September 2014 was slightly below normal as the statewide average temperature was 62.0°F resulting in 1.2°F below normal. For the state, it becomes the 43rd coolest Septembers since 1872 when statewide records began. The Des Moines CWA average temperature was also 62.0°F. The hottest temperature was 93°F that occurred at Des Moines and Newton on the 4th. The coldest temperature during September in the Des Moines CWA was 31°F in Webster City, Mason City and Estherville on the morning of the 13th. This was during the coldest stretch in September which was from the 11th to the 16th (See Figure 2) while the coldest day, with respect to average daily temperature, was on the 12th when much of central Iowa was 15 to 18 degrees below normal (See Figure 3). In fact, Lamoni, Mason City and Ottumwa all set new record low temperatures on the morning of the 13th (See Table 1). Also, a few areas of frost developed during the aforementioned cold stretch, mainly occurring across northern Iowa (See Figure 4).
The first couple of weeks in September were cool and wet as several days across the state recorded measurable precipitation in the first half of the month. In fact, the statewide average precipitation for Iowa was 4.37 inches or 0.99 inches above normal and the average precipitation for the Des Moines CWA was 4.07 inches during the month of September (See Figure 5). The highest monthly total, within the DMX CWA, was 7.41 inches in Indianola while the highest in the state was 8.63 inches near Norwalk. The greatest rainfall event came on the 9th where a widespread band of 1 to 4 inches affected central to southern Iowa (See Figure 6). Des Moines, Lamoni, and Ottumwa recorded 3.00”, 3.62”, and 2.20” respectively. Both Des Moines and Ottumwa set new daily rainfall records on the 9th. The previous record at Des Moines was 1.92” set in 1970 and was the 7th highest one-day rainfall total during the month of September (See Table 2). The previous record at Ottumwa was 2.00” set in 1921. Northern Iowa was closer to normal or even slightly below normal for monthly precipitation at some locations. Estherville, Mason City and Waterloo were all below normal during September.
Blog post by Kenny Podrazik – NWS Des Moines