657  
FXSA20 KWBC 081900  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 PM EST FRI DEC 08 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 08 AT 0000 UTC): GLOBAL MODELS  
AND ENSEMBLE MEMBERS CONTINUE SHOWING HIGH CONFIDENCE ON THE  
FORECAST EVOLUTION THROUGH THE CYCLE.  
 
SHORT WAVE TROUGH SPILLING THROUGH THE ANDES OF CENTRAL  
CHILE/CENTRAL ARGENTINA IS STIMULATING CONVECTION ACROSS  
ROSARIO/RIO DE LA PLATA/EASTERN PROVINCIA DE BUENOS AIRES. THIS IS  
TO PEAK ON FRIDAY EVENING...WHEN A FEW THUNDERSTORMS WILL HAVE THE  
POTENTIAL OF PRODUCING ACCUMULATIONS OF 10-35MM/DAY. QUIET PATTERN  
WILL THEN ESTABLISH AS AN UPPER LEVEL RIDGE ESTABLISHES OVER THE  
REGION. ANY CONVECTION IN ARGENTINA WILL GENERALLY CLUSTER TO THE  
EXTREME NORTHWEST PART OF THE COUNTRY.  
 
ALSO IN THE SOUTHERN CONE...MODELS CONTINUE SHOWING THE  
ESTABLISHMENT OF A ROBUST MID/UPPER RIDGE OVER THE EASTERN PACIFIC  
DURING THE WEEKEND. AS THE RIDGE PRESSES INTO THE LOW-LEVEL  
PRESSURES TO ITS SOUTH AND MEANDERS WESTWARD SLOWLY...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. THE MOST REMARKABLE FEATURE DURING THE  
FORECAST CYCLE WILL BE THE FORMATION OF THE SOUTH ATLANTIC  
CONVERGENCE ZONE (SACZ) EARLY. THIS WILL SUSTAIN HEAVY  
RAIN-PRODUCING THUNDERSTORMS THROUGH MOST OF THE CYCLE. THE SACZ  
AND ASSOCIATED STRONG THUNDERSTORMS ARE TO MEANDER NORTHWARD FROM  
ESPIRITO SANTO/BAHIA/MINAS GERAIS INTO SOUTHERN BOLIVIA ON  
FRIDAY...TO ESPIRITO SANTO-SOUTHERN PARA-SOUTHERN AMAZONAS AND  
CENTRAL/NORTHERN PERU BY EARLY NEXT WEEK. NOTE THAT MODELS ARE  
CONFIDENT ON DEVELOPING A SURFACE AND MID-LEVE CLOSED LOW OVER  
RONDONIA/BOLIVIA ON SUNDAY...TO LAST THROUGH TUESDAY. THIS WILL  
PROVIDE ADDITIONAL ENHANCEMENT IN THE REGION TO PRODUCE RAINFALL  
TOTALS OF 50-100MM/DAY WITH THE RISK OF MCS ON  
BOLIVIA/RONDONIA/ACRE AND SOUTHERN PERO FROM SUNDAY THROUGH  
TUESDAY. ACCUMULATIONS SHOULD START DECREASING AFTER.  
ELSEWHERE...IN ASSOCIATION WITH THE SACZ...EXPECTING RAINFALL  
MAXIMA IN THE ORDER OF 40-80MM/DAY ALSO WITH THE RISK OF MCS  
FORMATION.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  

 
 
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