There are three regions within the Plains, (1) the northern region, (2) the central region and (3) the southern region. How these regions are made and how we define the 14-day extreme precipitation periods can be found here.

Key Information

  • There were 49 periods within the northern region (1), 50 periods in the central region (2) and 54 periods the southern regions (3).
  • The typical wet season for the Great Lakes occurs from April to September.
  • Great Lakes periods occurred throughout the entire year, with a minimum in the summer (JJA).
  • Typical storm reports for a Great Lakes precipitation periods include Thunderstorm Wind, Hail, Flood, Flash Flood and Winter Storm

When do Great Lakes Extreme Periods occur?

Seen to the left, 14-Day periods within all Great Lakes regions are counted, based on month, from 1915 to 2018.

The Great Lakes typical wet season is from April to September. But there is a minimum in 14-day extreme precipitation periods in all regions during this time, specifically during the summer months of JJA (June/July/August). September has the highest total of extreme periods within the Great Lakes.

What are typical storm reports of Great Lakes Extreme Periods?

Using NCEI storm reports typical impacts of our 14-day extreme periods, past 1996, can be estimated. Beginning in 1996, 48 event types were recorded into the storm events database. Every report was recorded based on the county of occurrence by a National Weather Service forecast office (WFO) and then passed onto NCEI. Therefore, reports within 14-day extreme periods from 1996-2018 within Minnesota, Iowa, Missouri, Wisconsin, Illinois, Michigan, Indiana, Kentucky, and Ohio are counted as Great Lakes 14-day extreme periods reports. Definitions of all storm reports can be found within the NWSI, Appendix A.

The average number of storm reports during a wet season or a dry season extreme period, within both regions in the Great Lakes, from 1996 to 2018 are seen to the right. “Thunderstorm Wind”, “Hail”, and “Flash Flood” are the most frequent reports seen during periods.

Wet season 14-day extreme periods have larger averages of storm reports for a period, compared to dry season periods. However, similar storm reports are seen in both wet and dry season periods. Common reports during a wet season period are “Hail”, average of 253, “Thunderstorm Wind”, average of 380, and “Flash Flood”, average of 171. While common reports during a dry season period are “Flood”, average of 105, “Winter Storm”, average of 95 and “Hail”, average of 65. Therefore, dry season periods may tend to have more frozen precipitation, while both wet and dry season periods can be convective.

Point of contact: Melanie Schroers,