AWUS01 KWNH 191222
FFGMPD
OHZ000-KYZ000-INZ000-ILZ000-191720-

Mesoscale Precipitation Discussion 0145
NWS Weather Prediction Center College Park MD
822 AM EDT Sat Apr 19 2025

Areas affected...Southern IL...Southern IND...Adj Portions of
Northwest KY...Ext Southwest OH...

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

Valid 191220Z - 191720Z

SUMMARY...Limited instability, but favorable repeat/training,
solid moisture and fairly saturated soils pose a possible widely
scattered flash flooding incident or two through morning.

DISCUSSION...Regional RADAR denotes a line of broken convective
cells with a pair of stronger wave like convective elements
crossing Southern IL and into Southern IND, along the leading edge
of sagging cold front from stronger exiting wave across the
central Great Lakes into Ontario. This orientation is aligning
with deeper layer unidirectional steering flow along a
sharp/dominant ridge over the Southeast. Deep layer moisture
steaks along this boundary with total PWats up to 1.5", mainly
below 700mb. While RAP/HRRR suggests waning/limited instability,
there is solid remaining low level heating, with weak nearly
moist-adiabatic lapse rates but enough to eek out about 500 J/kg
enough to main ongoing convection. Additionally, 12z surface
analysis notes stronger below boundary layer convergence
particularly upstream with push of dying MCV/MCS energy across IL
increasing surface convergence from weak confluence (30 degrees)
further downstream to nearly opposition across S IL with weak
surface wave near MDH/HSB. As such, stronger cells will likely
continue to support .5-.75" in 15-30 minutes as noted by
observations. This generally matches the 15-minute totals from
the HRRR which has been fairly good in timing/orientation with the
past few runs.

The length of the confluence/convergence with the weak but
sufficient instability may allow for repeating/training elements
over the next few hours to support some localized spots of 1-1.5"
totals. Very slow southward sag of the boundary/training zone
will start to cross the strong soil saturation gradient across the
region where even with a bit of time to dry out, soil saturation
values remain near 60-70% in the upper 40cm; so with quick burst
of .5"/15 mins, with some maintained moderate shower activity
afterward. FFG values are 1.5"/hr which may suggest sub-hourly
totals may be nearing a critical value especially if they have
rebounded too quickly given recent high flooding. As such,
reduced infiltration is considered possible for a widely scattered
incident or two of flash flooding/ponding conditions particularly
in urban areas and near prone flashy bluffs.

Gallina

ATTN...WFO...ILN...ILX...IND...LMK...PAH...

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

LAT...LON 39838459 39378422 38968445 38188600 37468776
37158868 37308932 37888931 38578835 38918761
39248702 39618608 39818537

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