Mesoscale Precipitation Discussion 1048
NWS Weather Prediction Center College Park MD
1140 AM EST Sat Dec 08 2018

Areas affected...East Central MS...West Central AL...

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

Valid 081640Z - 082200Z

SUMMARY...Strong frontogenetic forcing/mst flux to produced
prolonged moderate rainfall that may exceed localized lower FFG
values at longer duration.

DISCUSSION...GOES-16 WV suite depicts a mature upper level low
across North Central TX with multiple wedge-shaped bands across
Eastern TX and northwest Gulf of Mexico with strong diffluence
entering the right entrance of 110kt 250mb jet over the Central MS
River valley into the TN River Valley.  The LLJ has responded with
45-50kts of slightly veered 850-7H flow (per JAN VWP) that is more
unidirectional near the front crossing central LA coast attm. 
850mb low continues to deepen in the dry slot forming over E TX
and W LA attm, but regional RADAR mosaic depicts the 900 to 850mb
frontal boundary quite well along the I-20 corridor intersecting
the deeper moisture near the MS River. 

The 12z SHV sounding denoted the enhanced northerly flow below the
front indicating a more vertical ascent likely at this interface.
Rainfall rates responded over the last 3hrs with 1.25-1.5" totals
observed in N LA and rates to .5"/hr.  This feature can be see as
far east as Elmore county, AL and given the eastward progression
of the front with reducing northerly influence, the boundary
should remain fairly static in the north-south sense for the
coming 3-6hrs.  RAP forecast suggests 850mb flow will increase to
over 50kts nosing the TPW values to near 1.75" intersecting this
boundary.  As such 925-850mb FGEN are very strong near 6-10K per
unit volume and likely to maintain the .25-.5"/hr rates with some
potential for slightly higher amounts.

This will total 1.5-2.5" over the next 3-6hrs, these totals are on
the threshold to eclipse FFG in the region but particularly in
lowest values in the lower Tombigbee River basin and the Jackson
metro vicinity.  The potential remains low for flash flooding
given the low rates, but warrants a possible flash flooding if
this localized increased vertical slope of the boundary supports
localized rates of .75-1"/hr.

Gallina

ATTN...WFO...BMX...JAN...MOB...

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

LAT...LON   33518767 33198721 32748729 32348772 32298826
            32238902 32209013 32569031 33059004 33408922
            33508866