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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1632Z Mar 13, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 PM EDT FRI MAR 13 2015

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

MODEL DISCUSSION (VALID FROM MARCH 13 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT ON FORECAST EVOLUTION
THROUGH 96-108 HRS. FORECAST CONFIDENCE STARTS DECREASING SOUTH OF
40S AFTERWARDS.

SUBTROPICAL RIDGE WILL CONTINUE CENTERING OFF THE COAST OF
NORTHERN CHILE AND MEANDERING INTO SOUTHERN PERU THROUGH THE
CYCLE. THE HIGH IS ALSO FORECAST TO EXPAND NORTHWARD...IMPROVING
VENTILATION ACROSS THE NORTHWESTERN AMAZON BASIN AND
ECUADOR/NORTHERN PERU. THIS...IN COMBINATION WITH THE ARRIVAL OF
THE DIVERGENT PHASE OF THE MJO...WILL LEAD TO AN INCREASE IN THE
COVERAGE OF CONVECTION AND ACCUMULATIONS. TO THE EAST...WEAKENING
TROUGH ACROSS CENTRAL BRASIL IS FORECAST TO LOSE DEFINITION DURING
SATURDAY AND MEANDER NORTHWARD TO ENHANCE VENTILATION ACROSS THE
CENTRAL AMAZON BASIN. LATER IN THE CYCLE...A NEW TROUGH WILL
GRADUALLY DIG ACROSS CENTRAL/WESTERN BRASIL TO EXTEND ALONG 
SOUTHERN BRASIL-EASTERN MATO GROSSO BY MONDAY-TUESDAY. THIS WILL
PROVIDE ADDITIONAL VENTILATION TO SUSTAIN HEAVY RAINFALL IN
CENTRAL PORTIONS OF TROPICAL SOUTH AMERICA. AT LOW-LEVELS...DEEP
MOIST AIRMASS REMNANT OF CONVECTION ASSOCIATED WITH THE WEAKENING
SACZ WILL MAKE IT WEST TO PROVIDE DEEP LAYER MOISTURE AND SUSTAIN
MODERATE TO HEAVY RAINFALL AMOUNTS. THROUGH EARLY SUNDAY EXPECTING
LARGEST AMOUNTS FROM THE AMAZON DELTA/TOCANTINS/MATO GROSSO
NORTHWEST INTO EASTERN ECUADOR WITH MAXIMA OF 25-50MM/DAY. DURING
SUNDAY INTO EARLY TUESDAY EXPECTING AN INCREASE IN MAXIMA TO
30-60MM/DAY FROM CENTRAL PARA WEST INTO EASTERN PERU/ECUADOR.
LARGEST AMOUNTS WILL THEN EXTEND FROM AMAZONAS IN BRASIL INTO
NORTHERN PERU/SOUTHERN COLOMBIA WITH MAXIMA OF 30-60MM/DAY.

ACTIVE CONVECTION IS ALSO EXPECTED ACROSS ANDEAN REGIONS OF
ECUADOR PERU AND BOLIVIA. DEEP MOISTURE POOL IS BUILDING IN THE
REGION WITH PRECIPITABLE WATER EXCEEDING 50MM ALONG COASTAL
ECUADOR INTO CENTRAL PERU. EAST OF THE ANDES PRECIPITABLE WATER IS
EXPECTED TO EXCEED 60MM STARTING SATURDAY INTO EARLY NEXT WEEK.
THIS...IN COMBINATION WITH VENTILATION AND ARRIVING DIVERGENT MJO
CONDITIONS WILL REACTIVATE DIURNAL CONVECTION IN THE REGION. IN
COASTAL ECUADOR AND THE WESTERN SLOPES OF THE ANDES EXPECTING
ACCUMULATIONS OF 20-40MM/DAY THROUGH EARLY SUNDAY INCREASING TO
25-50MM/DAY INTO EARLY NEXT WEEK. ISOLATED HIGHER AMOUNTS ARE
EXPECTED IN INTERACTION WITH OROGRAPHY. TO THE SOUTH ACROSS THE
PERUVIAN ANDES EXPECTING AMOUNTS IN THE ORDER OF 15-25MM/DAY
THROUGH THE CYCLE. AN ACTIVATION OF CONVECTION ACROSS THE BOLIVIAN
ALTIPLANO AND NORTHERN CHILE WILL LEAD TO MAXIMA OF 05-10MM/DAY
INTO EARLY NEXT WEEK.

ACROSS SOUTHERN SOUTH AMERICA...LONG WAVE PATTERN IS DOMINATING.
LARGE UPPER TROUGH IS CROSSING THE ANDES LEADING TO ABUNDANT COLD
AIR CUMULUS ACROSS SOUTHERN CHILE...WHERE EXPECTING MAXIMA OF
05-10MM/DAY THROUGH EARLY SATURDAY. ALSO THROUGH EARLY
SATURDAY...EAST OF THE ANDES...TROUGH/SURFACE FRONT INTERACTION
WITH MOIST AIR MASS AND LOW-LEVEL JET ACROSS CENTRAL ARGENTINA
WILL LEAD TO A NEW ROUND OF THUNDERSTORMS THAT WILL LEAD TO
ISOLATED MAXIMA OF 25-50MM/DAY FROM SAN LUIS/LA PAMPA INTO THE
CENTRAL AND SOUTHERN BUENOS AIRES PROVINCE. MAXIMA IS TO DECREASE
TO 15-20MM/DAY IN THUNDERSTORMS THAT DEVELOP DURING SATURDAY INTO
EARLY SUNDAY...MAINLY ACROSS CENTRAL ARGENTINA. ENHANCED EASTERLY
FLOW WILL INCREASE OROGRAPHIC UPLIFT ALONG THE NORTHERN
ARGENTINEAN ANDES TO PRODUCE SCATTERED MAXIMA OF 15-30MM/DAY
DURING SATURDAY INTO EARLY SUNDAY...DECREASING AFTERWARDS. MAIN
TROUGH WILL MOVE AWAY INTO THE ATLANTIC...YET NORTHERN TIER IS
FORECAST TO AMPLIFY ACROSS SOUTHWESTERN BRASIL/PARAGUAY. THIS WILL
SUSTAIN THE REDEVELOPMENT OF THE SOUTH ATLANTIC CONVERGENCE ZONE
INTO EARLY NEXT WEEK. AS THE SACZ RESTRUCTURES...EXPECTING
ACCUMULATIONS TO PEAK ACROSS THE SERRA DO MAR OF SANTA
CATARINA/PARANA/SAO PAULO ON MONDAY INTO TUESDAY TO PRODUCE
SCATTERED MAXIMA OF 25-50MM/DAY. AMOUNTS WILL DECREASE SLIGHTLY IN
COASTAL LOCATIONS AFTERWARDS TO CONCENTRATE INLAND ACROSS WESTERN
MINAS GERAIS/MATO GROSSO/.GOIAS/SOUTHERN PARA WITH MAXIMA OF
25-50MM/DAY DURING TUESDAY INTO WEDNESDAY.

LONG WAVE TROUGH ARRIVING IN CHILE DURING SUNDAY INTO MONDAY WILL
ARRIVE WITH A SUBTROPICAL CONNECTION AND TRAINS OF FRONTS THAT
WILL GENERATE LOCALLY HEAVY RAIN. EXPECTING LARGEST ACCUMULATIONS
DURING SUNDAY TO AFFECT AREAS FROM PUERTO MONTT SOUTH INTO THE
AYSEN REGION WHERE EXPECTING SCATTERED MAXIMA OF 25-50MM/DAY.
AMOUNTS ARE TO GRADUALLY DECREASE AFTERWARDS.

ARREAGA.....INAMHI (ECUADOR)
SCHNEIDER...INMET (BRASIL)
GALVEZ......WPC (USA)