The continued dryness and drought in and upstream of the HSA produced low flows on all rivers and streams during the month of September. The low flows and low stages on the Mississippi River created concerns for pleasure boaters hitting wing dams and commercial barge traffic hitting the bottom of the channel.
Rainfall for September 2012 was above normal in a small portion of extreme northeast Iowa and nearby locations, mainly from around Caledonia MN to Guttenberg IA. The bulk of these rains were produced by strong to severe thunderstorms on the 4th into the 5th. Much Like August, rainfall was below to much below normal elsewhere across the HSA, with the much below normal rainfall over the west and east sides of the HSA. An upper disturbance and slow moving low brought showers and storms with light to moderate rains to the entire HSA on the 3rd to the 5th, except for the locally heavy rains over far northeast IA. Most of the rain that fell during September occurred on these days. A cold front brought light to moderate rains to much of the HSA on the 12th into the 13th. Another cold front brought mainly light rain to the HSA on the 17th. An upper disturbance brought light to locally moderate rains to much of the HSA on the 21st. The last week of the month was dry.
Normal rainfall for September ranges from around 3.25 inches across the west and southwest ends of the HSA, to around 3.75 inches in the northeast end. Totals for this month ranged from 15 to 40 percent of normal across the west and east sides of the HSA, to mostly 40 to 80 percent of normal across the rest of the HSA. The small area of extreme northeast IA had 90 to 110 percent of normal September rainfall. Most totals for the month were 30 to 70 percent of normal. Extreme totals recorded for the month ranged from 0.36 inch at Zumbro Falls and 0.66 inch at Lake City, both in Wabasha Co. MN, to 4.22 inches at Dorchester in Allamakee Co. IA and 4.51 inches near Elkader in Clayton Co. IA.
Average temperatures for September 2012 were 58 to 62 degrees, which was one degree above to 2 degrees below the normal. Temperatures were above normal on the 1st to the 5th, near to below normal from the 6th to the 10th then much above normal on the 11th. The 12th to the 15th saw near normal temperatures, with the 16th having above normal readings. The 17th to the 28th generally saw near to below normal temperatures, but for some much below normal values on the 18th, 22nd and 23rd. The month ended with above normal temperatures on the 29th and 30th. Extremes for the month ranged from lows in the middle 20s to middle 30s, with widespread frost, on the morning of the 23rd, to highs in the upper 80s and lower 90s on the 4th.
Flows in all rivers and streams of the HSA were below normal during September. Crop development remained around 3 weeks ahead of normal during the month and was hastened toward maturity by the continued dryness and drought, and the frost on the morning of the 23rd. Fall harvest activity was 2 to 3 weeks ahead of normal at the end of the month. Early harvest reports indicated minor to major yield reductions across most of the HSA. However, isolated pockets where timely rains occurred in July, August and September were reporting very good yields from the row crops.