August 1-7, 2004
Midwest Weekly Highlights - August 1-7, 2004
Heavy rain and severe weather highlight
the first week of August in the Midwest.
Rainfall for the week was highly variable across the
region (Figure 1)
It was well above normal across most of Iowa, niorthern Missorui,
northern Illinois, and much of Kentucky. Rainfall was well below
normal across niorthern Minnesota, Wisconsin and Michigan, and from
central Illinois across central Indiana and most of Ohio.
Temperatures were 2F to 3F below normal across most of the region, but
4F to 5F below normal across northern Minnesota and northerneastern
Ohio (Figure 2).
The summer
average temperature (starting June 1) has been near to below normal
(Figure 3) with the coolest weather
over northern Minnesota and the
warmest in Ohio and Kentucky.
Tropical air streaming northward on the back side of high pressure
quickly returned warm, humid, conditions to the Midwest on August
2. During the early morning of August 2 thunderstorms erupted
over Iowa and northern Missouri, but the big show did not start until
the afternoon of August 3 as storms organized over southern Minnesota
and Iowa (Figure 4, RAP).
The mesoscale convective system (MCS) progressed east
during the day and evening,
bringing heavy rain and severe weather to much of Iowa. At least
two
tornadoes touched down in Iowa, and there were numerous reports of
one-inch hail (Figure 5, SPC).
Most damage was caused by high winds gusting as
high as 80
mph. 28,000 Iowa customers of Mid American Energy were without
power from Des Moines to the Quad Cities. By early evening the
thunderstorms were entering northern Illinois and southern
Wisconsin. A number of severe thunderstorm and tornado watches
were issued in advance of the storms. The storms maintained there
intensity through the evening hours (Figure 6, NWS). Wind damage was reported
across central Iowa into northeastern Illinois. Wind gusts of 70
mph were recorded at the National Weather Service Office in Romeoville,
IL, and the winds knocked out power for 90,000 Commonwealth Edison
customers in the Chicago area, with more than of those affected in the
south and southwest suburbs. Intense cloud-to-ground lightning
was responsible for at least three fires. In Wisconsin, golf ball
to baseball sized hail fell in a two-mile path from Fall River to
Columbus in Columbia
County, and officials reported that golf ball size
hail was still on the ground two hours after it ended. Winds
estimated at 75 mph damaged 100 homes in Fall River.
Heavy rain was also a significant story with the thunderstorms.
In Dane County,
WI, manhole covers were displaced by water and the
water was shooting up four feet into the air. Rainfall rates were
reported to be as high as two to three inches an hour. There were
numerous reports of flash flooding and urban flooding, and a number
of locations set new daily rainfall records for August 3.
8/3
rainfall Old Record
Des Moines, IA
2.35
1.52 in 1943
Waterloo, IA
1.89 1.38 in 1915
Madison, WI
2.18
1.68 in 1924
Rockford, IL
2.70 2.10 in 1959
As the front continued eastward on August 4 additional severe
thunderstorms hit Ohio and Kentucky (Figure 7, SPC).
As the front exited the region much cooler and drier air poured into
the Midwest behind the cold front
on August 4. Clear skies and dry air allowed the temperature to
drop into the upper 30s and low 40s across northern Wisconsin on the
mornings of August 5 and 6 (Figure 8, Unisys).
A number of low temperature records
were
set or tied from Minnesota into Ohio and Kentucky the last three days
of the week.