Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Apr 28 2025 05:46:47 AWUS01 KWNH 280545 FFGMPD SDZ000-NDZ000-MTZ000-281140- Mesoscale Precipitation Discussion 0189 NWS Weather Prediction Center College Park MD 145 AM EDT Mon Apr 28 2025 Areas affected...western ND/SD border Concerning...Heavy rainfall...Flash flooding possible Valid 280544Z - 281140Z SUMMARY...Isolated flash flooding will be possible in the vicinity of the western ND/SD border from slow movement of heavy rain over the next 3-6 hours. Rainfall rates occasionally exceeding 1 in/hr are expected to lead to spotty 2-3 inch totals through 12Z. DISCUSSION...GOES East infrared imagery and lightning data showed the slow eastward movement of a small cluster of thunderstorms which was located near the tri-state region of MT/ND/SD at 0520Z. A combination of 700 mb VAD wind plots, 850-700 mb LPW imagery along with RAP analysis data showed the upper level reflection of two surface lows over the High Plains. Using 700 mb as a representative level, the low centers were located over southeastern MT and southwestern SD, with a general weakness in the 850-300 mb steering flow near and southeast of the tri-state region. MUCAPE of approximately 500-1000 J/kg was in place from the eastern MT/WY border into the western ND/SD border via 05Z SPC mesoanalysis data. The weakness in the deeper layer flow is forecast by the RAP to maintain and perhaps deamplify the winds even more through 12Z across the region (as low as 5 kt). The weakness aloft will continue to allow for slow movement of heavy rain cores from along and east of the MT/ND/SD intersection into southwestern ND and northwestern SD. Instability values are likely to weaken as lower levels of the atmosphere cool in the wake of the stronger low over SD which is forecast to track northeastward, resulting in moisture wrapping around to the north and west of the low into an elongated commahead/deformation zone which will contain embedded heavy rainfall rates. The potential for hourly rainfall of 1 to 1.5 in/hr will be greatest through ~08Z, after which point the reduction in instability values should reduce rainfall intensity to a more steady/longer duration rainfall event. Through ~12Z, spotty additional rainfall totals of 2-3 inches will be possible which may support some isolated flash flooding. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_YM1yTafQONHrX6asL4cCmxvF6rHm5elBnRCKS1KoMRZ4qfUzSFtX5ibjcrCuWZPSoGW= uqe4GAagXgT8zpbaXfPOJA4$ for graphic product... ATTN...WFO...ABR...BIS...BYZ...UNR... ATTN...RFC...MBRFC...NWC... LAT...LON 46360150 45950026 45390049 45060185 44990334=20 45260426 45930437 46270349=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .