870  
FXSA20 KWBC 101710  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1210 PM EST WED JAN 10 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 10 AT 0000 UTC): THE GLOBAL  
MODELS ONCE AGAIN MAINTAIN GOOD CONTINUITY ON PATTERN EVOLUTION  
OVER THE CONTINENT-SOUTH ATLANTIC. OVER THE SOUTH PACIFIC THEY ARE  
SLOWLY REACHING A CONSENSUS ON HOW THE PATTERN IS GOING TO  
EVOLVE...WITH LESS VARIABILITY AMONG THE ENSEMBLE MEMBERS ON DAYS  
05-06 THAN PREVIOUSLY NOTED. THIS LEADS TO A HIGHER CONFIDENCE IN  
THE FORECAST THROUGH THE MEDIUM RANGE PERIOD.  
 
OVER THE SOUTHEAST PACIFIC...A PROGRESSIVE MID LEVEL TROUGH IS TO  
RACE ACROSS 120W/125W LATER THIS AFTERNOON...MOVING ACROSS 85W  
LATER ON THURSDAY. AS IT NEARS THE SOUTHERN CONE EARLY ON FRIDAY  
MORNING THE TROUGH IS TO FOCUS ITS SHORT WAVE ENERGY ON  
CONTINENTAL AREA TO THE SOUTH OF 38S. THE DEEP/HIGH AMPLITUDE  
TROUGH IS TO ALSO SUSTAIN A MOIST ADVECTIVE PATTERN...WITH DEEP  
PLUME OF SUBTROPICAL MOISTURE REACHING SOUTHERN PORTIONS OF CHILE.  
ON FRIDAY THE TROUGH MOVES ACROSS SOUTHERN CHILE TO  
PATAGONIA/CENTRAL PROVINCES IN ARGENTINA. AS IT CROSSES THE  
CONTINENT THIS WILL SUSTAIN HEIGHT FALLS OF 50-75GPM...WITH MOST  
INTENSE OVER LA PAMPA/BUENOS AIRES PROVINCE. FURTHERMORE...THE  
INFLOW OF MID LEVEL ENERGY ACROSS CENTRAL ARGENTINA IS LIKELY TO  
TRIGGER POCKETS OF SEVERE CONVECTION. ON SATURDAY THE TROUGH IS TO  
DAMPEN AS IT MOVES ACROSS 40W/50W. AT LOW LEVELS THIS SUSTAINS AN  
ELONGATED FRONT THAT MOVES TO THE DRAKE PASSAGE-TIERRA DEL FUEGO  
LATER TODAY...THEN NORTH ACROSS PATAGONIA ON THURSDAY-FRIDAY.  
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. OVER SOUTHERN CHILE THIS IS TO INITIALLY  
TRIGGER MODERATE CONVECTION WITH MAXIMA OF 15-20MM. ON  
THURSDAY...AS A DEEPER PLUME OF SUBTROPICAL MOISTURE REACHES  
SOUTHERN CHILE...THIS INCREASES TO 20-30MM. OVER LA PAMPA-BUENOS  
AIRES PREFRONTAL CONVECTION ON FRIDAY WILL SUSTAIN MAXIMA OF  
15-20MM...WHILE OVER MENDOZA-CORDOBA EXPECTING MAXIMA OF 25-50MM  
IN POTENTIALLY SEVERE CONVECTION. ON SATURDAY CONDITIONS APPEAR  
FAVORABLE FOR AN MCS TO DEVELOP OVER NORTHERN  
ARGENTINA-URUGUAY...WITH MAXIMA OF 40-80MM. 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 LOCALLY HIGHER  
AMOUNTS ARE HIGHLY PROBABLE.  
 
A LOW AMPLITUDE MID/UPPER LEVEL RIDGE OVER THE WESTERN SOUTH  
ATLANTIC SEPARATES THE LATTER FROM ANOTHER TROUGH TO THE EAST.  
EARLY IN THE PERIOD THE TROUGH WILL EXTEND BETWEEN 35W-05E AND TO  
THE SOUTH OF 28S. THE TROUGH IS FORECAST TO MEANDER EAST ACROSS  
10W LATER ON THURSDAY...NEARING 05W ON FRIDAY. AT LOW LEVELS THIS  
SUSTAINS AN ELONGATED FRONT OVER THE SOUTH ATLANTIC THAT EXTENDS  
WEST ALONG 25S TO 50W LATER TODAY. AS IT LOSES ITS UPPER LEVEL  
SUPPORT THE FRONT IS TO FRONTOLIZE OVER THE WESTERN ATLANTIC ON  
THURSDAY-FRIDAY. ALSO...OVER THE CONTINENT...THE FRONT SUSTAINS AN  
INDUCED TROUGH OVER SOUTHERN BRASIL-MATO GROSSO DO SUL TO NORTHERN  
BOLIVIA. BUT AS THE FRONT WEAKENS THE SURFACE TROUGH IS TO  
GRADUALLY FILL THROUGH MIDDAY ON FRIDAY. EARLY IN THE CYCLE THIS  
WILL BE THE FOCUS OF LOW LEVEL CONVERGENCE...WITH MAXIMA OF  
20-35MM OVER MATO GROSSO DO SUL-SOUTHERN BRASIL/SAO PAULO ON  
WEDNESDAY AND THURSDAY. ON FRIDAY THIS DECREASES TO 15-20MM. OVER  
NORTHERN BOLIVIA-ACRE/RONDONIA IN BRASIL TO SOUTHERN JUNGLE OF  
PERU THE MAXIMA PEAKS AT 30-60MM. ON TUESDAY-WEDNESDAY THIS  
DECREASES TO 25-50MM.  
NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE  
SUBTROPICAL RIDGE DOMINATES NORTHWEST SOUTH AMERICA WHILE  
CENTERING ON A CLOSED HIGH THAT IS TO MEANDER BETWEEN NORTHERN  
CHILE-SOUTHERN PERU AND LAKE TITICACA. EAST OF THIS RIDGE...A  
SHORT WAVE TROUGH EXTENDS ACROSS THE NORTHEAST STATES OF BRASIL.  
UNDER THE INFLUENCE OF THE RIDGE TO THE WEST AND SOUTH 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 ALONG THE NORTH COAST OF BRASIL...WITH MAXIMA  
OF 35-70MM EARLY IN THE PERIOD. ON THURSDAY THIS DECREASES TO  
20-35MM...WHILE ON FRIDAY EXPECTING ACCUMULATION OF 15-25MM/DAY.  
HEAVY CONVECTION IS ALSO EXPECTED ALONG THE NEAR EQUATORIAL TROUGH  
OVER AMAZONAS IN BRASIL...WITH MAXIMA OF 35-70MM. ON  
THURSDAY-FRIDAY THIS DECREASES TO 25-50MM. THE RIDGE ALOFT IS TO  
ALSO VENT CONVECTION ALONG THE SIERRA OF PERU TO THE ALTIPLANO OF  
BOLIVIA. INITIALLY EXPECTING ACCUMULATION OF 05-10MM/DAY. THROUGH  
FRIDAY THIS INCREASES TO 15-20MM.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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