June 24-30, 2007
Midwest Weekly Highlights - June 24-30, 2007
Heavy Rains Deluge Parts of the Midwest
The last week of June was abnormally wet from Missouri east through the southern two-thirds of Illinois and Indiana, and much of Kentucky (Figure 1). Rainfall in these was at least 200 percent of normal, and as high as five times normal in western Missouri. Much of this region received the equivalent of normal June rainfall in just a few days. In the northern half of the Midwest rainfall was much more scattered and well below normal for the week. The June 26 U.S. Drought Monitor reflected the early rainfall in the southern half of the region with a reduction in the Abnormally Dry regions in central Illinois and western Indiana (Figure 2). However, the heaviest rain fell the last several days of the week and its effects were not reflected in this map.
Temperatures this week were 2°F to 3°F below normal this week from northern Missouri through Iowa and east into Illinois, reflecting the predominantly cloudy and rainy weather in this region (Figure 3). Temperatures were 2°F to 3°F above normal south of the Ohio River as this region remained south of a quasi-stationary frontal boundary most of the week.
A Soggy, Stormy Week in the Central Midwest
A broad southwesterly flow drawing warm, humid air northward developed across the Midwest at the beginning of the week, with a cold front beginning to drop into the Midwest (Figure 4). A weak low pressure wave aloft was parked over the lower Midwest, and remained over the area for a few days helping to trigger the showers and thunderstorms ahead of the front (Figure 5). The cold front made slow progress through the Midwest, only reaching the central Midwest by June 28 (Figure 6), and not moving south of the Ohio River until June 30. This allowed showers and thunderstorms to redevelop each day in the moisture-laden air south of the frontal boundary. Early in the week showers and thunderstorms formed during the heating of the day, with coverage in the central Midwest from 30 to 50 percent. The thunderstorms were mainly heavy rain producers, although a few severe storms with occurred. On June 24 a number of funnel clouds were observed with thunderstorms in central Illinois, but no tornadoes resulted. Storms forming in the vicinity of the cold front in northern Minnesota produced one or two brief tornadoes which produced minor damage. Over the course of the week severe weather occurred in all nine states, with most reports damaging winds. As they front pushed south of the Midwest on June 30, thunderstorms in southwestern Missouri spawned at least two brief tornadoes which produced minor damage.
The primary issue this week in areas it rained was flash flooding. The torrential thunderstorms frequently dropped one or more inches of rain on areas in short periods of time resulting in flooded roads and small stream. Water two feet deep was reported over numerous roads in Monroe City, IN (Knox County) on June 25 after thunderstorm hit the area. On June 26 mid-afternoon thunderstorms rolling through the Chicago Metropolitan area tied up rush hour traffic, caused more than 350 flights to be cancelled at O'Hare Airport, and resulted in more than 800 reports of flooded basements. Unofficial estimates of up to six inches of rain falling in a 45 minute period were reported.
Flooding was especially persistent in western and southwestern Missouri this week. Missouri was on the eastern edge of an area of heavy precipitation that extended from Texas northward through Oklahoma and eastern Kansas. Many rivers and streams were experiencing flooding, and flash flooding was almost a daily occurrence in the rolling terrain of western and southwestern Missouri. On June 28 flash flood watches were in effect in an arc from southern Texas to western Illinois as moisture-laden air interacted with the cold front sagging south through the nation's midsection (Figure 7). Rainfall amounts for the week in western Missouri ranged from 5 to more than 9 inches (Figure 8). Among the higher amounts reported from NWS Cooperative observers were 10.54 inches in Elm (Putnam County); 9.30 inches in Drexel; and 8.47 inches in Butler (both in Bates County).
SDH