984  
FXSA20 KWBC 051558  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST FRI JAN 05 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 05 AT 0000 UTC): GLOBAL MODELS  
ARE IN GOOD AGREEMENT THROUGH 108-120 HRS...WITH A HIGHLY  
AMPLIFIED SINUSOIDAL WAVE PATTERN ESTABLISHING ACROSS THE SOUTH  
AMERICAN DOMAIN.  
 
A BUILDING MID LEVEL RIDGE IS TO DOMINATE THE FLOW ACROSS THE  
EASTERN PACIFIC DURING THE NEXT 60-72 HRS. UNDER INFLUENCE OF THIS  
RIDGE A TROUGH AMPLIFIED ACROSS SOUTHERN CHILE TO PATAGONIA IN  
ARGENTINA. THROUGH THIS EVENING THE TROUGH WILL RELOCATE ACROSS  
60W WHILE EXTENDING NORTH TO NORTHERN ARGENTINA. ON SATURDAY IT IS  
TO EXTEND BETWEEN 55W-30W TO 27S...MEANWHILE FOCUSING SHORT WAVE  
ENERGY ACROSS MID SECTIONS OF SOUTH AMERICA. LONG WAVE TROUGH AXIS  
IS TO THEN SLOWLY PULL TO THE EAST-SOUTHEAST EARLY NEXT WEEK. AT  
LOW LEVELS THIS SUSTAINS A SURFACE FRONT ACROSS RIO DE LA PLATA  
BASIN-MENDOZA IN ARGENTINA. UNDER INFLUENCE OF A PAMPERO LOW LEVEL  
JET THE FRONT MOVES NORTH ACROSS SOUTHERN BRASIL TO NORTHERN  
ARGENTINA LATER TODAY. ON SATURDAY IT MOVES NORTH ACROSS SOUTHERN  
BRASIL-SOUTHEAST PARAGUAY TO NORTHWEST ARGENTINA...WHERE IT IS TO  
REMAIN WHILE GRADUALLY WEAKENING EARLY NEXT WEEK. AS IT MOVES  
ACROSS THE RIO DE LA PLATA BASIN THE FRONT WILL SUSTAIN MODERATE  
CONVECTION WITH MAXIMA OF 15-20MM...WHILE OVER NORTHWEST ARGENTINA  
EXPECTING MAXIMA OF 20-30MM IN PREFRONTAL CONVECTION. ON SATURDAY  
THIS DECREASES TO 05-10MM IN ISOLATED CONVECTION. OVER  
PARANA-SANTA CATARINA-SAO PAULO THE SURGING FRONT WILL TRIGGER  
MAXIMA OF 20-45MM ON SATURDAY TO SUNDAY. ON SUNDAY TO MONDAY FOCUS  
OF THE CONVECTION SHIFTS TO SOUTHERN MINAS GERAIS-RIO DE  
JANEIRO...WITH MAXIMA IN THIS AREA INCREASING TO 50-100MM. HEAVY  
CONVECTION IS TO ALSO AFFECT CHACO PARAGUAYO-MATO GROSSO-RONDONIA  
IN BRASIL AND MOST OF BOLIVIA ON SATURDAY-SUNDAY...WITH MAXIMA OF  
50-100MM. ON SUNDAY TO MONDAY EXPECTING ADDITIONAL RAINFALL  
AMOUNTS OF 25-50MM. OVER SOUTHERN PERU...IN PREFRONTAL  
CONVECTION...THIS WILL SUSTAIN MAXIMA OF 25-50MM ON  
SATURDAY...INCREASING TO 35-70MM ON SUNDAY.  
 
A BROAD/HIGH AMPLITUDE TROUGH LIES TO THE WEST OF THE LONG WAVE  
RIDGE...EXTENDING OVER THE SOUTH PACIFIC BETWEEN 140W-95W AND TO  
THE SOUTH OF 25S. THIS IS TO SLOWLY MOVE EAST...MEANWHILE  
DISPLACING THE RIDGE TO SOUTHERN CHILE/PATAGONIA IN ARGENTINA  
LATER ON SUNDAY/MONDAY MORNING. ON MONDAY TO TUESDAY THE RIDGE  
WILL FINALLY YIELD TO THE POLAR TROUGH...WHICH IS TO THEN FOCUS  
ITS SHORT WAVE ENERGY AND SUBTROPICAL MOISTURE ACROSS SOUTHERN  
REGIONS OF CHILE. AT LOW LEVELS EXPECTING A SIMILAR  
EVOLUTION...WITH BROAD POLAR TROUGH TO MOVE TO THE BELLINGSHAUSEN  
SEA-SOUTHEAST PACIFIC LATER ON SUNDAY...WHILE THE ASSOCIATED FRONT  
MEANDERS EAST-SOUTHEAST ACROSS SOUTHERN CHILE TO SOUTHERN  
PATAGONIA/TIERRA DEL FUEGO. AS IT ENTERS EXTREME SOUTHERN PORTIONS  
OF CHILE THIS IS TO TRIGGER LIGHT TO MODERATE CONVECTION WITH  
ACCUMULATION OF 15-20MM/DAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...RIDGE TRAVERSES THE  
CONTINENT FROM WEST-TO-EAST BETWEEN 05S-25S. THIS IS TO INITIALLY  
ANCHOR ON TWO HIGHS...WITH ONE OVER BOLIVIA AND THE OTHER OVER  
SOUTHEAST STATES OF BRASIL. THROUGH SUNDAY EVENING THESE WILL  
COMBINE INTO A SINGLE HIGH OVER BOLIVIA. AS THE RIDGE HOLDS...A  
SHORT WAVE TROUGH IS TO MEANDER OVER NORTHEAST BRASIL WHILE  
CENTERING ON A CLOSED LOW TO THE EAST OF RECIFE. UNDER INFLUENCE  
OF THE RIDGE AND THE TROUGH SCATTERED DEEP CONVECTION OVER  
NORTHEAST BRASIL IS TO INITIALLY FAVOR RAINFALL MAXIMA OF 30-60MM.  
THIS GRADUALLY DECREASES TO 20-35MM LATER DURING THE WEAKEN. OTHER  
CONVECTION IS TO CLUSTER ALONG THE NEAR EQUATORIAL TROUGH OVER  
PARA-AMAZONAS IN BRASIL TO NORTHERN PERU...WITH MAXIMA OF 20-35MM  
IN SCATTERED DEEP CONVECTION. SIMILAR AMOUNTS ARE EXPECTED ACROSS  
ECUADOR DURING THE NEXT FEW DAYS.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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