River Levels and Rain: Weather records from 1993 compared to 2019

Weather graphic

With the recent flooding, many have been inquiring as to how the floods this month at Trenton compare to the floods of 1993.

Keep in mind, the first answer is that its spring versus summer flooding. Much of the 1993 flooding came in the summer especially during July which still ranks as the single month with the most rain ever in Trenton with 22.4 inches. For May 2019, rainfall in Trenton is 14.98 inches.

Consecutive days of rain and those amounts are more comparable when looking at May 2019 versus July in 1993. During a 12 day period beginning May 18th, measurable rain occurred on 11 days in 2019 with a trace on May 28th for a cumulative total of 10.47 inches. During a 12 day period that began July 1993, Trenton had measurable rain every day in the month adding up to 13 inches.

Questions also have been asked on flooding from the Thompson River at Trenton. But to analyze the reported crests from the two different years, the location of the Thompson River gauge changed.

This week, the Thompson crested more than seven feet above the current flood stage of 27 feet. The online graph for the National Weather Service on Wednesday showed a level of 34.38 feet, however, Grundy County Emergency Management Director Glen Briggs said the U.S. Geological Service has told him the Thompson gauge is only designed for a river level of up to 33 feet.

KTTN weather records from July 6th of 1993 show a crest of 22.4 feet, but the flood stage in 1993 was 20 feet. In the fall of 2004, the gauge was re-located, changing the flood stage for the Thompson to 30 feet. So in effect, Briggs said the Thompson, using today’s standard, would have been as much as 12 feet above that 1993 flood stage of 20 feet.

In late 2017, the National Weather Service re-set the Thompson River flood stage at the current 27 feet. The Thompson River level is receding today and will continue to do so.

In the first five months of 2019, Trenton has received two-thirds of our average precipitation total for the year. A little more than 26 inches have fallen since January 1st during the month of May 2019. That compares to 16.75 inches for the first five months of 1993. In the next four months, June through September, Trenton receives 42 inches of rain which led to a long term flooding in 1993.

Currently, Trenton precipitation year to date total is more than 12 inches above normal. but, one year ago, much of our area was entering what turned out to be a lengthy drought. As of late May 2018, Trenton had just 5.75 inches of rain and melted precipitation from January through May.