523
AWUS01 KWNH 181710
FFGMPD
ILZ000-MOZ000-182300-

Mesoscale Precipitation Discussion 1201
NWS Weather Prediction Center College Park MD
110 PM EDT Sat Oct 18 2025

Areas affected...Southeast Missouri...Southern Illinois...

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

Valid 181710Z - 182300Z

SUMMARY...Prolonged training of moderate rainfall with occasional
heavy bursts up to 1.5"/hr and localized totals of 2-3" and
perhaps an isolated 3.5"+.  Rates and totals are on the edge of
FFG exceedance in drought/hard ground conditions for a possible
incident or two of low-end flash flooding conditions, manly near
urban or prone locations.

DISCUSSION...GOES-E Visible/10.3um EIR loops depict a steadily
cooling and consolidating scattered line of convection across the
Eastern Ozark Plateau toward S IL.  The stronger southern stream
shortwave over central OK continues to progress and amply along
the southeast portion of the larger scale trough while strong
upper-level jet streak is finally rounding the base and expanding
toward 110kts across KS into north-central MO in the next hour or
so.  The combination of mid-level features and weak outflow from
convection is starting to combine the confluence/ascent axis
downstream of the orthogonal strong convergence along and
downstream of the southern stream shortwave over southern MO.  The
confluence axis is also aligning with the deeper moisture (up to
1.6" attm) and elevated instability axis (up to 1500 J/kg),
resulting in the uptick in convective vigor across south-central
MO into SW IL.  The overall coverage of cells remains scattered
though some embedded cores have be observed producing .25-.5"
totals in 15-30 minutes with hourly totals nearing 1-1.25".  As
low level flow and moisture flux continue to strengthen with
rapidly expanding divergence area aloft from the strong right
entrance region to the 110kt jet, occasional hourly totals up to
1.5" are not out of the possibility.

The key for flash flooding will be duration and soil conditions
along the training axis.  As the shortwave further amplifies, the
deep steering flow appears to favor a slight northward shift,
which should counteract the southeastward propagation expected
from cold pool generation.  This will allow the cells to remain
favorable for longer training of 1-3 hours, but the lack of
extreme instability and oblique convergence may continue to result
in scattered to widely scattered nature of the stronger cores,
limiting totals to 2-3", though an isolated spot of 3.5"+ is not
completely out of the realm of possibility, with best potential
upstream across south-central MO toward SE MO.

The good news is the core of the training cells appear to be
aligned ideally with the axis of the highest FFG values (2-3"/hr
and 3-4"/3hrs), though there are some urban and complex/hilly
terrain through the area that would be more prone.  Additionally,
the area has been in prolonged drought with 0-40 cm soil moisture
ratios below 30%, mainly less than 15%.  This is also suggestive
that soils are compacted and probably a bit hydrophobic, limiting
initial infiltration.  As such, if first rainfall is the intense
burst of those stronger cores, greater runoff should be expected.
As such,  an isolated to widely scattered incident or two of
low-end flash flooding remains possible though the afternoon.

Gallina

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

ATTN...WFO...ILX...LSX...PAH...SGF...

ATTN...RFC...KRF...MSR...ORN...TIR...NWC...

LAT...LON   39418894 39418811 38998773 38388802 37688947
            37229051 36939204 37589260 38239302 38809176
            39219019