The opening weekend of May was very windy and warm with temperatures reaching the mid to upper 80s both Saturday and Sunday. Temperatures on Monday could come close to 80 degrees again, especially if cloud cover is lacking during the first half of the day. However, the chance for showers and thunderstorms will increase by evening with the arrival of a cold front and low pressure.
Thunderstorms have really blossomed over Wisconsin along a stationary boundary Sunday evening and that’s where the greatest risk for storms will remain through the night. While an isolated shower or storm may occur north and west of Rockford, the majority of the overnight will be dry and mild.
Southerly winds will continue into Monday pushing dew point temperatures close to, and into, the low 60s during the afternoon. This will make it feel a little more muggy during the afternoon. While an isolated shower or storm may occur during the morning and early afternoon, our atmosphere will remain capped during that time. But by the evening the cap, or lid, should begin to weaken as an area of low pressure and cold front move into northwest Illinois. Thunderstorms will form along the front in Iowa, moving east across the Mississippi River and into northwest Illinois between 4pm and 6pm. Those storms will then move east, clearing the Stateline between 10pm and 11pm.
The amount of sunshine Monday before the storms move in will be key in determining just how strong storms could potentially be later in the evening. As of Sunday night, the Storm Prediction Center has northern Illinois highlighted under a ‘marginal risk’ for strong/severe storms, with the higher risk a little further downstate. Still, the risk for strong winds, hail and even an isolated tornado (closer to the approaching low) all remain a threat through Monday evening.