September 2018
Monthly Overview - September 2018
Heavy Precipitation Over Large Parts of Midwest
September precipitation across the Midwest ranked as the 11th wettest in history (since 1895) with 5.14 inches
(Figure 1), or 149% of normal. Seven states had statewide values above normal while only Michigan (93% of normal) and Missouri (86%) were drier than normal. Ohio ranked as the second wettest in its history with 198% of normal. Iowa (235%) and Kentucky (241%) both ranked as the third wettest in their respective histories. Two large areas in the Midwest had between 150% and 400% of normal (Figure 2), one included all of Iowa, northwestern Illinois, southwestern Wisconsin, and southern Minnesota while the other covered much of the Ohio River valley including most of Kentucky, southern Illinois and Indiana, and the southern two-thirds of Ohio. Over half of the stations in each of the Midwest’s nine states recorded at least one day in September with 1.00 inch or more of precipitation. Daily precipitation records were set nearly 700 times in September, with dozens in each Midwest state, and at least one record set on 25 of 30 days in September including 17 of those days with at least a dozen records.
Warm Temperatures to Start Fall
September temperatures in the Midwest ranked as the 11th warmest in history (since 1895) averaging 3.7° F above normal
(Figure 3). Ohio set a new record for the warmest September and four statewide values (Illinois 9th, Indiana 6th, Kentucky 7th, Michigan 9th) ranked among the top-10 warmest. The remaining four Midwest states were in the warmest 20 percent of their histories as well with all averaging at least 2.1° F above normal. Temperatures reached 100° F in Minnesota, Missouri, and Indiana and at least 93° F in all nine Midwest states. Daily temperature records numbered more than 1000 on the record high end of the scale compared to just over 300 on the record low side. Nearly all of the record low temperatures were record low maximum temperatures, many occurring from the 8th to the 11th or the 29th to 30th. The record highs were mostly recorded as record high minimum temperatures in the first week of September and a mix of record high maximums and minimums from the 14th to the 21st.
Drought Eased Slightly
Drought eased slightly in September. As of the August 28th US Drought Monitor (Figure 4), just over 16% of the Midwest was in drought, 7% in severe drought, 2% in extreme drought, and a half percent in exceptional drought. Those coverages dropped, particularly in the first half of the month, to 8.5%, 1.7%, 0.4%, and 0.01% respectively as of the September 25th Drought Monitor
(Figure 5).
Severe Weather and Flooding
Severe weather was reported on 19 days in September across the Midwest. Minnesota had more than 100 reports while Missouri had just a couple reports during the month. Tornadoes were reported on 7 days in September with at least one report in every state except Missouri. Large hail was reported a few dozen times with most occurring in Iowa and Minnesota. Flooding was a recurring problem in Iowa, Minnesota, and Wisconsin both during the first week of September and again during the third week of September.
Freezing Conditions Enter the Region
The first freeze of the season hit northeastern Minnesota early in September and then came to the northwestern part of the region in late September (Figure 6) which is near the median date for first freeze in that area
(Figure 7). The freeze brought an end to the growing season. Corn harvest in the Midwest was ahead of schedule across the region as September came to a close, however some areas were unable to get into their fields due to wet conditions. Soybeans were rated mature at rates ahead of average as well in all nine Midwest states.
-MST-