MESOSCALE PRECIPITATION DISCUSSION 0031
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 PM EST FRI JAN 20 2017
 
AREAS AFFECTED...SOUTHERN LA...EXT SOUTHEAST TX...EXT SOUTHWEST MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 210200Z - 210800Z
 
SUMMARY...DEVELOPING COMPLEX MAY EXPAND DOWNSTREAM TO ALLOW
TRAINING OF CONVECTION ALONG THE WARM FRONT INTO LA THROUGH LATE
EVENING/EARLY MORNING HOURS. 

DISCUSSION...WV LOOP SHOWS APEX OF ANTI-CYCLONIC JET STREAK
EXITING NORTHERN LA ATTM WITH A WEAK VORTICITY TWIST IN THE
MID-LEVEL CROSSING OUT OF THE HILL COUNTY OF TX.  THIS HAS DUALLY
SUPPORTED AMPLE DPVA AS WELL AS RIGHT JET ENTRANCE ASCENT FORCING
FOR A SMALL AREA OF STRONG DYNAMIC ASCENT.  THIS HAS SPURRED
SURFACE PRESSURE FALLS OVER SE TX AND STRENGTHENED SURFACE FLOW
AND BROAD CONVERGENCE THAT IS ISALLOBARICALLY ENHANCED PROVIDING
STRONG MST FLUX AND THE CAPABILITY FOR STRONG AND LARGE UPDRAFT
CORES.  FLUX OF SFC TDS AROUND 70 OFF THE GULF ALONG SUPPORTS RAIN
RATES OVER 2"/HR.  AS THE CONVECTION SE OF THE HOUSTON METROPLEX
IS EXPANDING THE OUTFLOW FROM THE FORWARD FLANK DOWNDRAFTS HAS
SHARPENED THE FRONTAL ZONE ALONG THE COAST AND EXPANDED NEW
CONVECTIVE DEVELOPMENT DOWN STREAM...ORIENTED IDEALLY GIVEN THE
CURRENT STEERING FLOW PARALLEL TO THE COAST AND DIRECTED TOWARD
THE I-10 CORRIDOR IN W LA THEN THE SW POINT OF MS WITH TIME.  WITH
RATES OF 2"/HR AND THE TRAINING IT IS NOT OUT OF THE REALM OF
POSSIBILITY FOR TOTALS OF 4-5" OVER THE NEXT 3 HOURS ACROSS SE TX
INTO SW LA.

AS TIME PROGRESSES AND THE SURFACE LOW CONTINUES TO DEEPEN...THE
WARM FRONT ALONG THE LA COAST SHOULD LIFT NORTH AND CONTINUE TO
ACT AS MST CONVERGENCE FOCUS FOR CONTINUED DEVELOPMENT AS THE
UPPER LOW AND RIGHT ENTRANCE REGION TO THE 130 KT JET EXITS INTO
THE TN VALLEY REGION.  THE POTENTIAL POSITIVE IS THAT INCREASED
INSTABILITY IN THE WARM SECTOR OVER THE GULF MAY FOCUS NEW
DEVELOPMENT OFF/ALONG SHORE...POTENTIALLY ROBBING THE BEST MST
FLUX/CONVERGENCE ALONG THE FRONT NORTH OF I-10 AND REDUCING THE
THREAT FOR TRAINING/FLASH FLOODING THERE.  THE CONVECTION ACROSS
THE GULF WOULD BE A BIT MORE SCATTERED AND LESS IDEALLY ALIGNED
FOR TRAINING AS THE OVERALL WAVE CONTINUES TO PROGRESS EAST
ADDITIONALLY AFFECTING AREAS NEARER THE COAST WITH THE ABILITY TO
RETAIN RAINFALL/RATES OF THESE MAGNITUDES (IE HIGHER FFG VALUES). 
 HI-RES CAMS SPLIT THESE SETUPS WITH THE
NSSL-WRF/WRF-NMMB/HRRR-EXP SUGGESTING THE INITIAL TRAINING SETUP
AND THE HRRR/ARW SUGGESTING OFFSHORE DEVELOPMENT.  THIS DOES NOT
PROVIDE CONFIDENCE IN ONE CAMP OVER THE OTHER...BUT CURRENT TRENDS
IN IR/WV WOULD SUGGEST THE NSSL-WRF AND MORE WORSE CASE SCENARIO
MAY UNFOLD.  STILL WITH CONFIDENCE BEING LOWER...CONDITIONS ONLY
SUGGEST FLASH FLOODING MAY BE POSSIBLE NOT LIKELY AT THIS TIME.  

GALLINA

ATTN...WFO...HGX...JAN...LCH...LIX...

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

LAT...LON   31299147 30459104 29519174 29669308 29659394 
            29579440 29799474 30369466 31119311