Weather Prediction Center issues Mesoscale Precipitation Discussion #1318 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE420
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Mesoscale Precipitation Discussion 1318
NWS Weather Prediction Center College Park MD
955 PM EDT Thu Sep 17 2026
Areas affected...Central to Southeast Indiana...Southwest Ohio...
Concerning...Heavy rainfall...Flash flooding possible
Valid 180155Z - 180720Z
SUMMARY...Slow moving, potentially repeating but highly efficient
thunderstorms capable of 2-2.5"/hr may pose scattered possible
flash flooding though early overnight, especially if tracking
northward over saturated grounds affected over the last day or so.
DISCUSSION...GOES-E 10.3um EIR loop and regional RADAR mosaic has
seen an expanding trend of convective initiation around the
incipient strong cell tracking into Tipton county, IND. A subtle
1020mb surface wave along the IND/IL border west of Lafayette, IND
has helped to back low level flow out of the southwest along and
ahead of the wave across central IND. Surface Tds in the upper
70s accompanied aloft by enhanced moisture (per CIRA LPW) results
in a total PWat over 2", perhaps locally reaching 2.25". Higher
theta-E pooled along the surface front remains conditionally
unstable enough for an axis of 1000-1500 J/kg of MLCAPE to exist
into southwest Ohio. As such, tops are cooling to -70C and
expanding along the flanking line to the west, though a few more
isolated, elevated cells are occurring further north as well.
Stronger surface to boundary layer moisture flux will support
rates of 2-2.5"/hr given the ample moisture and while the forward
speed is decent at 15-20kts, residency due to broadness of the
updrafts should allow for sub-hourly totals nearing 2" locally.
Deep layer steering flow is favorably oriented to the surface
front and instability axis while inflow should also be relatively
unobstructed. The uncertainty lies with flanking line or
upstream/back-building development. Hi-Res CAMs and trends
suggest this may be a bit more limited, though recent
strengthening an overall coverage along the upwind edge suggests a
potential remains for some short-term repeating. As of current
trends and placement of the front/instability axis, the best
potential for repeating or strongest cells will remain south and
west of the recently compromised soil conditions through the
northern Tilled Plains of Eastern IND and Western Ohio where FFG
values are below an 1" in parts through 1,3, and 6hr time steps.
While, current track will move through higher more normal
2-2.5"/hr and 3"/3hr values across central IND, but eventually
reduce again into Southwest Ohio (1-1.5"/hr & 1.5-2"/3hr). So
while there remains these contingencies, the efficiency of the
rates would still pose a risk in urban locations and overall there
remains a risk of possible flash flooding through the overnight
period.
Gallina
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ILN...IND...IWX...
ATTN...RFC...TIR...NWC...
LAT...LON 41148598 40988516 40508379 39828272 39158290
38958360 39178497 39558617 39968691 40308711
41008674
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #1318 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE---------------
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