Latest from the WPC:
SUMMARY…FLASH FLOODING THREAT IS RATCHETING DOWN A NOTCH FROM EXTREME LEVELS AS FOCUS OF HVY RAIN SHIFTS SOUTHWARD. STILL HVY RAINFALL AND FLASH FLOODING REMAINS LIKELY THROUGH THE EARLY NIGHTTIME HOURS.
DISCUSSION…LARGE SCALE PATTERN AND LINEAR MCS WITH TRAINING CONVECTION ACROSS CENTRAL LA INTO CENTRAL MS HAS BEGUN TO SHOW SIGNS OF WEAKENING AND COLD POOL GENERATION ALLOWING FOR SOUTHWARD SHIFT OF CONTINUED HEAVY RAINFALL THREAT. ADDITIONAL SUPPORT FOR THIS SOUTHWARD SHIFT RESIDES WITH VERY POTENT/COMPACT S/W FEATURE ADVANCING UNDER THE MEAN LARGE SCALE UPPER LOW CROSSING S TX ATTM
PROVIDING HEIGHT FALLS AND EXPANDING BETTER AXIS OF UPPER LEVEL DPVA/JET DIVERGENCE SOUTH. AS SUCH THE RESPONSE IN THE LOWER LEVELS AROUND THE BOUNDARY LAYER IS FOR INCREASED ASCENT WITHIN
BROAD ZONE OF DUE SOUTHERLY FLOW THAT EXPANDS FROM SW LA ALONG THE CENTRAL GULF COAST TO COASTAL MS. IN RESPONSE BANDED FEEDER LINES ARE CONVECTING GIVEN MODEST LOCALIZED CONVERGENCE AS WELL AS SOME MASS PILING ALONG THE COASTAL FRICTIONAL BOUNDARY PER RECENT RAP ANALYSIS SFC CONVERGENCE MAXIMA NEAR/ALONG COAST. THESE FEEDERS WITH SUPPORTED UPSTREAM HEIGHT ARE MERGING/ASCENDING OVER THE SOUTHWARD ADVANCING OUTFLOW BOUNDARY…INCREASING CONVECTIVE COVERAGE…MST FLUX AND RAINFALL RATES. CURRENTLY THE SPACING OF BANDS ARE FAIRLY WIDELY SPACED BUT EXPECTATION TOWARD 07-09Z IS A SQUEEZING OF THIS SPACING LIKELY AROUND CENTRAL TO SE LA/SW MS PROVIDING A NARROW N-S ORIENTED AREA OF MAXIMIZED RAINFALL LATER THIS EVENING AS WELL. RAIN RATES OF 1.5-2″/HR ARE LIKELY BUT WITH FORWARD ADVANCEMENT TOTALS OF 3-5″ ARE POSSIBLE ACROSS S CENTRAL LA AND S MS. HI-RES CAMS HAVE BEEN GENERALLY SLOW AND NORTH OF THIS TRANSITION TOWARD A FASTER COLD POOL GENERATION AND ARE LAGGING A BIT. THOUGH BEST GUIDANCE REMAINS NEAR THE HRRR AND 12Z NSSL-WRF OR SPC-WRF.OF ADDITIONAL CONCERN…IS THE SOUTHWARD ADVANCEMENT OF THE CONVECTION AS WELL AS THE TIMING OF THE BACK EDGE/UPSTREAM WEDGE OF THE MCS IN IR IS LIKELY TO CROSS OVER SATURATED AREAS AFFECTED FROM FLOODING RAINS A FEW DAYS AGO ALONG AND NORTH OF I-10 FROM LCH TO SW MS INCREASING THE LIKELIHOOD OF FF THERE AS WELL.
FURTHER EAST…MESO ANALYSIS AND RAP/HRRR INSTABILITY BELOW 1000 J/KG OF MUCAPE APPEARS TO BE A GOOD PROXY FOR THE EASTWARD LIMIT OF HVY RAINFALL CAPABLE OF FLASH FLOODING AS THIS SHOULD GENERALLY MATCH WELL JUST INSIDE THE CENTRAL AL/MS BORDER…MAINLY FOCUSED TOWARD SOME REPEAT TRACKS OF REMAINING EMBEDDED STRONGER MESOCYCLONE UPDRAFTS POSING A LOCALIZED FLOODING CONCERN ACROSS
THE CENTRAL WESTERN BORDER (PICKENS/SUMTER/GREENE COUNTIES).
