Mesoscale Precipitation Discussion 0892
NWS Weather Prediction Center College Park MD
204 PM EDT Mon Sep 24 2018

Areas affected...portions of the Mid-MS to lower OH valleys into
central KY/TN

Concerning...Heavy rainfall...Flash flooding possible

Valid 241803Z - 242330Z

Summary...Flooding/flash flooding will be possible across portions
of the Mid-MS to lower OH valleys into central KY/TN through early
evening. Rainfall rates peaking in the 1-2 in/hr range will lead
to localized 2-4 inch totals through 00Z.

Discussion...Water vapor imagery from 18Z showed a shortwave over
southern IL, progressing toward the northeast with a weak surface
wave noted in surface observations in the same vicinity. A diffuse
warm front extended southeastward from the low into central KY and
eastern TN with area precipitable water values near 2 inches. ML
and MUCAPE was greatest in the warm sector over western KY/TN with
the 17Z SPC mesoanalysis suggesting roughly 1000-2000 J/kg MLCAPE
present, with values falling off toward the northeast with less
than 500 J/kg over the IN/KY border. Regional radar imagery showed
widespread light to moderate rain across the region with embedded
heavier elements with rainfall rates peaking between 0.5 and 1.0
in/hr through 18Z.

As the shortwave progresses off toward the northeast through the
remainder of the afternoon, the warm front is expected to advance
toward the north, with greater moisture and instability working
northeastward toward the IN/KY border. Flow is unidirectional from
the SSW across the lower OH Valley which will be supportive of
training/repeating rounds of heavy rain given sufficient
instability and moisture. While the shortwave and its associated
forcing will be exiting the region through the next 3-6 hours,
mesoscale lift will aid in producing locally heavy rainfall, such
as an implied small scale circulation currently over the IL/MO
border via visible satellite imagery...previously associated with
rainfall rates near 1 in/hr over southeastern MO from 14-16Z.
Given wet antecedent conditions, Flash Flood Guidance values are
lower which when combined with locally higher rainfall rates will
support a threat for flash flooding. Locally 2-4 inches of rain
will be possible through 00Z.

Otto

ATTN...WFO...ILN...IND...LMK...MEG...OHX...PAH...

ATTN...RFC...LMRFC...NCRFC...OHRFC...

LAT...LON   39478544 39438488 39048494 38308554 37398593
            36768620 36578626 36098640 35768666 35698703
            35678774 35858941 35998996 36489003 37088970
            37878865 38578753 39218636