Illinois Soil Temperatures – Then and Now

You can find 4 and 8-inch soil temperatures for Illinois on the Water Survey’s web site at www.isws.illinois.edu/warm/soiltemp.asp. These data are from a network of 19 sites around Illinois that is maintained by the Survey.
Below are the maps of what the 4-inch soil temperatures looked like on Wednesday and a year ago on the same date. This year the soil temperatures are barely above freezing in northern Illinois and barely above 40 degrees in southern Illinois. On the same date in 2012, the 4-inch soil temperatures were in the upper 50s and lower 60s across the state.
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Latest Monthly and Seasonal Outlook Released

Yesterday NOAA’s Climate Prediction Center released their outlooks for February and beyond (see maps below). For February they call for an increased chance of below-average temperatures for the upper Midwest, including the northern two-thirds of Illinois. Precipitation in Illinois is expected to have equal chances (E.C.) of being above, below, or near average.
For February through April, temperatures have an equal chance of being above, below, or near average. It’s what I call a neutral forecast. On the other hand, there is an increased chance of above-average precipitation across the Great Lakes region, including the northern three-fourths of Illinois. That would be great news for the further recovery of drought conditions in Illinois, if it pans out.
The outlook for May through July indicates that a large part of the US is expected to have an increased chance of above-average temperatures (last map). The precipitation outlook for this period is neutral.
The outlook for August through October (not shown) is not very interesting for Illinois with equal chances of above, below, and near average temperature and precipitation. In other words, it is a very neutral outlook.
As of January 18, this month has been warm and wet. Temperatures have been almost 5 degrees above the long-term average. Precipitation, mostly in the form of rain, has ranged from less than an inch in northwest Illinois to over 5 inches in far southern Illinois. Current measurements of soil temperatures in Illinois show that the soils under grass at 4 inches remain unfrozen. So much of that rain and melted snow should have soaked in.

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One and three month outlooks from the NOAA Climate Prediction Center.

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Temperature outlook for May – July from the NOAA Climate Prediction Center.

Soil Temperatures in Fall in Illinois

The Illinois Agronomy Handbook recommends that fall N applications should be done when the daily maximum bare soil temperature at 4 inches is below 50 degrees. Fall application is not recommended south of Illinois Highway 16.
The Illinois State Water Survey’s Water and Atmospheric Resource Monitoring (WARM) program has a network of 19 sites around Illinois with daily soil temperature readings at 4 and 8 inches. You can see the reports from “yesterday” on their soil temperature page. Be sure to look at the daily maximum 4-inch bare soil temperature.
As of this writing (November 4), the daily maximum 4-inch bare soil temperature is below 50 degrees in the northwest part of the state. However, it is still in the low to mid 50s across northeastern and much of central Illinois.
Of course, the soil temperature in a particular field can vary due to the temperature, soil moisture, vegetation and tillage, and even soil color.
The figure below shows the average date when the 4-inch soil temperature reached 50 degrees in the fall. In general the average date was in mid-November. However, it can vary from year to year depending on weather and soil conditions.

Average date when soil temperatures at 4 inches reach 50 degrees.Click to enlarge.

Soil Temperatures in Illinois

With the arrival of spring, Illinois farmers are monitoring soil temperatures for decisions in the field. And the soil temperatures are on the rise.
The ISWS Water and Atmospheric Resources Monitoring (WARM) Program records soil temperatures at 4 and 8 inches under grass at 19 sites across the state. In addition, 4-inch bare soil temperatures are computed to represent a cultivated field. These data are available in map and tabular form for the past 7 days at http://www.isws.illinois.edu/warm/soiltemp.asp.
As of April 6, the 4-inch soil temperatures under grass during the day are into the upper 40s in northern Illinois, the low to mid 50s in central Illinois, and the mid 50s in southern Illinois. At night they are cooling off by about 4 to 6 degrees.
The statewide soil temperatures give a general idea of conditions; however, soil temperatures in an individual field will depend on factors such as soil moisture and tillage practices. Also, soil temperatures at the surface will warm up and cool off faster than in deeper layers.