On Thursday, NOAA’s Climate Prediction Center released their outlooks for September and the 3-month period of September – November. For Illinois, they foresee an increased risk of above-normal temperatures and below-normal precipitation in September. Also, they foresee an increased risk of above-normal temperatures for September – November. They are taking a neutral stand on fall precipitation, saying that there are equal chances of above, below and near-normal precipitation.
The other news they have is that their drought outlook (second figure) shows expected improvement in the drought north of Interstate 74 in the upcoming months. Some improvement is expected in southern Illinois. However, they expect drought to persist in western Illinois through at least the end of November.
September in Illinois – Cool
Based on preliminary numbers, the statewide average temperature for September in Illinois was 63.2 degrees, 3 degrees below average. That makes it the 13th coolest September on record for Illinois. The coolest September was 1918 with 59.3 degrees. Statewide records go back to 1895.
Despite the overall cool readings for the month, Labor Day weekend was very hot. Highs in the upper 90s and low 100s were common during that time. One of the hottest was Quincy with 104 on September 1. In all, at least 65 stations in Illinois either tied or broke daily records for high temperatures in early September (text file with details).
On the other extreme, the coldest spot for the month was Paw Paw with 32 degrees on September 15. Twenty-two stations either set or broke daily records for low temperatures (see text file for details).
The statewide average precipitation for September was 3.53 inches, 0.34 inches above average. Rainfall was stubbornly sparse in the areas hardest hit by drought where only 1-2 inches were common. Amounts in far southern and northern Illinois were much wetter at 4-8 inches.
The highest rainfall total for the month was by a CoCoRaHS observer in Bush, Illinois, with 8.42 inches. In second place was a CoCoRaHS observer in Harrisburg, Illinois, with 8.04 inches. The reported driest spot in the state was a CoCoRaHS observer in Warsaw with only 0.69 inches of rain for the month. CoCoRaHS observers are volunteers that use standard equipment and training. Therefore, their results are comparable to other networks.
Drought Eases In Illinois
The U.S. Drought Monitor has reduced the area in drought for Illinois (first map below). Generous rainfall in recent weeks (second map) along the northern and southern borders of the drought led to the reductions. It also helps that cooler temperatures and maturing field crops have reduced the demand on soil moisture.
Soil moisture measurements from a network of sites operated by the Illinois State Water Survey confirmed that soil moisture was recovering by September 28. The table below list the soil moisture at 2, 4, and 8 inches and are a percentage of the water by volume. For example, “24” at 2 inches in Belleville means that the water content of the soil at that point is 24 percent. For most soils in Illinois, values of 30 percent or more mean plenty of soil moisture, values in the 20 percent range are a little dry, and values in the 10 percent range are very dry. The very low values at Kilbourne are typical of the very sandy soil there. They tend to drain very quickly and are only high right after a significant rainfall events.
Location 2 in 4 in 8 in Belleville 24 28 27 Big Bend 24 29 23 Bondville 17 17 33 Brownstown 24 22 23 Champaign 21 31 32 Carbondale 28 34 32 DeKalb 38 37 38 Dixon Springs 33 36 38 Fairfield 37 34 35 Freeport 36 37 42 Kilbourne 3 4 3 Monmouth 24 30 24 Olney 26 30 32 Peoria 32 35 35 Perry 17 15 18 Springfield 25 23 14 Stelle 32 34 29 St. Charles 33 38 39 Rend Lake 26 39 40
Return of the Soil Moisture in Illinois
The natural rhythm of soil moisture in Illinois is to be abundant in spring (sometimes to the point of water standing in fields), followed by a prolonged draw-down during the growing season. Historically, soils are usually at their driest at the end of August and early September. However, soil moisture begins to recover in the September/October time frame as the temperatures cool and crops are harvested, even if rains are below average.
We are seeing some recovery in soil moisture now, according to our soil moisture network maintained at the Illinois State Water Survey. Here is the average soil moisture in the top 20 inches, expressed as a percent of what we saw on June 1 when soil moisture was very high. In other words, values near 100% show a near full recovery while values less than 100% need more rain to recover.
- Belleville: 88%
- Big Bend: 93%
- Bondville: 57%
- Brownstown: 68%
- Champaign: 75%
- Carbondale: 52%
- DeKalb: 75%
- Dixon Springs: 106%
- Fairfield: 89%
- Freeport: 86%
- Monmouth: 55%
- Olney: 78%
- Peoria: 87%
- Perry: 47%
- Springfield: 67%
- Stelle: 71%
- St. Charles: 58%
- Rend Lake: 71%