MESOSCALE PRECIPITATION DISCUSSION 0335
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
807 AM EDT WED JUN 20 2018

AREAS AFFECTED......SOUTH TEXAS AND THE RIO GRANDE VALLEY INTO THE
LOWER-MIDDLE TEXAS COAST...

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

VALID 201207Z - 201607Z

SUMMARY...A PIVOTING BAND OF HEAVY RAINFALL WILL PERSISTENT AND
EXACERBATE THE FLASH FLOOD THREAT THROUGH THIS MORNING,
PARTICULARLY FROM THE RIO GRANDE VALLEY UP THROUGH THE LOWER AND
MIDDLE TEXAS COAST.

DISCUSSION...THE LATEST COMPOSITE RADAR LOOPS ARE INDICATING A
PERSISTENT RAINFALL AXIS ON THE EASTERN FLANK OF A LOW-MID LEVEL
LOW...EXTENDING ACROSS THE RGV UP INTO THE MIDDLE TEXAS COAST. THE
LATEST SPC MESOANALYSIS INDICATES 925-850 MB SSE INFLOW BETWEEN
35-45 KTS JUST OFF THE COAST, ALONG AN INSTABILITY GRADIENT WITH
MUCAPES 1000-2000+ J/KG. THE LOW-MID LEVEL FLOW CONTINUES TO
MAINTAIN A DEEP SUBTROPICAL MOISTURE PROFILE...HIGHLY EFFICIENT
FOR WARM RAIN PROCESSES AND PRECIPITATION EFFICIENCY. PW VALUES
BETWEEN 2.5-2.75+" CONTINUE TO BE OBSERVED IN THE MPD AREA, WHICH
IS ABOUT 3.5 STANDARD DEVIATIONS ABOVE NORMAL FOR MID-LATE JUNE
(NEAR RECORD VALUES).

THE THERMODYNAMIC ENVIRONMENT -- AVAILABLE DEEP-LAYER CAPE
(TALL/SKINNY DISTRIBUTION) ALONG WITH THE OPTIMAL MOISTURE PROFILE
-- WILL CONTINUE TO FAVOR ROBUST SHORT-TERM RAINFALL RATES --
EASILY REACHING IF NOT EXCEEDING 2.5-3.0"/HOUR. THE MODELS DO SHOW
SOME RELAXATION IN THE ELEVATED LOW-LEVEL FLOW AS THE MORNING
PROGRESSES, WHICH CERTAINLY COULD DISRUPT THE EXTENT AND
ESPECIALLY THE INTENSITY OF THE ELONGATED RAINFALL BANDS THAT
PIVOT ACROSS THE MPD AREA.

WHILE CONTINUING TO NOTE SOME AREAL SPREAD WITH THE MAX RAINFALL
THROUGH THE REMAINDER OF THE MORNING, THE HIGH-RES CAM GUIDANCE DO
INDICATE ADDITIONAL RAINFALL TOTALS OF 3-5" WITH LOCALIZED TOTALS
OF 7+ THROUGH 16Z ASSOCIATED WITH THESE RAINFALL BANDS FROM THE
RGV THROUGH THE LOWER AND MIDDLE TEXAS COAST...INCLUDING
BROWNSVILLE AND CORPUS CHRISTI. GIVEN THE ANTECEDENT SOILS WITH
THE RECENT HEAVY RAINFALL, THESE AMOUNTS WOULD LEAD TO ADDITIONAL
AREAS OF FLASH FLOODING, ESPECIALLY IN AND NEAR THE BROWNSVILLE
AND CORPUS CHRISTI AREAS CONSIDERING THE LOW FLASH FLOOD GUIDANCE
VALUES.

HURLEY

ATTN...WFO...BRO...CRP...EWX...HGX...

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

LAT...LON   29059668 28729634 28169624 27339716 26259701
            25679699 25669756 25829833 26279903 26619928
            27469857 28379799 28989743