005  
FXSA20 KWBC 081620  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1120 AM EST MON JAN 08 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 08 AT 0000 UTC): THERE IS VERY  
GOOD CONTINUITY WITH THE PREVIOUS MODEL RUN...WITH GLOBAL MODEL  
GUIDANCE FOLLOWING A SIMILAR EVOLUTION THROUGH 132-144 HRS. THIS  
FORECAST IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL  
ENSEMBLES...LEADING TO HIGH CONFIDENCE IN THE FORECAST THROUGH THE  
MEDIUM RANGE PERIOD.  
 
A BROAD MID/UPPER LEVEL TROUGH LIES OVER THE SOUTHEAST  
PACIFIC...WITH AXIS ENVELOPING AREA BETWEEN 140W-60W AND TO THE  
SOUTH OF 30S. THIS IS PRESSING AGAINST A RIDGE TO THE EAST THAT  
EXTENDS NORTH-TO-SOUTH ACROSS CHILE/ARGENTINA TO THE DRAKE  
PASSAGE. UNDER PRESSURE THE RIDGE IS TO GRADUALLY FLATTEN WHILE  
SIMULTANEOUSLY RELOCATING TO THE WESTERN ATLANTIC. THE TROUGH IS  
TO THEN MOVE INLAND ACROSS SOUTHERN CHILE TO PATAGONIA IN  
ARGENTINA LATER ON THURSDAY...TO MOVE ACROSS THE SOUTHERN CONE TO  
THE SOUTHWEST ATLANTIC LATER ON FRIDAY. AT LOW LEVELS THE TROUGH  
ALOFT WILL SUSTAIN A BROAD OCCLUDED LOW OVER THE SOUTHEAST PACIFIC  
LATER TODAY... WITH AXIS TO MEANDER EAST ACROSS THE ANTARCTIC  
PENINSULA TO THE WEDDELL SEA ON WEDNESDAY-THURSDAY. AN ELONGATED  
FRONT IS TO BOUND THE NORTHERN FRINGES OF THIS TROUGH...TO EXTEND  
ACROSS SOUTHERN PATAGONIA- SOUTHERN CHILE LATER TODAY...TO THEN  
MEANDER NORTH ACROSS PATAGONIA TO LA PAMPA ON TUESDAY AS A  
SECONDARY BOUNDARY EXTENDS OVER TIERRA DEL FUEGO. THESE  
BOUNDARIES...AS THEY EXTEND ACROSS THE SOUTHERN CONE...ARE TO  
ENHANCE MOISTURE CONVERGENCE ACROSS CHILE SOUTH OF ISLA DE  
CHILOE...TO FAVOR MAXIMA OF 10-15MM THROUGH TUESDAY MORNING. ON  
WEDNESDAY THIS INCREASES TO 15-20MM...WHILE ON THURSDAY THE MAXIMA  
PEAK AROUND 20-30MM IN POTENTIALLY DEEP CONVECTION.  
 
DOWNSTREAM FROM THE CONTINENTAL RIDGE...A MID/UPPER LEVEL TROUGH  
EXTENDS OVER THE ATLANTIC BETWEEN 50W-20W AND TO THE SOUTH OF 30S.  
AS THE RIDGE TO THE WEST FLATTENS...THE TROUGH IS TO GRADUALLY  
PULL TO THE EAST-SOUTHEAST THROUGH THURSDAY MORNING. AT LOW LEVELS  
THIS SUPPORTS AN ELONGATED FRONT ACROSS THE SOUTH ATLANTIC TO  
SOUTHERN BRASIL-SOUTHEAST PARAGUAY/CORRIENTES IN ARGENTINA. THE  
BOUNDARY IS TO REMAIN NEARLY STATIONARY THROUGH WEDNESDAY  
AFTERNOON. ON WEDNESDAY-THURSDAY...AS THE UPPER TROUGH PULLS  
AWAY...THE SURFACE FRONT IS FORECAST TO FRONTOLIZE. ALSO AT LOW  
LEVELS...A TROUGH EXTENDS FROM NORTHERN BOLIVIA...ACROSS MATO  
GROSSO DO SUL TO SAO PAULO/PARANA IN BRASIL. THROUGH WEDNESDAY  
EVENING/ THURSDAY MORNING THE LOW LEVEL TROUGH IS EXPECTED TO  
WEAKEN. EARLY IN THE CYCLE MOISTURE IS TO CONVERGE ALONG THIS  
TROUGH...TO TRIGGER MODERATE TO HEAVY CONVECTION ACROSS NORTHERN  
BOLIVIA-RONDONIA-MATO GROSSO DO SUL/SAO PAULO IN BRASIL...WITH  
MAXIMA OF 35-70MM. ON TUESDAY THIS DECREASES TO 20-45MM...WHILE ON  
WEDNESDAY THE MAXIMA WILL PEAK AT 20-35MM. THIS IS TO THEN PERSIST  
THROUGH THURSDAY-FRIDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH NEAR LAKE TITICACA  
ANCHORS A RIDGE OVER NORTHWEST SOUTH AMERICA. A TROUGH TO THE  
EAST-NORTHEAST EXTENDS OVER NORTHEAST BRASIL WHILE CENTERING ON A  
CLOSED LOW NEAR RECIFE. UNDER INFLUENCE OF THE RIDGE TO THE WEST  
THE TROUGH/LOW IS TO MEANDER FARTHER EAST ACROSS NORTHEAST  
BRASIL...WITH CLOSED LOW NEARING NORTHERN PARA/ILHA DE MARAJO ON  
WEDNESDAY-THURSDAY. AS THE LOW/TROUGH MEANDERS WEST IT IS TO  
ENHANCE CONVECTION ON THE NORTHEAST STATES OF BRASIL. EARLY IN THE  
CYCLE THIS IS TO FAVOR MAXIMA OF 10-15MM. THROUGH  
WEDNESDAY/THURSDAY THE MAXIMA IN THIS AREA INCREASES TO 20-35MM IN  
SCATTERED DEEP CONVECTION. OTHER CONVECTION IS EXPECTED BETWEEN  
THIS TROUGH AND THE RIDGE TO THE WEST...TO ENVELOP MOST OF PARA IN  
BRASIL EARLY IN THE CYCLE. ON TUESDAY-WEDNESDAY...AS THE LOW  
RELOCATES ACROSS NORTHEAST BRASIL...FOCUS OF THE CONVECTION SHIFTS  
ACROSS PARA TO AMAZONAS IN BRASIL...WITH MAXIMA OF 20-45MM/DAY.  
ACROSS NORTHERN PERU-ECUADOR THIS IS TO INITIALLY FAVOR AN  
INCREASE IN CONVECTION...WITH MAXIMA OF 20-40MM ON TUESDAY. ON  
THURSDAY TO FRIDAY THE MAXIMA IN THIS AREA WILL PEAK AT 15-25MM.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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