Mesoscale Precipitation Discussion 0898
NWS Weather Prediction Center College Park MD
418 AM EDT Wed Sep 26 2018

Areas affected...Northern Mississippi, Southern Tennessee,
Northern Alabama

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

Valid 260817Z - 261400Z

Summary...Thunderstorms and heavy rain bands will increase through
the early morning across the Mid South, and may begin to train
repeatedly over some areas. Rain rates may reach 2-3 in/hr, which
could lead to flash flooding, especially if those rain rates occur
in cities and urbanized areas.

Discussion...Prior to 07Z, there was generally only one
concentrated cluster of thunderstorms in northeast Mississippi,
affecting the area near Tupelo. However, between 07Z and 08Z,
GOES-16 IR satellite channels have showed an expanding ribbon of
cooling cloud tops extending back as far southwest as Greenville,
MS. This convection was becoming more widespread and organized in
a very moist and unstable environment, and thus conditions are
favorable for continued growth of convective rain bands. RAP
analysis showed around 1000 j/kg of MLCAPE with limited CINH in an
inflow region also characterized by broadly confluent surface
winds. The developing convection was also nearly centered on a
substantial PW axis, with RAP analysis and CIRA blended PW product
showing values as high as 2.2 to 2.3 inches. The combination of
moderate instability and deep moisture will support organized
convection capable of producing rain rates upwards of 2 in/hr.
Although the flow in the inflow region had a greater southerly
component, it was gradually veering and becoming increasingly
aligned through a deep layer as it approached a cold front further
to the northwest. This was setting up a wind profile favorable for
training of convective rain bands over the Mid South this morning.
With higher PW and CAPE positioned upstream (southwest), the
pattern also favors backbuilding as well, and the combination of
backbuilding and training convection could produce locally
significant rainfall. Flash flooding will be possible where 2-3
in/hr rain rates can develop, and localized rainfall totals could
exceed 4 inches.

Lamers

ATTN...WFO...BMX...FFC...HUN...JAN...MEG...MRX...OHX...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   35578581 35328487 34608558 34018684 33218896
            33159034 34129053 35168861 35498718