Post by SKYSUMMIT on Aug 19, 2015 6:22:16 GMT -6
MESOSCALE PRECIPITATION DISCUSSION 0457
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
653 AM EDT WED AUG 19 2015
AREAS AFFECTED...CENTRAL/SOUTHERN LA & VICINITY
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 191053Z - 191623Z
SUMMARY...AN EXPANDING AREA OF THUNDERSTORMS IS MOVING ASHORE
SOUTHERN LA. WITH HOURLY RAIN RATES UP TO 2.5" ANTICIPATED, FLASH
FLOODING IS POSSIBLE.
DISCUSSION...PER COORDINATION WITH THE WPC INTERNATIONAL DESKS, A
SEGMENT OF A TROPICAL WAVE WHICH SPAWNED CONVECTION IN THE
SOUTHWEST GULF OF MEXICO THIS TIME YESTERDAY LEFT BEHIND A
VORTICITY MAXIMUM WHICH IS MOVING TOWARDS THE LA COAST ON THE EAST
SIDE OF AN UPPER LOW. AN EFFECTIVE SURFACE BOUNDARY LIES JUST
INLAND OF THE GULF COAST, SEPARATING AN AIRMASS WITH MID 80S
TEMPERATURES WITH A COOLER AIRMASS IN THE MID TO UPPER 70S INLAND.
THIS CAUSED A CONVECTIVE BLOWUP AT 08Z IN THE NORTHWEST GULF OF
MEXICO JUST TO ITS NORTHWEST, WHICH CONTINUES TO EXPAND AT THIS
HOUR. PRECIPITABLE WATER VALUES OF 2-2.25" ARE REPORTED BY GPS
WITHIN A REGION OF 25-30 KTS OF INFLOW AT 850 HPA. MUCAPES ARE
3000 J/KG NEAR THE COAST PER THE SPC MESOANALYSIS.
THE EXPECTATION IS FOR THE STORMS TO CONTINUE MOVING NORTHEAST AT
25-30 KTS. ORGANIZED ACTIVITY MAY ATTEMPT TO MOVE MORE
EAST-NORTHEASTWARD, PARALLEL TO 1000-850 HPA THICKNESS LINES. THE
MESOSCALE GUIDANCE HAS A SIGNAL FOR THIS ACTIVITY, WITH THE MORE
RECENT HRRR RUN INDICATING LOCAL AMOUNTS OF 5"+ NEAR THE COAST OF
CAMERON PARISH. THE 06Z SSEO NEIGHBORHOOD PROBABILITIES SUGGEST
THE EVENT PEAKS IN THE 14-16Z PERIOD, WITH HEAVY RAINFALL POSSIBLE
AS FAR NORTH AS CENTRAL LA. AFTER 14Z, INFLOW AT 850 HPA WEAKENS
ACROSS LA, WHICH SHOULD LEAD TO HEAVY RAIN ISSUES DECREASING FROM
EAST TO WEST AFTER THIS TIME. CONSIDERING HOURLY RAIN RATES UP TO
2.5" ARE POSSIBLE, HEAVY RAINS COULD FALL QUICKLY. CELL TRAINING
APPEARS TO BE THE MAIN ISSUE. RECENT RAINS HAVE BROUGHT DOWN
FLASH FLOOD GUIDANCE VALUES, THOUGH A DECENT PORTION OF THIS
REGION IS COMPOSED OF SWAMPLAND. THIS LED TO THE CHOOSING OF THE
POSSIBLE CATEGORY OVER THE LIKELY CATEGORY.
ROTH
