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).

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.

August 9, 2016

Deaths of Children in Hot Vehicles

Jan Null, certified meteorologist and professor at San Jose State University, CA, has been tracking child vehicular heatstroke deaths since 1998, creating a website on deaths of children in hot cars at noheatstroke.org
According to the website:

687 children have died since 1998
54% of the children were “forgotten” by the caregiver,
29% were playing unintended in a vehicle,
17% were intentionally left in vehicle by an adult,
and 1% were unknown
the inside of a car can heat up by 19 degrees in 10 minutes and 29 degrees by 20 minutes, cracking the window open had little effect on heating

And if you think that this tragedy only happens in the hotter climates of the US, think again. They have occurred in 46 out of the 50 states. Here is the distribution by state, including 16 in Illinois.

new_state_totals — Child Heat-Related Deaths in Vehicles by State, 1998-2015. Map by Jan Null, noheatstroke.org, 2016. By the way, that’s not 141 for Maryland. It’s 14 for Maryland and 1 for Delaware.

August 11, 2014

Sharp Contrast Between Chicago and Portland Temperatures This Summer

As impressive as this cool summer has been in Illinois, the experience here and across the Midwest stands in stark contrast to the West Coast. Here is the temperature contrast from the last full month – July (map below – click to enlarge). While the Corn Belt was 3 to 6 degrees below average in July, the West Coast and parts of the Rockies have been running 3 to 6 degrees, or more, above average.

The contrast between Chicago and Portland (OR), two of my favorite cities, show how different things have been. For July, the average high in Chicago was 79.8 degrees and the average low was 60.9 degrees. The average monthly temperature of 70.4 degrees meant that Chicago was 3.6 degrees below average.

On the other hand, the average high for July in Portland was 83.8 degrees and the average low was 59.8 degrees. As a result, their average monthly temperature of 71.8 degrees meant that Portland was 2.6 degrees above average.

Furthermore, while Chicago barely reached 90 degrees on one day in July, Portland reached or exceeded 90 degrees 7 days in July, including a reading of 99 on July 1.

The long-term average temperature for July in Chicago is 74 degrees and in Portland is 69 degrees.

It is no surprise that the NWS forecasts indicate that the heat will remain in the West for the next two weeks. However, it looks like Illinois has a good chance of seeing above-average temperatures for a change in the August 16-24 period.