956  
FXSA20 KWBC 201719  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1219 PM EST MON NOV 20 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 20 AT 0000 UTC): AT MID/UPPER  
LEVELS...UNDER THE INFLUENCE OF A HIGH AMPLITUDE LONG WAVE RIDGE  
OVER THE EASTERN SOUTH PACIFIC...A LONG WAVE TROUGH NOW EXTENDS  
OVER THE WESTERN SOUTH ATLANTIC TO CENTRAL SOUTH AMERICA. THE  
HIGHLY AMPLIFIED LONG WAVE PATTERN IS TO PERSIST THROUGH THURSDAY  
MORNING...TO THEN WEAKEN LATER IN THE WEEK AS THE RIDGE TO THE  
WEST FLATTENS.  
 
AT LOW LEVELS...THE BROAD TROUGH ALOFT SUSTAIN AN ELONGATED  
BAROCLINIC BOUNDARY ACROSS THE SOUTH ATLANTIC TO NORTHERN SAO  
PAULO/SOUTHERN MINAS GERAIS IN BRASIL THEN WEST ACROSS MATO GROSSO  
DO SUL TO SOUTHEAST BOLIVIA. TRAILING END OVER THE CONTINENT IS TO  
WEAKEN TO A TROUGH EARLY ON TUESDAY...TO PERSIST FOR THE NEXT FEW  
DAYS. MEANWHILE...THE SEGMENT OVER THE SOUTH ATLANTIC PERSISTS  
DURING THE NEXT THREE DAYS. THIS IS TO ENHANCE LOW LEVEL MOISTURE  
CONVERGENCE ACROSS RIO DE JANEIRO-ESPIRITO SANTO TO RESULT IN  
RAINFALL MAXIMA OF 35-70MM THROUGH TUESDAY MORNING...AND 30-60MM  
ON TUESDAY TO WEDNESDAY. THROUGH THURSDAY THIS IS TO THEN DECREASE  
TO MAXIMA OF 20-40MM. OTHER CONVECTION IS EXPECTED INLAND ACROSS  
BRASIL ALONG THE MEANDERING LOW LEVEL TROUGH. ACROSS MATO  
GROSSO-RONDONIA IN BRASIL EXPECTING MAXIMA OF 20-30MM/DAY OVER THE  
NEXT COUPLE OF DAYS. ON WEDNESDAY ACTIVITY BETWEEN MATO GROSSO AND  
MINAS GERAIS DECREASES TO 15-25MM...WHILE ACROSS  
ACRE-RONDONIA/NORTHERN BOLIVIA AND SOUTHERN JUNGLE OF PERU IT IS  
TO PEAK AT 20-35MM.  
 
A SECONDARY FRONT FOLLOWS...LIFTING ACROSS URUGUAY/SOUTHERN  
BRASIL-CENTRAL ARGENTINA EARLY IN THE CYCLE...WHERE IT IS TO FAVOR  
RAINFALL MAXIMA OF 15-20MM IN SCATTERED CONVECTION. ON TUESDAY THE  
FRONT IS TO MEANDER NORTH ACROSS SOUTHERN BRASIL TO PARAGUAY...AND  
ON WEDNESDAY IT MOVES TO THE SOUTHEAST STATES OF BRASIL WHERE IT  
IS TO REPLACE THE OLD FRONTAL BOUNDARY TO THE NORTH. OVER RIO DE  
JANEIRO-SOUTHERN MINAS GERAIS TO MATO GROSSO DO SUL THIS IS TO  
FAVOR RAINFALL MAXIMA OF 20-40MM ON THURSDAY...WHILE OVER  
RONDONIA/MATO GROSSO-ACRE TO NORTHERN BOLIVIA-SOUTHERN PERU THE  
MAXIMA IS TO PEAK AT 15-20MM.  
 
SIMULTANEOUSLY...A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN  
STREAM IS TO RACE ACROSS THE SOUTHEAST PACIFIC...REACHING THE  
BELLINGSHAUSEN SEA/DRAKE PASSAGE EARLY ON WEDNESDAY MORNING. THIS  
THEN LIFTS ACROSS PATAGONIA IN ARGENTINA LATER DURING THE DAY. AT  
LOW LEVELS THE ASSOCIATED FRONT ENTERS TIERRA DEL FUEGO-SOUTHERN  
CHILE ON TUESDAY EVENING...WEAKENING AS IT LIFTS NORTH ACROSS  
PATAGONIA TO LA PAMPA IN ARGENTINA ON WEDNESDAY TO THURSDAY. MOST  
ACTIVE CONVECTION WITH THIS FEATURE IS EXPECTED TO THE SOUTH OF  
ISLA DE CHILOE...WITH MAXIMA OF 05-10MM ON TUESDAY-WEDNESDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE  
SUBTROPICAL RIDGE DOMINATES THE FLOW OVER THE CONTINENT TO THE  
NORTH OF 30S WHILE CENTERING ON A CLOSED HIGH OVER RONDONIA IN  
BRASIL/NORTHERN BOLIVIA. EAST OF THIS RIDGE...A CLOSED LOW NEAR  
RECIFE ANCHORS A SHORT WAVE TROUGH OVER THE NORTHEAST STATES OF  
BRASIL. THIS PATTERN IS TO HOLD DURING THE NEXT FEW DAYS. RIDGE  
ALOFT IS TO VENT THE AFOREMENTIONED CONVECTION ACROSS THE  
SOUTHEAST-CENTRAL STATES OF BRASIL. IT IS TO ALSO VENT DIURNAL  
CONVECTION ACROSS SOUTHERN COLOMBIA-NORTHERN PERU/EASTERN  
ECUADOR...TO FAVOR MAXIMA OF 20-40MM THROUGH TUESDAY MORNING...AND  
15-20MM ON TUESDAY AND WEDNESDAY. OVER NORTHERN AMAZONAS IN BRASIL  
EXPECTING MAXIMA OF 20-35MM/DAY...WITH LOCALLY HIGHER AMOUNTS ON  
TUESDAY. UNDER INFLUENCE OF THE UPPER LEVEL LOW TO THE  
EAST...SCATTERED CONVECTION IS TO AFFECT TOCANTINS/GOIAS-AMAZON  
RIVER DELTA REGION...WITH MAXIMA OF 15-20MM OVER THE NEXT COUPLE  
OF DAY. THROUGH THE END OF THE WEEK THIS IS TO BECOME MORE  
ACTIVE/BETTER ORGANIZED.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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