086  
FXSA20 KWBC 071746  
PMDSA  
 
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)  

 
 
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