It’s almost the end of May and the spring rainy season… Time for our annual update on spring showers and local rainfall trends!

May 2018 Rainstorm

As far as I know, Wilmette’s first big downpour came late in the season this year, on May 21, 2018. Village staff have reported that rainfall lasted from 7AM to 2PM (7 hours), registering approximately 2 inches at the westside Storm Water Pump Station (a 1.5-yr storm) and 1.5 inches at the eastside Water Treatment Plant (a 6-month storm). The most intense portion was from around 10:30 AM to 11:30 AM, totaling 1 inch on the westside and .7 inch on the eastside.

As expected, the storm sewers on my street started backing up around 11:15 AM (shown above). Surcharging started at around a 1.5- or 2-year-storm level of intensity. Luckily, the worst rainfall ended within the hour, and the storm sewers cleared quickly.

Rainfalls of Record

While hunting for updated rainfall data, I secured some more information from the Village of Wilmette Water Plant. Staff provided a PDF table, listing Rainfall Storms of record for 1980-2017:

Note that the village measures rainfall using rain gauges at two locations:

• Eastside Wilmette: Water Treatment Plant (WTP)
• Westside Wilmette: Storm Water Pump Station (SWPS)

I converted the Water Department table into an Excel spreadsheet, added the preliminary May 21 storm stats, and sorted chronologically, to create this spreadsheet of 1980-2018 Storms of Record:

I’ll try to add more rainfall data as it becomes available. Any thoughts on trends/issues?