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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1615Z Jun 28, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EDT THU JUN 28 2018

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

MODEL DISCUSSION (VALID FROM JUN 28 AT 0000 UTC): MEANDERING
SURFACE FRONT EXTENDS ACROSS THE SOUTH ATLANTIC TO SOUTHERN
BRASIL-PARAGUAY. MID LEVEL TROUGH STREAMING ACROSS THE CONTINENT
IS TO INTERACT WITH THIS BOUNDARY...TRIGGERING SCATTERED DEEP
CONVECTION ACROSS PARAGUAY-CORRIENTES/MISIONES IN ARGENTINA AND
SOUTHERN BRASIL. IN THIS AREA THE MAXIMA IS FORECAST TO PEAK AT
20-40MM IN POTENTIALLY SEVERE CONVECTION. ON
FRIDAY-SATURDAY...UNDER INFLUENCE OF A NORTHERLY JET...THE FRONT
WILL SLOWLY MOVE SOUTH TO NORTHERN ARGENTINA. THIS IS TO THEN
FAVOR ISOLATED TO SCATTERED CONVECTION WITH ACCUMULATION OF
15-25MM/DAY.

FARTHER UPSTREAM...THE GLOBAL MODELS ARE SLOWLY REACHING A
CONSENSUS ON HOW DEEPENING MID LEVEL TROUGH ON THE NORTHERN STREAM
IS TO EVOLVE AS IT APPROACHES THE CENTRAL COAST OF CHILE EARLY ON
SATURDAY MORNING. ON SUNDAY THIS IS TO THEN RAPIDLY WEAKEN AS IT
SPILLS ACROSS THE CENTRAL ANDES TO ARGENTINA. AS THE MID LEVEL
TROUGH INTENSIFIES...THE SURFACE TROUGH WILL CENTER ON A DEEP LOW
OVER ARCHIPELAGO DE JUAN FERNANDEZ LATER ON SATURDAY. IN A TIGHT
PRESSURE GRADIENT...EXPECTING TROPICAL STORM INTENSITY WINDS ALONG
THE CENTRAL COAST OF CHILE ON SATURDAY-SUNDAY MORNING...WITH WINDS
TO PEAK AT 35-50KT. THE ASSOCIATED FRONT IS TO QUICKLY PUSH EAST
ACROSS THE CENTRAL ANDES TO CUYO IN ARGENTINA LATER ON
SATURDAY/EARLY SUNDAY MORNING. AS IT SPILLS ACROSS THE ANDES THIS
IS TO INTERACT WITH AFOREMENTIONED FRONT TO THE
NORTH...REINFORCING THE OLD BOUNDARY. ON THE CENTRAL REGIONS OF
CHILE THIS WILL TRIGGER SCATTERED COASTAL CONVECTION WITH MAXIMA
OF 15-20MM ON SATURDAY TO SUNDAY...WHILE OVER THE CENTRAL ANDES
EXPECTING SNOWFALL AMOUNTS OF 20-30CM. OVER RIO DE LA PLATA
BASIN-URUGUAY THIS IS TO SUSTAIN RAINFALL AMOUNTS OF 20-35MM IN
POTENTIALLY SEVERE CONVECTION.

ON THE SOUTHERN STREAM FLOW...A BROAD/LOW AMPLITUDE TROPOSPHERIC
TROUGH EXTENDS OVER THE DRAKE PASSAGE TO SOUTHERN CHILE/ARGENTINA.
OVER THE NEXT DAY OR SO THIS IS TO MEANDER EAST. AS IT PULLS
AWAY...UNDER INFLUENCE OF A BUILDING RIDGE TO THE WEST...A HIGHER
AMPLITUDE TROUGH IS TO THEN TAKE ITS PLACE. ON FRIDAY-SATURDAY THE
TROUGH AMPLIFIES ACROSS THE ANTARCTIC PENINSULA-DRAKE
PASSAGE...WHILE ON SATURDAY IT IS TO ENVELOP THE SOUTHERN CONE OF
SOUTH AMERICA. ON ITS WAKE A POLAR RIDGE IS TO THEN BUILD ACROSS
SOUTHERN CHILE TO ARGENTINA...TO ANCHOR ON A 1033-1035 HPA HIGH.
THE BUILDING POLAR RIDGE WILL ADVECT COLD AIR NORTH ACROSS
PATAGONIA TO CENTRAL PROVINCES IN ARGENTINA...WHERE IT IS TO
SUSTAIN BELOW FREEZING TEMPERATURES. OVER TIERRA DEL FUEGO AND THE
SOUTHERN ANDES THIS IS TO FAVOR SOLID PRECIPITATION...WITH
SNOWFALL AMOUNTS OF 05-10CM EARLY IN THE CYCLE...INCREASING TO
10-15CM ON SATURDAY. DUE TO STRONG TOPOGRAPHICAL FORCING LOCALLY
HIGHER AMOUNTS ARE HIGHLY PROBABLE.

NORTH OVER THE CONTINENT...AT 200 HPA...A SHORT WAVE TROUGH OVER
CENTRAL BRASIL SPLITS THE SUBTROPICAL RIDGE IN TWO CELLS. ONE CELL
CONFINES TO THE TROPICAL ATLANTIC/NORTHEAST SOUTH AMERICA...WHILE
THE OTHER DOMINATES THE TROPICAL EASTERN PACIFIC/NORTHWEST SOUTH
AMERICA. THE CELL TO THE WEST IS EXPECTED TO BUILD OVER THE NEXT
FEW DAYS. AS THE RIDGE BUILDS...IT WILL DISPLACE THE SHORT WAVE
TROUGH INTO NORTHEAST BRASIL EARLY ON FRIDAY MORNING. AS IT
STREAMS ACROSS EASTERN BRASIL THIS WILL BE ACCOMPANIED BY A FAIRLY
STRONG SUBTROPICAL JET MAXIMA. THE JET ALOFT IS TO FAVOR AN UPPER
DIVERGENT PATTERN ALONG THE COAST OF BRASIL BETWEEN RIO DE JANEIRO
AND SOUTHERN BAHIA. THIS WILL VENT COASTAL CONVECTION. EARLY IN
THE PERIOD EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY. THROUGH
SATURDAY THIS INCREASES TO 15-30MM...TO THEN WANE LATER IN THE
CYCLE. OTHER CONVECTION TO THE NORTH IS EXPECTED TO CLUSTER OVER
EQUATORIAL SOUTH AMERICA. IN THIS AREA EXPECTING RAINFALL MAXIMA
OF 15-20MM IN SCATTERED CONVECTION...WITH LOCALLY HIGHER AMOUNTS
TO AFFECT NORTHERN AMAZONAS IN BRASIL-SOUTHERN COLOMBIA...WHERE
THE MAXIMA WILL PEAK AT 20-30MM.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)