MESOSCALE PRECIPITATION DISCUSSION 0225
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
813 AM EDT SUN MAY 22 2016
 
AREAS AFFECTED...SERN TX...SW LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 221210Z - 221800Z
 
SUMMARY...RAINFALL RATES UP TO 2 IN/HR WITH SOME POTENTIAL
TRAINING/CELL REDEVELOPMENT MAY PRODUCE FLASH FLOODING.

DISCUSSION...OUTFLOW FROM EARLIER THUNDERSTORMS OVER SOUTHERN
LOUISIANA HAS PROPAGATED WESTWARD ALONG A STATIONARY SURFACE FRONT
AND IS NOW AIDING IN THUNDERSTORM DEVELOPMENT OVER EXTREME SERN
TX. AN IMPRESSIVELY MOIST AND UNSTABLE AIR MASS IS IN PLACE IN THE
INFLOW AIR JUST SOUTH OF THE FRONT, WITH SURFACE DEW POINTS NEAR
80 DEG F, AND MLCAPE AROUND 2000 J/KG PER LATEST SPC MESOANALYSIS.
ADDITIONALLY, PWAT VALUES ARE GREATER THAN 2" ALONG A LOW-LEVEL
CONVERGENCE AXIS EXTENDING NORTH INTO COASTAL SOUTHEASTERN TX.
EVACUATION OF AIR ALOFT DOES NOT APPEAR TO BE A PROBLEM GIVEN
UPPER-LEVEL SPEED DIVERGENCE NOTED ACROSS THE REGION ASSOCIATED
WITH A JET STREAK FROM LA EAST INTO THE FL PANHANDLE. SIMULATED
SOUNDINGS FROM THE RAP INDICATE THE POTENTIAL FOR VERY HIGH PRECIP
EFFICIENCY WITH AN IMPRESSIVE 4-5 KM WARM CLOUD LAYER DEPTH. GIVEN
THESE FACTORS, WOULD EXPECT THE POTENTIAL FOR 2 IN/HR (IF NOT
LOCALLY HIGHER) RAINFALL RATES, WHICH SEEMS TO BE SUPPORTED BY
LATEST HOURLY PRECIP ESTIMATES FROM RADAR. INDIVIDUAL CELL
MOVEMENT APPEARS TO BE SLOWLY SOUTHEASTWARD AT ABOUT 10 KT, BUT
REDEVELOPMENT OF NEW CELLS AS THE WESTWARD MOVING OUTFLOW
INTERSECTS THE SOUTHERLY LOW-LEVEL INFLOW IS RESULTING IN
REDEVELOPMENT OF CELLS OVER THE SAME AREAS AND SOME CELL TRAINING. 

MOST HI-RES CAM DO NOT APPEAR TO HAVE A GOOD HANDLE ON THE
CONVECTION, WITH ONLY THE HRRR AND HRRR-EXPERIMENTAL SHOWING SOME
SEMBLANCE OF THE CURRENT ACTIVITY (ALTHOUGH BOTH OF THESE APPEAR
UNDERDONE). THE HRRR-EXP SHOWS THE ACTIVITY PROPAGATING SLOWLY
WESTWARD ALONG THE FRONT THROUGH 18Z. GIVEN THE RELATIVE LACK OF
MOVEMENT IN THE BEST LOW-LEVEL INFLOW/CONVERGENCE AXIS, THE DEGREE
OF WESTWARD PROPAGATION APPEARS UNCERTAIN AT THIS TIME. THE
AFOREMENTIONED FAVORABLE FACTORS FOR MAINTENANCE OF CONVECTION ARE
FORECAST TO PERSIST THROUGH MIDDAY PER THE RAP. THE RAP EVEN
INDICATES THE POTENTIAL FOR AN AREA OF LOW PRESSURE TO DEVELOP
NEAR THE HOUSTON AREA ALONG THE FRONT, WHICH WOULD SLOW THE
WESTWARD PROGRESSION OF CONVECTION IF THAT OCCURRED. GIVEN AREAS
OF LOCALLY REDUCED FLASH FLOOD GUIDANCE ACROSS MUCH OF THE
OUTLINED AREA, FLASH FLOODING WOULD BE POSSIBLE IF THESE HIGHER
RAINFALL RATES WERE ABLE TO MATERIALIZE OVER THOSE LOCATIONS.


RYAN

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

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

LAT...LON   30439439 30319376 29789322 29679375 29649392 
            29309464 28869532 28739589 29229614 29899576 
            30229527 30379488