Wettest June and Now Second Month on Record for 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.


Wettest June and 4th Wettest Month on Record for Illinois

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.

  1. September 1926 at 9.62 inches
  2. October 1941 at 9.06 inches
  3. November 1985 at 9.05 inches
  4. June 2015 at 8.97 inches
  5. September 1911 at 8.96 inches


Tropical Storm Bill’s Rainfall in Illinois

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.

Click to enlarge.

So Far, Fifth Wettest June on Record for Illinois

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:

  1. 1902 with 8.27 inches
  2. 2010 with 7.71 inches
  3. 1998 with 7.64 inches
  4. 2000 with 7.34 inches
  5. 2015 with 7.11 inches (as of 6/21/2015)
  6. 1928 with 6.93 inches
  7. 1993 with 6.85 inches
  8. 1924 with 6.80 inches
  9. 2014 with 6.77 inches
  10. 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.

Click to enlarge.

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

Above-Average Rainfall Expected for Rest of June and July in Illinois

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.

6-10 Day Forecast. Areas in green have an increased chance of above-average precipitation. Click to enlarge.

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