National Weather Service Weather Forecast Office

1/9/2008 Storm Survey from Flooding in Pontiac, IL

On Wednesday, January 9^th, 2008, National Weather Service meteorologists traveled to Pontiac, Illinois to assess recent flooding that is currently occurring along the Vermilion River. 

The flooding is a result of recent snowmelt and very heavy rainfall. Water levels began to rise as above average/record temperatures that occurred across the region on the 6^th and 7^th of January, began to melt the snow cover which contained water equivalents of one half inch to an inch of water. The main problems started Monday night after a line of severe thunderstorms came through and dropped heavy rainfall across the Vermilion River Basin. NWS Doppler Radar estimates and cooperative observer reports indicated that around 3 to 6 inches of rain fell across the Vermillion River Basin from Monday night into Tuesday.

Figure 2: Precipitation 7-day total ending Jan 10, 2008.

The Vermilion River at Pontiac quickly rose to above flood stage on Tuesday morning and continued into major flooding stage very early on Wednesday morning. 

The record crest for Pontiac is 19.16 feet that occurred on December 4^th, 1982.

The preliminary crest for this event was 18.85 feet on January 9, 2008.

NWS survey team noted that the river gage fluctuations are due to the fact that the river is up to the height of the bridge and some damming effects were occurring with the water flow being pushed off to the side toward residential neighborhoods near the river (including the NWS COOP observer in Pontiac). The water on the other side of the bridge was quite turbulent and that is where the gage senses the height.

Here is picture of the Pontiac river gage site in normal winter low flow compared with the recent image from our flood survey team on January 9th.

The flooding from this event has been quite expansive across the city of Pontiac, leading to the evacuation of 42 residences and a trailer park where 50 of the 70 trailers had been evacuated as of noon Wednesday. The most serious flooding problems were immediately along the river and on the east side of town, which was still under water on Wednesday. 

For pictures from the survey, click HERE.