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South American Forecast Discussion
 
(Latest Discussion - Issued 1648Z Nov 22, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1148 AM EST WED NOV 22 2017

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM NOV 22 AT 0000 UTC): BROAD MID/UPPER
LEVEL TROUGH DOMINATES THE FLOW ACROSS THE WESTERN ATLANTIC...
ENVELOPING AREA BETWEEN 60W-20W AND TO THE SOUTH OF 20S. LATER
TODAY MEAN TROUGH AXIS RELOCATES ACROSS 40W...NEARING 20W LATER ON
THURSDAY. AT LOW LEVELS THIS SUSTAINS A SURFACE FRONT ACROSS
SOUTHEAST BRASIL-MATO GROSSO TO NORTHERN BOLIVIA. THE BOUNDARY IS
TO REMAIN NEARLY STATIONARY WHILE GRADUALLY WEAKENING LATER ON
FRIDAY. DEEP TROPICAL MOISTURE IS TO CONVERGE ALONG AND NORTH OF
THIS BOUNDARY. EARLY IN THE PERIOD THIS IS TO FAVOR HEAVY
CONVECTION ACROSS NORTHERN SAO PAULO-SOUTHERN MINAS GERAIS-RIO DE
JANEIRO...WITH MAXIMA OF 30-60MM. ON THURSDAY THIS DECREASES TO
20-45MM. ACROSS MATO GROSSO TO WESTERN MINAS GERAIS EXPECTING
MAXIMA OF 15-25MM OVER THE NEXT COUPLE OF DAYS...INCREASING TO
20-30MM ON FRIDAY-SATURDAY. OVER NORTHERN BOLIVIA TO SOUTHERN PERU
THIS IS TO ALSO FAVOR SCATTERED CONVECTION...WITH MAXIMA OF
20-45MM EXPECTED THROUGH THURSDAY MORNING...DECREASING TO 15-20MM
ON THURSDAY-FRIDAY.

SIMULTANEOUSLY...A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN
STREAM IS TO LIFT ACROSS THE BELLINGSHAUSEN SEA/DRAKE PASSAGE TO
PATAGONIA IN ARGENTINA LATER TODAY. IT IS TO QUICKLY MOVE OFF THE
COAST OF ARGENTINA ON THURSDAY AFTERNOON. THIS SUSTAINS A SURFACE
FRONT ACROSS PATAGONIA IN ARGENTINA LATER TODAY...REACHING RIO DE
LA PLATA BASIN ON THURSDAY...WHERE IT IS FORECAST TO STALL. AS IT
ENTERS SOUTHERN CHILE THIS IS TO FAVOR LIGHT CONVECTION WITH
MAXIMA OF 15-20MM...WHILE ACROSS PATAGONIA IN ARGENTINA/CENTRAL
PROVINCES IT IS TO ONLY TRIGGER WIDELY ISOLATED CONVECTION.

A 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 FRIDAY THE SHORT WAVE TROUGH WILL SPILL ACROSS THE
CENTRAL ANDES TO CUYO IN ARGENTINA...PULLING ACROSS
URUGUAY/SOUTHERN BRASIL LATER ON SATURDAY. AS IT SPILLS ACROSS THE
ANDES...THE MID LEVEL TROUGH WILL THEN INTERACT WITH THE SURFACE
FRONT MEANDERING OVER NORTHERN ARGENTINA. THIS IS TO SUSTAIN
CYCLOGENESIS WHILE INDUCING THE GRADUAL INTENSIFICATION OF THE
SURFACE FRONT. THIS WILL THEN DRIVE THE FRONT NORTH ACROSS
SOUTHERN BRASIL-PARAGUAY LATER ON SATURDAY. ON FRIDAY THIS IS TO
FAVOR LIGHT TO MODERATE CONVECTION ACROSS CHACO
ARGENTINO-CORRIENTES AND PORTIONS OF PARAGUAY. ON SATURDAY THE
MAXIMA OVER PARAGUAY IS TO PEAK AT 40-80MM...WHILE OVER RIO GRANDE
DO SUL IN SOUTHERN BRASIL THE MAXIMA PEAKS AT 20-40MM. OTHER
CONVECTION IS TO CLUSTER ACROSS THE ALTIPLANO OF BOLIVIA...WITH
MAXIMA OF 20-30MM.

NORTH OVER THE CONTINENT...IN A WELL DEFINED SUMMER FLOW
PATTERN...T 200 HPA HIGH OVER BOLIVIA IS TO ANCHOR A CELL OF THE
SUBTROPICAL RIDGE ACROSS NORTHERN SOUTH AMERICA. THE RIDGE IS TO
DOMINATE THE FLOW TO THE NORTH OF 25S/30S DURING THE NEXT FEW
DAYS. AS IT MEANDERS OVER THE CONTINENT A TROUGH TO THE EAST IS TO
EXTEND OVER THE NORTHEAST STATES OF BRASIL. THE RIDGE ALOFT IS TO
CONTINUE VENTING DEEP CONVECTION ACROSS NORTHERN SOUTH AMERICA.
MOST ACTIVE IS TO AFFECT AMAZONAS IN BRASIL-SOUTHERN
COLOMBIA-NORTHERN JUNGLE OF PERU/EASTERN ECUADOR...WITH MAXIMA OF
20-35MM/DAY. THROUGH FRIDAY AFTERNOON EXPECTING SLIGHT
INTENSIFICATION WHEN THE MAXIMA PEAKS AT 20-40MM. OVER NORTHEAST
BRASIL...MEANWHILE...THE UPPER LEVEL LOW/TROUGH IS TO SUSTAIN A
CONVERGENT PATTERN THAT IS TO INHIBIT ORGANIZED DEEP CONVECTION
DURING THE NEXT FEW DAYS.

OVIEDO...SHN (ARGENTINA)
VANNUCCI...SMN (ARGENTINA)
RIVAS...SENAMHI (PERU)
DAVISON...WPC (USA)