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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1655Z Apr 03, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1255 PM EDT FRI APR 03 2020

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

FORECAST DISCUSSION FROM APR 03/17UTC: OVER THE WESTERN ATLANTIC
AND PORTIONS OF SOUTH AMERICA...THE GLOBAL MODELS REMAIN IN GOOD
AGREEMENT THROUGH THE END OF THE CYCLE...FORECASTING TWO VERY
INTENSE MID LATITUDE CYCLONES TO DEVELOP. THE FIRST IS CURRENTLY
EXPERIENCING A RAPID RATE OF INTENSIFICATION AS IT MEANDERS OFF
THE SOUTH COAST OF BRASIL. THE NEXT IS TO FORM TO THE SOUTH OF 30S
AND BETWEEN 50W-40W ON MONDAY...WITH THE GLOBAL MODELS HINTING AT
POSSIBILITY OF EXPLOSIVE CYCLOGENESIS. UPSTREAM OVER THE EASTERN
PACIFIC...THE MODELS CONTINUE TO STRUGGLE WITH THE FORECAST
PATTERN DURING THE MEDIUM RANGE PERIOD...NOW FAVORING A STRONGER
RIDGE TO BUILD ACROSS THE SOUTHERN CONE TO THE DRAKE PASSAGE. THIS
CHANGE IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLES...SO
THE MODELS MIGHT BE TRENDING IN THE RIGHT DIRECTION.

AT 500 HPA...A CLOSED LOW ON THE NORTHERN STREAM LIES OFF THE
SOUTH COAST OF BRASIL...WITH AXIS TO GRADUALLY WEAKEN TO AN OPEN
TROUGH AS IT PULLS ACROSS 30W EARLY ON SUNDAY MORNING. AT LOW
LEVELS THE TROUGH ALOFT SUSTAINS A DEEPENING LOW...WITH AXIS
REACHING MAXIMUM INTENSITY EARLY IN THE CYCLE. IT IS TO THEN
SLOWLY WEAKEN WHILE MEANDERING TO THE EAST-SOUTHEAST ACROSS THE
SOUTHERN ATLANTIC. ASSOCIATED SURFACE FRONT MEANDERS NORTH ACROSS
SOUTHEAST BRASIL TO ALIGN ALONG 20S LATER TODAY. ON SATURDAY IT
LOSES UPPER LEVEL SUPPORT...WITH PORTION OVER THE CONTINENT
EXPECTED TO FRONTOLIZE. THE REMNANTS OVER THE ATLANTIC WILL
GRADUALLY WEAKEN THROUGH MONDAY EVENING. MEANWHILE...THIS WILL
ENHANCE LOW LEVEL MOISTURE CONVERGENCE ACROSS NORTHERN SAO
PAULO-RIO DE JANEIRO...TO SUSTAIN MODERATE CONVECTION WITH
ACCUMULATION OF 20-30MM/DAY. ON SUNDAY...AS THE FRONT WEAKENS TO A
SHEAR LINE...ACTIVITY ACROSS ESPIRITO SANTO WILL SURGE...TO
SUSTAIN MAXIMA OF 35-70MM. NOTE THAT DURING THIS PERIOD THE
ENVIRONMENTAL CONDITIONS MIGHT BECOME FAVORABLE FOR A HEAVY
RAINFALL PRODUCING ECHO TRAINING EVENT...WITH SOME OF THE MODELS
SHOWING LOCALIZED MAXIMA IN EXCESS OF 100MM.

FARTHER SOUTH...A BROAD MID LEVEL TROUGH ON THE SOUTHERN STREAM
EXTENDS NORTH FROM THE ANTARCTIC PENINSULA TO SOUTHERN PORTIONS OF
CHILE/PATAGONIA IN ARGENTINA. ON SUNDAY...AS A RIDGE BUILDS TO THE
WEST...IT IS TO SUSTAIN THE NORTHWARD AMPLIFICATION OF THE TROUGH
ACROSS PATAGONIA TO LA PAMPA/CENTRAL ARGENTINA. THE TROUGH REACHES
MAXIMUM AMPLITUDE ON MONDAY...WHEN IT IS TO EXTEND TO THE
NORTH-NORTHWEST ACROSS THE WESTERN ATLANTIC TO URUGUAY/SOUTHERN
BRASIL-SOUTHEAST PARAGUAY. EARLY ON TUESDAY THE MID LEVEL TROUGH
SPLITS IN TWO...SHEARING A SHORT WAVE TROUGH ON THE NORTHERN
STREAM THAT QUICKLY EVOLVES INTO A DEEP/CLOSED LOW TO THE
EAST-SOUTHEAST OF URUGUAY. AT LOW LEVELS...THIS REFLECTS AS A
BROAD TROUGH OVER THE SOUTHEAST PACIFIC-SOUTHERN CHILE/PATAGONIA
IN ARGENTINA...WITH A FRONTAL SYSTEM STREAMING ACROSS CHILE TO
PATAGONIA EARLY IN THE CYCLE. THESE ARE TO SUSTAIN MODERATE
RAINFALL AMOUNTS WITH MAXIMA OF 15-20MM/DAY. THROUGH SUNDAY
EVENING THE LOW LEVEL TROUGH IS TO AMPLIFY...DRIVING THE FRONT
NORTH ACROSS PATAGONIA TO LA PAMPA. BUILDING RIDGE TO THE SOUTH
AND WEST WILL TIGHTEN THE PRESSURE GRADIENT OVER THE SOUTHERN CONE
ON SUNDAY...FAVORING A PAMPERO LOW LEVEL JET THAT DISPLACES THE
FRONT NORTH ACROSS RIO DE LA PLATA BASIN-CUYO IN ARGENTINA. AS IT
ACCELERATES ACROSS MID SECTIONS OF SOUTH AMERICA ON MONDAY...THE
FRONT WILL THEN TRIGGER A HEAVY RAINFALL PRODUCING PREFRONTAL
SQUALL LINE ACROSS PARAGUAY-JUJUY/SALTA IN NORTHWEST ARGENTINA
INTO SOUTHERN BOLIVIA...WITH RAINFALL MAXIMA OF 50-100MM HIGHLY
PROBABLE. ACTIVITY IS TO THEN WRAP ALONG THE LEE OF THE ANDES OVER
CENTRAL BOLIVIA...WITH MAXIMA OF 40-80MM.

AT 250 HPA...AN ILL ORGANIZED CELL OF THE SUBTROPICAL RIDGE
CONFINES TO BOLIVIA-WESTERN BRASIL-PERU...WITH AXIS TO BECOME
SOMEWHAT BETTER ORGANIZED EARLY NEXT WEEK. MEANWHILE...IN
INTERACTION WITH THE SUBEQUATORIAL RIDGE OVER NORTHERN SOUTH
AMERICA...THIS WILL SUSTAIN A DIVERGENT PATTERN ALOFT THAT IS TO
VENT DEEP CONVECTION ACROSS NORTHERN BRASIL-AMAZONIA IN COLOMBIA
TO EASTERN ECUADOR. INITIALLY...MOST ACTIVE CONVECTION IS TO
CLUSTER ALONG AN EASTERLY WAVE/TRADE WIND SURGE RACING ACROSS
NORTHERN SOUTH AMERICA. AS IT ENTERS PARA IN BRASIL THIS WILL
RESULT IN ACCUMULATION OF 30-60MM IN SCATTERED DEEP CONVECTION. AS
IT BUILDS WESTWARD ACROSS AMAZONAS TO SOUTHERN COLOMBIA/NORTHERN
PERU ON SUNDAY...THE MAXIMA INCREASES TO 35-70MM. HEAVY CONVECTION
IS TO PERSIST THROUGH MONDAY EVENING WHILE BUILDING WESTWARD INTO
EASTERN ECUADOR. SIMULTANEOUSLY...ACTIVITY OVER PARA/AMAZON RIVER
DELTA IS TO GRADUALLY EBB DURING THE WEEKEND...DECREASING TO
MAXIMA OF 20-40MM/DAY...WITH LESSER AMOUNTS EXPECTED EARLY NEXT
WEEK.

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