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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1601Z Dec 04, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1101 AM EST THU DEC 04 2014

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

MODEL DISCUSSION (VALID FROM DECEMBER 04 AT 00UTC): THE GFS AND
EUROPEAN MODELS ARE SLOWLY REACHING A CONSENSUS ON HOW PATTERN IS
TO EVOLVE DURING THE NEXT FEW DAYS. THIS IS WELL SUPPORTED BY THE
MEAN OF THE GLOBAL ENSEMBLES. OUR CONFIDENCE IN THE FORECAST IS
HIGH.

AT MID/UPPER LEVELS A HIGH AMPLITUDE LONG WAVE TROUGH EXTENDS OVER
THE EASTERN PACIFIC. A RIDGE LIES TO THE EAST...WITH AXIS SOUTH
ACROSS ARGENTINA TO THE ANTARCTIC PENINSULA. AS THE TROUGH TO THE
WEST PRESSES EAST THIS WILL FORCE THE RIDGE TO FLATTEN. BUT IN
THIS PROCESS THE TROUGH IS TO SPLIT IN TWO...WITH SOUTHERN HALF TO
THEN ACCELERATE ACROSS THE ANTARCTIC PENINSULA/DRAKE PASSAGE WHILE
THE NORTHERN HALF STALLS OFF THE CENTRAL COAST OF CHILE. BY 60-72
HRS THE NORTHERN STREAM VORTEX IS TO SPILL ACROSS THE CENTRAL
ANDES OF CHILE TO CUYO IN ARGENTINA...AND BY 96 HRS IT IS TO PULL
ACROSS RIO DE LA PLATA BASIN/BUENOS AIRES PROVINCE. AT 250 HPA A
SUBTROPICAL JET IS TO ACCOMPANY THIS TROUGH AS IT MOVES ACROSS
CHILE TO ARGENTINA...TO SUSTAIN AN UPPER DIVERGENT PATTERN AS IT
PULLS ACROSS THE CONTINENT. AT LOW LEVELS THE LONG WAVE TROUGH
SUSTAINS AN ELONGATED FRONT ACROSS SOUTHERN CHILE/PATAGONIA.
THROUGH 48 HRS THE FRONT UNDULATES NORTH ACROSS LA PAMPA-SOUTHERN
CUYO. BY 72 HRS...AS THE MID LEVEL TROUGH MOVES ACROSS CHILE TO
ARGENTINA...A FRONTAL LOW IS TO DEVELOP OVER BUENOS AIRES
PROVINCE/RIO DE LA PLATA BASIN. THIS DEEPENS OVER THE WESTERN
ATLANTIC...DRAWING THE FRONT FARTHER NORTH ACROSS URUGUAY/RIO
GRANDE DO SUL TO THE NORTHERN PROVINCES IN ARGENTINA LATER IN THE
CYCLE. MOST ACTIVE CONVECTION OVER CHILE IS EXPECTED TO THE SOUTH
OF ISLA DE CHILOE...WHERE FRONT IS TO ENHANCE MOISTURE
CONVERGENCE. THIS IS TO PERSIST OVER THE NEXT COUPLE OF
DAYS...WITH RAINFALL AMOUNTS TO PEAK AT 10-15MM/DAY. OVER
ARGENTINA MOST ACTIVE IS EXPECTED ACROSS BUENOS AIRES
PROVINCE-CORDOBA LATER ON DAY 03...WITH MODERATE CONVECTION
EXPECTED TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM IN POTENTIALLY
SEVERE CONVECTION.

TIGHT BELT OF MID LEVEL WESTERLIES IS TO THEN ESTABLISH ACROSS THE
SOUTH PACIFIC TO THE SOUTHERN CONE OF SOUTH AMERICA. PROGRESSIVE
SHORT WAVE PERTURBATIONS ARE TO THEN STREAM ACROSS THE DRAKE
PASSAGE/SOUTHERN CONE...WITH ONE TO REACH SOUTHERN CHILE BY 84 HRS
AND ANOTHER BY 108-120 HRS. THESE ARE TO SUSTAIN AN ELONGATED
FRONT OVER THE SOUTHERN CONE OF SOUTH AMERICA...WITH MOISTURE
CONVERGING ACROSS EXTREME SOUTHERN PORTIONS OF CHILE. IN THIS AREA
EXPECTING SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM/DAY.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL HIGH IS TO
MEANDER WEST ACROSS BOLIVIA TO SOUTHERN PERU/NORTHERN CHILE
THROUGH 36-48 HRS. IT IS TO THEN REMAIN OVER THE EASTERN PACIFIC
OFF THE SOUTHERN COAST OF PERU THROUGH 132-144 HRS. AS THE HIGH
RELOCATES...ASSOCIATED RIDGE OVER THE CONTINENT IS TO GRADUALLY
WEAKEN. EARLY IN THE CYCLE IT IS TO ENVELOP PERU-BOLIVIA-NORTHWEST
BRASIL. BY THE END OF THE CYCLE IT IS TO CONFINE TO SOUTHERN
PERU-BOLIVIA AND NORTHERN CHILE. AS THE RIDGE RELOCATES TO THE
WEST...AN UPPER LEVEL TROUGH IS TO THEN ESTABLISH A FOOTHOLD
ACROSS CENTRAL/EASTERN BRASIL. THIS IS TO REMAIN WELL ORGANIZED
OVER THE NEXT FEW DAY. EARLY IN THE CYCLE...MOST ACTIVE CONVECTION
IS TO FOCUS ACROSS CENTRAL-NORTHERN PERU TO EASTERN ECUADOR...WITH
MAXIMA OF 30-60MM. BUT AS THE RIDGE WEAKENS IT IS TO DECREASE TO
15-20MM/DAY IN DIURNAL CONVECTION. ACROSS MATO GROSSO-BAHIA/MINAS
GERAIS THE TROUGH ALOFT IS TO SUSTAIN AN INCREASE IN CONVECTION
THROUGH 72-108 HRS...WITH DAILY MAXIMA OF 20-45MM. STRONG
TOPOGRAPHICAL FORCING OVER MINAS GERAIS AND PORTIONS OF BAHIA IS
LIKELY TO RESULT IN LOCALIZED MAXIMA IN EXCESS OF FORECAST
GUIDANCE.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)