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Mesoscale Precipitation Discussion 0460 NWS Weather Prediction Center College Park MD 529 PM EDT Thu Jul 09 2020 Areas affected...Southern WI....northern IL...far eastern IA Concerning...Heavy rainfall...Flash flooding possible Valid 092130Z - 100230Z Summary...Storms training along a boundary in a high moisture environment could produce hourly rainfall rates near 2.00 inches, which poses a flash flood threat into the evening hours. Discussion...Storms continue to develop/propagate along a boundary across southern WI into far northwest IL ahead of a strong short wave located over central IA. Ahead of the storms, the most recent RAP analysis showed a reservoir of 2500/3500 J/KG of MLCAPE in place, and the combination of synoptic scale ascent associated with the short wave and instability should be sufficient to support continued development across southern WI/northern IL into the evening hours. A 20 knot low level southerly flow replenishes to 1.50/1.75 inch precipitable air into the pre convective environment, which should be enough to support hourly rainfall rates between 1.50/2.00 inches. The most recent KARX hourly rainfall estimates have been as high as 2.00 inches, though mesonet observations has been closer to 1.50 inches over far southwest WI. Within the southerly flow ahead of the short wave, short term training and cell mergers are expected, mainly across southern WI through about 10/02z or so. Where the mergers and training occur, hourly rainfall rates could remain near 1.50 inches (which is depicted by the most recent HRRR runs). The HRRR runs also indicated the potential for local 3.00 inch rainfall amounts just north of the WI/IL line. These amounts are plausible were training and cell mergers continue. The National Water Model continues to show streamflow increasing to well above normal within the convection. Further south across northern IL, the mid level flow may veer enough with time to allow the storms to become more progressive, as they tap the deeper instability still in place and become more outflow driven. However, local 2.00 inch rainfall amounts are possible here as well. The potential for flash flooding could continue past 10/02z across portions of the area based on the most recent HRRR output, but it should be noted that much of the high resolution guidance lags reality by a couple of hours. Based on the above, flash flooding is considered possible this evening.