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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1546Z Mar 24, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 AM EDT TUE MAR 24 2015

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

MODEL DISCUSSION (VALID FROM MARCH 24 AT 0000 UTC): A DEEPENING
MID/UPPER LEVEL LOW ON THE NORTHERN STREAM CONTINUES TO THREATEN
MID SECTIONS OF SOUTH AMERICA...WITH MEANDERING LOW/TROUGH DRAWING
SUBTROPICAL MOISTURE FROM THE NORTH INTO CENTRAL/NORTHERN PORTIONS
OF CHILE. GLOBAL MODELS DIVERGE ON HOW THIS SYSTEM IS GOING TO
EVOLVE...WITH GFS PROJECTING A FASTER DECAY THAN WHAT THE EUROPEAN
AND MEAN OF GLOBAL ENSEMBLES SUGGEST. AS A RESULT...WE ARE GOING
WITH A STRONGER PERTURBATION TO MEANDER OFF THE COAST THROUGH DAY
05...THEN SPILL ACROSS THE ANDES LATER ON DAY 06. THE SLOW TO
EVOLVE TROUGH/LOW IS TO PROVIDE DYNAMICAL SUPPORT TO ORGANIZED
DEEP CONVECTION ACROSS NORTHERN PORTIONS OF CHILE...WITH RAINFALL
MAXIMA TO PEAK AT 25-50MM THROUGH 36 HRS...AND 20-40MM BY 36-60
HRS. LIGHT CONVECTION IS TO THEN PERSIST THROUGH 96-108 HRS. HEAVY
SNOWFALL AMOUNTS ARE EXPECTED ACROSS THE ANDES MOUNTAINS...WITH
STORM TOTAL AMOUNTS TO LIKELY EXCEED ONE METER OVER THE NEXT THREE
DAYS.

ALSO AT MID LEVELS...A DEEPENING TROUGH IN THE SOUTHERN STREAM IS
TO THEN LIFT ACROSS CENTRAL ARGENTINA TO RIO DE LA PLATA BASIN BY
36-48 HRS...TO THEN GRADUALLY MEANDER EAST INTO THE SOUTH
ATLANTIC. AT LOW LEVELS THIS WILL SUSTAIN A DEEPENING LOW OFF THE
COAST OF BUENOS AIRES EARLY IN THE CYCLE. THIS LOW IS FORECAST TO
RAPIDLY DEEPEN/INTENSIFY THROUGH 72-84 HRS. AS THE LOW DEEPENS IT
IS TO DRIVE A FRONT NORTH ACROSS THE BUENOS AIRES PROVINCE/LA
PAMPA IN ARGENTINA BY 24-36 HRS...THEN NORTH ACROSS URUGUAY-RIO
GRANDE DO SUL TO SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA
BY 48 HRS. THROUGH 72-84 HRS THE FRONT IS TO THEN MOVE NORTH
ACROSS SANTA CATARINA IN BRASIL TO SAO PAULO...WHILE TRAILING
ACROSS PARAGUAY. BOUNDARY IS TO THEN SLOWLY MEANDER NORTH ACROSS
SOUTHEAST BRASIL. AS IT SURGES NORTH ACROSS CENTRAL ARGENTINA THE
FRONT IS TO TRIGGER SCATTERED DEEP CONVECTION WITH ACCUMULATION OF
20-40MM. BUT AS IT MOVES TO SOUTHERN BRASIL-NORTHERN PROVINCES IN
ARGENTINA IT IS TO DECREASE TO 05-10MM. INFLOW OF SHORT WAVE
ENERGY FROM THE WEST IS TO THEN SUSTAIN AN INCREASE IN CONVECTION
ACROSS PARAGUAY-SOUTHERN BRASIL BY 60-84 HRS...WHEN THE MAXIMA IS
TO PEAK AT 20-35MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE MODELS CONTINUE TO
FORECAST THE SUBTROPICAL RIDGE TO GRADUALLY BECOME BETTER
ORGANIZED THROUGH 48-60 HRS...WITH AXIS TO THEN ANCHOR ON A CLOSED
HIGH OVER TOCANTINS/GOIAS. BUILDING RIDGE ALOFT IS TO VENT DEEP
CONVECTION ALONG THE NEAR EQUATORIAL TROUGH-INTER TROPICAL
CONVERGENCE ZONE OVER NORTHERN SOUTH AMERICA. UNDER FAVORABLE MJO
CONDITIONS... EXPECTING AREAS OF ORGANIZED CONVECTION TO DEVELOP
ACROSS THE CONTINENT TO THE NORTH OF 10S...TO AFFECT
ECUADOR-NORTHERN PERU-AMAZONAS-PARA-RORAIMA AND THE NORTHEAST
STATES OF BRASIL. IN THIS AREA THE DAILY MAXIMA IS TO PEAK AT
25-50MM...WITH LOCALLY HIGHER AMOUNTS EXPECTED TO PEAK AROUND
100MM DURING THE PERIOD OF MAXIMUM CONVECTION. BUT AS THE
SUBTROPICAL RIDGE STRENGTHENS...MAXIMA ACROSS NORTHEAST BRASIL
WILL DECREASE TO 10-15MM...WHILE OVER NORTHWEST BRASIL-NORTHERN
PERU/EASTERN ECUADOR THE HEAVY CONVECTION IS TO PERSIST. HEAVY
COASTAL CONVECTION IS TO ALSO AFFECT NORTHERN PERU-SOUTHWEST
ECUADOR OVER THE NEXT FEW DAYS. EARLY IN THE CYCLE MAXIMA IN THIS
AREA IS TO PEAK AT 25-50MM...AND BY 36-84 HRS THE DAILY MAXIMA IS
TO REACH 15-30MM.

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