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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1630Z Oct 23, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1230 PM EDT THU OCT 23 2014

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

MODEL DISCUSSION (VALID FROM OCTOBER 23 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN EXCELLENT AGREEMENT REGARDING FORECAST
EVOLUTION. FORECAST CONFIDENCE HAS INCREASED WITH RESPECT TO
PREVIOUS RUNS...WITH SOME DIFFERENCE IN THE SPEED OF THE SYSTEMS
SOUTH OF 40S AFTER 96-108 HRS..

EMBEDDED IN A TIGHT BELT OF WEST-SOUTHWESTERLIES...A SHORT WAVE
TROUGH WILL ENTER TIERRA DEL FUEGO LATER TODAY. THIS WILL PRODUCE
WIDESPREAD SHOWERS WITH MAXIMUM ACCUMULATIONS OF 05-10MM/DAY.
AMOUNTS ARE TO DECREASE AFTERWARDS WITH A SMALL INCREASE IN
SHOWERS EARLY NEXT WEEK.

NEXT SYSTEM TO AFFECT CHILE AND PORTIONS OF CENTRAL ARGENTINA IS A
LARGE NORTHERN STREAM TROUGH CURRENTLY BLOCKED TO THE EASTERN
PACIFIC AROUND 90W. THIS TROUGH WILL START MOVING TOWARDS THE
CONTINENT DURING SATURDAY...CROSSING THE ANDES DURING SUNDAY INTO
EARLY MONDAY. MODELS ARE FORECASTING A STRONG RIDGE BUILDING TO
THE EAST. THIS WILL CAUSE THE TROUGH TO BECOME NEGATIVELY TILTED
AND DEVELOP STRONG UPPER DIVERGENCE AND HEIGHT FALLS EXCEEDING 100
GPM/DAY AHEAD OF THE MAIN AXIS. THIS WILL INTERACT WITH MOIST AND
UNSTABLE AIR MASS BUILDING ACROSS CENTRAL ARGENTINA. ALTHOUGH THE
INSTABILITY IS NOT EXPECTED TO BE EXTREME AS IN OTHER CASES...THE
DYNAMICS WILL BE ROBUST ENOUGH TO SUSTAIN SEVERE CONVECTION AND
HEAVY RAINFALL. EXPECTING LOCALIZED MAXIMUM AMOUNTS OF 40-80MM/DAY
IN STRONGEST THUNDERSTORMS DEVELOPING DURING SUNDAY ACROSS LA
PAMPA AND SOUTHWESTERN BUENOS AIRES PROVINCE. A COLD FRONT WILL
THEN RAPIDLY MOVE TO EXTEND ALONG THE RIO DE LA PLATA-CORDOBA
REGIONS BY MONDAY EVENING. ASSOCIATED CONVECTION WILL PRODUCE
SIMILAR AMOUNTS WITH THE RISK OF SEVERE CELLS.

NORTH ACROSS THE CONTINENT...A SHORT WAVE TROUGH IS PROGRESSING
EAST ACROSS THE CENTRAL ANDES. THIS TROUGH IS INTERACTING WITH AN
UNSTABLE AIR MASS ESTABLISHED ACROSS SOUTHERN BOLIVIA AND
NORTHWESTERN ARGENTINA. LOW-LEVEL EASTERLIES WILL CONTINUE
ENHANCING OROGRAPHIC UPLIFT AND FEEDING DEVELOPING STORMS...TO
SUSTAIN MAXIMA OF 20-40MM/DAY FROM TUCUMAN/SANTIAGO DEL ESTERO
INTO THE CHACO PARAGUAYO AND SOUTHERN BOLIVIA THROUGH EARLY
FRIDAY. TROUGH IS FORECAST TO SLOW DOWN AFTERWARDS TO CONTINUE
VENTILATING CONVECTION ACROSS THE NORTHERN HALF OF PARAGUAY INTO
MOST OF THE BOLIVIAN LOWLANDS AND WESTERN BRASIL. THIS WILL LEAD
TO MAXIMA OF 20-45MM/DAY ON FRIDAY INTO EARLY SUNDAY...WITH FOCUS
OF CONVECTION GRADUALLY MEANDERING NORTHEASTWARD INTO WESTERN
BRASIL. OTHER REGION OF ACTIVE CONVECTION WILL BE THE NORTHEASTERN
AMAZON COVERING MOST OF PARA/EASTERN AMAZONAS INTO PARTS OF
MARANHAO AND TOCANTINS. HERE...VENTILATION WILL BE FAVORABLE AS
THE REGION WILL LIE UNDER THE DIFFLUENT PATTERN BETWEEN A BROAD
CAVADO DO NORDESTE ACROSS NORTHEASTERN BRASIL...AND A RETREATING
RIDGE TO THE WEST ACROSS THE WESTERN AMAZON. THIS WILL LEAD TO
MAXIMA OF 20-45MM/DAY EARLY IN THE CYCLE...GRADUALLY CONSTRAINING
TO CENTRAL AMAZONIA AS THE FORECAST CYCLE PROGRESSES. AN
ACTIVATION IS ALSO EXPECTED IN SOUTHEASTERN BRASIL AS SOUTHERN
TIER OF AFOREMENTIONED TROUGH AMPLIFIES. THIS WILL ENHANCE
VENTILATION AND INTERACT WITH UNSTABLE AIRMASS BUILDING ACROSS
GOIAS/MINAS GERAIS/ESPIRITO SANTO/EASTERN RIO DO JANEIRO.
EXPECTING SCATTERED THUNDERSTORMS TO DEVELOP ON SUNDAY AND MONDAY
WITH MAXIMA OF 25-50MM/DAY. ISOLATED HIGHER AMOUNTS ARE ALWAYS
POSSIBLE IN STRONGEST THUNDERSTORMS.

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