A line of strong to severe thunderstorms have been ongoing west of the Stateline, stretching from Wisconsin down through Missouri late Monday afternoon and evening. Numerous severe thunderstorm warnings, as well as tornado warnings, have been issued along this line. A severe thunderstorm watch is in effect for areas west of the Mississippi River until 10pm. Currently there are no watches or warnings in place for the immediate Stateline.
Thunderstorm chances are expected to go up, however, late Monday evening as the cold front moves in from the west. While the cold front is slowly shifting east, the thunderstorms themselves are moving more to the northeast thanks to strong southerly winds in the mid levels of the atmosphere. Eventually we’ll begin to see the storm motion more to the east, allowing the leading edge of the storms to move closer to northwest Illinois and southern Wisconsin between 8:30pm and 10pm. There is a risk for strong to severe thunderstorms west of Rockford, with strong winds being the primary concern. Even though the storms will be moving in after sunset and will be losing some instability in the atmosphere, there are very strong winds aloft tied in to a strong jet stream moving across the Midwest. The strong jet stream could allow some of the stronger storms to maintain their strength as they move into portions of northwest Illinois after 9pm.
The threat for thunderstorms will continue into the early overnight hours before moving out between 3am and 4am Tuesday. Cloud cover and a few light showers may linger through sunrise Tuesday following the cold front. Northwest winds are expected to increase a bit during the day, gusting to near 25 mph. Highs on Tuesday will rise to either side of 70 degrees for the afternoon.