September – Warm and Dry in Illinois

Strictly speaking, we are not done with September until the end of today. However, I went ahead and pulled together the September statistics because there is no rain in the forecast. All these statistics are based on data that have come in so far and may change slightly in the coming weeks.

Precipitation

The statewide precipitation for September was 1.87 inches, 1.39 inches below average and the 14th driest September on record. As the first two maps below illustrate, dry conditions were widespread. Only a few spots received 3 or more inches in Illinois, including the Chicago area, far western Illinois, and the southeast corner of the state. Several areas in the state received less than an inch of precipitation.

The second map shows the September data as a percent of average. Several areas had less than 25 percent of average (red). Even the “wet” areas had trouble achieving totals close to the 1981-2010 average. Overall, the precipitation departure for September was 57 percent of average.

This is the 6th driest July-September on record for Illinois with 6.64 inches (4.24 inches below average). Ironically, this came on the heels of the wettest January-June on record for Illinois with 28.96 inches (9.13 inches above average).

This is the third month in a row with below-average precipitation. In July, Illinois received 3.14 inches (0.91 inches below average). In August, Illinois received 1.63 inches (1.37 inches below average).

Temperature

The statewide temperature for Illinois in September was 68.8 degrees, 2.9 degrees above average. It was warm but not record-setting. The warmest September on record was 1925 with 72.7 degrees.

The above-average September reversed the pattern of the last three months (June, July, and August) which were below-average on temperature.

  • June: 71.4° (0.4° below average)
  • July: 72.9° (2.4° below average)
  • August: 72.5° (1.0° below average)
  • September: 68.8° (2.9° above average)

Statewide records began in 1895.

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Drought Expands in Illinois

The US Drought Monitor released their latest report this morning. It showed that drought has continued to expand in Illinois. The two areas to note are: 1) an expanded area of D2 “severe drought” in central Illinois, and 2) an expanded area of D0 “abnormally dry” into southern Illinois.

These changes are based on the lack of precipitation over the last 90 days, as well as reports of impacts on corn, soybeans, and pasture conditions. Several streams and rivers in central Illinois are beginning to have flows in the bottom 25th percentile (see USGS). The map of 90-day precipitation, expressed as a percent of average, is shown below. Much of the state experienced only 25 to 75 percent of average precipitation during this period.

Any precipitation at this point will have very limited benefit to the corn and soybean crops because most fields are nearing maturity. However, precipitation would benefit pastures as well as begin the recovery process for soil moisture that is key to the upcoming winter wheat crop and next year’s growing season. The next chance for precipitation in Illinois is on Saturday and Sunday as a cold front moves through the state.

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Rise and Fall of the Mississippi and Illinois Rivers

Both the Illinois and Mississippi Rivers have gone from very low levels in winter, to flood stage in spring, and now back to very low levels (first two graphs). Both rivers struggled with the 2012 drought into early 2013. However, above-average rainfall (first map) in April, May, and June, across the upper Midwest caused a rapid raise in the water levels in both rivers that lasted until July.  The pendulum swung back the other way since July with much drier conditions prevailing across much of the Midwest (second map). As a result, water levels once again dropped on both river systems and are at or near where they were earlier this year. 

With the NWS forecast out to 14 days showing below-average precipitation and the NWS outlook for both October and for October-December showing even odds on above, below, and near-average precipitation, recovery could take some time.

You can look at current and past river and stream levels at this USGS site. While I chose two river gauges to illustrate the changing levels, other sections of the rivers may have responded differently because of control structures and such. 

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New Drought Monitor Map and Fall Forecast

Busy day today with the release of the latest US Drought Monitor map showing an expansion of D0 (abnormally dry) farther into southern Illinois and some adjustments to D2 (severe drought) in west-central Illinois. I think we can rule out the “abnormally dry” conditions in parts of Cook county after Wednesday’s rain. While the impacts of the rapidly developing drought have been seen in crops and yards, the fall harvest is slowly getting underway.

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The new outlooks for October and October-November-December and beyond were released today by the NWS Climate Prediction Center. What is most significant about these latest forecast is that they have removed the increased chances of a wet fall. It has been replaced with “E.C.” which stands for equal chances of above, below, or near-average precipitation. However, there is an increased chance of above-average temperatures in October for Illinois.

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Colorado Flooding

The heavy rainfall and flooding in Colorado shows the absolute power of fast-moving water. Beyond the news media reports, several reports with more details are starting to emerge. Here are some – I will add more as they become available:

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First Half of September – Warm and Dry

The first half of September in Illinois has been both warmer and drier than average. The statewide average temperature is running about 2 degrees above the 30-year average.

The statewide average precipitation is at 0.92 inches, which is about half of the 30-year average through September 16. Of course that precipitation is not evenly distributed around the state. This snapshot below of the radar/raingauge product of the NWS for the last 14 days shows that parts of western, east-central, and northern Illinois received amounts of 1 to 3 inches of rain (shades of green and yellow). Meanwhile, large areas of the state have received far less than an inch of rain (shades of blue).

Here in Champaign-Urbana we have received a grand total of 0.22 inches for September. This follows on the heels of an August with only 0.36 inches. Carbondale, in the lighter shade of blue in southern Illinois, reported only 0.07 inches for September.

Dry as it is, the statewide average precipitation of 0.92 inches is only the fifth driest September on record and we still have half a month to go. The driest September on record was 0.49 inches back in 1979.

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14-day precipitation totals from NWS http://www.srh.noaa.gov/ridge2/RFC_Precip/  (click to enlarge).