Mesoscale Precipitation Discussion 0795
NWS Weather Prediction Center College Park MD
516 PM EDT Fri Sep 07 2018

Areas affected...Southern and Central Missouri and small parts of
adjacent states

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

Valid 072115Z - 080300Z

Summary...Coverage of rain will increase in southern and central
Missouri in the late afternoon, and continue during the early
evening hours. As the rain coverage increases, rain rates are
likely to begin to reach the 1-2 in/hr range more regularly, with
locally higher rates possible. This could lead to flash flooding
as bands of rain continue to develop and move very slowly around
the periphery of Tropical Depression Gordon, which is forecast to
move into southern Missouri overnight.

Discussion...Tropical Depression Gordon was clearly defined in
radar and satellite imagery over north-central Arkansas, and was
forecast to continue moving north toward southern Arkansas over
the next several hours. To the northwest, a band of low-mid level
deformation was increasing from far northeast Oklahoma into
southwest and central Missouri. Rain bands were developing and
becoming more focused along this axis, and given the gradual
northward motion of Gordon, the rain bands and associated forcing
may be nearly stationary into the early evening hours. Therefore,
a more concentrated area of heavy rainfall could develop in
southwest Missouri this evening. CIRA blended TPW indicated
precipitable water values were likely above 2 inches, and a recent
sounding launched from LMN (outside the main bubble of higher PW
near Gordon's center) showed a 2.1 inch PW. Therefore, PWs in
southern Missouri may be climbing into the 2.2 to 2.3 inch range
now in some areas, and this should promote efficient heavy rain
bands. With the freezing level around 14-15kft, a deep warm cloud
layer, and nearly saturated profile up to the tropopause, even
more frontally forced rain bands in the absence of strong
instability could produce substantial rain rates around 1-2 in/hr
(and perhaps locally higher in some cases).

In the northeast quadrant of the circulation of Gordon, low-level
inflow should increase over southeast Missouri into the evening
hours, as a curved LLJ to the east of the center shifts north in
response to the storm's motion. The combination of a regional max
in low-level moisture flux, with the typical diurnal cycle of
convection focusing closer to the center of warm core cyclones
overnight, should yield an increase in rain over the next several
hours in this area as well. RAP analysis indicates a ribbon of
stronger instability in the eastern half of Gordon's circulation
as well, with MLCAPE values around 1500-2000 j/kg. Some lightning
has been observed in a few of the scattered convective bands
already forming in southeast Missouri, and thus slightly deeper
and stronger convection may be favored in that area over the next
several hours. Rain rates of 1-2 in/hr will also be common in the
convection in this area, but higher rates around 3 in/hr will be
possible in regions of training. The flash flooding threat is
expected to persist beyond the expiration time of this discussion
(03Z) in southeast Missouri, and heavy rainfall later in the night
could exacerbate any flooding that develops this evening.

Lamers

ATTN...WFO...EAX...ICT...LSX...MEG...PAH...SGF...TSA...

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

LAT...LON   39299277 39069045 37808927 36748927 36118998
            36499067 36729226 36679372 36199489 36849541
            38039499