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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1529Z Sep 08, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 AM EDT TUE SEP 08 2020

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

FORECAST DISCUSSION FROM SEP 08/15UTC: THE GLOBAL MODELS AGREE ON
THEIR FORECAST OF A HIGHLY AMPLIFIED MID/UPPER LEVEL TROUGH TO
STREAM ACROSS THE EASTERN PACIFIC...WITH AXIS TO PULL ACROSS THE
SOUTHERN CONE OF SOUTH AMERICA TO THE WESTERN ATLANTIC EARLY ON
WEDNESDAY MORNING. AT LOW LEVELS THIS WILL SUSTAIN A PROGRESSIVE
FRONT THAT RACES ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA
EARLY IN THE PERIOD...REACHING LA PAMPA/CENTRAL CHILE LATER THIS
EVENING. UNDER INFLUENCE OF A SHORT WAVE RIDGE TO THE SOUTH...THE
FRONT WILL PROPAGATE ACROSS CENTRAL ARGENTINA ON WEDNESDAY. ON
THURSDAY THE BOUNDARY MOVES FARTHER NORTH...REACHING THE SOUTHERN
STATES OF BRASIL-NORTHERN ARGENTINA...WHERE IT MERGES WITH AN OLD
BOUNDARY TO THE NORTH. AS IT ENTERS SOUTHERN CHILE THIS WILL
SUSTAIN MODERATE COASTAL CONVECTION...WITH ACCUMULATION OF
10-15MM...WHILE OVER CENTRAL CHILE IT INCREASES TO 15-25MM. AS THE
FRONT RACES ACROSS NORTHERN ARGENTINA TO SOUTHERN BRASIL ON
THURSDAY IT WILL TRIGGER SEVERE CONVECTION AND MODERATE RAINFALL
AMOUNTS...WITH MAXIMA OF 20-40MM.

THE NEXT MID LEVEL PERTURBATION IS TO CLOSELY FOLLOW...REACHING
SOUTHERN/CENTRAL CHILE EARLY ON THURSDAY MORNING. THIS IS TO ALSO
QUICKLY STREAM ACROSS THE SOUTHERN CONE. AT LOW LEVELS THE TROUGH
ALOFT SUSTAINS A PROGRESSIVE FRONT WITH A DEEP OCCLUDED LOW
ENTERING SOUTHERN CHILE ON WEDNESDAY EVENING. DRIVEN BY A BUILDING
RIDGE TO THE WEST...THE FRONTAL TROUGH ACCELERATES ACROSS THE
SOUTHERN CONE ON THURSDAY...WITH THE FRONT RACING ACROSS CENTRAL
ARGENTINA/RIO DE LA PLATA BASIN ON FRIDAY. OVER SOUTHERN CHILE
THIS IS TO SUSTAIN A SECOND ROUND OF MODERATE CONVECTION...WITH
MAXIMA OF 15-20MM ON WEDNESDAY. ON THURSDAY...ACTIVITY BUILDS
NORTH ALONG THE COAST ACROSS TEMUCO TO CONCEPCION...WITH MAXIMA
DECREASING TO 10-15MM. OVER THE BUENOS AIRES PROVINCE THE
ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR A ROUND OF SEVERE
THUNDERSTORMS ON THURSDAY...WITH MAXIMA OF 15-20MM. THE RISK OF
SEVERE CONVECTION PERSISTS THROUGH FRIDAY AS THE FOCUS OF THE
FRONTAL CONVECTION SHIFTS TO NORTHERN URUGUAY/RIO GRANDE DO SUL
AND CORRIENTES IN ARGENTINA...WITH MAXIMA OF 25-50MM. ON SATURDAY
ACTIVITY WEAKENS...WITH MAXIMA OF 15-30MM.

UPSTREAM PATTERN CHANGES ON FRIDAY-SATURDAY...WITH THE GFS AND
ECMWF BOTH AGREEING ON A RIDGE TO BUILD SOUTH BETWEEN 110W-80W TO
60S. PROGRESSIVE PERTURBATIONS ARE TO STREAM TO THE SOUTH OF THIS
RIDGE...WITH A FAIRLY STRONG SHORT WAVE TROUGH ENTERING SOUTHERN
CHILE LATER ON FRIDAY EVENING. BUT AS IT MOVES ACROSS THE SOUTHERN
CONE TO THE WESTERN ATLANTIC THE TROUGH TENDS TO SLOW DOWN WHILE
AMPLIFYING NORTH ACROSS THE SOUTHERN CONE. OVER SOUTHERN CHILE
THIS IS TO SUSTAIN A PROGRESSIVE FRONT LATER IN THE WEEK...RACING
ACROSS PATAGONIA TO LA PAMPA ON SATURDAY MORNING. OVER SOUTHERN
CHILE THIS WILL LIKELY TRIGGER LIGHT TO MODERATE RAINFALL AMOUNTS
WITH MAXIMA OF 10-15MM...WITH POTENTIAL FOR MODERATE SNOWFALL
AMOUNTS ACROSS THE SOUTHERN ANDES.

NORTH OVER THE CONTINENT...AT 250 HPA...A SHORT WAVE RIDGE OVER
SOUTHEAST BRASIL IS TO DRIVE AN UPPER LEVEL TROUGH WEST ACROSS
EQUATORIAL SOUTH AMERICA...WITH UPPER LEVEL PERTURBATION MOVING
ACROSS PARA TO AMAZONAS IN BRASIL LATER TODAY. BUT AS IT REMAINS
CUT OFF FROM THE FLOW...THE TROUGH IS EXPECTED TO WEAKEN AS IT
MEANDERS WEST ACROSS SOUTHERN COLOMBIA-NORTHERN PERU TO EASTERN
ECUADOR ON THURSDAY-FRIDAY. MEANWHILE...THE COLD CORE TROUGH ALOFT
WILL ENHANCE CONVECTIVE INSTABILITY ACROSS PARA-AMAZONAS IN BRASIL
TO SOUTHERN COLOMBIA-NORTHERN JUNGLE OF PERU/EASTERN
ECUADOR...WHERE IT IS TO SUSTAIN MODERATE RAINFALL AMOUNTS WITH
ACCUMULATION OF 15-20MM. ACTIVITY PERSISTS THROUGH FRIDAY...BUT AS
THE UPPER LEVEL TROUGH WEAKENS THE DAILY MAXIMA WILL GRADUALLY
DECREASE TO 10-15MM IN SCATTERED DEEP CONVECTION.

DAVISON/GALVEZ...WPC (USA)