Flash Flood Guidance
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065 AWUS01 KWNH 072326 FFGMPD OHZ000-KYZ000-INZ000-080430- Mesoscale Precipitation Discussion 0237 NWS Weather Prediction Center College Park MD 725 PM EDT Tue May 07 2024 Areas affected...Central to Southeastern IND...West-Central to Southwestern OH... Concerning...Heavy rainfall...Flash flooding possible Valid 072325Z - 080430Z SUMMARY...Stripes of enhanced rainfall totals (1.5-3") as multiple discrete supercells orient to mean flow for repeating while slowing becoming more efficient in rainfall production with intense sub-hourly totals of 1-1.5". As such, scattered incidents of flash flooding possible to accompany ongoing severe weather threat. DISCUSSION...Regional RADAR mosaic depicts multiple discrete supercells extending from NE IND southward to west-central IND, along/just east of EML (noted well in CIRA LPW 700-500mb layer) with strongest supercells coincident with enhanced pocket of mid-level moisture from 850-500mb across south-central to southeast IND into SW OH. Combined with an increased area of surface Tds into the low 70s; a secondary warm frontal feature evident in Theta-E and MLCAPE fields as a tighter gradient extending near Muncie, IND southeastward into SW OH. Supercells are ingesting high moisture through the boundary layer with enhanced isallobaric influence flux convergence for moisture loading to the up/down drafts. Intense downdrafts of up to 1+"/15 minute (per HRRR/WoFs) are likely to expand with increasing LLJ expected in the next few hours. Even with right-turning, cell motions are still a negative factor toward FF, reducing duration, as well as, areal coverage with narrower downdrafts, at this time. However, stronger moisture flux should broaden updrafts and rainfall efficiency, but of greater concern is further upstream development along the SW to NE instability axis back into SW IND. Cells here, are also discrete but will be traversing similar paths and may intersect flanking line of initial cell to help corral tracks to similar paths. HRRR and WoFS runs continue to trend upward toward this evolution as well, suggesting narrow west to east streaks of 1.5-2.5" totals; though 90th percentile from recent WoFS runs continue to increas to as much as 3.5"...further bringing confidence to rainfall efficiency potential. Duration between rounds is likely to add to localized FF concern, which is reduced nearer the intersection of the SW to NE instability boundary and the NW to SE higher theta-E boundary which appears to maximize near I-70 between KIND and KDAY through the next 4-6 hours. Further spread in time across South-central IND into SW OH may allow creeks/streams to rebound, but FFGs are even lower across this area and soils are a bit more saturated per SPoRT LIS 0-40cm ratios. All considered the sub-hourly totals near 1hr FFG and spotty 2-2.5"/3hr also near the 3hr FFG especially further east, which aligns with better timing of low-level flux. As such, scattered incidents of flash flooding are considered possible. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CLE...ILN...IND...IWX... ATTN...RFC...OHRFC...NWC... LAT...LON 41198405 40918304 39788295 39148396 38958555 39128680 39698692 40308588