September Heat, Flooding, & Drought

This past month was tied for the 4th warmest September for Illinois (state average temperatures back to 1895), and the warmest September since 1933. Precipitation varied tremendously from north to south across the state.

Preliminary data suggest that September was tied for the 4th warmest on record for Illinois. The preliminary average statewide September temperature was 71.3 degrees, which is 4.9 degrees above the long-term average. Monthly temperatures ranged from 2 to 4 degrees warmer than normal in northeast Illinois to over 6 degrees warmer than normal in southwest Illinois. The preliminary average statewide precipitation was 5.34 inches, which is 1.9 inches above the long-term September average. However, the data also show large differences in September precipitation totals across the state, with northern Illinois receiving much more than average precipitation, and southern Illinois receiving much less than average.

Data are provisional and may change slightly over time.

Precipitation, Flooding, & Drought

September precipitation totals reveal a strong north-to-south gradient. Areas of northern and north-central Illinois received in excess of 12 inches of rainfall in September, while areas of southeast Illinois received less than 0.25 inches over the same time period (see maps below). Expressed as a percent of normal September precipitation, these totals ranged from 300 percent of normal in northern Illinois to less than 5 percent of normal in southeast Illinois. Locally, a station near Stockton (Jo Daviess County) observed 16.62 inches in September (nearly 13 inches more than normal), while the station at Smithland Lock & Dam (Pope County) recorded only 0.02 inches (3.5 inches less than normal).

August 2019 was the first months since September 2018 during which the U.S. Drought Monitor identified drought in the state. In September, dryness in east-central Illinois persisted but did not intensify. The latest U.S. Drought Monitor map (September 24) shows a pocket of moderate drought covering parts of Champaign, Ford, Iroquois, and Vermilion counties (see map below). Concurrently, below normal rainfall and above normal temperatures in the southern part of the state produced dryness in September. The latest U.S. Drought Monitor depicts abnormally dry conditions for most of Illinois south of I-64, and a pocket of moderate drought from Pope and Hardin counties in the southeast to Perry and Franklin counties in south-central Illinois. Conditions in southern Illinois have shown some signals of a flash drought, which is a rapidly intensifying drought event, often provoked by existing precipitation deficit combined with intense heat.

Reports from Illinois Farm Bureau CropWatchers regarding drought in east-central and southern Illinois are mixed. Some report the dryness and heat have helped late-planted crops reach maturity, while at the same time possibly sacrificing yield. The recent National Weather Service 7-day precipitation forecast calls for 1 to 4 inches of rain in the northern half of the state, with 7-day forecasted totals less than 0.5 inches in southern Illinois (see map below).

In contrast to the ongoing drought in southern and east-central Illinois, September was abnormally wet for most of northern and north-central Illinois. Persistent, heavy rains led to flooding impacts in parts of northern Illinois, including the closure of several state parks and significant flooding along the Fox and Des Plaines Rivers, among others. Areas in northern and north-central Illinois received in excess of 12 inches of rainfall in September. In most parts of Peoria, Woodford, Marshall, and Livingston Counties, most of the rainfall totals came in a 24-hour period between September 27 and 28. This event created dangerous flash flooding from Peoria into the southwest Chicago suburbs.

The COOP station in Minonk, Illinois (Woodford County) recorded 9.09 inches of rainfall over that 24-hour period, although that likely fell over a less than 12-hour window. This total approached the 24-hour, 500-year storm total of 9.53 inches and surpassed the 12-hour, 500-year storm total of 8.29 inches. A 500-year storm total refers to a precipitation accumulation over a given time period (e.g., 12, 24, 48 hours, etc.) and has a 0.2 percent chance of occurring in a given year. Impressively, the 9.09-inch total in Minonk broke, and nearly doubled, the all-time 24-hour precipitation total record at that station, which was just over 5 inches (data going back to 1895). Images of flooded fields in Woodford and Marshall Counties suggest this most recent heavy precipitation event may delay harvest.

Temperature

The September temperature was much more consistent across the state than precipitation, as the entire state experienced above normal temperatures this month (see maps below). Apart from the last full week in September, most of the state has been under the influence of a large high-pressure system this month, centered to our southeast. This system has allowed warm air to intrude from the south/southwest, generating warmer than normal conditions for this time of the year. In fact, the statewide September average temperature was 71.3 degrees, tying it for the 4th warmest September on record in Illinois (back to 1895). September average temperatures across the state ranged from 65 degrees in Jo Daviess County to 78 degrees in Lawrence County. The lowest minimum temperature reported in Illinois in September was 45 degrees in Jo Daviess County on September 5, and the highest maximum temperature reported in Illinois was 97 degrees in both Alexander and Pope Counties on September 16. Well over 100 local daily climate records were broken in Illinois in September, most of which were high daily minimum temperature records. This is attributed to several very warm nights, including the night of September 22, when the nighttime minimum temperature remained above 70 degrees as far north as Elizabeth (Jo Daviess County) and Freeport (Stephenson County). On the night of September 10, the station in Rock Island reported a nighttime minimum temperature of 77 degrees, besting the previous daily record by 3 degrees.

Short-term temperature forecasts call for continued above average temperatures for the first few days of October and then a regression to cooler, more seasonal conditions. Longer term Climate Forecast System (CFS) forecasts from the National Centers for Environmental Protection show probabilities of a 32-degree freeze in Illinois remain below 30 percent into the third week of October. The map below shows the probability of a daily minimum temperature below 32 degrees between October 14th and October 21st.

October 2019 Outlook

Looking into October, the 8 to14-day outlook from the Climate Prediction Center (CPC) shows elevated probabilities of above normal temperatures and elevated probabilities of above normal precipitation across the state.

The CPC monthly outlook for October still shows elevated probabilities for below normal temperatures across the northern half of the state, with equal chances (above normal, normal, below normal precipitation) for all but the very northwest corner of Illinois (see maps below).

September 3, 2019September 3, 2019

Unequal August Precipitation Leads to Drought in Illinois

August 2019 will be remembered for remarkable differences in monthly precipitation totals across Illinois, as well as the first appearance of drought in the state since September 2018.

It would be inappropriate to summarize August 2019 precipitation across the state using only one adjective. Preliminary data suggest that August was drier than average across much of the state north of I-72 and south of I-64, while much wetter than average conditions prevailed between the two interstates. The preliminary average statewide precipitation was 4.21 inches, which is 0.61 inches below the long-term August average. The preliminary average statewide August temperature was 72.8 degrees, which is 0.7 degrees below the long-term average.

Data are provisional and may change slightly over time

Precipitation & Drought

July 2019 was the first month since November 2018 that ended with below average statewide precipitation. Dryness in the northwest and east-central parts of the state that began in July persisted in August.

Areas in the south-central part of the state, particularly in the western extent of the St. Louis metro east, have received precipitation totals in August between 5 inches and 8 inches above normal, with a station near Patoka (Marion County) reporting the highest August rainfall total of 14.19 inches. Most areas of the state north of I-72 and south of I-64, in contrast, received below normal rainfall in August, in some cases up to 4 inches below normal. The driest area in August covered parts of Ford, Iroquois, and Vermilion counties in east-central Illinois, where precipitation totals were less than 50 percent of their August normal (see maps below).

The continued dry conditions from July to August led the U.S. Drought Monitor to identify moderate drought (D1) in northwest and east-central Illinois in their August 13 map. This was the first time the Drought Monitor identified drought in Illinois since September 2018, which represents the largest number of consecutive, drought-free weeks (48) since the Drought Monitor began 20 years ago. The latest Drought Monitor map, from August 29, shows moderate drought persistence in northwest and east-central Illinois (see figure below).

The combination of late planting, due to flooding, and multi-week drought has stressed crops and farmers across central Illinois. Reports from Illinois Farm Bureau CropWatchers discuss corn dropping ears and beans dropping leaves in parts of Champaign County. The recent National Weather Service precipitation forecast calls for between 0.75 inches and 2 inches over the next 7 days for most of the northern half of the state, with little to no precipitation in southern Illinois.

Temperature

Much of the state experienced near normal to slightly below normal temperatures in August. A strong cold front in the early part of the month and the last week of the month resulted in cooler conditions, with minimum temperatures ranging from the high 40s to high 50s across the state. This was particularly the case for the northwest quadrant of Illinois. However, all of the state experienced August temperatures within 2 degrees of the long-term August mean (see maps below). August average temperatures ranged from 79 degrees in Pulaski County to 68 degrees in Jo Davies County. The lowest minimum temperature reported in Illinois in August was 48 degrees in DeKalb County on August 2^nd, and the highest maximum temperature reported in Illinois was 98 degrees in Pulaski County on August 20^th.

September 2019 Outlook

Looking into September, the monthly outlook from the Climate Prediction Center (CPC) issued on August 31 shows slightly elevated probabilities of below normal temperatures across the northern half of the state, with equal chances of above normal, normal, and below normal temperatures in the southern half.

September precipitation probabilities slightly favor above normal precipitation in the northwest corner of the state, but are equal (above normal, normal, below normal) for the rest of Illinois (see maps below).

September 2019 Temperature Outlook

September 2019 Precipitation Outlook

August 1, 2019September 4, 2019

July 2019: Prolonged stretch of abnormally wet weather comes to an end, along with notable hot and humid conditions.

July 2019 signaled the end of a persistent and historic stretch of abnormally wet conditions across Illinois, along with several notable periods of significantly above average temperatures.

Preliminary data suggest that July 2019 concluded drier than average, with temperatures above the long-term average. The preliminary average statewide July temperature was 77.3°F, which is 1.9°F above the long-term average. The preliminary average statewide precipitation was 3.23 inches, which is 0.85 inches below the long-term average.

Data are provisional and may change slightly over time

Precipitation

After seven consecutive months of above average statewide precipitation, July 2019 marked the end of the historic wet streak with below average statewide precipitation for the first time since November 2018. Despite the overall below average designation, July precipitation across Illinois was not evenly distributed.

Many in southern and northeastern portions of the state experienced near to above average precipitation totals in July, with a station near Highland (Madison County) reporting the highest monthly rainfall total of 9.02 inches. In contrast, large regions of western and central Illinois saw below average rainfall. In fact, multiple localities near the Quad Cities and along the Mississippi River, as well as smaller regions in east-central Illinois received only 10 to 25% of average monthly precipitation (see maps below).

Dating back to June 1, these same regions have reported precipitation departures of around 2 to 4+ inches below the long-term average. This extended stretch of dry conditions prompted the August 1 map from the U.S Drought Monitor (using data through July 30) to continue to highlight areas of abnormally dry conditions across the western and central portions of the state.

Illinois Precipitation Departures Map — Midwest Regional Climate Center (MRCC), accessed 8/1/2019

Illinois Drought Map — U.S Drought Monitor (UDSM) Illinois, accessed 8/1/2019

Interactive July 2019 Climate Station Precipitation Map

Temperature

Despite an overall seasonable and pleasant ending, the first weeks of July brought several extended periods of heat and humidity to Illinois. Most notable was the heat wave that impacted the region from July 18 through July 21, in which every county in Illinois was under an Excessive Heat Warning at some point during the weekend. Throughout this event, daily maximum station temperatures soared into the 90s, with dew points in the mid- to upper 70s. This resulted in heat indices over 100 for many and approached 110 or higher in some localities. Daily temperature departures of 8 to 10+ degrees above average were common across the northern half of the state (see map below).

Overnight low temperatures during this event did not bring much, if any, relief from the heat. With a daily minimum temperature of only 80 degrees on July 19, Rockford (Winnebago County) set a new all-time record-high minimum temperature. Records for Rockford extend back to 1905.

Looking at July as a whole, the average station temperatures varied from the mid-70s to the low 80s, and monthly temperature departures of 1 to 4 degrees above the long-term average were common for the northern two-thirds of Illinois (see maps below). The highest temperature reading in the state of 98 degrees occurred at two stations, Flora (Clay County) on July 11, and Palestine (Crawford County) on July 21. The lowest minimum temperature of 51 degrees also occurred at two stations, one near Champaign (Champaign County) on July 23, and at a station near Paxton (Ford County) on July 25.

Interactive July 2019 Climate Station Temperature Map

August 2019 Outlook

For the remainder of August, the monthly outlook from the Climate Prediction Center (CPC) issued on July 31 favors probabilities for below average temperatures across Illinois and most of the upper Midwest. The outlook also favors near equal chances for below, near, or above average precipitation.

CPC August 2019 Temperature Outlook — August 2019 Temperature Outlook

CPC August 2019 Precipitation Outlook — August 2019 Precipitation Outlook

July 1, 2019July 2, 2019

June 2019: Stormy and Wet with a Warm Finish

June 2019 will be a month remembered for a continuation of above average precipitation and near to seasonably cool temperatures, despite an unseasonably warm finish.

Preliminary data suggest that June 2019 concluded wetter than average, with temperatures slightly below the long-term average. The preliminary average statewide June temperature was 71.0°F, which is 0.9°F below the long-term average. The preliminary average statewide precipitation was 5.39 inches, which is 1.18 inches above the long-term average.

Data are provisional and may change slightly over time

Precipitation and Flooding

After near historic crests at multiple gages along both the Illinois and Mississippi rivers early in the month, water levels continued to slowly recede for many regions heading into July. However, above average precipitation in June, combined with calculated soil moisture content remaining in the 90th to 99th percentile across Illinois, leaves the state with an elevated risk of continued flooding over the next month, especially in regions that may be affected by storms or locally heavy rainfall.

Flooding concerns along Lake Michigan were common in June. According to the U.S. Army Corps of Engineers, water levels in the Lake Michigan-Huron system have risen by nearly 5 inches throughout the month. By the end of June, average levels were reported to be 33 inches, or about 2.75 feet above the historical June average. These levels set a new June record by nearly 2 inches. Water levels of this magnitude haven’t been exceeded since 1986.

Preliminary results show that the June 2019 statewide precipitation total of 5.39 inches was 1.18 inches above the long-term average. This marks the 8th consecutive month in which no part of Illinois has been listed as in drought or abnormally dry by the U.S. Drought Monitor, and the 7th consecutive month with above average statewide precipitation.

June rainfall in Illinois was not evenly distributed. Several regions in the northern half of the state reported precipitation totals slightly below to near average for the month, with localized regions of above average precipitation. A large majority of the southern half of the state experienced more uniform above average precipitation departures, with numerous localities receiving 200 to 300% of normal (see maps below).

A gage near Cobden (Union County) reported the highest official precipitation total for June, with a reading of 10.73 inches.

Interactive June 2019 Climate Station Precipitation Map

Temperatures

Preliminary results show that June finished with a statewide average temperature of 71.0°F, which is 0.9°F below the long-term average.

The middle of the month was characterized by an extended period of unseasonably cool temperatures, while the start of astronomical summer brought a steady warming trend which allowed temperatures to reach into the upper 80s and 90s for the final days of June.

Temperature departures for the month were near to 1 to 3° below average, with average temperature values ranging from the mid-60s up into the mid-70s (see maps below).

The highest maximum temperature recorded in the state, at two separate stations, was 97°F, once at a station near Bentley (Hancock County) on June 5, and once at a station near Flora (Clay County) on June 30.

The lowest minimum temperature of only 43°F was reported in Danville (Vermilion County) on the morning of June 14.

Interactive June 2019 Climate Station Temperature Map

July 2019 Outlook

As we head into July, the monthly outlook from the Climate Prediction Center (CPC) favors slight probabilities for below average temperatures across most of the state, as well as continued probabilities of wetter than average conditions statewide.