184 AWUS01 KWNH 182056 FFGMPD KYZ000-INZ000-ILZ000-MOZ000-190245- Mesoscale Precipitation Discussion 0186 NWS Weather Prediction Center College Park MD 455 PM EDT Mon May 18 2026 Areas affected...Southern MO...Southern IL...Southern IND...Adj. Northwestern KY... Concerning...Heavy rainfall...Flash flooding likely Valid 182100Z - 190245Z SUMMARY...Continued over-running redevelopment within favorable repeating/training flow regime will continue potential for 1.5-2"/hr rates and additional 2-3" streaks in proximity to areas currently flooding or approaching. As such, localized incidents of new or renewed flash flooding are likely through evening. DISCUSSION...Regional RADAR mosaic and 21z surface analysis denotes the main push of the squall line and stronger thunderstorms from the Lower Peninsula of MI across NW OH into far SE IND before the boundary orients more parallel to the deeper steering flow aloft and acts more of an outflow boundary and isentropic ascent surface from around KBAK, IND across IL passing KLWV to KMVN before passing KFAM, TBN across S MO and fading to the mean environment just north of KFSK in E KS. South of which broad south to southwesterly flow with unseasonably high (ten-year climo maximum, per CIRA LPW) low level moisture with Tds in the upper 60s to low 70s along the length. CIRA LPW notes that the surface to 850mb layer is very broad back into the central Plains, but the keep to the higher moisture flux occurs with the core of the 850-700 and 700-500mb layers over eastern AR through southern IL resulting in total PWats at or just above 2" across S IL with 1.75" extending back through the Ozark plateau. While GOES-E WV suite shows the main shortwave/vorticity center exiting across the central Great Lakes (aiding forward propagating squall line across OH), there does remain favorable divergence aloft within the right entrance of the jet across N MO into a 90 kt speed max across WI; which continues to drive the broad and generally confluent LLJ to maximize convergence along the upwind edge of the outflow boundary. RAP analysis still shows a source of 1500-2000 J/kg across the Ozark Plateau into S IL; though with some capping remaining. The convergence along the isentropic surface still aids scattered convective initiation and maintenance from south-central MO. This will continue to develop in the favorable ascent regime and with ample deep layer moisture should remain fairly effective with 1.75"/hr rates occasionally increasing to 2" with strongest updrafts. As noted above, the deep layer steering flow remains parallel to the ascent plane and only subtly south of the earlier axis of convective activity. The overlap with the saturated/actively flooding areas of southern MO into S IL and SW IND, have a solid potential of renewing localized flash flooding through the evening as the core of the warm conveyor belt and mid to upper-level forcing shift eastward. Streaks of additional 2-3" totals (isolated locally 4" psbl) may further expand the risk of inducing new incidents of flash flooding further south of the initial axis as well. This may also affect some flash flood prone urban centers along the Ohio River as well, if cold pool/outflow generation is stronger than currently forecast...so have included portions of NW KY and extended the MPD, though the band is more likely to remain north. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ILN...ILX...IND...LMK...LSX...PAH...SGF... ATTN...RFC...KRF...MSR...ORN...TIR...NWC... LAT...LON 39918552 39138483 38298507 37758607 37238839 37059076 37249252 37589377 38139360 39039122 39388880 39748743