Mesoscale Precipitation Discussion 1078
NWS Weather Prediction Center College Park MD
1048 AM EST Mon Dec 31 2018

Areas affected...Mid-MS into TN Valleys

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

Valid 311548Z - 312148Z

Summary....A few lines of convection through this afternoon will
be capable of producing hourly totals as high as 1.5" which may
induce localized flash flooding over saturated soils and other
sensitive areas.

Discussion...A 15z surface analysis showed a warm front lifting
northward through the TN Valley while a cold front was analyzed
west of the MS River in AR and LA. In the warm sector, anomalously
high moisture was evident with dewpoints in the mid to upper 60s
as far north as northern MS. 12z JAN upper air sounding had a PWAT
of 1.35", which is in the 95th percentile for late December.
Overall, PWATs in the 1.3 to 1.7" range will continue to surge
northward through the day as a strong mid/upper level wave lifts
through the southern/central Plains. 850 mb flow is expected to
increase from 50 to 70 kts across the region. Despite limited
clearing, MUCAPE of 500 to 1000 J/kg is likely to develop by early
afternoon, which should help contribute to higher rain rates.
Finally, line and cell storm motions will be nearly parallel to
the overall mean wind, which suggests potential for training and
redevelopment.

Antecedent conditions also favor the threat for flash flooding
where 7 day departures from normal are running 200-300 percent of
normal. 1-hr Flash Flood Guidance values are as low as 0.75" with
a large area of 1.0-1.5", largely as a result of rainfall fallen
in the last 24 hours.

Hi-res models and the latest HREF mean show potential for these
values to be met or exceeded for a few hours into this afternoon
as convection picks up and moves across the area The latest runs
of the HRRR show potential for a quick 2-3" in localized spots,
which if trains over saturated or sensitive areas, could result in
flash flooding. The greatest threat area appears to be from
northern MS into middle TN, and perhaps into extreme southern KY,
if any instability builds that far north.

Taylor

ATTN...WFO...BMX...HUN...JAN...LMK...MEG...OHX...PAH...

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

LAT...LON   36768799 36678538 34658673 33518781 33108894
            32619063 33729095 34509059 36088997