August 22-31, 2004
Midwest Weekly Highlights - August 22-31, 2004
Although a few records lows continued to be
set the first
few days of the period, for the most part the last ten days of August
where
characterized by more typical summer weather. The
lack of rainfall the first three weeks of the month
was more than
made up for by heavy rains that occurred as frontal systems stalled out
over
the Midwest, particularly over the central
third of the
region. Western and northern Missouri were particularly hard hit,
and a number of locations received more than 10 inches of rain
during August. Rainfall for the month across the northern third
of Missorui was from three to six times normal (Figure 1).
Temperatures for the period August 22-31
ranged from 7F to 8F below normal in
northwestern Minnesota to 0F to 1F above normal in Indiana and Ohio (Figure 2). The warmer conditions the last ten days of the month
forestalled the march to a record cold August for many locations in the
Midwest. Nevertheless,
August 2004 will be remembered for its unusally cold weather.
While record cold was the big news during the middle two weeks of the month, heavy rain became the major weather news the closing days of August.
The central Midwest was hammered by a series of mesoscale convective systems that developed along a stalled front during the first few days of the period (Figure 3). In western Missouri the thunderstorms produced widespread flash flooding, with rainfall rates as high as 3 to 4 inches per hour. Between 10:00 p.m. and 11:00 p.m. on August 23 an official National Weather Service reported 3.62 inches of rain near Gardner, MO, in Johnson County. On August 24 this complex of storms moved into eastern Missouri and Illinois, while another MCS took shape over western Missouri (Figure 4, NWS). The early morning storms on August 24 produced additional flash flooding in the Kansas City area. Later in the day severe storms developed over northern Illinois producing 1.75 inch hail and spawning at least one tornado. Severe thunderstorm winds downed trees, powers lines, and damaged some buildings in the St. Louis metro area and in southeastern Missouri. This was followed on August 25 by another MCS that organized over western Illinois and brought heavy rain in a broad band across central Illinois from the Mississippi River to the Illinois-Indiana state line. Numerous flash flood and flood warnings were issued across this region. Rainfall amounts generally ranged from 1 to 3 inches, with some amounts in excess of 8 inches in western Illinois.
The last in the series of thunderstorm complexes developed
over western Missouri on
August
27 ahead of a strong cold front. Training
thunderstorms (thunderstorms developing and
moving over the
same areas) resulted in more than 8 inches of rain in some locations in
Kansas
City Metro area as well as the northern portion of the state.
Heavy rain was observed across northern Missouri all the way to the
Mississippi River and into western Illinois (Figure 5). Payson, IL (Adams
County) received an additional 6 inches of rain on top of the 6 inches
received days earlier, and accumulated 14.81 inches of rain for the
month!
The severe thunderstorms also produced some
wind damage.
The cold front responsible for the heavy rain in Missouri produced more general rainfall across the central Midwest on August 27 and 28. In the colder air behind the front. a few low temperature and record low maximum temperatures were set in Minnesota and Wisconsin on August 28. The front finally pushed south of the Ohio River on the 29th. The month ended with high pressure bringing pleasant weather to most of the region. The exception was across Minnesota, Wisconsin, and Michigan, where another cold front triggered showers producing rainfall amounts around 0.10 inch.