Mesoscale Discussion on severe thunderstorm potential across a portion of the Chicago area this afternoon
Isolated severe thunderstorms with a damaging wind/hail risk may develop this Tuesday
afternoon across northern Illinois, southeastern Wisconsin, northwest Indiana and
southwestern Lower Michigan (see escalloped area on the headlined map). A Severe
Thunderstorm Watch issuance is possible this afternoon, depending upon radar trends.
Following is the National Storm Prediction Discussion….
Mesoscale Discussion 1242 NWS Storm Prediction Center Norman OK 0110 PM CDT Tue Jun 25 2019 Areas affected...Portions of southern WI...northern IL...northwestern IN...and southwestern Lower MI Concerning...Severe potential...Watch possible Valid 251810Z - 252015Z Probability of Watch Issuance...40 percent DISCUSSION...A well-defined MCV that originated from convection earlier this morning across NE will continue moving quickly eastward around 40 kt along the WI/IL border this afternoon. Low-level airmass recovery is still underway to the east of this MCV, with the environment only weakly unstable. But, surface dewpoints have generally increased into the upper 50s and lower 60s across north-central/northeastern IL. Recent VWP profiles from KDVN and KLOT show strong westerly flow around 35-50 kt in the 2-4 km AGL layer in association with the MCV. There is some concern that as low-level lapse rates continue to steepen, some of these enhanced winds aloft could reach the surface if a small thunderstorm complex can develop. Radar imagery from 18Z shows a recent increase in reflectivity along the WI/IL border, and this could be the first attempt at the formation of a bowing segment. Isolated strong to damaging winds appear to be the main threat, although hail could occur in the strongest updrafts as mid-level lapse rates gradually steepen. Although watch issuance is not immediately likely, an increase in convective coverage/intensity may warrant a Severe Thunderstorm Watch at some point this afternoon.