455  
FXSA20 KWBC 111639  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1139 AM EST THU JAN 11 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 11 AT 0000 UTC): THE GFS AND  
EUROPEAN MODELS ONLY MADE MINOR CORRECTIONS TO PREVIOUS  
FORECAST...A SOLUTION WELL SUPPORTED BY THE GLOBAL ENSEMBLE  
MEMBERS. IN THIS PATTERN...CONFIDENCE IN THE FORECAST IS HIGH.  
 
OVER THE SOUTH PACIFIC...A PROGRESSIVE MID LEVEL TROUGH RACES  
ACROSS 85W TO 37S LATER TODAY. AS IT NEARS THE SOUTHERN CONE EARLY  
ON FRIDAY MORNING THE HIGH AMPLITUDE TROUGH IS TO FOCUS ITS SHORT  
WAVE ENERGY AND SUBTROPICAL MOISTURE ON CONTINENTAL AREA TO THE  
SOUTH OF 38S. LATER ON FRIDAY THE TROUGH WILL MOVES ACROSS  
SOUTHERN CHILE TO PATAGONIA-CENTRAL PROVINCES IN ARGENTINA. OVER  
CENTRAL ARGENTINA THIS IS TO THEN SUSTAIN HEIGHT FALLS OF  
50-75GPM...WITH MOST INTENSE OVER LA PAMPA/BUENOS AIRES PROVINCE.  
AT LOW LEVELS...THE ASSOCIATED FRONT WILL EXTEND OVER SOUTHERN  
PATAGONIA-SOUTHERN CHILE TO THE EASTERN PACIFIC LATER TODAY. ON  
FRIDAY THE FRONT MOVES NORTH TO LA PAMPA-MENDOZA IN ARGENTINA INTO  
THE EASTERN PACIFIC ALONG 33S. A BUILDING POLAR RIDGE OVER  
SOUTHERN CHILE/PATAGONIA WILL THEN DRIVE THIS BOUNDARY NORTH TO LA  
PAMPA/SOUTHERN BUENOS AIRES PROVINCE-SOUTHERN CUYO LATER ON FRIDAY  
EVENING. ON SATURDAY THE FRONT WILL MOVE NORTH ACROSS RIO DE LA  
PLATA BASIN TO NORTHERN PROVINCES IN ARGENTINA...TO STALL OVER  
SOUTHERN BRASIL-NORTHERN ARGENTINA LATER IN THE CYCLE. OVER  
SOUTHERN CHILE THIS IS TO TRIGGER MODERATE CONVECTION WITH MAXIMA  
OF 20-30MM. OVER LA PAMPA-BUENOS AIRES PREFRONTAL CONVECTION ON  
FRIDAY WILL SUSTAIN MAXIMA OF 15-20MM...WHILE OVER MENDOZA-CORDOBA  
EXPECTING MAXIMA OF 30-60MM IN POTENTIALLY SEVERE CONVECTION. ON  
SATURDAY CONDITIONS APPEAR FAVORABLE FOR AN MCS TO DEVELOP AHEAD  
AND ALONG THIS FRONT...WITH ORGANIZED CONVECTION TO CLUSTER ACROSS  
URUGUAY-CORRIENTES/ENTRE RIOS IN ARGENTINA. IN THIS AREA EXPECTING  
RAINFALL MAXIMA OF 40-80MM IN POTENTIALLY SEVERE CONVECTION. ON  
SUNDAY...IN A SOUTHERLY FLOW ACROSS NORTHERN  
ARGENTINA/PARAGUAY...HEAVY CONVECTION OVER NORTHERN  
BOLIVIA-SOUTHERN PERU-ACRE/RONDONIA IN BRASIL WILL TRIGGER MAXIMA  
OF 40-80MM. IN THIS AREA...DUE TO STRONG TOPOGRAPHICAL FORCING...  
LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE.  
 
DOWNSTREAM FROM THIS TROUGH...OVER THE WESTERN SOUTH ATLANTIC...A  
RIDGE EXTENDS BETWEEN 60W-30W TO THE WEDDELL SEA/ANTARCTIC  
PENINSULA. AS THE AFOREMENTIONED TROUGH PUSHES EAST ACROSS THE  
SOUTHERN CONE THE RIDGE IS TO RELOCATE ACROSS 20W LATER ON  
SATURDAY...NEARING 00W ON SUNDAY. AS THE RIDGE RELOCATES ACROSS  
THE SOUTH ATLANTIC IT IS TO DISPLACE A TROUGH TO THE EAST. LATER  
TODAY THE TROUGH WILL EXTEND NORTH ALONG 00W/10W TO 25S. THE  
TROUGH IS TO MEANDER EAST ACROSS 10E LATER ON FRIDAY/SATURDAY. AS  
IT PULLS AWAY...THE ASSOCIATED SURFACE FRONT IS TO FRONTOLIZE.  
REMNANTS OVER THE CONTINENT ARE TO INITIALLY FAVOR SCATTERED DEEP  
CONVECTION ACROSS MATO GROSSO-PARANA/SAO PAULO IN SOUTHEAST  
BRASIL...WITH MAXIMA OF 20-35MM. ON FRIDAY-SATURDAY THIS DECREASES  
TO 15-20MM.  
 
AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES  
CONTINENTAL AREA TO THE NORTH OF 35S/40S...WITH AXIS ANCHORING ON  
A CLOSED HIGH OVER SOUTHERN BOLIVIA. THE RIDGE ALOFT IS PROVIDING  
THE STEERING FLOW TO A TROUGH TO THE WEST...AND TO A TUTT OVER  
NORTHEAST BRASIL. THE FIRST MEANDERS OFF THE NORTH COAST OF CHILE.  
UNDER INFLUENCE OF THE RIDGE THIS TROUGH MOVES TOWARDS NORTHERN  
CHILE EARLY ON FRIDAY. ON FRIDAY-SATURDAY IT IS TO SLOWLY SHEAR  
ACROSS THE NORTHERN ANDES INTO NORTHERN ARGENTINA...MEANWHILE  
PROVIDING THE DYNAMICAL SUPPORT TO ORGANIZED CONVECTION BUILDING  
ACROSS MID SECTIONS OF SOUTH AMERICA. THIS IS TO ALSO ENHANCE  
CONVECTION ACROSS SOUTHERN SIERRA OF PERU-ALTIPLANO OF  
BOLIVIA...WITH MAXIMA INCREASING FROM 10-15MM/DAY EARLY IN THE  
CYCLE TO 15-20MM ON FRIDAY-SATURDAY.  
 
THE OTHER UPPER LEVEL TROUGH IS TO MEANDER OVER NORTHEAST BRASIL  
DURING THE NEXT 36-48 HRS...THEN STARTS TO WEAKEN WHILE REFORMING  
FARTHER TO THE EAST OVER THE ATLANTIC OCEAN. EARLY IN THE CYCLE  
THIS IS TO ENHANCE DIURNAL CONVECTION ACROSS NORTHEAST BRASIL TO  
FAVOR MAXIMA OF 20-45MM. AS THE TROUGH WEAKENS MAXIMA IN THIS AREA  
DECREASES TO 15-25MM ON FRIDAY TO SATURDAY. OTHER CONVECTION IS TO  
CLUSTER ON THE AMAZON RIVER DELTA REGION...WITH RAINFALL MAXIMA OF  
20-30MM/DAY. UNDER INFLUENCE OF THE RIDGE...SCATTERED DEEP  
CONVECTION OVER SOUTHERN/SOUTHEAST STATES OF BRASIL IS TO  
INITIALLY TRIGGER RAINFALL AMOUNTS OF 20-35MM. ON FRIDAY-SATURDAY  
THIS DECREASES TO MAXIMA OF 15-25MM. HIGHER AMOUNTS ARE EXPECTED  
FROM NORTHERN BOLIVIA TO AMAZONAS IN BRASIL...WITH MAXIMA OF  
20-45MM OVER THE NEXT TWO DAYS. THROUGH SATURDAY THIS DECREASES TO  
15-25MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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