Northern and central Illinois saw widespread heavy rains on April 18-19, 2013. As a result, widespread flooding occurred first at the local level and then along major rivers by the weekend. Last year we had the drought; this year we have what I’m calling the “anti-drought”.
Below is the multi-sensor precipitation map for the 7-day period ending April 19, 2013. This map is based on radar-estimated precipitation and calibrated using available raingauges. Some of the heaviest rains fell north of a line between Quincy and Kankakee. Areas in purple reported between 6 and 8 inches, while the areas in the two shades of red were between 4 and 6 inches. Areas to the south of Interstate 70 escaped the heavier rains.
The second map is the precipitation situation for the year to date, expressed as a percent of “normal” or long-term average. The entire state is above average with the percentages getting larger (wetter) northward. In general, I would characterize the southern third of the state as being 110 to 150 percent of average so far. The central third of Illinois is between 150 and 200 percent of average and the northern third is between 200 and 300 percent of average.
The last figure is a photo that I took on my commercial flight from Chicago to Champaign on Thursday afternoon, just after the worst of the rain had fallen. It is not the best photo in the world because it was gloomy, foggy, and the flight was rough. But it does show how saturated the fields were at this point.
Widespread Rain Across Illinois
I was driving back from a meeting yesterday and saw creeks that were bank full and water standing in fields. That’s the first time I’ve seen those sights in a while, maybe over a year ago in this part of Illinois (Champaign County).
In the last 7 days, widespread rainfall amounts of 1 to 3 inches have been reported across the state. See the map below. This is a National Weather Service product that combines high-resolution radar estimates calibrated with rain gauge measurements (see map below). The heaviest rains fell in northern Illinois, an area considered to have been in some stage of drought earlier this week. Because some of the rain fell after the cutoff for this week’s Drought Monitor, I would expect to see the effects of these rains in next week’s map.
Another bit of good news is that the soils appeared to be unfrozen across most of the state during this rain event, thanks to the warm temperatures early in the week. See the second map below from our network of 19 soil temperature sites across Illinois. As a result, much of this rain should have had a chance to soak in and recharge the soil moisture profile.
Finally, the abundant and widespread rainfall across the state has increased the flow in streams and rivers across the state. Many stream gauges report levels that are in the upper 90th percentile for this time of year. In fact, the National Weather Service has reported some minor flooding along the Kaskaskia and Little Wabash Rivers. The result is that much more water is flowing into the critically low Mississippi River. The Mississippi River stage at Chester Illinois (below St. Louis) has risen seven feet and is expected to rise another four feet in the next day or two (last figure).
While the recent rains should provide some temporary relief for barge traffic on the Mississippi River, levels are expected to start dropping again in a few days. The larger problem is that about 80 percent of the Missouri River and Upper Mississippi River basins are in some stage of drought, according to the U.S. Drought Monitor. Until those two basins are in better shape, concerns with Mississippi River flows will remain for some time.
South-central Illinois Drought Free
The latest US Drought Monitor map shows an expanded area in south-central Illinois that is completely drought-free at this point (7% of the state). In general, that area has received 8 to 16 inches of rain since August 1, which is about 4 to 8 inches above normal. The largest station total was 23.38 inches in Grayville, followed by Centralia IL with 20.01 inches.
Meanwhile, western and northern Illinois have not seen significant drought recovery so far this fall. Those areas have received only 2 to 6 inches of rain, where normal rainfall in that region is on the order of 8 inches.
Another thing that has helped recently with the drought situation in Illinois is that temperatures have run below normal since August. Most recently, October 1-10 has been 6 degrees below normal.
Rainfall Totals from Tropical Storm Isaac
Tropical Storm Isaac dropped a lot of rain on Illinois over the Labor Day weekend. As noted in an earlier post, tropical storms are rare in Illinois but they do happen. However, this one was especially interesting because the heavy rains fell over areas in drought across the state. In a normal year, such heavy rains would have produced widespread flooding in low areas, streams, and small rivers. But not this year. I have not heard any reports of significant flooding. This suggests that the dry soils absorbed most of the rainfall. And what little runoff was produced, ended up in streams that were much below-normal. More on this in another post.
The first map shows the 7-day rainfall totals from Tropical Storm (TS) Isaac. The areas in red had over 4 inches of rain. Areas north of Interstate 80 saw little of the rainfall.
The second map shows the 30-day rainfall totals. Parts of Illinois already had substantial rainfall before TS Isaac. With the addition of the rainfall from Isaac, much of central and southern Illinois had accumulated over 4 inches of rain. In fact, some areas had over 6 inches of rain (areas shaded in yellow or red).
The third map shows the 30-day rainfall departures from normal. Areas in green and blue are above normal. The areas in the two shades of blue are 2 to 4 inches above normal. The areas in purple and violet (?) are 4 to 8 inches above normal. Clearly, areas with much above normal rainfall will have a significant impact on the drought.
