Mesoscale Precipitation Discussion 0998
NWS Weather Prediction Center College Park MD
315 PM EDT Wed Oct 31 2018

Areas affected...ArkLaTexOma

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

Valid 311914Z - 010114Z

Summary...Convergence of tropical moisture with a surface cold
front with a jet streak entering from the south will raise a flash
flood threat with hourly rates of up to 2 inches possible into
this evening.

Discussion...A cold front driven by widespread convective activity
across north TX (with a squall shifting east across north TX this
afternoon) and southeast OK will continue to drift east/southeast
over northeast TX and into AR/LA into this evening. Surface based
activity ahead of the front will encounter instability of 1500
J/kg per latest RAP mesoanalysis in a zone of low 70 degree
dewpoints. PWATs are on the order of 1.6-1.8" per 18Z GPS data,
which is 2 standard deviations above normal. Furthermore, a 100kt
SWly jet is nosing into south TX per 250mb and above derived
motion winds from GOES-16.

A favorable flash flood setup is developing over Northeast TX and
farther northeast into AR/LA with low level moisture convergence,
mid level flow parallel to the surface front, and increasingly the
left exit of the jet that will drift southeast over south TX per
12Z guidance consensus. Am in agreement with recent HRRR runs
highlighting this area with potential excessive rain despite near
or below normal rainfall in the past week for much of the threat
area.

Activity has remained progressive this afternoon across north TX
and since rain cooled air continues to win the battle at the
front, so the flash flood threat should be isolated going into
this evening with localized rain rates up to 2 in/hr.

Jackson

ATTN...WFO...EWX...FWD...HGX...LZK...SHV...TSA...

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

LAT...LON   35129400 33379298 30519561 30589863 32579700
            33959555