Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 03 2025 02:31:11 AWUS01 KWNH 030231 FFGMPD SDZ000-NDZ000-030800- Mesoscale Precipitation Discussion 0857 NWS Weather Prediction Center College Park MD 1030 PM EDT Sat Aug 02 2025 Areas affected...Northeast SDak...South-central NDak... Concerning...Heavy rainfall...Flash flooding possible Valid 030230Z - 030800Z SUMMARY...Increasing isentropic ascent to support back-building/repeating thunderstorms along western side of stalled elongated upper-level shortwave. Small cluster of 2-4" totals may result in flash flooding overnight. DISCUSSION...GOES-E 10.3um EIR and KABR RADAR shows incipient thunderstorm cluster over Hand and Spink counties with solid convection that resulted in over 1.15" in last hour with bulk coming in less than 30 minutes in Redfield. GOES-E WV suite shows core of upper-level shortwave is just east of the thunderstorm complex and remains fairly stagnant as it continues to elongate NNW to SSE across SD. VWP network and RAP analysis denotes strengthening southerly 850mb LLJ across the Central Plains with values currently around 25kts from the due south and gradient of deeper moisture axis is centered along 99W with values of 1.5". Additionally, at the nose of the jet remains a pocket of remaining unstable air with 1000-1500 J/kg of MUCAPE along the eastern edge of the LLJ. With the stronger MCV and 7H mb low to the east; isentropic ascent is fairly oblique at this time and thunderstorms are slowly propagating along this MUCAPE gradient toward more stable air. However, proximity to the 700-500mb low; allows for slow cell motions and increased overall duration to support rates of 1.5"/hr.=20 However, slow nocturnal veering of the LLJ will orient much more favorably to the convective line and mid to upper level trough axis as well as increasing toward 30-35kts by 06-07z. Greater orthogonal ascent and broader exposure to the instability axis should help to expand, perhaps back-build convection upstream of the slow mean flow to further intensify thunderstorm activity and increase rainfall efficiency toward 1.75"/hr. The shortwave is not expected to shift eastward much, so with repeating/increased duration an axis of enhanced rainfall of 2-4" may locally form.=20 While this axis may align with the overall higher FFG values (2"+/hr; 2.5-3"/3hrs), eventually localized exceedance is expected and localized flash flooding will become increasingly possible through 09z. However, the greatest remaining uncertainty Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_JTYvzNMZwQNpK4oIgWB7Iv0c3f-B8aIsBvGJY6LdYf9nnFU_GpoAI15vy9E5FAlWhCz= bhsZwMXuKhHcfU3YCen9K7I$ for graphic product... ATTN...WFO...ABR...BIS...FSD... ATTN...RFC...KRF...NWC... LAT...LON 46249858 45359747 44369694 43929712 43909790=20 44309863 45329949 45999956=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .