MESOSCALE PRECIPITATION DISCUSSION 0943
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
356 PM EST TUE DEC 19 2017

AREAS AFFECTED...NORTHEAST TX...SOUTHERN AR...NORTHERN LA...CENT
WESTERN MS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 192100Z - 200300Z

SUMMARY...INGREDIENTS FOR BACKBUILDING AND TRAINING EFFICIENT
RAINFALL PRODUCING CONVECTION SUPPORT ISOLATED FLASH FLOODING
THREAT THIS EVENING/EARLY OVERNIGHT.

DISCUSSION...GOES-16 AIRMASS RGB DEPICTS A SIGNIFICANT +PV ANOMALY
WITH BRIGHT PINKS/REDS WITH UPPER LOW ACROSS THE TWO TX
PANHANDLES.  THE STRONGER BASE VORT CENTER IS PRIMING TO SWING OUT
ACROSS CENTRAL TX PROVIDING AMPLE DPVA TO ACCOMPANY AND STRENGTHEN
ALREADY IMPRESSIVE DIFFLUENT/DIVERGENT FLOW ACROSS NE TX SPILLING
INTO AR/FAR N LA.  THE STRONG DPVA WILL BE THE SPARK TO REACTIVATE
CONVECTION AT OR JUST AFTER 00Z ALONG A N-S FRONTAL BOUNDARY
SEPARATING WESTERN GULF MT AIR DEPICTED BY SFC TDS IN THE LOW 70S
FROM MODIFIED AIR TO THE WEST THAT IS A COMBINATION OF SOME MIXING
OF TROPICAL CONNECTION ACROSS MEXICO IN THE 850-700H AND RESIDUAL
MODIFIED CP AIR AHEAD OF MAIN DRY PUNCH FROM THE EML OFF THE
MEXICAN PLATEAU (GENERALLY WEST OF UL CIRRUS STREAK SEEN IN
3-CHANNEL WV SUITE) AND COLD CONTINENTAL AIR MIXING OUT OF THE
CENTRAL ROCKIES LATER (AS THE SFC CYCLONE RAPIDLY DEVELOPS LATER
TONIGHT).  GIVEN THE CELLS WILL BE ON THE WESTERN EDGE OF THE
DEEPER MOISTURE AND ALLOW FOR CONTINUED RAINFALL EFFICIENCY OF
1.5-2"/HR.

THIS ALONE WOULD NOT LIKELY BE SUFFICIENT FOR FLOODING CONCERNS
EXCEPT IN MOST PRONE/URBAN SETTINGS DUE TO INITIAL
DOWNPOURS...HOWEVER THIS IS IN COMBINATION WITH ONGOING SHOWERS
WITH EMBEDDED CONVECTIVE ELEMENTS ALONG AND NORTH OF THE WARM
FRONT THAT EXTENDS ACROSS NE TX AND ALONG THE AR/LA BORDER. 
SOUTHERLY FLOW CONTINUES WITHIN THE WARM SECTOR OF SE TX/LA AND IS
LIFTING ISENTROPICALLY ALONG THE FRONT...AIDED BY THE 3H SHORTWAVE
RIDGING FEEDING INTO THE 110KT RIGHT ENTRANCE ACROSS AR/E OK HAS
SPARKED A FEW ISOLATED DEEPER CELLS TO -65C WITH OCCASIONAL
LIGHTNING STRIKES...CLOUD BARING FLOW IS SLIGHTLY OFF ANGLE TO THE
NORTH OF THE FRONT TO LIMIT MOST IDEAL TRAINING BUT GIVEN UPSTREAM
HEIGHT FALLS...THE POTENTIAL FOR ADDITIONAL UPSTREAM REDEVELOPMENT
IS LIKELY TO PRODUCE A BROAD AREA OF 1-2" WITH A FEW EMBEDDED
STREAKS OF 2-3" POSSIBLE IN THE NEXT 3-4 HOURS MAINLY FROM CRS TO
TYR/TO N OF SHV.

HI-RES GUIDANCE SUCH AS THE 12Z ARW AND RECENT HRRR RUNS DEPICT
BEST AGREEMENT OF THE AXIS AND SUGGEST SOME SPOTS MAY EXCEED 3 TO
6HR FFG VALUES AND AS SUCH FF IS CONSIDERED POSSIBLE. 

GALLINA

ATTN...WFO...FWD...JAN...LZK...MEG...SHV...

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

LAT...LON   34259230 34229102 32909070 32789166 32529341
            31909516 31569658 32429664 33799397