June 17-23, 2007
Midwest Weekly Highlights - June 17-23, 2007
Heavy Rains Bring Relief from Dryness
Frequent and heavy rains developing along a stationary front bisecting the Midwest brought anywhere from one to three inches of rain to a large portion of the central Midwest, alleviating the dry conditions that have existed for the last two months. Weekly rainfall amounts from two to three times normal occurred from southeastern Minnesota through most of Iowa, and the northern half of Illinois (Figure 1). The heaviest rain fell in southeastern Iowa into western Illinois, with amounts exceeding 8 inches in places. Another band of above normal rainfall occurred from northern Minnesota across northeastern Wisconsin and the Michigan Upper Peninsula. With the rain this week, totals for the month to date are now at or above 50 percent of normal from central Illinois northward (Figure 2). The June 19th U.S. Drought Monitor (Figure 3) showed conditions continuing to improve in the northern Midwest, but conditions deteriorating in the Ohio Valley south through Kentucky. A small portion of south-central Kentucky is now experiencing Extreme Drought. The significant rains this week occurred after the issuance of this week's Drought Monitor and are not reflected on this map.
Temperatures this week were quite variable across the region, ranging from 3°F to 4°F above across much of Minnesota to 2°F below normal in southeastern Kentucky (Figure 4). Over the central Midwest temperatures were generally 1°F to 2°F above normal. The cooler weather over the central and southern Midwest was largely due to clouds and rain associated with the fronts that oscillated across the region.
Scattered Thunderstorms and Severe Weather
For the first five days of this week, a fairly typical summer weather pattern was in place over the Midwest, with a broad upper level ridge situated over the central United States (Figure 5). Early in the week an upper level wave worked its way through the ridge, triggering showers and thunderstorms in northwestern Minnesota, northern Wisconsin, and the Michigan UP. There were a number of severe storm reports, including a tornado that touched down in Polk County, MN producing some minor damage. Thunderstorm wind gusts of 73 mph were reported by two Minnesota Department of Transportation weather stations in northwestern Minnesota. In north-central Wisconsin, one-inch hail covered the ground three inches deep west of Tomahawk, WI (Lincoln County). Severe weather was also reported in Indiana and Ohio.
On June 18, severe weather, mostly high winds, occurred from northeastern Wisconsin into northeastern Illinois, and in southwestern Missouri. A brief tornado touched down in Christian County, MO causing some minor damage. On June 19 the upper level disturbance causing the thunderstorms was moving out of the Great Lakes, and severe weather in the Midwest was limited to an area from central Ohio eastward.
A cold front dropping out of Canada and into the northern Great Lakes on June 20 set off severe thunderstorms from the southeastern quarter of Minnesota through the northern half of Wisconsin and the Michigan UP. Most of the severe weather was large hail, with numerous reports of 1.75 inch hail in Wisconsin and Minnesota. The largest hail occurred in Minnesota, where hail 4.25 inches in diameter fell in Chisago County. In Marquette, MI (Marquette County) hail two inches deep reportedly covered the ground in some parts of the city. Greens at the Marquette Golf and Country Club suffered severe damage from the hail, according to the course superintendent. The cold front pushed slowly south, entering Iowa and southern Wisconsin on June 23. Severe storms occurred across much of Iowa and into northern Illinois. Four tornadoes, most brief and causing only minor damage, touched down in Iowa. Hail again comprised most of the severe weather reports for June 21, with several reports of hail stones to 2.5 inches in Iowa. A few severe storms also were reported in western Indiana and in northeastern Ohio on the 21st, mostly producing damage to trees and power lines.
Stage is Set for Heavy Rain
The front stalled out across the central Midwest on June 22 (Figure 6), with the first in a series of low pressure waves to ride along the front entering Iowa. The front marked the boundary of the convergence of warm, humid air from the south and cooler, drier air from the north. Thunderstorms with torrential rains repeatedly developed and moved southeast from eastern Iowa into western Illinois. Radar-estimated rainfall on the morning of June 22 ranged from 5.00 to 8.00 inches in the band, with the area or heaviest rain in McDonough County, IL and in Muscatine County, IA (Figure 7). A CoCoRaHS observer in Macomb, IL (McDonough County) reported 5.25 inches of rain on the morning of June 22. The rain caused widespread flash flooding and flash flood warnings were issued for a number of counties through June 22 (green polygons). Thunderstorms continued to pound this same area through June 23, with 72-hour measured rainfall totals (NWS) topping nine inches in Iowa. Thunderstorms also developed and rolled through central and southeastern Illinois and Indiana through June 23. Most of this region received more than half the normal rainfall for the month of June in the span of three days (Figure 8), much to the delight of agricultural producers who were beginning to become concerned with the extended period of dry weather. Despite the abundant rainfall in Iowa, Illinois, and Indiana, the southern and eastern portions of the region still are in needed of significant precipitation.
SDH