Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 04 2023 21:38:38 AWUS01 KWNH 042138 FFGMPD NEZ000-SDZ000-NDZ000-MTZ000-WYZ000-050330- Mesoscale Precipitation Discussion 0863...Corrected NWS Weather Prediction Center College Park MD 538 PM EDT Fri Aug 04 2023 Corrected for Concerning line from Possible to Likely Areas affected...Southern ND...South Dakota...Adj portions of northern NEB, MT & WY... Concerning...Heavy rainfall...Flash flooding likely Valid 042130Z - 050330Z SUMMARY...Broad area of cyclogenesis within very deep moisture/unstable environment resulting in numerous thunderstorms with 2-2.5"/hr rates, some slow moving with potential mergers.=20 Areas of 2-5" are highly probable, likely inducing multiple localized instances of flash flooding through early overnight period. DISCUSSION...Well defined large scale deep cyclone currently centered at the MT/WY & Dakotas border continues to have very favorable structure for low level cyclogenesis with solid, near dual jet structure outflow to support convective upscale growth from clusters to complex(es). Additionally, there remains solid vertical tilt with height through the system with a broad ribbon of enhanced moisture bisecting the circulation along this deep cyclongensis axis from SE MT across central SD toward E NEB, with confluent low level streamlines enhancing FGEN forcing along boundaries from surface through 700mb. CIRA LPW denotes broad moisture plume through the Missouri River Valley with 1.5" total PWat into SE MT and 1.75" across central SD with 2" values toward the central MO valley in E NEB/IA. A surface front corrals the low to mid-level moisture from central IA to the apex of the cyclone along the ND/SD border with mid to upper 60s Tds at the Sfc but core of .5" in both the 850-700mb and 700-500 mb layers across central NEB to central SD. This will support multiple bands of strong moisture flux convergence in vicinity of strong FGEN. Sfc analysis shows a surface low at the MT/WY/SD border with an effective warm front angling along the ND/SD boarder to near MDX/BKX and into central IA. Strong northeasterly flow north of the boundary combined with confluent SSE/SEly flow along it, supports convective development along it, eventually overrunning toward a TROWAL-like feature across south-central ND. Cells are slow moving, but may have greatest moisture flux convergence throughout the system, but with slow cell motions, weakly unstable environment may give way to cold pool generation and slow southward sinking across north-central SD. Spot of 2-3" are probable with 1.5-2"/hr rates inducing some spotty flash flooding A cold front drops south from the low arching SW across WY, though strong convergence along/ahead, especially along eastern face of the Black Hills and slightly steepening lapse rates aloft with weak mid-level drying should support vigorous updrafts with intense rain-rates but forward propagation may limit duration, with spotty risk of flash flooding with 2"/hr totals in proximity to urban centers along I-90 in W SD having best risk in the short-term.=20=20 The greatest potential for likely flash flooding conditions is expected along the deepening surface cyclone and associated pre-frontal pressure trough that generally bisects SD. This axis also generally aligns with instability axis with 1500-2000 J/kg of MLCAPE. Strong isallobaric component to the low level flow will also enhance moisture flux convergence, while deep layer steering flow will be weak within the larger scale short-wave ridging in the 700-400mb layer. As such, very slow moving thunderstorms with rates of 2-2.5"/hr with potential for cell mergers is probable to evolve with very slow eastward propagation (as the ridge slides east slowly). Spots of 2-4" are likely within this axis across central SD, with some spots of up to 5" possible especially north or northeast of the deepening surface to 850mb cyclone, though this may be a delicate balance if upstream inflow is obstructed by other thunderstorms to the south. Still instances of flash flooding are considered likely through the 03z tonight across the area of concern. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6NV-jiz1Vs1Iz5IYiS4NzOA0kRe6xjM43vuWJA2eRmUJP1B7IWeOOv7wZgiNZvb0AIPz= yobaZARpPdSkMMWW5jP1GiM$ for graphic product... ATTN...WFO...ABR...BIS...BYZ...FSD...LBF...UNR... ATTN...RFC...MBRFC...NWC... LAT...LON 47060088 46609958 45809799 44609683 43769692=20 43419808 42519907 42760047 43030272 43560357=20 44050399 44930427 45340445 46120412 46980252=20 =20=20=20=20=20=20=20=20=20=20=20=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .