Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 13 2025 21:18:13 AWUS01 KWNH 132118 FFGMPD NDZ000-MTZ000-140230- Mesoscale Precipitation Discussion 1083 NWS Weather Prediction Center College Park MD 517 PM EDT Sat Sep 13 2025 Areas affected...Northwest NDak...East-central & Northeast MT... Concerning...Heavy rainfall...Flash flooding possible Valid 132115Z - 140230Z SUMMARY...Highly anomalous moisture, increasing instability and slow cell motions with some back-building training possible.=20 Rates of 1.5"/hr and localized 2-3" totals may result in possible scattered incidents of flash flooding through early overnight period. DISCUSSION...GOES-E WV suite shows a conducive dynamic environment aloft to maintain and support new convective development within a seasonally, highly anomalous moisture regime. The northern, smaller closed low/short-wave to the parent large scale meridional trough is well defined and compact over central MT. It is connected via a boundary layer convergence/confluence axis that waves eastward before turning north along/just west of the MT/ND border where it eventually connects back up to the exiting vorticity center over southwest Canada. Along and east of the confluence boundary, deep layer moisture with highly anomalous (2-4 standard anomaly units) above average exists across the Northern Plains. Upper 60 to low 70s Tds with southeasterly flow strengthening to 20kts at 850 provide deep layer convergence to the boundary.=20 GOES-E Visible imagery shows developing overshooting tops through the mid-level cloud deck along the boundary, some denoting some Wedge/'V' shaped signatures. This is indicative of the exiting upper level 70kt speed max and the cells moving into better right entrance ascent. Combine this with sharply arched cirrus canopy over central SD denoting the nose of the next speed max suggests this favorable divergence aloft will likely maintain for quite a few hours into the early overnight period. Limited motion of the convergence boundary is expected given the surface to low level flow, providing a solid opportunity for convective cells to train/repeat over NW ND through the evening. The limiting factor continues to be the lack of surface heating due to the mid-level canopy, so vertical vigor may limit overall rainfall production/intensity in the range of 1-1.5" (given total PWat values of 1.5-1.7") and CAPE 500-750 J/kg. As such spots of 2-4" are possible resulting in possible flash flooding. Further west, Clearer skies, has supported some low level heating near the stationary mid-level feature and eastward along the low to mid-level shear axis into eastern MT. A few stronger cells have developed, utilizing the enhanced surface heating and weak to moderate convergence. Limiting factor with these cells mainly in in the deeper moisture profile. While still above normal Tds in the low 50s and total Pwats range from 1-1.25". This should reduce overall efficiency and rates to around 1-1.25"/hr but slow cell motions perhaps even stationary near the vorticity center itself could result in localized 2-3" totals in 3-6hrs. Recent rainfall and FFG values in the 1-1.5"/hr & 1.5-2"/3hrs suggest these rates/totals may result in an incident or two of flash flooding through the evening.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-9oKTOZFx8OhC-Giohk7XbHE7S77PP1jzDox3MeYvKRp4E6NkOBkJ_UIGAPtfcy9q9Nf= 1nVl_4wd0IyWEGVeN8arw8c$ for graphic product... ATTN...WFO...BIS...BYZ...GGW...TFX... ATTN...RFC...KRF...MSR...NWC... LAT...LON 49100372 49100195 48970143 47790197 47080269=20 46510356 46050498 46160712 46190863 46330927=20 46850995 47500964 47690877 47730798 47970679=20 48390554 49050456=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) .