829  
FXSA20 KWBC 211703  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1203 PM EST TUE NOV 21 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 21 AT 0000 UTC): AS PREVIOUSLY  
NOTED...A HIGH AMPLITUDE MID/UPPER LEVEL TROUGH DOMINATES THE FLOW  
ACROSS THE WESTERN ATLANTIC TO MID SECTIONS OF SOUTH AMERICA.  
THROUGH WEDNESDAY EVENING THE TROUGH IS TO SLOWLY PULL ACROSS  
40WW...ACCELERATING ACROSS 20W ON THURSDAY. AT LOW LEVELS THIS  
SUSTAINS A BROAD TROUGH OVER THE WEDDELL SEA/SOUTHWEST  
ATLANTIC...WITH SUCCESSIVE POLAR FRONTS REVOLVING AROUND THIS  
AXIS. IN THIS PATTERN...AN ELONGATED FRONT STRETCHES ACROSS THE  
SOUTH ATLANTIC TO SAO PAULO-MATO GROSSO IN BRASIL. A SECONDARY  
BOUNDARY FOLLOWS...SURGING ACROSS SOUTHERN BRASIL-NORTHERN  
ARGENTINA TO PARAGUAY LATER THIS EVENING. IT IS TO THEN MERGE  
WITH/REPLACE THE OLD BOUNDARY TO THE NORTH. ACROSS SAO PAULO/RIO  
DE JANEIRO-SOUTHERN MINAS GERAIS THIS IS TO FAVOR SCATTERED DEEP  
CONVECTION WITH MAXIMA OF 30-60MM THROUGH WEDNESDAY MORNING...AND  
25-50MM ON WEDNESDAY-THURSDAY. OVER MATO GROSSO/MATO GROSSO DO  
SUL-RONDONIA IN BRASIL-NORTHERN BOLIVIA EXPECTING DEEP CONVECTION  
TO SUSTAIN MAXIMA OF 20-40MM THROUGH WEDNESDAY  
MORNING...DECREASING TO 15-20MM ON WEDNESDAY-THURSDAY. AS ACTIVITY  
OVER CENTRAL BRASIL WANES...CONVECTION TO THE NORTHWEST IS TO  
INTENSIFY...WITH MAXIMA OF 20-35MM EXPECTED ACROSS  
AMAZONAS-ACRE/SOUTHERN JUNGLE OF PERU TO SOUTHERN COLOMBIA ON  
WEDNESDAY. ON THURSDAY MOST ACTIVE IS EXPECTED OVER NORTHERN  
AMAZONAS-SOUTHERN COLOMBIA/NORTHERN JUNGLE OF PERU WITH MAXIMA OF  
20-35MM.  
 
CONSISTENT WITH PREVIOUS FORECASTS...A PROGRESSIVE MID LEVEL  
TROUGH ON THE SOUTHERN STREAM IS TO RACE ACROSS THE SOUTHEAST  
PACIFIC EARLY IN THE CYCLE...WITH MID LEVEL PERTURBATION REACHING  
THE BELLINGSHAUSEN SEA/DRAKE PASSAGE EARLY ON WEDNESDAY MORNING.  
THIS THEN LIFTS ACROSS PATAGONIA IN ARGENTINA LATER DURING THE  
DAY. ON THURSDAY IT IS TO MEANDER OFF THE COAST OF  
ARGENTINA...WITH AXIS NORTH ALONG 50W TO 30S. ON FRIDAY IT  
ACCELERATES ACROSS 30W/35W. AT LOW LEVELS THE ASSOCIATED FRONT  
ENTERS TIERRA DEL FUEGO-SOUTHERN CHILE LATER THIS EVENING...MOVING  
ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA EARLY ON THURSDAY...THEN  
NORTH ACROSS URUGUAY-ENTRE RIOS ARGENTINA TO MENDOZA LATER ON  
THURSDAY. ON FRIDAY IT IS TO MEANDER NORTH ACROSS SOUTHERN BRASIL  
TO NORTHERN ARGENTINA.  
 
SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO SLOWLY MOVE ACROSS  
THE EASTERN PACIFIC TO THE CENTRAL REGIONS OF CHILE LATER ON  
THURSDAY. ON THURSDAY IT SPILLS ACROSS THE CENTRAL ANDES TO CUYO  
IN ARGENTINA...PULLING ACROSS URUGUAY/SOUTHERN BRASIL LATER ON  
SATURDAY. AT LOW LEVELS THIS IS TO THEN INTERACT WITH MEANDERING  
FRONT OVER NORTHERN ARGENTINA...TO FAVOR CYCLOGENESIS ALONG THIS  
BOUNDARY. THIS IS TO THEN DRAW THE FRONT FARTHER NORTH ACROSS MID  
SECTIONS OF SOUTH AMERICA. ON FRIDAY THIS IS TO FAVOR LIGHT TO  
MODERATE CONVECTION WITH MAXIMA OF 20-30MM. ON SATURDAY...AS  
DEEPER MOISTURE POOLS ALONG THE MEANDERING FRONT OVER  
PARAGUAY...THE MAXIMA WILL INCREASE TO 35-70MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH OVER RONDONIA IN  
BRASIL/NORTHERN BOLIVIA ANCHORS A BROAD CELL OF THE SUBTROPICAL  
RIDGE ACROSS THE CONTINENT TO THE NORTH OF 25S/30S. EAST OF THIS  
RIDGE...A CLOSED LOW NEAR RECIFE IN NORTHEAST BRASIL ANCHORS A  
SHORT WAVE TROUGH OVER THE NORTHEAST STATES OF BRASIL. THIS  
PATTERN IS TO GENERALLY HOLD DURING THE NEXT FEW DAYS. THE RIDGE  
ALOFT IS TO VENT THE AFOREMENTIONED CONVECTION ACROSS THE  
SOUTHEAST-CENTRAL STATES OF BRASIL...AS WELL AS ACROSS NORTHWEST  
SOUTH AMERICA. OVER SOUTHERN COLOMBIA-NORTHERN PERU/EASTERN  
ECUADOR AND NORTHERN AMAZONAS IN BRASIL EXPECTING MODERATE  
CONVECTION WITH ACCUMULATION OF 20-35MM/DAY. UNDER THE INFLUENCE  
OF THE UPPER LEVEL LOW TO THE EAST...SCATTERED CONVECTION IS TO  
AFFECT TOCANTINS/GOIAS-AMAZON RIVER DELTA REGION IN BRASIL...WITH  
MAXIMA OF 15-20MM/DAY OVER THE NEXT COUPLE OF DAY. THROUGH THE END  
OF THE WEEK THIS IS TO BECOME MORE ACTIVE/BETTER ORGANIZED...WITH  
MAXIMA OF 20-35MM ON THURSDAY AND 30-60MM ON FRIDAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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