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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1707Z Nov 19, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1207 PM EST WED NOV 19 2014

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

MODEL DISCUSSION (VALID FROM NOVEMBER 19 AT 00UTC): THE SYSTEM OF
CONCERN IS A MID LEVEL TROUGH ENTERING THE SOUTHERN CONE EARLY IN
THE CYCLE. THE GLOBAL MODELS ARE SLOWLY COMING TO AN AGREEMENT ON
HOW THIS FEATURE IS GOING TO EVOLVE. BUT THE GFS IN PARTICULAR IS
EXPERIENCING TIMING PROBLEMS THAT NEED TO BE RESOLVED...AS IT IS
DISPLAYING POOR CYCLE-TO-CYCLE CONTINUITY.

THE 500 HPA TROUGH ENTERS SOUTHERN-CENTRAL CHILE EARLY IN THE
CYCLE. THROUGH 54-60 HRS IT IS TO STALL OVER AND WEST OF THE
ANDES...BUT BY 54-60 HRS IT IS TO THEN SPILL ACROSS CUYO IN
ARGENTINA. THROUGH 78-84 HRS IT IS TO THEN TRACK ACROSS RIO DE LA
PLATA BASIN-URUGUAY... ENTERING THE WESTERN ATLANTIC BY 96 HRS.
ALTHOUGH THE MODELS AGREE ON THE TIMING OF THIS WAVE...THE
EUROPEAN MODELS TEND TO FAVOR A SLIGHTLY DEEPER/STRONGER
PERTURBATION THAN THE GFS...AND THIS IS FAIRLY CONSISTENT WITH
PREVIOUS FORECASTS. AS SUGGESTED BY THE MEAN OF THE GLOBAL
ENSEMBLES...THERE IS A GOOD CHANCE THAT THE GFS IS TO START
CORRECTING IN FAVOR OF A DEEPER TROUGH PATTERN.
AT LOW LEVELS THIS SI TO SUSTAIN A SURFACE FRONT ACROSS RIO DE LA
PLATA/URUGUAY TO NORTHWEST ARGENTINA EARLY IN THE CYCLE...WHERE IT
IS TO MEANDER THROUGH 60-72 HRS. BY 84-96 HRS...UNDER INFLUENCE OF
THE MID LEVEL TROUGH...A FRONTAL WAVE IS TO DEVELOP OFF THE COAST
OF BUENOS AIRES. THIS IS TO QUICKLY DEEPEN AS IT MEANDERS EAST
INTO THE WESTERN SOUTH ATLANTIC. AS THE FRONT MEANDERS NORTH
ACROSS CENTRAL TO NORTHERN ARGENTINA THIS IS TO SUSTAIN DEEP
CONVECTION WITH MAXIMA OF 25-50MM. BY 36-60 HRS...AS SHORT WAVE
ENERGY SPILLS ACROSS THE ANDES...THIS IS TO INCREASE TO 40-80MM IN
POSSIBLE MESO SCALE CONVECTIVE SYSTEM. THROUGH 72-84 HRS THE HEAVY
RAINS ARE TO SPREAD NORTH INTO EASTERN BOLIVIA-PARAGUAY-SOUTHERN
STATES OF BRASIL. BUT AS THE MID LEVEL TROUGH MEANDERS
AWAY...ACTIVITY IS TO QUICKLY WEAKEN LATER IN THE CYCLE.

MID/UPPER LEVEL RIDGE IS TO THEN ESTABLISH ACROSS THE EASTERN
PACIFIC. PROGRESSIVE SHORT WAVE PERTURBATIONS ARE TO THEN STREAM
ACROSS THE DRAKE PASSAGE/TIERRA DEL FUEGO. THROUGH 72-96 HRS THE
RIDGE WEAKENS AS THE TROUGHS DEEPEN INTO THE SOUTHERN CONE OF
SOUTH AMERICA. EARLY IN THE CYCLE ENERGY IS TO FOCUS ON
CONTINENTAL AREA TO THE SOUTH OF 48S. BUT THROUGH 84-96 HRS
EXPECTING THIS TO AMPLIFY NORTH INTO SOUTHERN CHILE/PATAGONIA TO
ENVELOP AREA SOUTH OF 40S. AT LOW LEVELS IT IS TO THEN SUSTAIN AN
ELONGATED FRONT ACROSS TIERRA DEL FUEGO/EXTREME SOUTHERN PORTIONS
OF CHILE EARLY IN THE CYCLE... WITH BOUNDARY TO GRADUALLY MEANDER
NORTH INTO PATAGONIA/SOUTHERN CHILE BY 66-72 HRS. THROUGH 72-84
HRS THIS IS TO SUSTAIN AN INCREASE IN CONVECTION ACROSS CHILE
SOUTH OF PUERTO MONTT...WITH RAINFALL MAXIMA IN THE AREA EXPECTED
TO PEAK AT 05-10MM. SCATTERED CONVECTION IS TO THEN PERSIST
THROUGH 120-132 HRS.

NORTH OVER THE CONTINENT...BROAD RIDGE IS TO DOMINATE NORTHERN
SOUTH AMERICA OVER THE NEXT FEW DAYS...AS IT IS TO CENTER ON A
CLOSED HIGH THAT MEANDERS BETWEEN RONDONIA-MATO GROSSO IN BRASIL.
PERSISTENT RIDGE ALOFT IS TO VENT DEEP CONVECTION ACROSS BRASIL
AND PERU...WITH MOST ACTIVE CONVECTION EXPECTED TO THE NORTH OF
13S/14S TO CLUSTER BETWEEN ACRE-AMAZONAS AND PARA-MATO
GROSSO...WITH DAILY MAXIMA TO RANGE BETWEEN 20-35MM IN SCATTERED
CONVECTION. LOCALLY HIGHER AMOUNTS...HOWEVER...ARE HIGHLY LIKELY.
OTHER CONVECTION IS EXPECTED ACROSS THE CENTRAL-SOUTHERN JUNGLE OF
PERU TO NORTHERN PORTIONS OF BOLIVIA. IN THIS AREA LOW LEVEL
NORTHERLY WINDS ARE TO SUSTAIN TOPOGRAPHICALLY INDUCED
CONVECTION...WITH RAINFALL AMOUNTS OF 15-30MM OVER THE NEXT THREE
DAYS.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)