USDA Soil Moisture Report for Illinois

Yesterday, the USDA released their report on soil moisture conditions for Illinois. Overall the state looks moist, especially in southern Illinois after weeks of rain. Statewide, 95 percent of the topsoil moisture and 93 percent of the subsoil moisture is rated as either “adequate” or “surplus”.


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Tracking Illinois Soil Temperatures

As the snow turns to mud this week, this is a good time to advertise links for the soil temperatures in Illinois. The Water Survey operates a 19-station network of sites around the state collecting hourly soil temperatures at 4 and 8 inches under grass as well as an estimate under bare ground.

All this information can be found at the Illinois Climate Network Soil Data site. Below is just a screenshot of that page to show where you would find that information on the real web page.


Here is a snapshot of 4-inch soil temperatures as of 10 am, March 13, 2015. Soil temperatures are still near the freezing mark in the northern half of the state, but warm into the 40s and low 50s in the southern half of the state.


Halfway Through January

Back in the office after the first round of the 2014 Corn and Soybean Classics. There are two remaining dates, January 21 in Mt. Vernon and January 28 in Champaign.

It is no surprise that the first 15 days of January have been colder than average. The statewide average temperature for this period was 19.9 degrees and 3.9 degrees below the 1981-2010 average for this period.

While Illinois experienced some very cold temperatures, especially on January 6 and 7, very few records were broken. Here is a list of:

This list is not final as more stations will file reports at the end of the month.

The snowfall in January has been impressive so far. There was a large area across the state with 10 to 15 inches, mostly as a result of the January 5-6 winter storm (first map). Compared to the average for the first half of January, this January’s snowfall has been above average for almost all the state (second map). The largest departures from average were in central and eastern Illinois and ranged from 8 to 12 inches above average.

The statewide average precipitation (rainfall and the water content of any snow or ice) for the first 15 days of January was 1.48 inches and 165 percent of the long-term average for this period.

Probably some of that moisture has made its way into the soils if they have thawed out. We have 4-inch soil temperatures across the state and they have been in the mid-30s across southern Illinois and parts of central Illinois for some time now. So it is likely that the frost depth is less than 4 inches in most of those areas.  I did see a lot of water ponded and frozen in low-lying areas of fields across much of northern Illinois this week as those soils are more deeply frozen.

Most of the rivers and streams across the state are in better shape now than they were a month ago, especially across the central part of the state. Check out the USGS streamflow reports.



Dryness Continues Across the Corn Belt

What a change in fortunes. After the wettest January-July on record in Illinois with 29 inches and 9.5 inches above average, we are now facing exceptionally dry conditions in the last 30-45 days across much of Illinois as well as the Corn Belt.

As the map of precipitation percent of average since July 1 shows, a large part of the Corn Belt is running at less than 50% (shaded dark orange to red).  Until recently we saw few impacts on crops because of cooler-than-average temperatures and the excess of soil moisture at the beginning of July. But all that is beginning to change. Warmer weather has returned this week and is expected to continue for at least the next 14 days, according to the NWS.

The soil moisture reports from the USDA NASS indicate that soil moisture is beginning to run low. Topsoil moisture a month ago was rated at 16 percent short and 0 percent very short. Monday’s report rated it at 50 percent short and 11 percent very short.

Subsoil moisture a month ago was rated at 9 percent short and 0 percent very short. Now it is rated at 35 percent short and 8 percent very short.

The Illinois State Water Survey reported lower soil moisture levels at their sites.

The one bright spot in the forecast is that there is a chance of rain in the next five days (second map). However, the potential amounts are modest. Northeast Illinois could see between 0.5 and 1.0 inches. The rest of the state is more likely to see 0.5 inches or less.  If the forecast holds, parts of Iowa, Minnesota, and Wisconsin could see some relief from the current dry conditions.

30-day precipitation percent of average for period ending August 21, 2013, based on radar and rain gauge data. Click to enlarge.
5-day potential precipitation amounts from the NWS, August 21, 2013. Click to enlarge.

Abnormally Dry Weather Creeps into Western Illinois

The latest US Drought Monitor has an area of “abnormally dry” conditions in western Illinois. This does not mean drought but it means that it is an “area of interest” to paraphrase what they say on TV when they have suspicions about someone but have no hard evidence.

In this particular case, the only evidence are widespread watering in towns and stressed corn and soybeans – especially the late planted fields with shallow root systems.

Rainfall amounts in those areas have been small and widely scattered (second figure). For example, Quincy airport has received only 0.25 since July 1. Combined with the high rates of evapotranspiration in July, roughly two-tenths of an inch per day, this situation can lead to the rapid withdrawal of topsoil moisture. Other areas in north-central Illinois may be candidates for the “abnormally dry” status in coming weeks if the rains do not return.



April 4th Wettest On Record


This April was the 4th wettest on record for Illinois with 6.90 inches, based on the preliminary numbers. That was 3.13 inches above the long-term average of 3.77 inches.

To show you how wet it was, this April easily beat out the combined statewide rainfall totals for Illinois in May, June, and July of 2012 during the worst of the drought. The total rainfall for those months in 2012 were 2.50 inches, 1.80 inches, 1.48 inches, respectively, which led to a total of only 5.78 inches. That was 1.12 inches less than this April!

The first map below shows the spectacular rainfall totals across much of the state. The areas in yellow and orange were 6 to 9 inches. A few areas in pink and red were 9 to 11 inches. This product has a 4 kilometer resolution and is based on radar estimates calibrated with rain gauges.

The second map shows the same rainfall amounts expressed as a percentage of the long-term average. There was a small patch of below-average rainfall in far southern Illinois. Otherwise the rainfall across the rest of the state was much above average. Many areas in the dark blue were 2 to 3 times their long-average rainfall.

Speaking of rain gauges, the two largest monthly totals for April so far were Augusta with 12.28 inches and Naperville with 11.03 inches. Several more stations reported totals in the 10-inch range.

There were two major impacts of the wet April. One was widespread flooding on the Illinois, Wabash, and Mississippi Rivers and their tributaries. Several sites along the Illinois reported record high river crests in April. Because the flooding included the Chicago area, the dollar damages and number of people affected will be quite large.

The second impact of the wet April was the delay in fieldwork. In the April 29 USDA NASS report, only 1 percent of the corn crop was planted, compared to 76 percent last April, and a five-year average of 36 percent.


The statewide average temperature was 50.1 degrees and 2.3 degrees below average. That was not record-setting but reflects the fact that we had a lot of cool, cloudy days in April.


The April 2013 precipitation, ending with reports on the morning of May 1. Click to enlarge.
April 2013 precipitation, ending with reports on the morning of May 1. Click to enlarge.
April precipitation, expressed as a percent of the long-term average. Click to enlarge.
April precipitation, expressed as a percent of the long-term average, for reports ending on the morning of May 1. Click to enlarge.

Impact of Tropical Storm Isaac on Illinois Soil Moisture

In an earlier post, I discussed the sizable rainfall totals across central and southern Illinois from Tropical Storm Isaac. Its impact on soil moisture has been dramatic. We measure soil moisture at 19 sites across Illinois as part of the Illinois State Water Survey WARM program. Here are the 4, 8, and 20 inch soil moisture maps based on readings at midnight on September 3.

We measure the soil moisture as the fraction of water in the soil by volume. So a value of 0.4 means that 4/10 of the soil is water by volume. Or you could view it as 40 percent of the soil is water by volume.

  • Values in the 0.4 to 0.5 range means the soil is close to or at saturation;
  • Values in the range of 0.3 to 0.4 are typical of a moist soil;
  • Values less than 0.3 are getting dry;
  • values between 0.1 and 0.15 are pretty much at the lower limit of what plants can use.

Below are the maps for 4, 8, and 20 inches. For most of Illinois, the fraction of water by volume is in the range of 0.3 to 0.4 – that’s good, especially for this time of year. There are a few places over 0.4, which means they are getting close to saturation at that level of the soil. A month ago a lot of stations were in the 0.10 to 0.15 range, which is pretty much the lower limit of what plants can use.

These numbers suggest that soil moisture conditions in much of Illinois have improved dramatically after Tropical Storm Isaac. However, they still have room for improvement in northern Illinois. And the rains came too late for the corn crop and much of the soybean crop. Even so, it is reassuring that we have gone a long ways towards recharging the soil moisture as we move into fall.

By the way, you’ll notice the 0.06 values in west-central IL. Those are in an extremely sandy soil near Havana in the Illinois River floodplain. They drop quickly after a rain event and stay very low most of the year.

Four-inch soil moisture, expressed as the fraction of water in the soil by volume. Click to enlarge.
Eight-inch soil moisture, expressed as the fraction of water in the soil by volume. Click to enlarge.
Twenty-inch soil moisture, expressed as the fraction of water in the soil by volume. Click to enlarge.