AWUS01 KWNH 011154
FFGMPD
MOZ000-011700-

Mesoscale Precipitation Discussion 0825
NWS Weather Prediction Center College Park MD
754 AM EDT Tue Aug 01 2023

Areas affected...Missouri

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

Valid 011153Z - 011700Z

Summary...Showers and thunderstorms will continue to train to the
southeast this morning with rain rates of 1-2"/hr. This will
produce additional rainfall of 2-4" in some areas, falling atop
pre-saturated soils. Flash flooding is likely.

Discussion...The GOES-E IR imagery this morning shows a persistent
MCS over central Missouri with continued cloud top cooling
occurring on the upwind side of this system. Recent cloud top
temperatures have fallen below -70C, indicative of still
strengthening updrafts across the area. Synoptic level ascent is
modest overall driven by a weak impulse rotating within NW flow
around the periphery of an expansive mid-level ridge to the south.
However a slow veering of the 30-40 kt LLJ noted in regional VWPs
is surging moisture flux above +3 sigma according to the SREF into
the Central Plains/MS VLY, and converging efficiently along the
nose of this jet noted by a collapse of moisture transport vector
length. This ascent is occurring within favorable thermodynamics
characterized by PWs of 1.8-2.0 inches, and MUCAPE of around 2000
J/kg, which has resulted in a narrow axis of 1-4" of rain
overnight, with local amounts to 6" noted in mesonets.

The recent HRRR and ARW runs are handling the current radar pretty
well this morning, and are relied upon most heavily for the
evolution. As the LLJ continues to veer to become westerly, it
should result in a slow weakening of the MCS. The speed at which
this occurs though is probably going to be slower than guidance
suggests due to continued thermodynamic advection and modest
thickness diffluence to support intensity of convection. The HREF
suggests rainfall rates will persist at 1-2"/hr for several more
hours, and with the mean 0-6km wind aligned to the nose of the
LLJ, training of cells is likely. Additionally, there may be some
backbuilding of echoes both to the NW and W, into the greater
instability, which will lengthen the duration of heavy rain. Where
the most intense cells can train most efficiently, 2-4" of rain is
possible as reflected by HREF exceedance probabilities for 3+"
reaching 30-40%. By late morning/early aftn this MCS should wane
more rapidly as it begins to advect more strongly to the east and
into weaker thermodynamics.

Rainfall overnight has saturated the soils noted by HRRR 1cm soil
moisture of 100% in some areas. FFG is as low as 1.5-2"/1hr for
which the HREF has a 20% chance of exceedance, although FFG is
likely lower than that in many areas due to the overnight rain.
While some uncertainty exists in the evolution this morning, it is
likely anywhere training can occur of these rain rates, flash
flooding will occur, but will be most likely should training occur
atop the most vulnerable soils where any additional rainfall will
rapidly become runoff.


Weiss

ATTN...WFO...EAX...LSX...SGF...

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

LAT...LON 40309371 39979256 39109156 37979115 37239119
36929160 37229244 37729310 38329370 38869405
39299421 39959419

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