The National Centers for Environmental Information (formerly NCDC) released their numbers for June, showing that Illinois did indeed have its wettest June on record with 9.30 inches (according to their calculations). That made Illinois the wettest state** in the US for the month.
Here are the national maps showing the statewide precipitation values for June 2015. While Illinois received 9.3 inches of precipitation, California received only 0.23 inches – an amount 40 times less than Illinois.
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 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.