Prognostic Meteorological Discussion
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FXSA20 KWBC 231725
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
125 PM EDT TUE AUG 23 2016

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM AUG 23 AT 0000 UTC): FORECAST
CONFIDENCE CONTINUES HIGH THROUGH 120-132 HRS AS GLOBAL MODELS AND
ENSEMBLE MEMBERS AGREE QUITE WELL ON THE EVOLUTION.

A REGION OF INTEREST THROUGH THE CYCLE WILL BE THE COASTS OF BAHIA
AND SERGIPE. A COLD FRONT WILL BECOME STATIONARY AND LINGER IN THE
REGION THROUGH FRIDAY/EARLY SATURDAY. A SHEAR LINE WILL ALSO BE
PRESENT ON TUESDAY...TO THEN LOSE DEFINITION. MODELS AGREE ON
PRECIPITABLE WATER VARYING FROM 40 TO 50MM THROUGH THURSDAY...TO
THEN  START DECREASING. TRADE WIND SPEEDS OF 25-35KT AT 850 WILL
ENHANCE LOW-LEVEL MOISTURE CONVERGENCE TO TRIGGER MODERATE
RAINFALL AMOUNTS. EXPECTING ACCUMULATIONS OF 20-40MM/DAY THROUGH
EARLY FRIDAY. ACCUMULATIONS ARE TO DECREASE TO MAXIMA OF 15-20MM
ON FRIDAY-SATURDAY AND CONTINUE DECREASING AFTERWARDS.

ALSO IN NORTHERN SOUTH AMERICA...THE SOUTHERN TAIL OF A TROPICAL
WAVE IS PROPAGATING WESTWARD FROM 55-58W ON TUESDAY...TO 70-72W BY
FRIDAY. CONVECTION SI ENHANCED ALONG THIS TROUGH...AND WILL BE
FURTHER ENHANCED BY VENTILATION IN THE BASE OF A SOUTHERN
HEMISPHERE TROUGH THAT WILL RELOCATE FROM THE AMAZON DELTA/PARA IN
BRASIL ON TUESDAY...TO AMAZONAS-BRASIL ON FRIDAY. EXPECTING MAXIMA
OF 15-30MM/DAY IN THE THUNDERSTORMS THAT DEVELOP ALONG THIS TROUGH
AS THEY PROPAGATE WESTWARD ACROSS THE NORTHERN AMAZON BASIN. A
DECREASING TREND IN ACCUMULATIONS AND COVERAGE IS EXPECTED THROUGH
THE CYCLE.

A WEAK SUBTROPICAL MOISTURE CONNECTION IS UNDERWAY FOR SOUTHERN
CHILE. THIS CONNECTION WILL ARRIVE ON WEDNESDAY. MODELS ARE
SHOWING LARGEST HEIGHT FALLS FOR WEDNESDAY-EARLY THURSDAY. THIS
WILL LEAD TO SCATTERED SHOWERS ALONG SOUTHERN CHILE. BY
WEDNESDAY-EARLY THURSDAY THESE ARE TO PRODUCE ACCUMULATIONS OF
15-30MM/DAY BETWEEN LOS RIOS/LOS LAGOS AND THE AYSEN REGION.
ACCUMULATIONS WILL START DECREASING AFTER. STILL...DURING
THURSDAY...REMNANT ACTIVITY WILL LEAD TO MAXIMA OF 15-20MM/DAY IN
THE LOS LAGOS/AYSEN REGIONS AND MAXIMA OF 05-10MM/DAY TO THE NORTH
INTO BIO BIO. NOTE THAT ISOLATED LARGER AMOUNTS ARE EXPECTED ALONG
THE PRECORDILLERA. THE UPPER TROUGH ASSOCIATED WITH THIS EVENT IS
FORECAST TO AMPLIFY OFF THE COAST OF CHILE ON THURSDAY THROUGH
SATURDAY. THIS WILL LEAD TO HEIGHT FALLS ACROSS CENTRAL CHILE ON
FRIDAY...AND ACROSS CENTRAL/NORTHWESTERN ARGENTINA AND NORTHERN
CHILE ON SATURDAY. THIS PERSISTENT AND AMPLIFYING TROUGH WILL
ENHANCE UPPER DIVERGENCE OVER THE ANDES TO STIMULATE PRECIPITATION
IN THE CORDILLERA BY THE LATE FORECAST CYCLE. ALTHOUGH SNOWFALL
AMOUNTS ARE STILL UNCERTAIN AND LIKELY CONSERVATIVE...THE PATTERN
EVOLUTION SUGGESTS SCATTERED SNOW SHOWERS DEVELOPING IN THE
CORDILLERA OF ANTOFAGASTA/ATACAMA AND PARTS OF CENTRAL CHILE BY
SATURDAY. NOTE THAT THE AMPLIFICATION OF THE UPPER TROUGH WILL
ENHANCE THE SPEEDS OF AN UPPER JET OVER NORTHERN CHILE. THIS WILL
ENHANCE DE RISK FOR STRONG BOUNDARY LAYER WINDS IN THE NORTHERN
CORDILLERA AND IN SOUTHERN PARTS OF THE ALTIPLANO/NORTHWESTERN
ARGENTINEAN ANDES.

OTHER REGION OF INTEREST IS THE RIO DE LA PLATA BASIN BY LATE
CYCLE. AS THE AFOREMENTIONED UPPER TROUGH STARTS SHEARING CYCLONIC
VORTICITY INTO THE REGION...EXPECTING CYCLOGENESIS AND
FRONTOGENESIS TO DEVELOP BY FRIDAY. A LOW-LEVEL JET FROM BOLIVIA
WILL BE PRESENT STARTING ON WEDNESDAY. THIS WILL BUILD A MOISTURE
POOL OF 40+MM OF PRECIPITABLE WATER BY FRIDAY AND SATURDAY. MODELS
ARE ALL AGREEING ON A STRONG UPPER DIVERGENT PATTERN SETTING UP ON
SATURDAY AS THE DIVERGENT ENTRANCE OF AN UPPER JET SETS OVER THE
REGION. ALTHOUGH INSTABILITY WILL BE LIMITED...AS LIFTED INDEX
VALUES ONLY DIP TO NEAR -3...THE CONFIGURATION WILL BE CONDUCIVE
FOR LOCALLY HEAVY RAINS BETWEEN ENTRE RIOS AND URUGUAY. THE EVENT
WILL UNRAVEL LATE ON FRIDAY WHEN EXECTING ACCUMULATIONS OF
15-20MM/DAY IN THE FORM OF EVENING/NOCTURNAL THUNDERSTORMS.
AMOUNTS ARE TO INCREASE TO MAXIMA OF 30-60MM/DAY DURING
SATURDAY-SUNDAY.

OSORIO...DMC (CHILE)
CASTILLO...UCR (COSTA RICA)
ALVA...SENAMHI (PERU)
GALVEZ...WPC (USA)
$$





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