Weather Prediction Center issues Mesoscale Precipitation Discussion #1342 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE443
AWUS01 KWNH 202236
FFGMPD
WVZ000-OHZ000-KYZ000-INZ000-ILZ000-210430-
Mesoscale Precipitation Discussion 1342
NWS Weather Prediction Center College Park MD
635 PM EDT Sun Sep 20 2026
Areas affected...south-central IL into IN, western/southern OH and
the upper OH River Valley
Concerning...Heavy rainfall...Flash flooding possible
Valid 202233Z - 210430Z
SUMMARY...Isolated flash flooding will be possible from
south-central IL into IN, western/southern OH and the upper OH
Valley through 04Z. Training of cells will produce hourly rainfall
of 1-2 inches with storm totals of 2-4 inches possible into the
early overnight.
DISCUSSION...Water vapor imagery from 22Z showed a mid-level
vorticity max over southwestern Lower MI, tracking east, and
preceded by stratiform light to moderate rain. A lack of
instability was preventing higher rates across northern IN/OH into
southern Lower MI. However, a few widely scattered showers and
thunderstorms with heavy rainfall were observed to the south of
the vorticity max, located just north of a west-east oriented
quasi-stationary front, and ahead of a subtle impulse over
east-central IL. The stronger cells were located within the
northern end of an instability pool containing 500-1500 J/kg
MLCAPE and precipitable water values of 1.6 to 1.9 inches, via 22Z
SPC mesoanalysis data, along and just north of the frontal
boundary, supportive of high rainfall rates.
Given the recent uptick in the intensity of cells and a forecast
for the front to begin advancing south over the next 6 hours,
current thinking is that shower and thunderstorms will continue to
increase in coverage across IN/OH and possibly IL within the mean
westerly steering flow. Instances of training will be possible as
storm coverage increases. Aiding ascent will be diffluent winds
aloft, with upper level winds from the west across northern
IL/IN/OH but veering toward the southeast as one moves south,
around an upper ridge axis extending northeastward into the lower
OH Valley.
Training of cells will produce hourly rainfall of 1 to 2 inches
(locally higher) with the potential for peak storm totals to reach
2 to 4 inches through 04Z. Current thinking is that any flash
flooding will remain isolated in coverage, though lower flash
flood guidance values of 2 inches or less in 3 hours across OH may
present a locally higher risk if stronger cells are able to train
across these eastern locations.
Otto
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...CLE...ILN...ILX...IND...IWX...LMK...LSX...PAH...
PBZ...RLX...
ATTN...RFC...MSR...TIR...NWC...
LAT...LON 40988481 40868395 40618269 40198173 39378149
38808167 38388212 38318288 38758448 38778596
38538751 38538895 38738957 39028977 39428974
39718931 39898880 40088766 40338693 40778589
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #1342 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE---------------
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