Post by SKYSUMMIT on Apr 2, 2017 21:36:37 GMT -6
MESOSCALE PRECIPITATION DISCUSSION 0095
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 PM EDT SUN APR 02 2017
AREAS AFFECTED...SOUTHERN LA...SOUTHERN/CENTRAL MS...EXT WEST
CENTRAL AL
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 030329Z - 030929Z
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).
GALLINA
