Severe Weather Possible Friday

After a gorgeous Thursday in the Stateline, stronger, possibly severe, thunderstorms are possible late Friday.

On Thursday, temperatures warmed to the daily normal again in Rockford for the first time since Sunday and dewpoints in the middle 50’s made conditions all the more comfortable. However, a storm system centered in the far northern plains as of Thursday evening will propagate southeastward through the night on Thursday. The system is dragging along with it a warm front and a cold front, both of which will present a chance for thunderstorms on Friday. Cloud cover will increase through the night and into the predawn hours of Friday as dewpoint temperatures climb ahead of the warm front. The warm front is expected to pass over the Stateline early Friday morning which will likely lead to a line of morning showers and thunderstorms. While in the storm’s warm sector, the area in between the warm and cold fronts, from the late morning through the afternoon, sporadic showers and thunderstorms can be expected here in the Stateline.

As the day progresses, the dynamics for severe weather build up over the Stateline. Dewpoints in the warm sector could approach the middle 70’s at the surface with sufficient moisture present through the mid-levels of our atmosphere. With temperatures expected to reach the upper 80’s, plenty of instability is expected over the area with as many as 3500 J/kg of CAPE building by the evening. A good directional shear profile could provide some additional low level vorticity but a lack of speed shear will likely keep the tornado chances low. A lifting condensation level above 1km above ground level with a level of free convection near 3km above ground level should keep any organized convection from forming prior to the arrival of the cold front. However, the cold front should provide more than enough lift to pull the warm, moist air down near the surface into the highly unstable airmass which sits just under 3km above ground level. This front should arrive in the Stateline in the early evening which is when the severe threat begins. Storms will propagate from north to south and the severe chances should exit the Stateline by around 10:00PM.

As of Thursday evening, the Storm Prediction Center has a slight risk (category 2 of 5) for severe weather over the Stateline with an enhanced risk (category 3 of 5) positioned just to our northeast and includes far northeast Walworth County in Wisconsin. The primary concerns with these storms are gusty winds and sizeable hail while the tornado threat remains relatively low. Torrential downpours are also possible which could result in flash flooding.