AWUS01 KWNH 221348 FFGMPD MIZ000-221930- Mesoscale Precipitation Discussion 1110 NWS Weather Prediction Center College Park MD 947 AM EDT Sat Aug 22 2026 Areas affected...Lower Peninsula of Michigan... Concerning...Heavy rainfall...Flash flooding possible Valid 221350Z - 221930Z SUMMARY...Multiple rounds of thunderstorms capable of 1.5"/hr with localized slow motions further north and back-building/repeating further south may allow for localized flash flooding concerns through early afternoon. DISCUSSION...GOES-E WV shows a broad longwave trof centered over the LP of MI this morning with a stronger upstream shortwave digging out of WI providing height-falls and strengthening/sharpening of the surface low near the Mackinaw Strait with an attendant cold front angling southwest just crossing the far southeast side of Lake Michigan into SW MI at this time. A upstream exiting MCV between Lake Erie and Ontario allows for broadening downstream portion of the longwave trough with solid diffluence aloft to promote ascent along and well ahead of the cold front. Instability has been a limiting factor through eastern MI but RAP analysis modified by recent surface temperatures suggests weakly capped 1000-1500 J/kg of MLCAPE reducing to 250 J/kg in far E MI, with initial, early morning convection exhausting much of it. However, that convection helped develop a WSW to ENE boundary and with favorable southerly component to low level winds and available unstable air has been able to develop stronger flanking development with somewhat favorable orientation to the deep layer mean flow to increase residency. Surface Tds in the low 60s and modest mid-level moisture with the effective warm conveyor pressed eastward is limiting overall available moisture to around 1.25"; so localized convergence/flux will be the driving force for rates of 1.5" with occasionally higher localized peaks. This is falling generally over the core of the sandier soils of central LP where FFGs are high, but proximity to urban locations along the I-96 corridor may still pose urban flash flooding, but at least prep the area for later developing convection from the cold front toward early afternoon. Further north, as the shortwave sharpens the mean steering flow will reduce in the trough especially along/east of the strengthening surface wave. So cells will increase in residency toward NE LP. This is also where FFGs are naturally a bit lower with spots of 1-1.5"/hr and 1.5-2.5"/3hrs. As such, with multiple rounds and possible mergers due to the sharpening/pivot in the line, localized totals of 2-3" are possible and may result in localized flash flooding concerns toward afternoon. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...APX...DTX...GRR... ATTN...RFC...MSR...NWC... LAT...LON 45408442 45358357 44998319 44348316 44148285 43718246 42678240 42378281 42188307 42148364 42158500 42578530 43298490 43808493 44228553 45058512