Midwest Weekly Highlights - September 1-7, 2006

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The first week of September was largely tranquil, albeit on the cool side for most.  The average daily temperature departures across the Midwest indicate that much of the Midwest was below average for this time of year, with the exception being across the northern tier states (Figure 1).  The northernmost portion of the Midwest, including locations from west-central Minnesota eastward into northern lower Michigan were 1-3°F above average, while locations across Kentucky, southern Missouri, and southern Ohio were below average by 5-8°F.  A more robust temperature gradient existed from parts of Iowa eastward into Indiana.  In these states, the northern portions were very near average, while the central and southern portions of these states were a good 2-4°F below average.

Precipitation for the week was largely sporadic but exceptionally heavy in areas that saw strong, "training" thunderstorms.  The heaviest precipitation this week fell across western Minnesota, north-central Illinois, and extreme eastern Kentucky and southern Ohio (Figure 2).  These locations saw precipitation totals that were 200 to 500% of normal for this time of year, generating some flooding concerns, and alleviating drought issues all the same.  Meanwhile, northern Wisconsin, the Upper Peninsula of Michigan, and extreme southern Missouri saw precipitation totals that were only 0 to 5% of normal, exacerbating drought concerns across these areas, especially across Missouri and Wisconsin, where the first 12" of soil moisture are running incredibly dry (Figure 3).  Elsewhere, precipitation during the first week of September was 25 to 75% of normal.  Drought remains an issue across these areas, and there was little change in official drought status from the final week of August (Figure 4).  Interestingly, the summer drought across Minnesota has affected the rate at which the corn and soybean crops have matured.  The soybean crop analysis across Minnesota showed that already 50% of the state's soybeans were turning yellow, compared to a 5-year average of just 38%.  Moreover, 13% of the crop was already beginning to lose its leaves, compared to just 7% on the average.  In fact, many of the major crop industries across the state were at stages ahead of the 5-year normal period (USDA).  

100-Year Flash Flood Hits Northern Illinois

September began where August ended...cooler than normal with a sluggish upper-level flow pattern.  Tropical Storm Ernesto moved up the East Coast of the United States on September 1-2, bringing its associated rain shield to portions of eastern Kentucky and southern Ohio (Figure 5).  A slow-moving upper level low pressure system (Figure 6) brought some interesting late summer  weather to the Midwest later in the week.  On September 3rd, the cold-core system brought a few large hail reports to western Iowa, as well as beneficial rains to portions of Iowa, Minnesota, and western Illinois.  Record rains fell in Mason City, IA, where the cooperative weather observer reported 2.54" of rain on the 3rd, breaking the old single-day record of just 0.90" set back in 1906.  

The hail and heavy rain threat jogged eastward on the 4th bringing 1.75" hail to Rockford, IL, and 1.61" of rain to St. Cloud, MN, setting a new daily record breaking the old one of 1.37" set in 1980.  The heavy rain threat materialized over the northern  portions of Illinois on the 4th as well, where rain was falling at the rate of 1-2 inches per hour, creating some destructive flooding issues.  The cooperative weather observer for Rockford, IL reported 5.60" of rain on the 4th, which occurred primarily between 3pm and 6pm CDT.  The heavy rain in such a short time resulted in cars and large trash bins floating down area streets, forcing the evacuation of several dozen persons to higher grounds, collapsing garages, shattering basement windows, and weakening the foundation of at least one residential home.  The Governor of Illinois eventually declared Winnebago County, where Rockford, IL is located, a state disaster area.  Over $61,000 in damages were incurred by the Rockford Park District alone in the reparation and clean-up after the 100-year flash flood.  The same upper level feature brought a few scattered reports of large hail to northern Indiana on September 5th, and lower Michigan on September 6th, but no widespread impacts were received.

Cool high pressure settled in towards the end of the first week, bringing near normal temperatures and abundant sunshine to nearly the entire Midwest.  A few afternoon "instability showers" dotted the region from the 5th through the 7th, bringing a quick 0.50 to 1.00" of rain to those locations that found themselves underneath these slow moving thunderstorms.  In addition, numerous cold-air funnels were observed across Illinois during this time frame, and fortunately none of them touched the ground.

    
Record Cool To Start The Month

The persistent upper-level low pressure system that was responsible for the large hail and deluge in Rockford, IL, also brought record cool daytime maximum temperatures to portions of the Midwest.  In addition, persistent clouds and light precipitation from Tropical Storm Ernesto added insult to injury in setting new low maximum temperature records.  These new temperature records are summarized in the table below.

Date	Location	New Record	Old Record & Year
September 1	Jackson, KY	66°F	72°F, 1994
September 2	Youngstown, OH	58°F	61°F, 1994
	Akron, OH	61°F	62°F, 1909
	Mansfield, OH	63°F	65°F, 1994
	Jackson, KY	65°F	72°F, 1994
	London, KY	65°F	69°F, 1976
	Bowling Green, KY	68°F	72°F, 1924
	Louisville, KY	68°F	69°F, 1935
	Lexington, KY	66°F	70°F, 1952
September 3	Jackson, KY	69°F	72°F, 1994

The long-range forecast for the second week of September suggests cooler than normal conditions will prevail.  Will any new record temperatures be set in the second week of September, and how will the cool weather affect the beginning of the fall harvest?  Find out in next week's edition of the Midwest Climate Watch.

Kruk