Mesoscale Precipitation Discussion 0778
NWS Weather Prediction Center College Park MD
240 AM EDT Thu Sep 06 2018

Areas affected...Western MS...Southeast AR...Ext Northeast LA...

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

Valid 060645Z - 061230Z

SUMMARY...Slow eastward progression of band with embedded south to
north training with efficient warm rainfall processes support
possible flash flooding through early morning.

DISCUSSION...06z Surface analysis shows the center of T.D. Gordon
just NW of GLH with an inverted trof extending southwest into
northern LA.  WV and TPW analysis depicts the dry slot remains
well south of the circulation over southern MS and is not likely
to inject/detract from the deep moisture near the center of Gordon
where Total PWAT values are in the 2.25-2.5" range and saturated
to 400mb.  RAP analysis/forecast suggest some increased low level
WAA supports increased instability with MLCAPEs to 1000 J/kg
nosing toward the strongest moisture convergence point in the SE
quadrant of Gordon at the base of the outer band.  LLJ per VWP
network suggests a slight increase in winds to enhance convergence
which is expected to maximize near 08-9z.  Mean cloud bearing
winds will continue to support northward training though inflow is
nearly equal to the cell motions suggesting stationary/slow
southward propagation along the band remains possible.  Rain rates
of 2.5"/hr are expected.

The most significant change over the last few hours was the low
level convergence band has shifted west of the upper level trof
axis and is now experiencing northeasterly shear at 10-20kts
generally in the entrance to a jet streak over S AR/N LA,
providing modest divergence for continued evacuation/outflow to
maintain convection.  Orientation of the overall circulation is
more N-S and so overall steering flow is very weak to the east
supporting a longer duration of rainfall supporting 3-5" totals
over 3-4 hours before moving east.  As such flash flooding remains
possible over the early morning hours.  

Gallina

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

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

LAT...LON   34829081 34709043 34438994 34088976 33728969
            33288970 32888983 32609000 32379031 32279074
            32349109 32489118 32709123 33019123 33369137
            33559157 33719171 34039189 34449181 34709159
            34809126