Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 24 2025 01:57:09 AWUS01 KWNH 240155 FFGMPD MNZ000-IAZ000-NEZ000-SDZ000-240600- Mesoscale Precipitation Discussion 0789 NWS Weather Prediction Center College Park MD 955 PM EDT Wed Jul 23 2025 Areas affected...Eastern Nebraska through Southeast Minnesota Concerning...Heavy rainfall...Flash flooding possible Valid 240154Z - 240600Z Summary...Showers and thunderstorms developing ahead of a cold front will continue to expand and gradually shift east tonight. Rainfall rates of 1-3"/hr are possible, which through training could produce 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The GOES-E IR imagery this evening depicts two impressive areas of cooling cloud tops across the Central Plains/Upper Midwest. One is associated with an MCS and developing MCV moving across eastern Nebraska, while a secondary area is strengthening along a low-level convergence axis/pre-frontal trough near the IA/MN border. Forcing for ascent is being provided via convergence in the vicinity of these features, aided by directional divergence aloft near an upper low centered over NW Missouri, and increasing isentropic ascent of the LLJ into IA/MN. With respect to the LLJ, regional VWPs across IA/MO suggest the 850mb winds have increased to 30-35 kts from the S/SW, which is contributing to an impressive plume of LPW in the sfc-850mb layer lifting northward. Total column PW within the pre-convective airmass was measured between 1.74 and 2.02 inches on the 00Z U/A soundings from KTOP to KOAX, respectively, which is combining with MUCAPE of more than 4000 J/kg to produce extreme thermodynamics. The result of this setup has been an expansion of convection, especially from far northeast NE into southern MN, along a merged surface trough/outflow boundary, and it is this area that should continue to be the focus for heavy rainfall into tonight. The persistent LLJ lifting isentropically into this boundary will provide favorable thermodynamic resupply to support rainfall rates for which the HREF indicates has a 20-40% chance of exceeding 2"/hr, with brief 3+"/hr rates progged by the 15-min HRRR. This is concerning because as the LLJ slowly veers more to the SW tonight and aligns to the approaching front and this surface trough, Corfidi vectors will likely collapse and veer to become more aligned anti-parallel to the mean wind. This suggests that backbuilding/training will become common, especially near and along the IA/MN border. Farther south, the MCV surging eastward into the most intense instability and elevated DCAPE may provide a more progressive MCS moving forward, but with similarly impressive rain rates. The heaviest rainfall is expected from eastern Nebraska through northwest Iowa and into south-central Minnesota. This is supported by elevated 3"/6hr HREF/REFS neighborhood probabilities and 1"/6hr EAS probabilities. Despite this, FFG exceedance probabilities are modest due to generally elevated 3-hr FFG of 2-2.5 inches. However, since these extreme thermodynamic will support intense rain rates, rapid runoff is possible, especially in the area of greatest training. Where this occurs, instances of flash flooding could occur. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9Oh17E9QYncQQMD1G8LnXcviKv_0rUvzOMDGKcjFfDie_9Jhk6gtK0XLQaAA4aN5AA2S= LfLeZfeYG_2774LhElxwi3w$ for graphic product... ATTN...WFO...ARX...DMX...FSD...GID...MPX...OAX... ATTN...RFC...KRF...MSR...NWC... LAT...LON 44319471 44209271 43619196 42899218 41919379=20 41299529 40999666 40939783 41159836 41669830=20 42069799 43259701 44249562=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) .