Heavy rains have fallen in western and central Illinois over the last three days. Here is the overall picture showing the heavy rains in southern Iowa and northern Missouri as well. Areas in yellow, orange, and red experienced 2.5 to 8 inches of rain. Much of the rest of Illinois received 1 to 2 inches.
The largest three-day total comes out of Rushville with 8.06 inches with most of that falling on one day (6.96 inches on September 10). To put that in perspective, the average September rainfall at Rushville is 3.65 inches. So this three-day period was over twice the average for the entire month. Continue reading “Heavy Rains in Western and Central Illinois”
The recent rains and associated flooding in the Chicago area are reflecting the long-term pattern of wetter conditions in the region. Here are a few samples of that pattern.
First of all, northeast Illinois (Cook and several surrounding counties – see map below) has experienced a shift in precipitation over the last 120 years. This plot shows the amounts for each year as green dots, and an 11-year running average showing longer periods of dry conditions (brown) and wet conditions (green). There is a pretty remarkable shift from a drier climate between 1895 and 1965 with lots of brown, towards a wetter climate from 1966 to present where green dominates.
If you compare the average annual precipitation between the two periods, you get 32.9 inches for the earlier period and 36.8 inches for the later period. That is a 3.9 inch increase, or about 12 percent.
If you look at the 10 wettest years in the record, 8 out of the 10 came after the shift in 1965. The two exceptions were 1902 at #1 and 1954 at #10.
Of course, we have still experienced drought conditions in this later wet period, as noted in 2005 and 2012. However, the wetter years far outnumber the dry years since 1965. BTW, this pattern is not unique. I have seen this across the state.
Here is the same plot for northeast Illinois for just the month of August. The green shading comes in a little later, showing generally wetter conditions since the 1980s. What is startling is the number of very wet Augusts in the last 50 years. The two wettest were 1987 with 10.04 inches and 2007 with 10.88 inches, which is more than double the long-term average.
As this plots show, the issue is not just a shift towards a wetter period over time but a shift towards wetter extremes as well.
As of August 27, 2014, the northeast region is at 5.4 inches, 1.83 inches above average.
Here is the region used in this discussion (aka Climate Division 2). Climate divisions are regions of roughly similar climate. The advantages of a regional average are no missing data and increased statistical confidence in the resulting values. You can read more about them here.
Heavy rains fell across the Chicago metropolitan area again today (August 22, 2014). Here is the map of rainfall amounts from our volunteer CoCoRaHS network. You will get a slightly larger and more clear image if you click on the map below. Many sites in the orange have received the average August rainfall in just 1 day. The largest total so far is from an observer in Bloomingdale in DuPage County with 5.45 inches.
Here are the reports for the morning of August 22, 2014, ranked from high to low. Most observers report between 7 and 8 am.
After a wet start to the 2014 growing season, we have seen a significant drop in rainfall across parts of northern and central Illinois in the last few weeks. Here is the 30-day rainfall as a percent of average. Areas in the orange are 25 to 75 percent of average while the areas in red are less than 25 percent of average. There are reports of soil moisture running low in some areas. On the other hand, southern Illinois has received above-average rainfall in the last 30 days.
Besides the switch from too wet to too dry in northern and central Illinois, and too much rain in southern Illinois, the other issue is that temperatures have been running about 4 degrees below average for the past 30 days. We are getting some heat this week. However, the longer-term forecasts indicate a return to cooler temperatures and more rain after this week through September 1.
If you look at the last 90 days the heavier rains in June and early July masks the recent dryness (map below). In fact, at the 90 day time scale rainfall in Illinois is generally at or above long-term average (1981-2010), as denoted by the grays and greens. This is one of the challenges of drought monitoring – sorting out short-term dryness versus long-term wetness or vice versa.
Heavy rains fell over Champaign-Urbana, Illinois on Saturday with more rain early Sunday morning. The two-day total through Sunday morning was 4.42 inches at the official NWS COOP station at the Illinois State Water Survey near the corner of First and Windsor in Champaign. Here is the breakdown by day, with the official observation time at 8 am:
0.09 inches of rain by 8 am July 12
4.33 inches of rain by 8 am July 13
The 4.33 inches for July 13, 2014, at the official, long-term site for Champaign-Urbana, falls short of the historical record 1-day total, which is 5.32 inches of rain from August 12, 1993.
Here are the reports from the CoCoRaHS network for Champaign-Urbana, showing two reports of over 5 inches, and several reports of between 4 and 5 inches.
Here is a wider view showing the rains of the last two days from a NWS product that combines radar and rain gage information. The amounts of 2.5 to 4 inches stretches from Chicago down to east-central Illinois with the heaviest amounts of possibly up to 6 inches in Champaign, Piatt, McLean, and Ford counties.
The statewide average precipitation for June 2014 in Illinois was 6.78 inches, 2.58 inches above average and the 8th wettest June on record. The wettest June on record was 1902 with 8.27 inches. Four out of the last five June’s have been wetter than average in Illinois:
2010: 7.71 inches, 3.51 inches above average
2011: 6.69 inches, 2.49 inches above average
2012: 1.73 inches, 2.47 inches below average
2013: 5.33 inches, 1.13 inches above average
2014: 6.78 inches, 2.58 inches above average
The statewide average temperature for June 2014 in Illinois was 72.9 degrees, 1.1 degrees above average.
Here are the maps of accumulated rainfall in June, 2014, as well as the departure from the 1981-2010 average. The rainfall was widespread across the state, and above-average as well. The area with the highest departures was the northwest corner of the state. There were 13 stations with 10 or more inches of rain in June. The wettest was Galena with 12.42 inches of rain for the month.
Much of the Corn Belt was wetter than average for June (last map) with precipitation departures from average in the range of 6 to 10 inches. That’s more than double the average in many locations. The results are high flows on many rivers and streams and flooding along the main stem of the Mississippi River south of Dubuque, IA.
Based on preliminary numbers, the statewide average precipitation for June 2013 in Illinois was 5.19 inches. That was 0.99 inches above the 1981-2010 average. It was more than double the June 2012 total of 1.80 inches.
In the first map below, the two wettest areas in Illinois were in northern Illinois and an area just to the south of Interstate 70. The area in northern Illinois was part of a larger area of heavy amounts in northeastern Iowa and southern Wisconsin. The area in southern Illinois extended into southern Indiana and Kentucky. Both regions had rainfall totals in excess of 8 inches and even 10 or more inches in the red and purple areas.
By contrast, much of the rest of the state was close to average precipitation for June with 3 to 6 inches very common (shades of green on the map). The few areas in blue (representing less than 3 inches) in western and north central Illinois are not alarming yet because they followed a wet spring. In fact, much of the Midwest experienced a wet June, including the Ohio River Valley which experienced drier conditions early in the month.
The second map zooms in on Illinois and shows the departures from average for June. The wet areas in northern and south-central Illinois stand out with rainfall totals 3 to 5 inches above average. Areas in central and southwestern Illinois were below average.
The year to date (January-June) statewide precipitation for Illinois was 28.74. That was 8.91 inches above the 1981-2010 average and the wettest January-June on record. The statewide records go back to 1895. It is more than double the 12.67 inches accumulate in January-June of 2012 during the height of the drought.
The statewide average temperature was 71.5 degrees, which was 0.3 degrees below the 1981-2010 average.
Wettest Locations In Illinois in June
Location and June precipitation total in inches, ranked high to low. List cut off for sites with less than 5 inches to keep the list somewhat short.
More rain fell over Illinois over the Memorial Day weekend. The heaviest amounts were in the central part of the state and ranged from 2 to 6 inches (yellow to dark red in the map below).
Right now the statewide average rainfall for May stands at 5.03 inches, based on preliminary data. More rain is forecasted for today and much of this week. So this total is likely to increase as we go through the week. By contrast, Illinois received only 2.5 inches in May 2012.
[updated to show Midwest 7-day rainfall map] Over the last 7 days a slow-moving system produced heavy rains over western and southwestern Illinois. The first map for Illinois below is based on the highly detailed radar-estimated precipitation that has been calibrated with available rain gauges. The rains decreased eastward with the lowest totals in the northeast. The largest station total in Illinois was at La Harpe with 4.17 inches. Several nearby stations had totals of just under 4 inches.
Illinois was not the only state to experience heavy rains. The second map shows that substantial rains fell across much of Missouri, Iowa, southeast Minnesota, and western Wisconsin. To the east of Illinois, heavy rains fell in southern Indiana and almost all of Kentucky.
If last year was the year of the drought, I think this year can be called the year of the anti-drought.
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.