Thunderstorms return to the Stateline Tuesday after a rather prolonged stretch of dry and storm free days. The last day there was measurable precipitation in Rockford was back around the 23rd of October. And the last time we had a risk for severe weather was back in August when the large derecho moved through.
While it’s not a high risk Tuesday, the Storm Prediction Center has included southern Wisconsin and northern Illinois in a ‘Marginal Risk’ for strong/severe storms during the afternoon and evening. A rather strong cold front, currently moving through the Midwest Monday evening, will move across the Stateline Tuesday afternoon. Moisture will increase ahead of the front as southerly winds increase, gusting at times to 35mph late morning and afternoon. The cold front will move through the area between 2pm and 6pm, although a few showers are likely as early as daybreak Tuesday. A strong jet stream moving into Iowa and Wisconsin behind the front will help increase the lift (forcing) throughout the atmosphere as the cold front comes through.
Instability isn’t overly high Tuesday afternoon, but the wind shear in the atmosphere is. This could cause a few storms to become severe, posing a risk for mainly damaging winds. While low, there is also a risk for an isolated tornado – given how strong the storm system moving in will be. There is, however, a warm layer that will be present around 10,000ft in the atmosphere. This warm layer could act as a ‘lid’ preventing much activity from developing initially along the front. As colder air arrives in the upper part of the atmosphere arrives behind the front it should help erode away at that lid, allowing storms to develop. Rainfall will also be heavy at times with a few areas possibly seeing an inch of rain by Tuesday evening.
Most of the storm activity will be passing east of the Stateline by 7pm with skies quickly turning partly cloudy by Wednesday morning. Temperatures will fall into the 30s during the morning, rising to near 50 degrees by the afternoon.