Mesoscale Precipitation Discussion 0865
NWS Weather Prediction Center College Park MD
811 PM EDT Fri Aug 04 2023

Areas affected...Missouri...Extreme western Illinois...

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

Valid 050010Z - 050600Z

SUMMARY...Flash flooding to continue across northern Missouri with
expanding thunderstorm development along flanking mid-level trof
into S MO. Cells will cross fully saturated grounds likely to
induce another bout of flash flooding into the early overnight
hours.

DISCUSSION...GOES-E WV suite denotes a well defined MCV/Shortwave
across north-central MO continuing to slowly drift eastward under
continued favorable upper-level outflow pattern.  The imagery in
combination with CIRA LPW denotes a narrow stripe of enhanced deep
layer moisture pooling along the shortwave's effective trailing
mid-level trof; north of which mid-level dry air is rotating into
the system across central MO.  Strong convective response remains
within the southeast quadrant of the circulation inducing a
surface low near CDJ, with effective frontal structure oriented in
a classical manner with warm front from IRK to HAE to STL/BLV. 
Deep moisture remains pooled near the centroid with 2.25"+ total
PWat, which extends along and southeast around the effective warm
front through the Mississippi Valley with 2-2.4" values strung
out, with 2"+ values along the trailing mid-level trof from NE OK
into S MO.

The dry air aloft has steepened lapse rates for very high
instability along/ahead of the effective cold front into the dry
slot, though deeper moisture intersection near the surface low and
northward should have ample narrow skinny CAPE for strong updrafts
and moisture flux for 2-3"/hr rates into the overnight period. 
Slow, nearly due eastward progression of the MCV/surface wave
should keep orientation of some cells to align favorably for
longer duration and support a swath of highest rainfall totals of
3-5". Some guidance suggests higher values, but reduced
instability and updraft strength may limit the rates to more
extreme values, but a spot of 6"+ cannot be fully ruled out
through this axis.

Southward, stronger updrafts with some rotation should support
very strong isallobaric response for extreme moisture flux
convergence.  Instantaneous rates will be very high in this
efficiency, but forward speed will likely limit overall totals.
However, streaks of 2-4" are probable with the cores of these
supercells and as they cross compromised soils from Saline to
Madison county are likely to once again induce flash flooding. 
Cells within the core of the dry slot should be fastest moving;
however, southward in the anticyclonic rotor of the dry slot
punch, forward propagation may be a bit slower and in proximity to
the aforementioned deeper moisture axis, some back-building will
be possible and cell motions will be slower, again allowing for
slightly increased totals of 2-5" are possible but should become
more scattered in nature due to slightly less favorable deeper
layer convergence further from the MCV. 

Gallina

ATTN...WFO...DMX...DVN...EAX...LSX...SGF...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...NWC...

LAT...LON   40869346 40809291 40459204 40149146 39789102
            39209039 38089019 37319079 36719198 36519374
            36789427 37229370 37809288 38409279 38869364
            39039386 39399431 39639448 39989461 40439452
            40819409