July 18-24, 2006
Midwest Weekly Highlights - July 18-24, 2006
The third week of July featured dangerous thunderstorms, frequent lightning, and extreme heat. The average daily temperature departures across the Midwest indicate that much of the region was near normal for this time of year (Figure 1), with localized areas of above and below average temperatures. The northernmost portion of the Midwest, including locations from northern Minnesota eastward into northwest Wisconsin were 3-5°F above average, while locations across southern Wisconsin, northern Illinois, and eastern Michigan were below average by 1 to 3°F. The remaining portions of the Midwest fell between 1°F below average to 1-2°F above average. The above average temperatures across the upper Midwest were due to severe drought conditions and a lack of significant precipitation.
Precipitation for the
week was largely sporadic but heavy in areas that saw strong to severe
thunderstorms. The heaviest precipitation
this
week fell across southern Wisconsin, northern Illinois, and western
Michigan. In these areas, locations received between 150 and 200%
of
normal precipitation, causing numerous flash floods, while much of
north central Minnesota into northwestern Wisconsin saw less than 25%
of normal precipitation (Figure 2).
Southwestern Missouri also escaped much of the rainfall this
week, with most areas receiving less than 10% of normal precipitation
across this part of the state. Elsewhere, and generally along and
east of the Mississippi River, precipitation was between 75 and 125% of
normal for the third week of July. The lack of widespread,
significant precipitation
across northern Minnesota and especially north central Wisconsin has
continued the drought status in this area of the Midwest (Figure 3).
In fact, soil moisture values are well below average across the
northern portion of the Midwest, especially across Minnesota and
Wisconsin
(Figure 4).
In northern Wisconsin, soil moisture values to a depth of 72
inches, is running some 30% below normal for this time of year.
The lack of precipitation this week has exacerbated the
already
stressed environment across this area, and fire danger remains very
high and even extreme in some locales, with 20,000 acres of forested
area ablaze across the Arrowhead of Minnesota.
Extreme Heat
The upper levels of the atmosphere at the beginning of the third week of July closely resembled that near the end of the second week in July, with a heat ridge dominating much of the lower 48 states, keeping the main branch of the jet stream confined to northernmost locations near the Canadian border (Figure 5). This heat ridge resulted in a continuation of extreme heat and humidity across much of the Midwest from July 18-20. High temperatures on July 18 soared into the lower 100's (°F) across southern Missouri, while peaking over 90°F across much of Illinois, Kentucky, and Indiana (Figure 6). On July 19, nearly the entire state of Missouri recorded maximum temperatures at or above 100°F! As of July 20, a total of 7 people have died as a result of the heat in Chicago, IL. Six of these seven people were under the age of 60.Three persons have also died in St. Louis, MO due to no electricity (see why below), and extreme temperatures near 100°F for nearly 4 consecutive days. One woman was found with an internal body temperature of 106°F, and one 92-year old man was found dead in his apartment, with no electricity, and an ambient air temperature in the middle to upper 80's (°F). The third person walked into downed power lines on account of strong thunderstorms, and was electrocuted.
Damaging Thunderstorms Strike St. Louis and Chicago
A strong area of low pressure, and attendant cold front, swept across Minnesota, Iowa, and Wisconsin on July 19, producing widespread severe weather, at least one fatality, and a number of injuries. Early in the morning on July 19, an area of intensifying thunderstorms moved across southern Minnesota (Figure 7), producing some wind damage and dropping a few large hailstones just south of the greater Minneapolis, MN area. This complex of thunderstorms moved east-southeast towards the Quad Cities, IA area, producing more wind damage, including the downing of trees and power lines as it crossed the Mississippi River into Illinois (Figure 8). As the storms moved into Illinois, they encountered an increasingly unstable airmass, characterized by temperatures in the lower 90's and dewpoint temperatures in the middle 70's. The storms intensified, producing widespread wind damage across much of central Illinois, including wind gusts in excess of 70 mph, and hail to the size of golf balls. Trees were downed, knocking out power and falling into parked cars across Sangamon County, IL, the site of the March 12 tornado that ripped through the capital city of Illinois.
As the late afternoon progressed, the storms took a southerly, then eventually a southwesterly turn straight towards St. Louis, MO, who had high temperatures in the lower 100's just prior to the storms arrival (Figure 9). Once the storms hit, they hit very hard causing widespread damage. At Busch Stadium in downtown St. Louis, the storms struck just after the National Anthem was sung prior to the Atlanta Braves taking on the St. Louis Cardinals. Winds then blasted through the city, gusting over 80mph at times, blowing out windows in the sky box at the Stadium, pushing firetrucks off surrounding interstates, forcing traffic to stop completely on major roads, and lifting 60 foot portions of the roof off of St. Louis Lambert Airport and tossing it hastily into I-70. At least 30 persons were injured, and five were taken to the hospital for dislocated shoulders and hips [they were struck by flying concession stands]. One man was critically injured, and later diagnosed as paralyzed from the waist down, as a tavern brick wall fell on him during the storm, burying him. As if this wasn't enough, three buildings in downtown St. Louis, MO collapsed, causing three additional injuries. One of these buildings was the historic Switzer building near the Mississippi river. AmerenUE, who is responsible for the electricity in the area, reported at least 500,000 customers without power stating that this was the worst infrastructural damage in the history of the company in more than 100 years of service (Figure 10, AmerenUE). The areas shaded in red indicate more than 10,000 customers without power.
The next morning, on July 20, a complex of thunderstorms
developed across extreme northern Iowa, and moved east-southeastward
into northern Illinois (Figure 11).
This bow echo produced additional wind damage across the Chicago,
IL suburbs, and knocked out power to some 33,000 customers. The
National Weather Service in Chicago, IL reported that at the height of
the storm, there were nearly 14,000 lightning strokes per hour, while
winds gusted to 50mph at O'Hare International Airport. This
prompted 90 to 100 minute departure and arrival delays at O'Hare, and
roughly 30 minute delays at Chicago Midway Airport. The storms
also caused localized flash flooding before heading southeast and
weakening across extreme eastern Illinois and much of Indiana.
Southern Wisconsin was also particularly hard hit by these early
morning storms, and resulted in numerous reports of wind damage (7am July 19 - 7am July 20 storm reports).
Bow Echo Clobbers St. Louis...Again...
On July 21, a cold front was located across the I-70 corridor in southern Illinois (Figure 12), stretching westward to near Springfield, MO, and eastward along the Ohio River. An upper level disturbance, tracking eastward out of the Plains, ignited dangerous thunderstorms west of St. Louis, MO during the mid-morning hours (Figure 13). These storms then "rode" along the existing cold frontal boundary, tapping extreme instability and moisture in place from the recent heat wave. These storms intensified quickly, and then plowed right through the greater metropolitan area of St. Louis once again. Power outages were common, increasing from an estimated 300,000 people without power prior to the storm's arrival, to over 500,000 customers without power, in St. Louis alone, after the storms exited. Damage was extensive, ranging from 12 inch tree limbs down, half-mile wide swaths of straight-line wind damage, destruction of sturdy structures, snapped power poles, and debris littering the interstate highways. Sadly, a construction worker was killed after a gust of wind blew him into an 8-foot deep trench. The mature bow echo moved east-southeast across southern Illinois, continuing a swath of destruction and knocking out power along the way (Figure 14). One semi-tractor trailer was blown off of I-57, and modular homes were blown apart by the winds and tossed into the interstate.
The bow echo continued across southern Illinois, south of
I-64, through Evansville, IN, and eventually into Kentucky. On July 22, 2006, the Governor of Illinois declared Clinton and Jefferson counties in Illinois state disaster areas. Damage surveys
conducted by various National Weather Service employees indicates that
several hundred, perhaps even thousands of acres of corn were damaged
or flattened by the storms on the 21st. Some of the corn was only
bent and was expected to recover. The most significant crop
damage was reported in Madison, Clinton, and Washington counties in southern Illinois.
A Return to Average Conditions
As the frontal boundary responsible for the recurrent severe weather continued to drop southward into the southern U.S., the hot and humid airmass was replaced by cooler and drier weather. Temperatures during the end of the third week of July were below normal in the central Midwest, and near normal in the southern portions (Figure 15). Another cold front dropped down out of Canada in northwesterly flow aloft on Monday, July 24, sparking severe thunderstorm development across central Wisconsin (Figure 16). A few of these storms produced wind damage, and hail to 1.75" in diameter before weakening after sunset. The storms produced severe weather that stretched from southern Minnesota eastward to Green Bay, WI (July 24 storm reports).Will the final week of July be as destructive as the third, or will the weather quiet down? Find out in next week's edition of the Midwest Climate Watch.
Kruk