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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1746Z Dec 07, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1246 PM EST THU DEC 07 2017

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

MODEL DISCUSSION (VALID FROM DEC 07 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS CONTINUE IMPROVING THEIR AGREEMENT ON
FORECAST EVOLUTION. THEY CONVERGE BETTER UP TO 120-132 HRS...AS
THEY SHOW A STRONG AND LARGE UPPER RIDGE MEANDERING FROM THE
PACIFIC INTO THE SOUTHERN CONE. THIS WILL LEAD TO STRONG 50-70KT
WINDS IN TIERRA DEL FUEGO ON SUNDAY.

A WEAK UPPER TROUGH LINGERS OFF THE COAST OF CENTRAL CHILE. MODELS
ARE CONFIDENT ABOUT THIS SOUTH SHEARING A SHORT WAVE AXIS ACROSS
THE ANDES DURING THURSDAY AND FRIDAY. THIS WILL INITIALLY
STIMULATE CONVECTION ACROSS INTERIOR PORTIONS OF CENTRAL
ARGENTINA...YET...UNDER LIMITED DEE-PAYER MOISTURE EXPECTING
MAXIMA GENERALLY UNDER 5MM/DAY ON THURSDAY. YET...A BETTER
ORGANIZED SHORT WAVE WILL STIMULATE CONVECTION ACROSS ROSARIO/RIO
DE LA PLATA/EASTERN PROVINCIA DE BUENOS AIRES ON FRIDAY
EVENING...WHEN A FEW THUNDERSTORMS WILL HAVE THE POTENTIAL OF
PRODUCING ACCUMULATIONS OF 15-25MM/DAY. QUIET PATTERN WILL THEN
ESTABLISH AS AN UPPER LEVEL RIDGE ESTABLISHES OVER THE REGION.

ALSO IN THE SOUTHERN CONE...MODELS HAVE GAINED CONFIDENCE ON THE
ESTABLISHMENT OF A ROBUST MID/UPPER RIDGE OVER THE EASTERN
PACIFIC. AS THE RIDGE PRESSES INTO THE LOW-LEVEL PRESSURES TO ITS
SOUTH...IT WILL ESTABLISH A TIGHT BELT OF WESTERLIES. THIS WILL
LEAD TO WIND SPEEDS OF 45-60KT IN PARTS OF TIERRA DEL
FUEGO/MAGALLANES PEAKING ON SUNDAY EVENING. IN TERMS OF
PRECIPITATION...OROGRAPHIC ENHANCEMENT WILL SUSTAIN ISOLATED
MAXIMA OF 10-15MM/DAY IN WESTERN AND SOUTHWESTERN SLOPES OF THE
SOUTHERN ANDES ON SUNDAY-MONDAY.

MOST ACTIVE CONVECTION WILL LINGER IN TROPICAL SOUTH
AMERICA...WHERE DEEP-LAYER MOIST POOL WILL CONTINUE IN PLACE...AND
VENTILATION UNDER AND IN THE PERIPHERY OF A STRONG SUBTROPICAL
RIDGE/BOLIVIAN HIGH WILL CONTINUE PERSISTING. AS A RIDGE
ESTABLISHES FROM THE WEST ACROSS NORTHERN CHILE AND NORTHERN
ARGENTINA...SOUTHERLY FLOW TO ITS EAST WILL SUSTAIN THE
AMPLIFICATION OF AN UPPER TROUGH ACROSS SOUTHEASTERN SOUTH
AMERICA. THIS WILL FURTHER LEAD TO THE ORGANIZATION OF THE SOUTH
ATLANTIC CONVERGENCE ZONE  SACZ  WHICH IS FORECAST TO FORM ON
FRIDAY AND LINTER AT LEAST INTO EARLY NEXT WEEK. THE SACZ IS
FORECAST TO MEANDER FROM ESPIRITO SANTO-NORTHERN MINAS GERAIS INTO
SOUTHERN BOLIVIA ON FRIDAY...TO NORTHERN ESPIRITO SANTO-NORTHERN
MINAS GERAIS-MATO GROSSO-RONDONIA-SOUTHERN PERU BY SUNDAY-MONDAY.
THE SACZ WILL BE A FOCUS FOR SCATTERED CONVECTION AND LOCALLY
HEAVY RAINFALL...THUS WE ARE EXPECTING DAILY ACCUMULATIONS IN THE
ORDER OF 40-80MM/DAY. THIS INCLUDES THE RISK OF MCS FORMATION.
ELSEWHERE IN TROPICAL SOUTH AMERICA...ANDEAN CONVECTION WILL
CONTINUE ALONG THE ECUADORIAN-PERUVIAN AND BOLIVIAN ANDES...BUT
DAILY ACCUMULATIONS WILL GENERALLY BE UNDER 15MM/DAY.

OVIEDO...SHN (ARGENTINA)
POMIER...SENAMHI (BOLIVIA)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)