September 2021 Weather and Its Impacts on Missouri

Pat Guinan
State Climatologist
University of Missouri Extension

Summerlike weather continued into September with above average daily temperatures for most of the month, Figure 1. Preliminary data indicate a statewide average temperature of 71.5 °F, or 3.3 degrees above the long-term average. The mild month followed the trend over the past decade with only 3 out of the past 10 Septembers cooler than average, Figure 2. It was the fifth above average month for the year, Figure 3.

Dry conditions impacted most of Missouri in September with preliminary data indicating a statewide average of 2.39 inches, 1.71 inches below the long-term average. It was the fifth consecutive dry September for the state and eighth time in the past decade where September had below normal rainfall, Figure 4. It was also the second consecutive dry month and third for the year, Figure 5. The August-September average statewide rainfall total was 5.41 inches, 2.40 inches below average, and the driest August-September in over two decades, or since 1999, Figure 6.

September rainfall totals were variable across Missouri with radar-estimates indicating highest amounts in parts of west central and southeastern Missouri and a driest conditions across portions of northern Missouri, Figure 7. Some of the heaviest and lightest rain gauge reports for September are listed in Table 1.

Missouri High and Low Rainfall Extremes for September 2021*
  Station Name* County Rainfall (in.)

HeaviestAppleton City 1.9NWBates 6.99
  Nevada 3.4NE Vernon 6.47
  Ste. Genevieve 0.5SSte. Genevieve6.19
  Lowry City 3.8ESE St. Clair 6.04
  Steelville 10.2SSE Crawford 5.62

LightestAlbany 0.7NE Gentry 0.35
  Kirksville 1.4SAdair 0.40
  Owensville 0.5SGasconade 0.52
  Spickard 7W Grundy 0.52
  Macon 1.5N Macon 0.58
*Rain gauges are from the NWS Cooperative Network and CoCoRaHS observations.
Table 1.

The U.S. Drought Monitor map for September 28, 2021 showed over half of Missouri experiencing abnormally dry conditions to moderate drought, Figure 8. Driest conditions were localized and impacting portions of southern Missouri.

According to the Missouri Agricultural Statistics Service, as of September 26, 2021, the majority of the corn crop was in good to excellent condition at 54% and 13%, respectively. Remaining corn conditions this year were 24% fair, 7% poor and 2% very poor. Corn harvest was on pace with the 5-year average at 34%. The majority of the soybean crop this year was also reported in good (56%) to excellent (8%) condition compared to 61% good and 20% excellent at the same time last year.

The majority of hay and roughages were adequate (85%) to surplus (5%) this year with 8% short and 2% very short. Stock water supplies were mostly adequate at 82%, with 15% short and 3% very short. The majority of pastures were reported in fair (41%) to good (40%) condition with 3% in excellent condition and 16% in poor or very poor condition.

The majority of topsoil moisture conditions were 52% adequate and 0% surplus while 40% were reported short and 8% very short. The majority of subsoil moisture conditions were also reported to be adequate (64%) to surplus (0%) with 31% short and 5% very short.

Most sections of the Missouri will experience their first fall frost during October, Figure 9. Using climatology, the northern quarter of Missouri and eastern Ozarks will generally experience a light freeze (32°F 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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Columbia, MO, September Daily Max/Min Temperature Normal vs 2021

Figure 1.

Missouri Average September Temperature* 1895-2021

Figure 2.

Missouri Monthly Temperature Departure from Average* January - September 2021**

Figure 3.

Missouri Average September Precipitation* 1895-2021

Figure 4.

Missouri Monthly Precip. Departure from Average* January - September 2021**

Figure 5.

Missouri Average Aug-Sep Precipitation* 1895-2021

Figure 6.

Radar-estimated rainfall (in.) for Missouri, September 2021

Figure 7.

U.S. Drought Monitor - Missouri - September 2021

Figure 8.

Median Date for Fall Temperature ≤ 32°F

Period of Record 1981-2010

Note: 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.

For more information, please visit Missouri Frost/Freeze Probabilities Guide.

Median Date for Fall Temperature ≤ 32°F

Figure 9.

Average Temperature (°F) September 01, 2021 to September 30, 2021

Average Temperature (°F): Departure from 1991-2020 Normals September 01, 2021 to September 30, 2021

Accumulated Precipitation (in) September 01, 2021 to September 30, 2021

Accumulated Precipitation (in): Departure from 1991-2020 Normals September 01, 2021 to September 30, 2021

Source: Pat Guinan, 573-882-5908