MESOSCALE PRECIPITATION DISCUSSION 0322
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
625 PM EDT MON JUN 18 2018

AREAS AFFECTED...SOUTHEAST TX...SOUTHWEST LA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 182225Z - 190425Z

SUMMARY...EXTREMELY HEAVY RAINFALL CAN BE EXPECTED THROUGH THE
EVENING HOURS. RAINFALL RATES OF AS HIGH AS 3 INCHES/HR FALLING ON
TOP OF EARLIER HEAVY RAINS WILL RESULT IN FLASH FLOODING WHICH MAY
BE SIGNIFICANT.

DISCUSSION...AN IMPRESSIVE CONVECTIVE BAND WITH VERY HEAVY
RAINFALL RATES CONTINUES TO IMPACT THE FAR UPPER TX COAST NEAR THE
BEAUMONT/PORT-ARTHUR AREA ALONG WITH ADJACENT AREAS OF EXTREME
SOUTHWEST LA TO TO THE SOUTHWEST OF LAKE CHARLES. ALREADY AS MUCH
AS 3 TO 5 INCHES OF RAIN HAS BEEN REPORTED...AND THE LATEST RADAR
IMAGERY SHOWS ADDITIONAL BANDS OF CONVECTION OFFSHORE OVER THE
NORTHWEST GULF OF MEXICO THAT IS ADVANCING OFF TO THE NORTHWEST.

THE GOES-16 10.3 MICRON/IR SATELLITE IMAGERY SHOWS A PERSISTENCE
OF COLD CONVECTIVE TOPS WITH THIS ACTIVITY WHICH IS ALL FOCUSED
AROUND THE NORTHEAST FLANK OF A BROAD MID LEVEL AREA OF LOW
PRESSURE ALONG THE SOUTH-CENTRAL TX COAST WHICH IS MOVING VERY
SLOWLY WEST. THE CONVECTION THOUGH IS BEING STRONGLY AIDED BY THE
PRESENCE OF A LOW LEVEL TROUGH ALONG THE IMMEDIATE GULF COAST AND
THE STRONGLY CONFLUENT FLOW INTO THIS LOW LEVEL TROUGH COUPLED
WITH THE NOSE OF 1000 TO 2000 J/KG OF MLCAPE IS SUSTAINING THE
CONVECTIVE DEVELOPMENT.

THE DEEP LAYER CYCLONIC FLOW OVER THE REGION MEANWHILE IS
TRANSPORTING A DEEP COLUMN OF TROPICAL MOISTURE ACROSS MUCH OF THE
WESTERN GULF COAST REGION. IN FACT...THE PWATS THIS AFTERNOON HAVE
BEEN IMPRESSIVELY HIGH...AND RANGING GENERALLY BETWEEN 2.3 AND 2.5
INCHES BASED ON HOURLY GPS-DERIVED DATA AND AN 18Z RAOB FROM KCRP.

HIGHLY EFFICIENT RAINFALL PROCESSES ARE IN PLACE GIVEN THE
CONCENTRATION OF MOISTURE SEEN IN THE 500/300 MB LAYER AS PER THE
LATEST CIRA-LPW DATA AT 21Z. THIS COUPLED WITH THE VERY COLD
CONVECTIVE TOPS WILL CONTRIBUTE TO VERY HIGH RAINFALL RATES THAT
MAY APPROACH OR EXCEED 3 INCHES/HR.

THE LATEST HRRR/HRRRX GUIDANCE FROM 21Z SUPPORTS A SUSTAINABLE
CONVECTIVE BAND THROUGH MID-EVENING WITH ADDITIONAL RAINFALL
AMOUNTS OF 4 TO 8 INCHES POSSIBLE. FLASH FLOODING IS LIKELY...WITH
SIGNIFICANT RUNOFF PROBLEMS ANTICIPATED. THIS WILL ESPECIALLY BE
THE CASE IN AND AROUND THE BEAUMONT/PORT-ARTHUR AREA.

ORRISON

ATTN...WFO...HGX...LCH...

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

LAT...LON   30619434 30549384 30129315 29809285 29669290
            29679334 29669346 29529424 29259478 29279513
            29659538 30209527 30499486