August 18-24, 2005
Midwest Weekly Highlights - August 18-24, 2005
More Heavy Rain for Drought-Stricken Areas
Widespread and often heavy rain across the drought areas of the central Midwest, while by no means ending the drought, did bring some improvement. Precipitation for the period was well above normal across most of Missouri, eastern Iowa, and northern Illinois, areas which have been in Extreme drought (Figure 1). Northern lower Michigan and the eastern Upper Peninsula also received significant rainfall. Some of the greatest amounts fell in the core of the drought area (Figure 2). As a result, the area of Extreme drought was reduced in areal coverage on the August 23 edition of the U.S. Drought Monitor and now only exists in northwestern Illinois and a small adjacent portion of southeastern Iowa (Figure 3). Rainfall for the month through August 24 has been well above normal across most of Missouri, near to above normal across the southern half of Illinois, southwestern Indiana, and western Kentucky. Rainfall has also been near to above normal from in a band from southern Minnesota across northeastern Iowa, northern Illinois, and into northeastern Indiana (Figure 4). Northern lower Michigan has received much above normal rainfall. Notable dry areas extend from northeastern Minnesota into northwestern Wisconsin, in southern lower Michigan, and in southern Ohio, where less than half the normal rainfall has fallen.
The temperature pattern for the week readily depicted the general position of the frontal sytem through the Midwest (Figure 5). There was a northwest to southeast gradient, with temperatures ranging from 6°F below normal in northwestern Minnesota to 5°F above normal in southern Kentucky. Crop reports for the week ending August 21 indicated some improvement in soybeans in both Illinois and Missouri, while there was little change in the condition of the corn. The most significant improvement from the rainfall was in pasture conditions. In Illinois pasture conditions improved from 83 percent in poor to very poor condition for the week ending August 14 to 66 percent for the week ending August 21. Table 1 shows reported crop conditions for Illinois and Missouri over the past two weeks according to the respective state’s Agricultural Statistics Service.
Week Starts with Heavy Rain, Severe Weather
On the morning of August 18 a surface low pressure system extended from North Dakota to western Iowa (Figure 6). During the day the low pressure system moved east across Iowa toward southern Lower Michigan. The atmosphere east of this system was very unstable, and wind profiles in the atmosphere were favorable for severe storms and tornadoes. Heavy thunderstorms moved through northern Illinois during the morning hours, while a large area of rain moved east across southern Wisconsin (Figure 7, NWS).
Rockford, IL received 2.23 inches of rain from these storms, setting a new daily rainfall record. The old record was 1.77 inches set in 1960. Rockford had only received 6.57 inches of rain since June 1 compared to a normal of 10.64 inches for the same period. In general one to three inches of rain fell across extreme northwest and northern Illinois, southern Wisconsin, and northeastern Iowa from the storms on August 18. Further south, an upper air disturbance moving through Missouri set off heavy thunderstorms. In northwestern Missouri St. Joseph received 3.78 inches of rain on August 18, breaking the old record of 1.90 inches set in 1963. The torrential rain caused flash flooding, and there were reports of water one to two feet deep over roads in St. Joseph.
Wisconsin Tornado Outbreak
Skies cleared behind the
morning storms, the August sun warmed
the atmosphere. At 2:51 p.m. CDT the Storm Prediction Center
issued tornado watch was issued for extreme northeast Iowa, extreme
southeastern Minnesota, and central and southern Wisconsin (the
counties of Marquette, Green Lake, Sauk, Columbia, Iowa, Dane,
Lafayette and Green). A second watch was issued at 5:51 p.m. CDT for
the remainder of south-central and southeast Wisconsin. Thunderstorms
developed in the warm, humid, and unstable air during the afternoon
hours and quickly reached severe levels. In the early
afternoon a
F0 tornado touched down in southeastern Minnesota and some minor crop,
tree, and building damage. The first tornado to touch down in
Wisconsin was in Centerville (Trempealeau County) at 2:18 p.m. CDT. This
was a small weak tornado (rated F0
on the Fujita Scale) and caused damage mainly to a grove of trees. The
next tornado touched down at 3:36 p.m. in Vernon County, marking the
beginning of the main outbreak across Wisconsin. Over the next six
hours an additional 22 tornadoes touched down across central and
southern Wisconsin (Figure 8, SPC). The most
damaging tornado occurred in Dane County. The tornado
touched down south of Madison and moved
in a general eastward direction through the north side of the town of Stoughton,
hitting the town at 6:30 p.m. (Figure 9).
This tornado, rated F3 on the Fujita Scale, destroyed more than 60
homes in Stoughton. One person was killed and 21 people were
reportedly injured by this tornado. A tornado rated as F2
struck
the village of Viola (Vernon County) in southwestern
Wisconsin, damaging 70 to 80 homes and
injuring three people. On August 22 officials estimated the tornadoes
caused an estimated $21 million in damage. The National
Weather
Service was still investigating the August 18 tornadoes across
Wisconsin as of this writing, and tornado paths and counts may yet
change. The preliminary count is 27 tornadoes on August 18, breaking
the record for the most tornadoes in a day in Wisconsin, originally set
on May 8, 1988. A record 57 tornadoes have struck Wisconsin
so
far this year, eclipsing the previous record of 43 in
1980. (Note:
Tornado count updated August 25.)
In
addition to the tornadoes, the heavy thunderstorms caused urban
flooding in a number of locations in central Wisconsin. Scattered
Severe Storms in Central Midwest As the cold front
associated with the low moving through
Wisconsin pressed farther south it triggered thunderstorms across
Missouri, Illinois, Indiana, and Kentucky on the evening of August 18
and the early morning hours of August 19. A few of these were
severe. The scattered severe storms knocked down trees and
powers
lines, and produced some large hail. Thunderstorms winds in
Springfield, IL knocked out power to the Illinois State Fairgrounds,
delaying the opening of the State Fair on August 19 until repair crews
could restore power. Quiet
End The cold front weakened
as it moved to the Ohio Valley
provided only slight relief from the humid conditions of the previous
days. Over the next three days two more frontal systems
pushed
south through the Midwest, each bringing cooler and drier
air. By
the evening of August 23 dew point temperatures were in the 50s as far
south as the Ohio River. The front was more diffuse
through
southern Missouri and dew points there remained in the upper 60s and
low 70s. Thunderstorms developed along the front in south-central
Missouri overnight August 22 and during the afternoon and evening hours
of August 23, dropping two to four inches of rain in a number of
locations and producing flash flooding. On the morning of August 23
Embarrass, MN reported a low temperature of 29F, and a few other
locations reported sub-freezing temperatures for the first time since
spring. Most of the region enjoyed cool, dry weather as the
period ended. The exception was Missouri where dew points
remained in the upper 60s and low 70s. -SDH-