Mesoscale Precipitation Discussion 0786
NWS Weather Prediction Center College Park MD
912 PM EDT Thu Sep 06 2018

Areas affected...Western MS, extreme NE LA, and SE AR

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

Valid 070111Z - 070611Z

Summary...Developing convective band to the east of Tropical
Depression Gordon will strengthen and expand NW from MS into AR
this evening. Training of echoes will produce very heavy rainfall
rates, and 2-4" of rainfall will likely produce flash flooding.

Discussion...The center of T.D. Gordon was located across central
Arkansas this evening. Despite the disorganized look of convection
around this feature, a strengthening band of thunderstorms was
developing in a region of confluent 850mb flow SE of the
circulation center. Anomalously high PWAT analyzed on the 00Z LZK
sounding of 2.1 inches is above the 90th percentile for the date,
and RAP soundings suggest these will climb even higher. In this
environment, low-level confluence is working in tandem with
diffluence aloft within the anticyclone atop Gordon noted on
GOES-16 WV Imagery and MLCape over 1000 J/kg to drive strong omega
supportive of thunderstorms despite overall weak lapse rates less
than 6C/km.

Efficient warm rainfall processes are expected in warm cloud
depths approaching 15 kft, and although recent KDP observations
from KDGX show values greater than 2 in the stronger storms, even
the less-efficient rain processes there will produce rainfall
rates of 1-2+" per hour. 0-6km mean wind of around 15 kts will
allow storms to move relatively quickly to the N/NW around Gordon,
but training of cells is likely. Total rainfall of 2-4" is
expected, with isolated higher amounts, and flash flooding is
likely across the threat area, especially across NW MS and SE AR.

Weiss

ATTN...WFO...JAN...LZK...MEG...

ATTN...RFC...ABRFC...LMRFC...

LAT...LON   36079186 36019140 35809076 35429046 35049020
            34338993 34048995 33768995 33429002 33139005
            32789014 32389034 31959056 31889070 31859098
            31859111 31969129 32219147 32659155 33069165
            33309166 33849166 34259179 34949194 35709221
            36019209