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Severe Weather Expected for the South on Tuesday; Winter Weather Conditions for the West, Central Plains, and Upper Mississippi River Valley

Severe weather is forecast across the middle and lower Mississippi Valley Tuesday afternoon where tornadoes and damaging winds are expected. A strong cold front will track across the Intermountain West accompanied by strong winds, heavy snow and elevated fire weather conditions for portions of the western High Plains with heavy snow likely for Upper Mississippi Valley Tuesday. Read More >

Overview

Environment

During the overnight hours of Friday, July 22 into Saturday, July 23, thunderstorms developed across portions of Winnebago, Boone, McHenry, and Lake counties in northern Illinois. These initial thunderstorms trained, or re-developed continuously, over the same areas for several hours which led to significant flash flooding across parts of Lake County. As these storms moved to the southeast, they dropped copious rainfall over these same counties with parts of Lake and McHenry counties quickly picking up 2-6+ inches of rain, in part due to precipitable water (PWAT) values in excess of 1.5 inches during the overnight hours. In addition to the heavy rain, the storms initially dropped hail up to 1.75 inches in diameter in Lake and McHenry Counties. This hail was also accompanied by strong winds which brought down trees and damaged roofs in some areas.

As the night went on, more storms began to fire near the Freeport/Rockford area and moved off towards the southeast. These storms sporadically dropped large hail and produced scattered damaging wind gusts near the I-88 corridor. Eventually, as the storms continued to congeal together towards daybreak, they developed into a Quasi-Linear Convective System (QLCS) as they moved into the Chicago metro. A few areas of embedded rotation eventually developed within this line of storms, and one of these areas of rotation went on to produce a cyclic path of 3 brief tornadoes in Will County. In the process, these storms continued to produce scattered strong wind gusts and large hail as they moved off to the east and southeast. As the initial storms moved out of the area, they left behind a boundary upon which additional storms developed through the morning and early afternoon hours. These storms produced up to a few additional inches of rainfall along and south of a Dixon to Joliet to Rensselaer line along with isolated instances of hail up to 1.75 inches in diameter.

As the morning and early afternoon storms died off and moved out of the region, it was quiet within the area until late in the night when the final round of storms arrived from the west. These storms were a bit weaker than the previous rounds of storms but still produced a few damaging wind gusts and added to the high rainfall totals in already soaked areas.

 

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