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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1826Z Feb 15, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 PM EST THU FEB 15 2018

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

MODEL DISCUSSION (VALID FROM FEB 15 AT 0000 UTC): CONFIDENCE IN
THE FORECAST DECREASES RAPIDLY FROM 96-108 HRS TO THE SOUTH OF
30S. ALSO...UNDER A WEAK STEERING FLOW IN TROPICAL SOUTH AMERICA
BY MID-LATE CYCLE...MODELS DIVERGE SIGNIFICANTLY ON THEIR SOLUTION
OF THE PLACEMENT AND INTENSITY OF THE AREAS OF CONVECTION AND
PRECIPITATION AFTER 84-96 HRS. CONFIDENCE IS HIGH THROUGH 84 HRS
AND DECREASES AFTER.

SOUTHERN SOUTH AMERICA

INTERMITTENT MOISTURE PLUMES ARE ARRIVING INTO SOUTHERN CHILE. THE
NEXT PLUME WILL ARRIVE LATE ON THURSDAY TO PRODUCE MAXIMA OF
15-30MM/DAY IN AYSEN/LOS LAGOS IN CHILE. ANOTHER FRONT WILL ARRIVE
WITH A SUBTROPICAL MOISTURE PLUME ON FRIDAY EVENING. THIS WILL
SUSTAIN ACCUMULATIONS OF 15-20MM/DAY DURING FRIDAY-EARLY SATURDAY.
AFTER THIS PERIODS...ACTIVITY WILL CONSTRAIN TO COLD AIR CUMULUS.
THIS WILL SUSTAIN MAXIMA OF 10-15MM/DAY BY
SATURDAY-SUNDAY...DECREASING AFTER

TO THE EAST ACROSS ARGENTINA...MOISTURE WILL GRADUALLY RETURN FROM
THE CYCLE AS A NORTHERLY LOW-LEVEL JET PERSISTS FROM NORTHERN
ARGENTINA INTO PATAGONIA. TWO WEAK SHORT WAVE TROUGHS WILL CROSS
THE ANDES ONE ON THURSDAY AND THE SECOND ON FRIDAY. AS A
RESPONSE...ISOLATED THUNDERSTORMS WILL INCREASE IN COVERAGE
THROUGH FRIDAY. BY FRIDAY-SATURDAY EXPECTING MAXIMA PEAKING AT
15-25MM/DAY IN INTERIOR PORTIONS OF CENTRAL AND NORTHERN
ARGENTINA...WHILE EXPECTING MAXIMA OF 10-15MM/DAY IN LA
PAMPA/NORTHERN PATAGONIA. A NEW BURST IN ACTIVITY IS EXPECTED BY
SUNDAY-MONDAY IN ASSOCIATION WITH A COLD FRONT FORECAST TO EXTEND
ACROSS NORTHERN PATAGONIA-CUYO BY SUNDAY EVENING. THIS WILL
SUSTAIN MAXIMA OF 15-25MM/DAY...WITH THE RISK OF ISOLATED SEVERE
CONVECTION. ACCUMULATIONS WILL DECREASE AFTER.

TROPICAL SOUTH AMERICA

THE SUBTROPICAL UPPER RIDGE/BOLIVIAN HIGH IS FORECAST TO MEANDER
OVER SOUTHERN PERU/PACIFIC OCEAN EARLY IN THE CYCLE TO THEN WEAKEN
AND LOSE STRUCTURE. BY SATURDAY EVENING...MODELS SUGGEST THE RIDGE
CENTERING OVER ICA IN SOUTHWESTERN PERU...WHILE A DISORGANIZED
PATTERN EXTENDS ACROSS THE AMAZON BASIN. THIS SHOULD LEAD TO A
DECREASE IN ACCUMULATIONS IN THE CENTRAL/SOUTHERN AMAZON BY THE
LATE WEEKEND...AND A MEANDERING OF STRONGEST CONVECTION INTO THE
NORTHERN AMAZON. MODELS SUGGEST THE RIDGE REFORMING IN MATO
GROSSO-SOUTHEASTERN BRASIL DURING EARLY NEXT WEEK. AT LOW
LEVELS...ENHANCED MOISTURE CONVERGENCE EARLY IN THE CYCLE WILL
SUSTAIN ACCUMULATIONS OF 35-70MM/DAY IN CENTRAL/NORTHERN PERU AND
ECUADOR...TO DECREASE AFTER FRIDAY. EAST ACROSS THE CENTRAL AMAZON
EXPECTING MAXIMA OF 20-35MM. BY FRIDAY-SUNDAY...UNDER THE AID OF A
DIVERGENT PULSE OF THE MADDEN JULIAN OSCILLATION...EXPECTING
ACCUMULATIONS TO INCREASE ACROSS THE NORTHERN AMAZON. EXPECTING
MAXIMA OF 20-40MM/DAY STRETCHING FROM EASTERN ECUADOR ACROSS MOST
OF NORTHWESTERN BRASIL INTO CENTRAL PARA.

TO THE EAST ACROSS THE BRAZILIAN NORDESTE/NORTHERN COAST...AN
UPPER TROUGH EXTENDING ZONALLY ALONG THE AMAZON DELTA IS ENHANCING
UPPER DIVERGENCE. AT LOS LEVELS THE SOUTH ATLANTIC ITCZ BAND HAS
FORMED AND IS ENHANCING MOISTURE CONVERGENCE. THIS WILL PERSIST
THROUGH THE CYCLE TO SUSTAIN ACCUMULATIONS OF 25-50MM/DAY ON A
DAILY BASIS.

IN CENTRAL-WESTERN SOUTH AMERICA...CHACO...NORTHERN
PARAGUAY...BOLIVIA...AN INCREASE IN PRECIPITATION IS EXPECTED ON
FRIDAY THROUGH SUNDAY IN ASSOCIATION WITH INCREASING PRECIPITABLE
WATER...AND DYNAMICAL FORCING ENHANCED BY APPROACHING UPPER
TROUGH. THIS WILL LOWER THE PRESSURES AND ENHANCE MOISTURE
CONVERGENCE IN SOUTHERN BOLIVIA/CHACO ON FRIDAY EVENING THROUGH
SATURDAY MORNING. THIS WILL SUSTAIN ACCUMULATIONS OF 20-40MM/DAY
FROM FRIDAY AFTERNOON THROUGH EARLY SATURDAY WITH THE RISK OF
NOCTURNAL MCS FORMATION. DURING SATURDAY-SUNDAY...EXPECTING THE
DEVELOPMENT OF HEAVY RAIN PRODUCING THUNDERSTORMS ALONF THE SELVA
ALTA OF SOUTHERN/CENTRAL PERU INTO THE BO0LIVIAN YUNGAS AND THE
CHACO...TO SUSTAIN MAXIMA OF 25-50MM/DAY. BY
SUNDAY-MONDAY...LARGEST ACCUMULATIONS WILL ORGANIZE ACROSS
PARAGUAY/SOUTHERN BOLIVIA...WHERE EXPECTING MAXIMA OF 30-60MM/DAY.

IN THE ALTIPLANO...EXPECTING A GRADUAL DECREASE IN ACCUMULATIONS
AS THE SUBTROPICAL UPPER RIDGE RELOCATES AND FAVORS THE
DEVELOPMENT OF MID-UPPER WESTERLIES MEANDERING NORTHWARD FROM
SOUTHERN BOLIVIA ON WEDNESDAY...TO THE LAKE TITICACA REGION BY
SUNDAY. DAILY ACCUMULATIONS WILL BE IN THE 10-15MM/DAY RANGE WHERE
CONVECTION OCCURS. LOCALLY HIGHER AMOUNTS ARE EXPECTED IN SOUTHERN
PERU ON THURSDAY...AND THE EASTERN CORDILLERA OF SOUTHERN PERU AND
BOLIVIA ON FRIDAY...WHERE MAXIMA WILL REACH 15-25MM/DAY. IN
ECUADOR...ENHANCED MOISTURE CONVERGENCE WILL SUSTAIN MAXIMA OF
25-50MM/DAY ON THURSDAY. THIS WILL DECREASE ON FRIDAY TO INCREASE
ONCE AGAIN ON SATURDAY TO MAXIMA OF 25-50MM/DAY. A DECREASE
FOLLOWS.

BALBINO...INMET (BRASIL)
POMIER...SENAMHI (BOLIVIA)
GALVEZ...WPC (USA)