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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1647Z Mar 26, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1247 PM EDT THU MAR 26 2020

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

FORECAST DISCUSSION FROM MARCH 26/17UTC: THE GFS AND THE EUROPEAN
MODELS ARE SLOWLY COMING TO A CONSENSUS ON HOW THE PATTERN IS
GOING TO EVOLVE THROUGH 96-108 HRS...WITH THE GFS IN PARTICULAR
MAKING MAJOR CORRECTIONS TO ITS PREVIOUS FORECAST.
THIS...HOWEVER...DOES NOT LAST THROUGH THE MEDIUM RANGE
PERIOD...WITH MODELS ONCE AGAIN DIVERGING ON THE AMPLITUDE AND
SPEED OF PROPAGATION OF PERTURBATIONS ENTERING THE SOUTH AMERICAN
DOMAIN ON DAYS 05-07. THUS...OUR CONFIDENCE IN THE FORECAST BEYOND
96/108 HRS REMAINS LOW.

MEANDERING CELL OF THE SUBTROPICAL RIDGE TO THE NORTH IS STEERING
A MID LEVEL SHORT WAVE TROUGH ACROSS NORTHERN ARGENTINA...TO MOVE
TO URUGUAY/SOUTHERN BRASIL EARLY ON SATURDAY MORNING. THIS IS TO
THEN AMPLIFY ACROSS THE SOUTHERN TO THE SOUTHEAST STATES OF BRASIL
LATER DURING THE WEEKEND. OVER CENTRAL ARGENTINA THIS IS TO
SUSTAIN SCATTERED CONVECTION DURING THE NEXT DAY OR SO...WITH
ACCUMULATION OF 10-15MM. OVER CENTRAL BOLIVIA-SOUTHERN JUNGLE OF
PERU...THIS WILL TRIGGER A MESO SCALE CONVECTIVE SYSTEM...WITH
MAXIMA OF 40-80MM THROUGH FRIDAY MORNING. ON FRIDAY-SATURDAY
EXPECTING ADDITIONAL RAINFALL AMOUNTS OF 25-50MM...WITH MOST
ACTIVE ON THE CENTRAL AND SOUTHERN JUNGLE OF PERU. OVER PARAGUAY
THIS WILL SUSTAIN SCATTERED CONVECTION ON FRIDAY...WITH
ACCUMULATION OF 25-50MM. ON SATURDAY THIS INCREASES TO 30-60MM
WHILE BUILDING EAST ACROSS MISIONES IN ARGENTINA TO PARANA/SANTA
CATARINA IN SOUTHERN BRASIL. ON SUNDAY-MONDAY...AS THE MID LEVEL
TROUGH AMPLIFIES ACROSS SOUTHEAST BRASIL...IT WILL SUSTAIN
SCATTERED DEEP CONVECTION ACROSS SAO PAULO-MATO GROSSO...WITH
MAXIMA OF 20-30MM.

A SLOW TO EVOLVE MID/UPPER LEVEL TROUGH ON THE SOUTHERN STREAM IS
TO EXTEND OFF THE COAST OF CHILE EARLY IN THE CYCLE. THIS IS TO
THEN MEANDER EAST ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA ON
FRIDAY-SATURDAY. AS IT EMERGES OVER THE WESTERN ATLANTIC LATER ON
SATURDAY...THE GFS NOW FORECASTS THE TROUGH TO WEAKEN WHILE
SHEARING SHORT WAVE ENERGY UNDER A RIDGE TO THE EAST. AT LOW
LEVELS...THIS SUSTAINS A FRONTAL TROUGH OVER THE SOUTHERN
CONE...WITH FRONT TO MEANDER ACROSS SOUTHERN PATAGONIA-CHILE LATER
TODAY. THROUGH SATURDAY THE FRONT ADVANCES ACROSS LA PAMPA/CENTRAL
ARGENTINA...WHERE IT IS NOW EXPECTED TO STALL. OVER SOUTHERN CHILE
MOST ACTIVE CONVECTION IS EXPECTED EARLY IN THE CYCLE...TO SUSTAIN
MAXIMA OF 15-20MM. AS IT MEANDERS NORTH ACROSS LA PAMPA TO CENTRAL
ARGENTINA...THIS IS TO SUSTAIN LIGHT TO MODERATE CONVECTION ON
SATURDAY...WITH MAXIMA OF 05-10MM. THROUGH MONDAY...UNDER
FAVORABLE JET DYNAMICS...THIS GRADUALLY INCREASES TO 15-30MM/DAY.

AT 250 HPA...THE SUBTROPICAL RIDGE WILL CONFINE TO THE EASTERN
PACIFIC-PERU-BOLIVIA/ACRE-AMAZONAS IN BRASIL...WITH AXIS TO CENTER
ON A CLOSED HIGH THAT IS TO MEANDER BETWEEN THE SOUTHERN SIERRA OF
PERU AND THE ALTIPLANO OF BOLIVIA. AS THE RIDGE HOLDS...A TROUGH
IS TO INITIALLY EXTEND ACROSS SOUTHEAST TO CENTRAL BRASIL. BUT
THIS IS TO GRADUALLY WEAKEN ON FRIDAY-SATURDAY. AS PREVIOUSLY
INDICATED...THIS WILL BE REPLACED BY A DEEPENING TROUGH LATER
DURING THE WEEKEND. OVER NORTHEAST BRASIL THIS IS TO INITIALLY
FAVOR SCATTERED CONVECTION WITH MAXIMA OF 25-50MM. THROUGH
SATURDAY THIS IS TO WEAKEN...DECREASING TO 15-30MM WHILE SHIFTING
WEST TO TOCANTINS/GOIAS-PARA IN BRASIL. OTHER CONVECTION IS TO
CLUSTER ALONG THE NEAR EQUATORIAL TROUGH OVER NORTHERN
BRASIL...WITH MAXIMA OF 20-35MM. THIS TENDS TO BECOME MORE ACTIVE
THROUGH THE WEEKEND...WITH FOCUS OF THE ORGANIZED CONVECTION
SHIFTING WEST ACROSS AMAZONAS IN BRASIL TO SOUTHERN
COLOMBIA/NORTHERN PERU...WITH MAXIMA OF 30-60MM IN SCATTERED DEEP
CONVECTION. OTHER CONVECTION IS EXPECTED ACROSS WESTERN
ECUADOR...WITH CONVECTION EXPECTED TO GRADUALLY INTENSIFY AS
ENHANCED BY A DEEPENING LOW LEVEL TROUGH TO THE WEST. IN THIS AREA
THE MAXIMA IS EXPECTED TO PEAK AT 20-40MM/DAY.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)