New Outlook for Summer, Hot in Illinois

The new NOAA Climate Prediction Center outlook was released. Illinois has an increased chance of being warmer than average for July and for the July-September period. So far June has been warm with temperatures running 3.5 degrees above normal. There are no indications of how precipitation will behave in July and July-September. I’m most concerned with the dryness in western Illinois.


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Parts of Illinois Abnormally Dry

The US Drought Monitor has declared nearly 36 percent of Illinois to be “abnormally dry”. This is the first stage before drought is declared. Other areas that are in the same conditions are Marshall, Woodford, and western McLean Counties in the western region and probably not so much in Grundy, Livingston, and Ford Counties (especially when you look at the 90-day precipitation deficits). We can pass along impacts to the Drought Monitor, so please send me any observations that you have. Thank you.

US Drought Monitor Map for Illinois



30-Day Precipitation Map for Illinois (Departure from Normal)

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Dry Across Illinois and Corn Belt Last 30 Days

It has been dry across Illinois and most of the Corn Belt in the last 30 days. Below-normal precipitation has occurred from the eastern Dakotas, Nebraska, through parts of Minnesota, Iowa, and Missouri, and across much of Illinois, Indiana, Kentucky, Ohio, and Michigan.

For Illinois, temperatures were close to normal in the second half of May. However, temperatures for the first 12 days of June have been running 2.7 degrees above normal. Meanwhile, the statewide average precipitation for June so far is 1.52 inches, which is 0.7 inches below normal.

Measurements over the last five days here at the Water Survey indicate that we are using approximately 0.2 inches of water per day in the field or about 1.4 inches per week. So if we aren’t getting that much rain per week to make up for the loss, then plants have to rely more on soil moisture to continue growing. In the short term, it is not cause for alarm. For example, it is not unusual for water usage to run ahead of rainfall in June, July, and August. We just don’t want usage to run so far ahead as to deplete all the soil moisture reserves.

According to the National Weather Service, there are chances of rain and thunderstorms through Wednesday before slightly cooler and less humid weather finishes out the week. The potential rainfall totals over the next three days ranges from 0.25 to 0.50 inches in the southern third of Illinois and from 0.50 to 1.25 inches in central and northern Illinois. As you would expect in summer,  the rainfall totals could be locally heavy while nearby areas see little or nothing.

30-Day Departure from Normal Precipitation

Areas in yellow are down to 1.5 inches below normal, while areas in the lighter shade of orange are down to 3 inches below average. At the same time, the demand on soil moisture has been increasingly rapidly as crops and vegetation develop.  30dPDeptMRCC

30-Day Percent of Normal Precipitation

Areas in orange represent precipitation that is 50 to 90 percent of normal. Areas in red are less than 50 percent of normal and are of greatest concern. 30dPNormMRCC


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Spring in Illinois, Warm with Wet and Dry Patches

Climatological spring is defined as March, April, and May. Here are how things looked this Spring for precipitation and temperatures. For most of Illinois, precipitation in Spring was close to the 1981-2010 average (normal) with some wet areas in northeast and southern Illinois. Temperatures ended up on the warm side for Spring.


The accumulated precipitation in spring, ranging from 15-20 inches far southern Illinois, to only 5-7.5 inches in small patches near the Illinois River. Most of the state was either 10-15 inches (dark green) or 7.5 to 10 inches (medium green).


The Spring precipitation departures from normal show wet and dry areas of the state. Areas in southern and northeast Illinois were wetter with with amounts 2 to 6 inches above normal (darker shades of green). Areas in western Illinois were 2 to 6 inches below normal. The rest of the state was within 2 inches of normal. 


The temperature departures from normal for Spring show that most of the state was running 1 to 2 degrees warmer than normal. Obviously, there were some stretches of colder than normal weather during Spring but the warmer than normal temperatures prevailed. 

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Heavy Rains Strike Parts of Illinois in May

Summary: For Illinois, the statewide average temperature for May was 62.2 degrees, just 0.5 degrees below normal. Underneath the benign numbers were some stretches of cold weather at the beginning and middle of the month before summer-like conditions arrived in the last 10 days of the month.  The statewide average precipitation was 4.52 inches, just 0.08 inches below normal. However, heavy rains struck parts of Illinois, causing flooding. Some areas received up to 9-10 inches of precipitation by the end of the month.


The first map shows the accumulated precipitation for May. Areas from Chicago westward, most of far southern Illinois, and McLean County received 5 to 9 inches.  A few locations received over 9 inches, including Countryside (Cook County) with 10.56 inches, West Aurora with 9.32 inches, and Aurora with 9.27 inches.


This map shows the departures from the 1981-2010 normals. Areas in light green were up to 2 inches above normal, while areas in the next darker green were 2 to 4 inches above normal.



Temperatures were within a degree of normal for the state, except for parts of eastern and southern Illinois where they were 1 to 2 degrees below normal. We saw a lot of week to week variability in the temperatures. In the end the warm and cold weather canceled each other out.


Here is how the average daily temperature at Chicago O’Hare looked, expressed as a departure from the daily normal. This was typical of sites around Illinois in May with a stretch of cooler than normal weather in the first week, followed by near-normal temperatures, before a second wave of cold weather struck around mid-month. However, the last 10 days were above normal, which mostly cancelled out the earlier colder-than-normal weather.


Severe Weather

NOAA’s Storm Prediction Center reported 5 tornadoes in Illinois in May, as well as 35 hail and 86 wind damage reports. You can examined the day by day reports from the Center and move backward and forward in time.



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May Update, Cool with Near-Normal Rains

Looking at the latest numbers for May to date, Illinois is 3.5 degrees cooler than normal. Rainfall is within an inch of normal for most areas. Click on the  images to enlarge.

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Outlook for Summer, Fall in Illinois

The National Weather Service released their latest outlooks for this summer and fall today. Looks like a warmer summer and fall may be in store for Illinois.

Transition from El Niño to La Niña

Most models predict the end of El Niño and a brief period of ENSO-neutral by early summer. La Niña is favored to develop during the summer, with about a 75% chance of La Niña during the fall and winter 2016-17. La Niña occurs when colder-than-average waters appears in the eastern Pacific Ocean. It is the opposite phase of El Niño although the effects on the US are not as strong or as clearcut as an El Niño event. I will post more on La Niña soon.


Here are the outlooks for June. Click on the maps to enlarge. Most of Illinois, except for the far north, has an increased chance of being wetter than normal (green). Meanwhile, the eastern third of Illinois has an increased chance of being warmer than normal (red). Areas not shaded and marked EC indicated areas where there are no strong evidence of conditions being too cool, too dry, too wet, or too dry as the case may be. EC stands for Equal Chances of above, below, and near-normal conditions.  EC is not a bad place to be.


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