward near the Twin Cities (Figure 5), National Weather Service - NWS). The storms continued into the morning of the 4th. In the western suburbs, precipitation totals exceeded 5 inches in places (Figure 6, NWS), and 2 inch hail was reported in two locations in the area (black triangles in (Figure 7, Storm Prediction Center). A lightning strike caused a fire that resulted in $500,000 damage to a home in Minnetrista. Flash flooding was common, wind damaged several hangers at an airport in Faribault, and there was some isolated crop damage. Storms traveled south into Iowa, leaving swaths of large precipitation totals as far south as Iowa City (Figure 8, NWS). Two men were struck by lightning on a golf course in the Cedar Rapids area, with one dead and one seriously injured.
More Rain Along the Front
On the 5th, the cold front advanced against the warm and humid air in Minnesota and Iowa. A line of storms formed briefly ahead of the front (Figure 9, courtesy of Unisys), but the line quickly broke into two clusters of thunderstorms, one of which brought moderate precipitation to western Iowa but did not dent the drought area, while the second cluster traveled through Minnesota once again. The front advanced and then stalled to the north of Illinois, and provided the focus for more convection in the afternoon and evening of the 7th. Storms moved across the region from southern Minnesota, through Wisconsin, and into northern lower Michigan (Figure 10, University Corporation for Atmospheric Research). Rain amounts of more than 1 inch were common from southwest Minnesota (Figure 11, NWS) to northern lower Michigan (Figure 12, NWS), especially near Grand Traverse Bay.
Drought Remains Intense
The week ended as the storms on the 7th faded in Michigan, bringing some relief to dry areas in Wisconsin and Michigan, and some hope that the precipitation may reach further south into the core drought regions in the next week. The drought has caused more than $1 billion in damage to crops in Illinois alone, but the agricultural season is nearing its end, and dry conditions in mid-September actually aid rapid grain drying and a speedy harvest. The farmers of the Midwest also face an unusual problem this year, as it could be weeks at least before the Hurricane Katrina damage to the grain shipping port in New Orleans is corrected to the point of allowing grain exports to flow. Now the drought centered in Illinois is entering the hydrological phase, as it has been dry enough long enough to reduce groundwater levels, river base flows, and lake levels. Both Lake Superior and Lake Michigan-Huron levels started declining in August, a full month ahead of the normal lake level seasonal cycle. The U.S. Army Corp of Engineers has reduced the flow of Lake Superior water into Lakes Michigan and Huron by 14% to slow the rate of fall of Lake Superior levels. Lake Michigan-Huron levels are now a couple inches lower than last year at this time (green line in Figure 13, Great Lakes Environmental Research Laboratory - GLERL), erasing recent improvements in lake level. The Michigan-Huron level is now creeping once again towards low lake stand records (Figure 14, GLERL). While a few wet weeks can greatly help the soil moisture situation, as happened in August, the long term hydrological dryness will require months of copious moisture during the cold season to recover fully.