Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 22 2023 22:32:20 AWUS01 KWNH 222232 FFGMPD WIZ000-MNZ000-IAZ000-230400- Mesoscale Precipitation Discussion 1091 NWS Weather Prediction Center College Park MD 631 PM EDT Fri Sep 22 2023 Areas affected...northeastern IA into southeastern MN and western WI Concerning...Heavy rainfall...Flash flooding possible Valid 222230Z - 230400Z Summary...A localized flash flood threat will exist across northeastern IA into adjacent portions of MN/WI through 04Z. Slow movement of heavy rain with rates of 1 to 2+ in/hr may produce isolated 3-5 inch totals. Discussion...Trends in local radar imagery over the past hour across northeastern IA have shown an increase in the organization and intensity of thunderstorms just ahead of an MCV located 20-25 miles northwest of ALO at 22Z. The MCV has been tracking toward the ENE between 25-30 kt and has become associated with a slow moving area of showers/thunderstorms producing a quick 1-2 inches of rain with shorter term rates ranging between 0.5 and 0.75 inches in 15 minutes (per area Wunderground.com observing stations) across northern Grundy and Butler counties. A narrow axis of thunderstorms also extended SSE from the MCV into east-central IA, co-located with a subtle zone of 925-850 mb convergence/confluence and 500 to 1000+ J/kg MLCAPE via the 21Z SPC mesoanalysis over the southeastern quadrant of IA. Weak instability near 500 J/kg was also estimated to be over southwestern WI. GPS precipitable water values ranged between 1.4 to 1.6 inches across the region. While instability across northern IA into MN/WI is rather modest, slow movement of convection forced just ahead of the MCV could generate localized totals in excess of 3 inches in less than 2 hours. To the southeast of the MCV center, sufficient instability and upper level diffluent flow should persist for another few hours to allow for continued thunderstorm development, some of which could be slow moving and/or train due to steering flow oriented quasi-parallel to the low level confluence/convergence axis in eastern IA. Rainfall rates of 1-2 in/hr, locally in excess of 2 in/hr, will be possible across a small portion of eastern IA, nearing the northeastern border but with rates being limited with northward extent given limited instability. Dry antecedent conditions and correspondingly high FFG of 3 inches in 3 hours should limit any flash flooding to an isolated region or two across the MPD threat area. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4B8pWGSHsgppc6yMfNs-nlSvpsT_4U91un_tmF9uM7t0Nlj9AOKVIoHHwOsmHy4AMi6R= ACCIzZrFOSVro0ITmVxu6aM$ for graphic product... ATTN...WFO...ARX...DMX...DVN...MPX... ATTN...RFC...NCRFC...NWC... LAT...LON 44529180 44349122 44069077 43329062 42519071=20 41879100 41399148 41509239 41989263 42679296=20 43299310 44009296 44419241=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) .