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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1639Z Mar 31, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 PM EDT TUE MAR 31 2020

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

FORECAST DISCUSSION FROM MARCH 30/17UTC: AN UPPER LEVEL CELL OF
THE SUBTROPICAL RIDGE SPANS FROM NORTHWEST ARGENTINA...ACROSS
BOLIVIA TO WESTERN BRASIL. THIS IS TO HOLD NEARLY UNCHANGED DURING
THE NEXT FEW DAYS...THEN GRADUALLY WEAKEN LATER IN THE WEEK.
MEANWHILE...THE RIDGE ALOFT IS STEERING A SHORT WAVE TROUGH ACROSS
THE SOUTHEAST STATES OF BRASIL TO THE WESTERN ATLANTIC...WHERE IT
IS EXPECTED TO AMPLIFY AS IT PHASES WITH OTHER PERTURBATIONS TO
THE SOUTH. AT LOW LEVELS...THE TROUGH ALOFT INTERACTS WITH A
SURFACE FRONT THAT TRAILS ACROSS THE SOUTH ATLANTIC TO NORTHERN
SAO PAULO-RIO DE JANEIRO IN BRASIL...WHILE ALSO FAVORING A
PREFRONTAL SHEAR LINE ACROSS SOUTHERN BAHIA. THE SHEAR LINE IS TO
FAVOR SCATTERED COASTAL CONVECTION...WITH ACCUMULATION OF
20-30MM/DAY OVER THE NEXT THREE DAYS. OVER RIO DE JANEIRO-NORTHERN
SAO PAULO TO MATO GROSSO...INITIALLY EXPECTING ACCUMULATION OF
15-20MM/DAY. ON TUESDAY THIS INCREASES TO 2-30MM WITH MOST INTENSE
FOCUSING OVER NORTHERN SAO PAULO/RIO DE JANEIRO-SOUTHERN MINAS
GERAIS...WHILE ON WEDNESDAY EXPECTING MAXIMA OF 20-40MM.

A MID LEVEL TROUGH ON THE NORTHERN STREAM FLOW IS TO CLOSELY
FOLLOW...ENTERING SOUTHERN/CENTRAL CHILE LATER ON TUESDAY. THROUGH
THURSDAY MORNING THIS IS TO THEN LIFT ACROSS THE RIO DE LA PLATA
BASIN...WHERE UNDER FAVORABLE JET DYNAMICS THE TROUGH IS FORECAST
TO INTENSIFY. AT LOW LEVELS...THIS WILL SUSTAIN CYCLOGENESIS ALONG
A MEANDERING FRONT OVER CENTRAL ARGENTINA LATER ON TUESDAY...WITH
THE SURFACE LOW DEEPENING AS IT LIFTS FROM LA PAMPA TO THE RIO DE
LA PLATA BASIN LATER ON WEDNESDAY. ON THURSDAY THE LOW IS TO
EXPERIENCE A RAPID RATE OF INTENSIFICATION WILE MEANDERING OFF THE
SOUTH COAST OF BRASIL. THIS...IN-TURN...WILL SUSTAIN A SOUTHERLY
LOW LEVEL JET ACROSS CENTRAL TO NORTHERN
ARGENTINA/PARAGUAY-SOUTHERN BOLIVIA. THIS WILL THEN DRIVE THE
SURFACE FRONT NORTH ACROSS CENTRAL TO NORTHERN ARGENTINA LATER ON
WEDNESDAY/EARLY ON THURSDAY MORNING...WHILE ALSO FAVORING A
PREFRONTAL SQUALL LINE. LATER ON THURSDAY THE FRONT MOVES NORTH
ACROSS PARANA/SANTA CATARINA IN SOUTHERN BRASIL TO CHACO
PARAGUAYO/SOUTHERN BOLIVIA. THE FRONT IS TO THEN ALIGN ALONG 20S
LATER ON FRIDAY. ACROSS THE BUENOS AIRES PROVINCE TO CENTRAL
ARGENTINA THIS IS TO SUSTAIN MAXIMA OF 35-70MM IN POTENTIALLY
SEVERE CONVECTION LATER ON TUESDAY AFTERNOON. THIS INCREASES TO
40-80MM ACROSS URUGUAY-NORTHERN ARGENTINA/SOUTHERN BOLIVIA ON
WEDNESDAY-THURSDAY. OVER CENTRAL BOLIVIA PEAK IN CONVECTION IS
EXPECTED ON THURSDAY-FRIDAY...WHEN THE SURGING SOUTHERLY FLOW WILL
LIKELY TRIGGER A HEAVY RAINFALL PRODUCING MCS WITH MAXIMA OF
50-100MM. THROUGH FRIDAY THE ACTIVITY STARTS TO WANE WHILE
BUILDING WEST ACROSS SOUTHERN TO CENTRAL JUNGLE IN PERU...WHERE IT
IS TO SUSTAIN MAXIMA OF 20-40MM.

A HIGHER AMPLITUDE TROUGH WILL THEN STREAM ACROSS THE SOUTHEAST
PACIFIC LATER IN THE WEEK...WITH BROAD/LONG WAVE TROUGH TO
ESTABLISH A SUBTROPICAL CONNECTION AS IT NEARS THE SOUTHERN CONE
OF SOUTH AMERICA. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH
OVER THE SOUTHEAST PACIFIC LATER ON WEDNESDAY...THAT AMPLIFIES
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER IN THE WEEK.
THE ASSOCIATED FRONT MOVES ACROSS TIERRA DEL FUEGO TO SOUTHERN
PATAGONIA EARLY ON THURSDAY MORNING...THEN NORTH ACROSS LA PAMPA
TO CENTRAL ARGENTINA/CHILE ON SATURDAY-SUNDAY. OVER SOUTHERN CHILE
THIS WILL TRIGGER MODERATE RAINFALL AMOUNTS WITH MAXIMA OF 10-15MM
EARLY ON THURSDAY. THROUGH THE DAY THIS IS TO INTENSIFY WHILE
BUILDING NORTH TO ISLA DE CHILOE...WITH MAXIMA INCREASING TO
15-20MM.

OTHER CONVECTION TO THE NORTH IS TO CLUSTER ALONG THE NEAR
EQUATORIAL TROUGH/ATLANTIC ITCZ AS IT MEANDERS OVER NORTHERN
BRASIL. IN THIS AREA...AS ENHANCED BY SHORT WAVE TROUGHS IN THE
EASTERLY TRADES...THERE IS A HIGH RISK OF MODERATE TO HEAVY
CONVECTION DURING THE NEXT 48-60 HRS. ALONG THE NORTH COAST OF
BRASIL TO NORTHERN PARA THE MAXIMA IS TO PEAK AT 25-50MM OVER THE
NEXT TWO DAYS...DECREASING TO 20-30MM ON WEDNESDAY. OVER WEASTERN
PARA--AMAZONAS TO SOUTHERN COLOMBIA/NORTHERN PERU...INITIALLY
EXPECTING MAXIMA OF 30-60MM. THIS SI TO GRADUALLY WEAKEN TO
20-40MM/DAY ON WEDNESDAY-THURSDAY...WHILE DURING THE LATTER PART
OF THE WEEK THE MAXIMA IN THIS AREA DECREASES TO 20-40MM.

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