Daily General Weather Discussion Thread #19

MESOSCALE PRECIPITATION DISCUSSION 0250
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 PM EDT FRI MAY 27 2016

AREAS AFFECTED...SOUTHEAST TX...WESTERN/CENTRAL LA

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

VALID 272025Z - 280025Z

SUMMARY...SLOW-MOVING AND HEAVY SHOWERS AND THUNDERSTORMS WILL
SETTLE GRADUALLY SOUTHEAST THROUGH THE LATE-AFTERNOON AND EVENING
HOURS TOWARD THE WESTERN GULF COAST. FLASH FLOODING IS LIKELY AS
THIS ACTIVITY MOVES THROUGH.

DISCUSSION...AN ELONGATED AND VERY COLD-TOPPED MCS IS GRADUALLY
SETTLING SOUTHEAST AND WILL BE REACHING THE MIDDLE AND UPPER TX
COAST OVER THE NEXT COUPLE OF HOURS WHILE ALSO EXTENDING EAST
ACROSS WESTERN AND CENTRAL LA.

RAINFALL RATES WITHIN THIS STRONG BAND OF CONVECTION HAVE ALREADY
BEEN EXCEEDING 2 INCHES/HR...AND THESE RATES ARE EXPECTED TO
CONTINUE OVER THE NEXT FEW HOURS AS AREA VWPS SHOW A DEEP FEED OF
VERY MOIST AND UNSTABLE AIR LIFTING NORTH FROM THE WESTERN GULF OF
MEXICO AND FOCUSING ESPECIALLY ACROSS THE IMMEDIATE SOUTHEAST TX
COASTAL PLAIN.

RAP ANALYSES ARE SHOWING MLCAPE VALUES OF 2000 TO 3000 J/KG ALONG
THE UPPER TX COAST...AND EVEN GREATER VALUES FARTHER SOUTHWEST
BETWEEN HOUSTON AND VICTORIA. INSTABILITY PARAMETERS ARE A BIT
WEAKER ACROSS CENTRAL AND WESTERN LA AND CLOSER TO 1500 J/KG.
GPS-DERIVED PWATS ARE NEAR 2 INCHES ACROSS THE SOUTHEAST TX
COASTAL PLAIN WITH SOMEWHAT LOWER NUMBERS OVER LA. THUS
OVERALL...A HIGHLY FAVORABLE THERMODYNAMIC ENVIRONMENT FOR
SUSTAINABLE CONVECTION AND VERY HIGH RAINFALL RATES.

THE LAST FEW HRRR RUNS HAVE BEEN APPEARING A TAD SLOW TO ADVANCE
THE CONVECTION SOUTHEAST TOWARD THE GULF COAST...WHICH APPEARS TO
BE RELATED TO A MISHANDLING OF THE STRENGTH OF THE MCS COLD POOL.
NEVERTHELESS...THE GUIDANCE HAS BEEN INSISTING OF VERY HEAVY
RAINFALL TOTALS....AND ADDITIONAL RAINFALL AMOUNTS THROUGH 00Z ARE
EXPECTED TO BE ON THE ORDER OF 3 TO 6 INCHES. SOME OF THE AREAS
WITHIN THE THE MPD THREAT AREA HAVE SEEN HEAVY RAINS
RECENTLY...AND SO THESE ADDITIONAL RAINS ARE LIKELY TO CAUSE FLASH
FLOODING...AND THE MORE URBANIZED AREAS INVOLVING THE HOUSTON
METROPOLITAN AREA SHOULD BE ON ALERT FOR LOCALLY SIGNIFICANT URBAN
FLOODING CONCERNS. WILL CONTINUE TO MONITOR.

ORRISON

HRRR doesn't do much with it. This is for about midnight.

Odd, my viewer was showing it still trekking across the Lafayette area at midnight on HRRR.

Bayou Country Superfest will be getting wet....

Didn't get a chance to take a photo but the cell due south of New Orleans had a pretty spectacular structure from my vantage point for a while. Looks past its prime at this point visually.

from Bayou Blue:

The next "decent" shot of rain is looking like this coming Friday, but even that's up in the air right now.