According to the rainfall reports through yesterday (6/29), the statewide average precipitation is now 9.37 inches.
The old record for June was 8.27 inches set in 1902.
The current 9.37 inches beats the old record by 1.10 inches.
The current 9.37 inches is 5.17 inches above the June average of 4.20 inches.
The current 9.37 inches make this the second wettest month in Illinois history.
Only September 1926 was a wetter month at 9.62 inches.
Statewide records for Illinois go back to 1895.
The statewide average precipitation is based on records from about 650 rain gauges across the state. A majority of the reports come from two networks with trained volunteers and standardized equipment and procedures. One network is called CoCoRaHS and the other is the NWS Cooperative Observer Network or COOP for short. These dedicated observers give timely and accurate information with outstanding coverage across the state.
Tomorrow we will be able to do the calculation through June 30.
The statewide average for June is now 8.97 inches. That is based on rainfall data collected around the state through yesterday. I’m sure we will see that number move up as we include last night’s rainfall.
Right now June 2015 is the fourth wettest month on record for Illinois. If you look at the top 5 wettest months in Illinois history (below), all the other wet months were in the fall.
The remains of Tropical Storm Bill moved through Texas and Oklahoma and up through the Midwest. As a result, it produced quite a bit of rain in southern Illinois.
While it is difficult to separate out the rainfall exclusively from Tropical Storm Bill, this radar-estimated rainfall image of the past 7 days shows the pattern. Areas in yellow and red received at least 3 inches of rainfall. The widespread areas in red south of Interstate 70 received in the neighborhood of 6 to 8 inches of rain.
Missouri, Indiana, Ohio, and Kentucky received significant rainfall as well.
Even before today’s rain, the statewide average rainfall for June in Illinois is 7.11 inches. That makes it the 5th wettest June on record. And June is not over. Here are the top ten wettest June totals on record and where we stand:
1902 with 8.27 inches
2010 with 7.71 inches
1998 with 7.64 inches
2000 with 7.34 inches
2015 with 7.11 inches (as of 6/21/2015)
1928 with 6.93 inches
1993 with 6.85 inches
1924 with 6.80 inches
2014 with 6.77 inches
2011 with 6.69 inches
Notice anything unusual about that list? Five out of the 10 wettest June totals have occurred since 2000. Our statewide records go back to 1895.
Due to the heavy rains of June, we first saw flooding on the smaller rivers and streams in Illinois. Now the larger rivers are responding to the wet conditions. The NWS can keep you posted on the latest flooding issues at www.weather.gov
The post from this morning documented the above-average rainfall received so far in June across Illinois. On top of that, the latest NWS forecasts indicate that wetter-than-average conditions are expected for the rest of June as well as July in Illinois.
The first map shows the 6-10 day forecast with Illinois and most of the Corn Belt having an increased chance of wetter-than-average conditions. The second map shows the 8-14 day forecast with the same wet pattern.
The third map shows the month of July with an increased chance of wetter-than-average conditions across all of Illinois. The fourth map shows the three-month forecast for July-September. At that point, the chance for wetter-than-average conditions is confined to western Illinois.
June 2015 has been wet across the Midwest and we still have 12 more days in the month. Wet conditions extend from Kansas/Nebraska and eastward through Missouri, Iowa, Illinois, Indiana, and Ohio. Amounts in those areas are in the 4 to 8 inch range.
Monthly totals from a few stations are in the 10 inch range, including 10.44 inches at Lacon, IL (north of Peoria) and 10.41 inches in Stockton, IL (in the northwest corner).
While this is very preliminary, the statewide average precipitation is 5.3 inches for June. The monthly average is 4.2 inches, so we would already have an above-average month if it stopped raining today. The record for June is 8.27 inches set in 1902.
Rainfall across Illinois and the central US has been substantial for June so far. This map represents the June rainfall through this morning. Large portions of the Missouri and Upper Mississippi River Basins have seen between 2 to 5 inches (yellows and oranges), while some spots in Illinois, Missouri, Nebraska, and Kansas have received 5 or more inches (red).
Zooming in on Illinois, the map below shows how far above average the wet areas have become. The areas in blue are 2 to 4 inches above average while the areas in green are 0.5 to 2 inches above average. Only small areas northwest of Chicago and south of Carbondale are below-average on rainfall.
The potential rainfall amounts over the next week are significant. The 7-day precipitation forecast from the National Weather Service shows that central Illinois could see between 4 and 6 inches of rain, while the northern third of the state could see 2 to 4 inches. The southern third of Illinois could see 1 to 3 inches. Since much of this rain will come from thunderstorms, local amounts could be much higher or lower.
The reason for this rain is that a somewhat stationary front is sitting over Illinois and will remain so over the next week. Rain will continue to develop along and south of that front as warm, moist air flows northward.
The current record for the heaviest 24-hour rainfall total in Illinois is 16.94 inches at the NWS cooperative observer gauge in Aurora on July 17-18, 1996. An entire Water Survey report was written on the storm that produced this record.
The previous record 24-hour rainfall was 16.54 inches set on June 14-15, 1957, near Millstadt in St. Clair County (near East St. Louis), according to a Water Survey report. While the 1996 event occurred over 24 hours, the 1957 storm lasted only 12 hours – essentially producing the same amount of rain in less than half the time.
But here is the next interesting fact. Before the 1957 storm, the previous record 24-hour rainfall was 10.48 inches on October 1, 1954 set at Aurora, IL.
So Aurora held the statewide record 24-hour rainfall for about three years until it lost out in 1957 only to regained the crown in 1996, where the record remains to this day. I’m not sure if they deserve the golden rain gauge or the golden sump pump award for this honor.