June 1-9, 2005
Midwest Weekly Highlights - June 1-9, 2005
Weather Patterns Change, But the Results Stay the Same
After cool and dry northerly winds resulted in much of the central Midwest becoming abnormally dry during spring, a circulation pattern change allowed more heat and moisture into the region during the first nine days of June. Unfortunately, the upper air disturbances essential for triggering summer thunderstorms stayed for the most part over the western portion of the region, resulting in the moist areas of the Midwest getting 3-5 inches of rain while the dry swath from southern Missouri to southern Michigan received less than 1 inch except in isolated locations (Figure 1). Precipitation for the period exceeded 200% of normal in northwestern Missouri, western Iowa, and almost all of Minnesota (Figure 2). The core of the dry Midwest received closer to 75% of normal precipitation, while large areas of the Ohio Valley received less than 50% of normal. There was a band of drought-relieving precipitation near Lake Michigan and into central Lower Michigan, and some spotty relief in southern Missouri. Temperatures were 6-10°F above normal in the Great Lakes area, but only 2-4°F above normal on the western and southern edges of the region (Figure 3). The general lack of precipitation during the spring halted the recovery of Lake Michigan-Huron levels from previous lows earlier during this decade. Overall, the area considered to be in moderate drought on the U.S. Drought Monitor map has increased in both north-south and east-west dimensions, covering now southeastern Missouri, most of Illinois, and parts of northern Indiana and southern Michigan (Figure 4), National Drought Mitigation Center).
Pattern Change Brings Severe Weather
As June started, the mid-tropospheric steering currents were beginning to change from the northwest flow predominant during May (Figure 5a, Climate Diagnostic Center - CDC). By the middle of the period, a trough had been established over the western U.S., and southwestern flow was entering the western Midwest (Figure 5b, CDC). June 1-3 had scattered precipitation, especially on the western and southern edges of the Midwest, but it was not until June 4 that the first major upper air disturbance reached the Midwest. With enhanced instability and southerly surface moisture flowing into the region, an outbreak of severe weather and heavy rain began in northwestern Missouri and southern Iowa and encompassed most of the northwestern half of the Midwest by the time it ended on June 5.
Early in the period, on the afternoon of June 4th, a severe squall line formed in northeastern Illinois (Figure 6, College of DuPage - COD) and proceeded through the Chicago metro area with 60 mph winds. More than 40,000 homes lost power due to fallen lines and trees. But the main upper air support was just reaching the Midwest from Kansas, and a line of tornadic supercell thunderstorms scraped by the northwestern suburbs of Kansas City, MO (Figure 7, NWS). This was part of a much larger severe weather outbreak through Missouri into Iowa and Wisconsin (Figure 8, University Corporations for Atmospheric Research - UCAR). A large number of tornadoes were reported in northwestern Missouri and central Wisconsin, along with many reports of severe wind and hail events (Figure 9, Storm Prediction Center - SPC). Despite more than a dozen tornado reports, no fatalities were reported, and only a few structures were severely damaged or destroyed in both rural areas. Unfortunately, though, the rain very carefully kept to the northwest of the driest areas of the Midwest, except for the several inches of precipitation south of Chicago (Figure 10, NWS).
Another outbreak of severe weather started in the early afternoon on the 5th, but this time, upper air support was favorable in the eastern Midwest. Large thunderstorms broke out in far eastern Illinois, again missing most of the drought areas of the state (Figure 11, NWS). By late afternoon, a vigorous squall line had reached central-northern Indiana, and more supercells erupted in Michigan (Figure 12, COD). Around the surface low, several lines of storms also formed in Minnesota and Wisconsin. However, the greatest amount of severe weather reports were found starting in Illinois and sweeping eastward (Figure 13, SPC), along with the greatest amounts of precipitation. Between the two days, 28 tornadoes, 109 severe hail events, and 233 severe wind events were reported in the Midwest states.
The first weather fatality in many months in the Midwest occurred in Elkhart County, Indiana, where a person outside during the storm was crushed to death when winds gusting to more than 90 mph tore his roof off his barn and the debris fell on him. More than 35,000 lost power in northern Indiana, and at least 187,000 customers lost power in southern Michigan, including 103,000 in the Detroit area. More than 30,000 were still without power more than 24 hours later, and a great deal of minor structural damage and tree damage was reported. This was especially difficult given the warm and humid conditions in the area and the lack of air conditioning in locations without power. Muskegon, MI, and Mansfield, OH, had tied record warm temperatures for the 5th, and South Bend, IN, set a new record for the day of 93°F. Jackson and London, KY, set new high temperature records on the 6th. For many places in the eastern Midwest, this week was the first time temperatures exceeded 90°F since the summer of 2003.
Round Two
Another strong disturbance rode the jet stream through the northwest portion of the region on June 7-8. A surface low in the Dakotas pushed a warm front through Minnesota and Wisconsin on the 7th, which returned slightly southward with heavy convection on the evening of the 7th (Figure 14, UCAR). By the morning of the 8th, as the low center moved north through Minnesota, a trailing cold front triggered another round of storms, this time slowly moving eastward through the western Midwest (Figure 15, UCAR). By later in the afternoon, a squall line formed and bowed out toward the dry regions of Illinois (Figure 16, UCAR). Unfortunately, it was now leaving the region of favorable upper level support, and the system weakened, although it did provide substantial rain in a hit-or-miss pattern through the moderate drought area (Figure 17, NWS). The far western region of Illinois probably received the most significant drought help. The far southwestern Missouri region also received significant relief from an unrelated mesoscale convective system, and in fact had some flash flooding as a result (Figure 18, NWS).
The waves of convective activity did bring a significant amount of severe weather to the region. Most of the severe events reported on the 7th were limited to Minnesota and Wisconsin (Figure 19, SPC), while the action moved further south into Iowa, Missouri, and western Illinois on the 8th (Figure 20, SPC). Minneapolis, Kansas City, and St. Louis were the hardest hit metro areas during this severe weather outbreak, with 94,000, 44,000, and 25,000 customers respectively, losing power. One person in southern Minnesota was swept off a road by a flash flood and drowned. Continuing active weather is expected in the Midwest during the next period, including a potential for the tropical system Arlene to bring moisture to the Midwest at mid-week.