Illinois has warm, wet June

[July 10, 2018]    Illinois experienced its 11th warmest and 14th wettest June on record, according to State Climatologist Jim Angel at the Illinois State Water Survey.

The statewide average temperature was 75.0 degrees, 3.1 degrees above normal. The statewide average precipitation was 6.36 inches, 2.15 inches above normal.

The greatest monthly total precipitation for June in Illinois was 14.58 inches at Rockford. In addition, the Rockford Airport reported 14.23 inches, their wettest June and wettest month on record.

Precipitation was especially heavy across northern, east-central, and southeastern Illinois with widespread amounts in the 10 to 14 inch range. Meanwhile, parts of western and southern Illinois received less than 3 inches of rain.

June precipitation for Illinois has shown an upward trend and increased variability in recent decades. Over the past century, annual precipitation in Illinois has increased by about 10 to 15 percent, depending on the location. As a result, there have been more problems with flooding but fewer problems with long-term drought.

At the end of the month, the U.S. Drought Monitor showed “abnormally dry” and “moderate drought” conditions persisting in western Illinois.

Hot weather was common in June. The number of days that hit 90 degrees or higher ranged from about 3 to 4 days in northern Illinois to about half the month in the St. Louis area. By the end of June, the combination of high temperatures and high humidity led to excessive heat warnings by the National Weather Service.

The July forecast shows that Illinois has an increased chance of above-normal temperatures. Meanwhile, the precipitation forecast is for equal chances (EC) between above, below, and near-normal precipitation for Illinois. EC is a common forecast for summer precipitation since it largely depends on short-term, local conditions (such as the passing of a cold front), rather than large-scale patterns such as El Niño.

The forecast for the next 14 days (through July 15) suggests that drier conditions will prevail across most of central and northern Illinois, but the southern third of Illinois has an increased chance of above-normal precipitation.

[Lisa A Sheppard]