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Fast Facts:

  • An area of 3 to 6 inches of rain fell in about a 3-hour period over southeastern and east central LaSalle County into western Grundy County on Monday evening, July 12. The maximum estimated point rainfall amount was nearly 7 inches.
  • The result was significant flash flooding in this area along numerous creeks, including impacts to multiple structures, multiple roadways, and channel erosion. Damage to roadways occurred in at least 4 locations, with one injury reported when the approach to a bridge on River Road washed out.
  • A Flash Flood Warning was issued at 8:42 p.m. Monday evening, and upgraded to a "considerable" threat at 10:07 p.m.
  • The meteorology responsible for this event was on several scales:
    • High atmospheric moisture, particularly in the lowest 10,000 ft of the troposphere
    • ‚ÄčAn atypical-for-summer, slow-moving low pressure system over western Illinois inching its way northeast throughout Monday
    • A near-stationary warm front that had lifted northward during the day was parked in the area of the heavy rain on Monday evening
    • A semi-organized, small scale complex of heavy showers and some storms remained nearly stationary along these focus areas, resulting in convergence of the rich moisture and replenishment for re-firing heavy rain showers and storms

For detailed information about this event, see Analysis of the July 12-13, 2021, Flash flood near Seneca, IL, a NWS Technical Paper detailing the rainfall, flooding, and impacts.


Event Summary

Radar Loop (8 - 11 PM CDT)

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