869
AWUS01 KWNH 270146
FFGMPD
OHZ000-TNZ000-KYZ000-INZ000-ILZ000-MOZ000-ARZ000-270745-

Mesoscale Precipitation Discussion 0331
NWS Weather Prediction Center College Park MD
945 PM EDT Sun May 26 2024

Areas affected...Portions of the OH Valley into the Mid-South

Concerning...Heavy rainfall...Flash flooding likely

Valid 270145Z - 270745Z

SUMMARY...A strong QLCS evolution is anticipated overnight with
locally enhanced rainfall totals expected to fall over areas with
very moist antecedent conditions. Numerous instances of flash
flooding are likely, with locally significant impacts expected.

DISCUSSION...The evening GOES-E IR satellite imagery shows a
blossoming axis of very cold-top convection stretching across
areas of southeast MO northeastward through southern IL as
supercell thunderstorms continue to organize and gradually
consolidate into a strong forward propagating QLCS. Meanwhile,
radar imagery has been showing more discrete supercell
thunderstorm development downwind of the QLCS closer to the OH
River involving southwest IN and western KY. This activity has
been related to strong warm air advection interacting with a
long-lived residual outflow boundary.

A southwest low-level jet 40 to 50 kts is advancing northeast up
into the lower OH Valley out ahead of a cold front and wave of low
pressure that continues to traverse the middle MS Valley. The
airmass being transported by this low-level jet is very unstable
and especially from northeast AR through southeast MO where MLCAPE
values of 3500 to 4500+ J/kg are noted. Areas of southern IL,
southwest IN and far western KY have MLCAPE values of 2500 to
3500+ J/kg which is where there has been a significant airmass
destabilization over the last 3 to 6 hours associated with
late-day diurnal heating, warm air advection, and a well-defined
EML which shows up very well in the CIRA-ALPW 700/500mb layer.

This strongly unstable airmass will continue to advance downstream
into adjacent areas of the OH Valley overnight with an extension
of it back down into the Mid-South where the low-level jet will be
aligned. Strong vertical shear parameters working in tandem with
the instability will sustain a well-organized QLCS threat deep
into the night that will advance off to the east and eventually
southeast once a more organized cold pool evolves.

Very impressive sub-hourly rainfall rates will be possible in this
environment where the stronger supercell thunderstorms occur. As
much as 1.5 to 2 inches of rain in 30 minutes will be possible
locally, with some spotty 3 inch/hour totals, and especially where
any cell-mergers occur.

Overall, the HRRR guidance looks somewhat underdone with the
rainfall potential overnight given the high rainfall rate
environment and concerns for cell-mergers and cell-training. Some
rainfall totals are expected to reach 3 to 5 inches, with isolated
heavier totals possible. The antecedent conditions are locally
quite sensitive given the recent heavy rainfall, and especially
over areas of southeast MO through western/central KY and far
northern TN. Numerous areas of flash flooding are likely given the
setup, and some of the flash flooding is expected to be
significant.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...ILN...ILX...IND...JKL...LMK...LZK...MEG...MRX...
OHX...PAH...

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

LAT...LON   39738522 39558417 38868336 37728345 36878424
            36368509 36048607 35848733 35818871 35928996
            36429085 37089064 37378973 38158863 39038801
            39468730 39718620