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Mesoscale Precipitation Discussion 0749 NWS Weather Prediction Center College Park MD 620 PM EDT Mon Aug 12 2019 Areas affected...Northern IN...Northwest OH...Far Southern Lower MI Concerning...Heavy rainfall...Flash flooding possible Valid 122220Z - 130220Z SUMMARY...Some brief training of heavy showers and thunderstorms will be possible this evening which may pose a short-term flash flood threat. DISCUSSION...A narrow axis of heavy showers and a few thunderstorms is expected this evening across portions of northern IN and northwest OH. The convection is expected to form in vicinity of a weak surface trough downstream of an approaching MCV which is currently moving through northern IL. The thermodynamic environment is modest with generally less than 1000 j/kg of MLCAPE across the MPD threat area, but there is some relatively favorable shear profiles with effective bulk shear on the order of 30 to 40 kts. Meanwhile, the column is quite moist with PWATs on the order of 1.9 to 2.1 inches per the latest GPS-derived data sets. An examination of the shower activity that has been developing upstream across areas of northern IL and adjacent to Lake Michigan over the last couple of hours suggests an environment of warm-topped/shallow convection. Given this and the high PWAT environment, warm-rain processes are likely in place and suggestive of very efficient convection for enhanced rainfall rates. The latest radar imagery is showing some subtle cooling of the cloud tops with a west/east axis of showers across northern IN currently which appears to be developing near a weak surface trough. The 12Z HREF suite of guidance generally appears to be too far north with its axis of heavier rainfall as compared to the latest radar trends. However, several runs of the experimental HRRR were doing a bit better, and the last available run from 18Z supported as much as 2 to 3 inches of rain through 03Z with isolated heavier amounts. The general axis is expected to along and adjacent the surface trough axis as mentioned across northern IN and over into northwest OH. Far southern lower MI may also see some of this activity. Despite rather high FFG values, the warm-rain processes and tropical moisture environment pose at least a localized concern for some excessive rainfall. Additionally, there is some signal for at least some episodic training/repeating of convective cells which may result in enhanced rainfall totals. A couple instances of flash flooding as a result cannot be ruled out.