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South American Forecast Discussion
 
(Latest Discussion - Issued 1555Z Apr 24, 2019)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EDT WED APR 24 2019

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

MODEL DISCUSSION FROM APRIL 24/00 UTC: THE GLOBAL MODELS DISPLAY
POOR CYCLE-TO-CYCLE CONTINUITY OVER THE SOUTH PACIFIC...MAKING
NUMEROUS ADJUSTMENTS TO AMPLITUDE AND SPEED OF SHORT WAVE
PERTURBATIONS ENTERING THE DOMAIN. THIS LEADS TO A LOWER
CONFIDENCE IN THE FORECAST DURING THE MEDIUM RANGE PERIOD. OVER
THE CONTINENT...CONTINUITY IS GOOD THROUGH 84-96 HRS...THEN START
TO DIVERGE ON HOW SHORT WAVE TROUGH SPILLING ACROSS THE NORTHERN
ANDES OF CHILE EVOLVES.

PROGRESSIVE MID/UPPER LEVEL TROUGH RACES ACROSS THE SOUTHEAST
PACIFIC TO THE DRAKE PASSAGE/ANTARCTIC PENINSULA EARLY ON FRIDAY
MORNING. DURING THE DAY IT PULLS ACROSS THE SOUTHERN
CONE/ANTARCTIC PENINSULA TO THE SOUTHWEST ATLANTIC. AT LOW LEVELS
THIS WILL SUSTAIN A DEEPENING LOW OVER THE BELLINGSHAUSEN SEA
LATER ON THURSDAY...THAT WEAKENS AS IT PULLS ACROSS THE ANTARCTIC
PENINSULA TO THE WEDDELL SEA ON FRIDAY. ASSOCIATED FRONT MAKES
LANDFALL OVER SOUTHERN CHILE EARLY ON FRIDAY MORNING...TO MEANDER
NORTH ACROSS PATAGONIA IN ARGENTINA-SOUTHERN CHILE ON
FRIDAY-SATURDAY. AS IT MAKES LANDFALL THIS WILL SUSTAIN SCATTERED
CONVECTION WITH ACCUMULATION OF 10-15MM ON FRIDAY AND 05-10MM ON
SATURDAY.

A DEEPER TROUGH IS TO FOLLOW...WITH THE GFS/UKMET FORECASTING MID
LEVEL AXIS TO RACE ACROSS 100W TO 30S ON SATURDAY. THIS ENTERS
SOUTHERN REGIONS OF CHILE ON SUNDAY. AT LOW LEVEL THIS IS TO ALSO
SUSTAIN A BROAD TROUGH OVER THE SOUTHEAST PACIFIC LATER ON
SATURDAY...THAT MOVES EAST ACROSS THE SOUTHERN CONE ON SUNDAY. THE
HIGHER AMPLITUDE TROUGH WILL SUSTAIN A SUBTROPICAL CONNECTION AS
IT ENTERS SOUTHERN CHILE ON SUNDAY...FAVORING LIGHT TO MODERATE
RAINFALL AMOUNTS IN POTENTIALLY DEEP CONVECTION.

ON THE NORTHERN STREAM...AT 500 HPA...SHORT WAVE TROUGH MEANDERS
OFF THE CENTRAL/NORTHERN COAST OF CHILE WHILE CENTERING ON A
CLOSED LOW TO THE WEST OF SANTIAGO/VALPARAISO CHILE. AS IT
MEANDERS OFF THE COAST OF CHILE...THIS IS TO SHEAR SHORT WAVE
ENERGY EAST ACROSS THE ANDES INTO NORTHERN ARGENTINA. THIS PATTERN
PERSISTS THROUGH THURSDAY EVENING...WITH AXIS THEN SPILLING ACROSS
THE ANDES TO MID SECTIONS OF SOUTH AMERICA ON FRIDAY. OVER
URUGUAY-MESOPOTAMIA VALLEY IN ARGENTINA AND RIO GRANDE DO SUL IN
BRASIL THIS IS TO THEN FAVOR HEIGHT FALLS OF 40-60GPM. THE TROUGH
IS TO THEN SLOWLY PULL ACROSS PARAGUAY/SOUTHERN BRASIL...CLEARING
THE SOUTH COAST OF BRASIL ON SUNDAY. AT LOW LEVELS...THE TROUGH
ALOFT WILL INTERACT WITH A MEANDERING SURFACE FRONT OVER SOUTHERN
BRASIL-NORTHERN ARGENTINA. THIS IS TO INITIALLY TRIGGER ORGANIZED
DEEP CONVECTION/MESO SCALE CONVECTIVE SYSTEM WITH MAXIMA OF
40-80MM...WITH SLIGHT RISK OF SEVERE CONVECTION. THROUGH
FRIDAY...INFLOW OF MID LEVEL ENERGY WILL SUSTAIN A FRONTAL WAVE
OVER ENTRE RIOS/CORRIENTES IN ARGENTINA...THAT IS TO OCCLUDE ON
SATURDAY. AS THE SYSTEM INTENSIFIES...THIS IS TO SUSTAIN HEAVY
RAINFALL AMOUNTS ACROSS CORRIENTES-MISIONES IN ARGENTINA/SOUTHEAST
PARAGUAY AND RIO GRANDE DO SUL IN BRASIL...WITH MAXIMA IN THIS
AREA INCREASING TO 50-100MM. OVER PARAGUAY-MATO GROSSO DO SUL AND
PARANA/SANTA CATARINA THE MAXIMA WILL RANGE BETWEEN 30-60MM.


NORTH OVER THE CONTINENT...A 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE IS THE DOMINANT FEATURE TO THE NORTH OF 20S. A
RETROGRESSING LOW/TROUGH WILL MEANDER WEST ACROSS BAHIA IN BRASIL
EARLY IN THE CYCLE...TO TOCANTINS/GOIAS LATER ON THURSDAY...WHERE
IT IS TO REMAIN THROUGH THE WEEKEND. THE SUBEQUATORIAL RIDGE TO
THE NORTH...MEANWHILE...EXTENDS WEST FROM THE TROPICAL ATLANTIC TO
EQUATORIAL SOUTH AMERICA...WITH AXIS FAVORING A DIVERGENT PATTERN
ALOFT THAT IS VENTING DEEP CONVECTION ALONG THE NEAR EQUATORIAL
TROUGH IN BRASIL. THIS...IN COMBINATION WITH EASTERLY WAVES
PROPAGATING OVER THE TROPICAL ATLANTIC...WILL CONTINUE FAVORING
PERIODS OF HEAVY RAINFALL AMOUNTS ALONG THE NORTH COAST OF
BRASIL...WESTWARD ACROSS PARA-AMAZONAS-SOUTHERN COLOMBIA/NORTHERN
PERU. ACROSS PARA-NORTHERN AMAZONAS HEAVY CONVECTION WILL SUSTAIN
MAXIMA OF 50-100MM...WHILE OVER AMAZONAS THE MAXIMA IS TO PEAK AT
40-80MM WITH THESE PERTURBATIONS.

DIAZ... DMC (CHILE)
MATHIAS...CHM (BRASIL)
DAVISON...WPC (USA)