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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1639Z Mar 24, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 PM EDT TUE MAR 24 2020

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

FORECAST DISCUSSION FROM MARCH 24/17UTC: THE GLOBAL MODELS
CONTINUE TO STRUGGLE DURING THE MEDIUM RANGE PERIOD...FAILING TO
REACH A CONSENSUS ON HOW PERTURBATIONS ENTERING THE SOUTHERN CONE
ARE TO EVOLVE. THEY REMAIN IN DISAGREEMENT ON THE AMPLITUDE AND
SPEED OF THE SHORT WAVE TROUGHS REACHING THE DOMAIN... WHILE ALSO
FAILING TO MAINTAIN CYCLE-TO-CYCLE CONTINUITY. AS A RESULT...OUR
CONFIDENCE IN THE FORECAST BEYOND 72/84 HRS IS LOW.

A MID LEVEL TROUGH OFF THE CENTRAL COAST OF CHILE REMAINS THE
SYSTEM OF CONCERN DURING THE SHORT RANGE PERIOD. THIS IS TO
MEANDER OFF THE COAST OF CHILE THROUGH WEDNESDAY MORNING...TO THEN
SPILL ACROSS THE CENTRAL ANDES TO CENTRAL ARGENTINA LATER IN THE
DAY...WHERE IT REMAINS WHILE GRADUALLY WEAKENING. AT LOW
LEVELS...THE MID LEVEL TROUGH WILL INTERACT WITH A SURFACE FRONT
MOVING TO CENTRAL ARGENTINA EARLY IN THE CYCLE. UNDER FAVORABLE
UPPER DYNAMICS...THE MODELS CONSISTENTLY FORESEE FAVORABLE
CONDITIONS FOR AN MCS TO FORM OVER CENTRAL ARGENTINA EARLY ON
WEDNESDAY MORNING. THIS WILL SUSTAIN HEAVY/POTENTIALLY SEVERE
CONVECTION..WITH RAINFALL AMOUNTS OF 35-70MM.  ON WEDNESDAY TO
THURSDAY THE FOCUS OF THE ACTIVITY SHIFTS TO MENDOZA-CORDOBA IN
ARGENTINA...WITH MAXIMA DECREASING TO 30-60MM...WITH SIMILAR
AMOUNTS OVER JUJUY/SALTA TO THE NORTHWEST DURING THE AFTERNOON TO
EARLY MORNING HOURS ON THURSDAY. ON THURSDAY-FRIDAY ACTIVITY
ACROSS CENTRAL ARGENTINA WEAKENS TO 10-15MM/DAY.

MID LEVEL RIDGE TO THE SOUTH...MEANWHILE...EXTENDS FROM SRN CHILE
TO THE DRAKE PASSAGE/BELLINGSHAUSEN SEA. THIS RIDGE HOLDS ITS
GROUND THROUGH THURSDAY AFTERNOON...THEN WEAKENS UNDER PRESSURE
FROM LONG WAVE TROUGH STREAMING TOWARDS THE SOUTHERN CONE. AS IT
CLASHES WITH THE RIDGE...THE TROUGH WILL SPLIT IN TWO...WITH ITS
SOUTHERN HALF TO QUICKLY PULL ACROSS THE DRAKE PASSAGE/ANTARCTIC
PENINSULA WHILE TRAILING NORTHERN END REMAINS OFF THE SOUTH COAST
OF CHILE. THIS IS TO THEN MEANDER EAST ACROSS SOUTHERN CHILE TO
PATAGONIA IN ARGENTINA LATER ON FRIDAY. AT LOW LEVELS...AN
ELONGATED FRONT WILL STREAM ACROSS TIERRA DEL FUEGO TO SOUTHERN
CHILE LATER ON WEDNESDAY...WITH A DEEP FRONTAL LOW REACHING SRN
CHILE LATER ON THURSDAY.THIS WILL THEN PULL ACROSS THE SRN
CONE...DRIVING THE FRONT NORTH ACROSS PATAGONIA TO LA
PAMPA-CENTRAL CHILE ON FRIDAY EVENING. OVER SOUTHERN CHILE THIS
WILL INITIALLY TRIGGER MODERATE CONVECTION WITH ACCUMULATION OF
10-15MM. THROUGH SATURDAY THIS INTENSIFIES...INCREASING TO
15-20MM. OVER CENTRAL ARGENTINA...EXPECTING SIMILAR AMOUNTS ON
SATURDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH OVER THE ALTIPLANO
OF BOLIVIA ANCHORS THE SUBTROPICAL RIDGE OVER NORTHWEST SOUTH
AMERICA. THIS TENDS TO WEAKEN WHILE MEANDERING WEST INTO THE
EASTERN PACIFIC LATER DURING THE WEEK. MEANWHILE...IT IS TO INDUCE
THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS THE NORTHEAST
STATES OF BRASIL.  THE DEEPENING TROUGH WILL SUSTAIN ORGANIZED
DEEP CONVECTION ACROSS THE NORTHEAST STATES OF BRASIL. INITIALLY
THIS IS TO RESULT IN MAXIMA OF 35-70MM. ON THURSDAY THIS DECREASES
TO 25-50MM...WITH LESSER AMOUNTS LATER IN THE WEEK. OVER MATO
GROSSO-RONDONIA TO THE WEST...ACTIVITY IS TO CLUSTER ALONG A LOW
LEVEL TROUGH OVER BRASIL...WITH MAXIMA OF 20-35MM/DAY. OVER
CENTRAL BOLIVIA-SOUTHERN PERU...MEANWHILE...ACTIVITY IS EXPECTED
TO INTENSIFY ON WEDNESDAY-THURSDAY...INCREASING TO 40-80MM WHILE
BUILDING NORTH ACROSS SOUTHERN TO CENTRAL JUNGLE OF PERU. AS IT
BUILDS NORTH...THE MAXIMA DECREASES TO 25-50MM ON FRIDAY-SATURDAY..

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