Post by Briella - Houma on Jun 29, 2017 5:26:36 GMT -6
MESOSCALE PRECIPITATION DISCUSSION 0409
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
724 AM EDT THU JUN 29 2017
AREAS AFFECTED...COASTAL TX...SOUTHWEST LA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 291125Z - 291630Z
SUMMARY...SLOW MOVING CONVECTION WITH UPSTREAM/BACKBUILDING
PROPAGATION VECTORS AND AMPLE MOISTURE FOR RATES OVER 2.5"/HR POSE
LIKELY FLASH FLOOD THREAT OVER NE COASTAL TX INTO SW/SOUTH CENTRAL
LA THIS MORNING.
DISCUSSION...MID-LEVEL STACKED ELONGATED TROF LIES COINCIDENT WITH
THE CENTRAL AND EASTERN TX COAST TOWARD APEX OF THE TROF/POSSIBLE
CLOSED CIRCULATION NEAR 7-5H LOW JUST NORTH OF LCH. STRONG SLY
ONSHORE SURFACE FLOW (20+KTS) AIDED BY FRICTIONAL CONVERGENCE HAS
SPARKED A LINE OF CONVECTION THAT CONTINUES TO COOL WITH
PURCOLLATING OVERSHOOTING TOPS NOTED IN EIR OF GOES-16 10.3 UM IR
WINDOW. VEERING TO SWLY FLOW AT THE BOUNDARY LAYER/WEAK INVERSION
NEAR 850MB PARALLEL TO THE TX COASTLINE SUPPORTS SOLID INFLOW/MUST
FLUX TO CELL AND WITH HIGHLY ELONGATED TROF THAT IS STACKED...CELL
MOTIONS ARE NEAR ZERO SUPPORTING C-VECTORS WITH SW PROPAGATION
FAIRLY PARALLEL TO THE CONVERGENCE BAND. THIS SHOULD SUPPORT
REPEAT/BACKBUILDING CYCLING CONVECTION CAPABLE OF SHORT BURSTS OF
HEAVY RAINFALL. AVAILABLE MOISTURE THROUGH THE UPDRAFT DEPTH
SUPPORTS TPWS AOA 2.0" AND WITH FLUX MAY REACH RATES OF 2.5"/HR OR
GREATER. THIS IS THE CASE OF STATIONARY CELL LOCATED CALCASIEU
PARISH WHICH WOULD HAVE THE LEAST STEERING FLOW GIVEN PROXIMITY TO
THE APEX/CENTER OF THE TROF. WITH THE BACKBUILDING AND SLIGHT
NORTHEASTWARD DRIFT THERE SHOULD BE ADDITIONAL BOUTS OF HEAVY
RAINFALL IN THE VICINITY AND IT IS HIGHLY PLAUSIBLE FOR EXTREME
RAINFALL TOTALS PARTICLULARLY OVER SW LA TO COMPILE WITH 4-6"
TOTALS OVER THE NEXT FEW HOURS AS SUPPORTED BY THE TRENDS IN THE
RAP/HRRR/HRRRV3. STILL THE THREAT FOR FLOODING RAINS EXTENDS FROM
THE CENTRAL TX COAST THROUGH THE LENGTH OF THE TROF AND FLASH
FLOODING IS CONSIDERED LIKELY THROUGH THE EARLY MORNING.
