052  
FXSA20 KWBC 221648  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1148 AM EST WED NOV 22 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 22 AT 0000 UTC): BROAD MID/UPPER  
LEVEL TROUGH DOMINATES THE FLOW ACROSS THE WESTERN ATLANTIC...  
ENVELOPING AREA BETWEEN 60W-20W AND TO THE SOUTH OF 20S. LATER  
TODAY MEAN TROUGH AXIS RELOCATES ACROSS 40W...NEARING 20W LATER ON  
THURSDAY. AT LOW LEVELS THIS SUSTAINS A SURFACE FRONT ACROSS  
SOUTHEAST BRASIL-MATO GROSSO TO NORTHERN BOLIVIA. THE BOUNDARY IS  
TO REMAIN NEARLY STATIONARY WHILE GRADUALLY WEAKENING LATER ON  
FRIDAY. DEEP TROPICAL MOISTURE IS TO CONVERGE ALONG AND NORTH OF  
THIS BOUNDARY. EARLY IN THE PERIOD THIS IS TO FAVOR HEAVY  
CONVECTION ACROSS NORTHERN SAO PAULO-SOUTHERN MINAS GERAIS-RIO DE  
JANEIRO...WITH MAXIMA OF 30-60MM. ON THURSDAY THIS DECREASES TO  
20-45MM. ACROSS MATO GROSSO TO WESTERN MINAS GERAIS EXPECTING  
MAXIMA OF 15-25MM OVER THE NEXT COUPLE OF DAYS...INCREASING TO  
20-30MM ON FRIDAY-SATURDAY. OVER NORTHERN BOLIVIA TO SOUTHERN PERU  
THIS IS TO ALSO FAVOR SCATTERED CONVECTION...WITH MAXIMA OF  
20-45MM EXPECTED THROUGH THURSDAY MORNING...DECREASING TO 15-20MM  
ON THURSDAY-FRIDAY.  
 
SIMULTANEOUSLY...A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN  
STREAM IS TO LIFT ACROSS THE BELLINGSHAUSEN SEA/DRAKE PASSAGE TO  
PATAGONIA IN ARGENTINA LATER TODAY. IT IS TO QUICKLY MOVE OFF THE  
COAST OF ARGENTINA ON THURSDAY AFTERNOON. THIS SUSTAINS A SURFACE  
FRONT ACROSS PATAGONIA IN ARGENTINA LATER TODAY...REACHING RIO DE  
LA PLATA BASIN ON THURSDAY...WHERE IT IS FORECAST TO STALL. AS IT  
ENTERS SOUTHERN CHILE THIS IS TO FAVOR LIGHT CONVECTION WITH  
MAXIMA OF 15-20MM...WHILE ACROSS PATAGONIA IN ARGENTINA/CENTRAL  
PROVINCES IT IS TO ONLY TRIGGER WIDELY ISOLATED CONVECTION.  
 
A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO SLOWLY MOVE  
ACROSS THE EASTERN PACIFIC TO THE CENTRAL REGIONS OF CHILE LATER  
ON THURSDAY. ON FRIDAY THE SHORT WAVE TROUGH WILL SPILL ACROSS THE  
CENTRAL ANDES TO CUYO IN ARGENTINA...PULLING ACROSS  
URUGUAY/SOUTHERN BRASIL LATER ON SATURDAY. AS IT SPILLS ACROSS THE  
ANDES...THE MID LEVEL TROUGH WILL THEN INTERACT WITH THE SURFACE  
FRONT MEANDERING OVER NORTHERN ARGENTINA. THIS IS TO SUSTAIN  
CYCLOGENESIS WHILE INDUCING THE GRADUAL INTENSIFICATION OF THE  
SURFACE FRONT. THIS WILL THEN DRIVE THE FRONT NORTH ACROSS  
SOUTHERN BRASIL-PARAGUAY LATER ON SATURDAY. ON FRIDAY THIS IS TO  
FAVOR LIGHT TO MODERATE CONVECTION ACROSS CHACO  
ARGENTINO-CORRIENTES AND PORTIONS OF PARAGUAY. ON SATURDAY THE  
MAXIMA OVER PARAGUAY IS TO PEAK AT 40-80MM...WHILE OVER RIO GRANDE  
DO SUL IN SOUTHERN BRASIL THE MAXIMA PEAKS AT 20-40MM. OTHER  
CONVECTION IS TO CLUSTER ACROSS THE ALTIPLANO OF BOLIVIA...WITH  
MAXIMA OF 20-30MM.  
 
NORTH OVER THE CONTINENT...IN A WELL DEFINED SUMMER FLOW  
PATTERN...T 200 HPA HIGH OVER BOLIVIA IS TO ANCHOR A CELL OF THE  
SUBTROPICAL RIDGE ACROSS NORTHERN SOUTH AMERICA. THE RIDGE IS TO  
DOMINATE THE FLOW TO THE NORTH OF 25S/30S DURING THE NEXT FEW  
DAYS. AS IT MEANDERS OVER THE CONTINENT A TROUGH TO THE EAST IS TO  
EXTEND OVER THE NORTHEAST STATES OF BRASIL. THE RIDGE ALOFT IS TO  
CONTINUE VENTING DEEP CONVECTION ACROSS NORTHERN SOUTH AMERICA.  
MOST ACTIVE IS TO AFFECT AMAZONAS IN BRASIL-SOUTHERN  
COLOMBIA-NORTHERN JUNGLE OF PERU/EASTERN ECUADOR...WITH MAXIMA OF  
20-35MM/DAY. THROUGH FRIDAY AFTERNOON EXPECTING SLIGHT  
INTENSIFICATION WHEN THE MAXIMA PEAKS AT 20-40MM. OVER NORTHEAST  
BRASIL...MEANWHILE...THE UPPER LEVEL LOW/TROUGH IS TO SUSTAIN A  
CONVERGENT PATTERN THAT IS TO INHIBIT ORGANIZED DEEP CONVECTION  
DURING THE NEXT FEW DAYS.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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