Mesoscale Precipitation Discussion 1077
NWS Weather Prediction Center College Park MD
1030 PM EST Sun Dec 30 2018

Areas affected...portions of the lower Mississippi to lower Ohio
Valleys

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

Valid 310329Z - 310920Z

Summary...Flash flooding will be possible for portions of the
lower Mississippi Valley into western Tennessee and the lower Ohio
Valley through 09Z. Rainfall rates peaking near 1 in/hr along with
periods of training will allow for 2-4 inches of rain in a few
locations over a 6 hour duration.

Discussion...03Z radar imagery showed a broad area of light to
moderate rain with embedded heavy elements in southeastern
Arkansas into northern Mississippi. Heavy rain was occurring at
the leading edge of a strengthening 850 mb surge of winds with
02-03Z VAD wind plots showing 40-45 kt at KPOE and KDGX but only
10-20 kt at KLZK and KNQA from the south to south-southwest. The
axis of strong low level speed convergence currently extending
from southern Arkansas into northern Mississippi is forecast by
the RAP to track toward the north-northeast, reaching northeastern
Arkansas to the western Kentucky/Tennessee border by 09Z along
with 850 mb wind speeds peaking near 60 kt.

00-02Z Precipitable water values (per sounding and GPS data) were
anomalously high at LZK, JAN, SHV with values ranging between 1.4
to 1.7 inches, near the 95th percentile, but MUCAPE was somewhat
lacking, only near 500 J/kg across southern Arkansas and northern
Mississippi with less than 100 J/kg in western Tennessee. Mean
storm motions are very close to the 850 mb wind direction which
will promote periods of training with a general movement off
toward the east with time. 3-hourly rainfall rates are expected to
eclipse 2 inches in a few locations which is what Flash Flood
Guidance currently shows across roughly half of the MPD threat
area, with 6 hour totals between 2-4 inches. While these rains are
forecast to occur in a relative min of 7-14 day rainfall
departures from normal, flash flooding may still occur in a few
locations given the proximity to Flash Flood Guidance and locally
sensitive locations.

Otto

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

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

LAT...LON   37108739 36948644 36658601 36108595 35248650
            34498749 33878891 33289078 33189123 33169199
            33549221 34289191 36088999 36938877