September 2016 Weather and Its Impacts on Missouri

Pat Guinan
State Climatologist
Commercial Agriculture/University of Missouri Extension

Warm and humid were the dominant conditions for Missouri during September. Preliminary data indicate a statewide average monthly temperature of 71.6°F, or 3.3 degrees above the long-term average, Figure 1. The warm weather trend has prevailed over the past couple years, where only 4 months since January 2015 have averaged cooler than normal, Figure 2. Dew point temperatures also remained uncomfortably high for much of September. Columbia reported the highest average September dew point since 1998, Figure 3. The only notable reprieve of cool, less humid conditions occurred during the last week of the month.

The majority of rain fell during the first 2.5 weeks of September and it was the third consecutive wet month for the state, Figure 4. Preliminary data indicate the monthly average statewide total was 4.32 inches, or 0.25 inches above the long-term average, Figure 5. Precipitation was variable with wettest conditions over northwestern, central and south central sections, where 4-6 inches were common. Parts of northeast and far southern Missouri observed below normal rainfall, with some locations reporting less than 3-inches.

There were three significant rainfall events during the month. The first event occurred over much of the state on Sep 8-10, another one impacted parts of northwestern Missouri on Sep 13-14, and the final event occurred over southern sections on Sep 16-17. Extreme daily rainfall totals were observed the morning of September 9th over parts of east central Missouri where a rain gauge north of Union, in Franklin county, reported 6.08 inches. A CoCoRaHS observer in Moniteau county reported 5.60 inches the morning of Sep 10. A steady rain, with occasional downpours, fell for several hours on Sep 13-14 around the St. Joseph area and resulted in flash flooding, road closures and flooded basements. Reports of six or more inches were common.

According to the Missouri Agricultural Statistics Service, as of October 2, 75% of the corn and soybean crop was reported in good to excellent condition. Greater than 90% of the hay and stock water supplies were adequate to surplus. Corn harvest was advancing at an average pace (56%) due to drier weather during the latter half of the month. More than 2/3 of the pastures were reported in good to excellent condition.

Most sections of the state will experience their first fall frost during October, Figure 6. Using climatology, the northern quarter of Missouri and eastern Ozarks will generally experience a light freeze (32° or cooler) by mid-October. Central Missouri and the western Ozarks will experience a light freeze by October 21st, and a few days later in urban areas. The Bootheel will have a light freeze typically toward the end of October or early November. For more information on frost/freeze probabilities for Missouri, including additional temperature thresholds, please visit the following link:

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Missouri Average September Temperature 1895-2016*

Figure 1.

Missouri Monthly Temperature Departure from Long-Term Average* Jan 2015 - Sep 2016**

Figure 2.

Average September Dew Point Temperature Columbia, MO 1920-2016

Figure 3.

Missouri Monthly Precip. Departure from Average* Jan - Sep 2016**

Figure 4.

Missouri Average September Precipitation (in.) 1895-2016*

Figure 5.

Median Date for Fall Temperature ≤ 32°F

Period of Record 1981-2010
Frost/Freeze dates will likely vary each year and can depend on local conditions.
Median Date = There is a 50% chance a temperature ≤ 32°F will occur before the designated date.

Median Date for Fall Temperature ≤ 32°F

Figure 6.

Average Temperature (°F): September 01, 2016 to September 30, 2016

Average Temperature (°F): Departure from 1981-2010 Normals September 01, 2016 to September 30, 2016

Accumulated Precipitation (in): September 01, 2016 to September 30, 2016
Accumulated Precipitation (in): Departure from 1981-2010 Normals September 01, 2016 to September 30, 2016

Source: Pat Guinan, 573-882-5908