Weather Update for Thursday, February 22, 2018 Wintery Mix – Flood Warning still exists for many rivers in the Chicago area
Much or all of the precipitation tonight should be confined to the far southern portions of the area, mostly south of the Illinois and Kankakee Rivers. It looks like any precipitation should be very light. While surface temperatures will be below freezing, it looks like the precipitation will be either light freezing rain or sleet mixing with snow. Any wintry mix precipitation should be of a relatively short duration. Temperatures Thursday should rebound back into the upper 30s to lower 40s and any lingering precipitation Thursday morning would likely change over to all rain. Since precipitation amounts are expected to remain light, any precipitation should not have an impact on forecast river stages.
For those of you concerned about the amount of rain we received, look at the rainfall chart below.
Many have also asked why the Little Calumet was not included in the flood warnings/watch. NOAA’s National Weather Service in conjunction with the NSGS use a hydrogram to determine if a warning should be issued. I have included a hydrogram below the rainfall totals. Even though the Little Calumet rose enough to justify closing the overpass at Kennedy, it did not fall into the classification for a warning. There are many reasons that this may be. First keep in mind the hydrogram does not take into consideration any man made structures in its determination to generate a watch or warning. We will let you connect the dots there. However the natural indicator that would have justified a warning did not exist. It may have come close but again, did not exist. Here is the existing flood warnings for both the Chicago area and Indiana.
…The Flood Warning continues for the following rivers in
Iroquois River at Iroquois affecting Iroquois County
Iroquois River near Chebanse affecting Iroquois and Kankakee
Kankakee River near Wilmington affecting Grundy and Will Counties
Mazon River near Coal City affecting Grundy County
Vermilion River at Pontiac affecting Livingston County
Vermilion River near Leonore affecting La Salle County
…The Flood Warning continues for the following rivers in Indiana…
Iroquois River at Rensselaer affecting Jasper County
Kankakee River at Dunns Bridge affecting Porter County
Kankakee River at Shelby affecting Lake and Newton Counties
Kankakee River at Momence affecting Kankakee County
Sugar Creek at Milford affecting Iroquois County