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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1656Z Feb 25, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EST WED FEB 25 2015

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

MODEL DISCUSSION (VALID FROM FEBRUARY 25 AT 00UTC): MID LEVEL LOW
IS TO MEANDER OFF THE COAST OF CHILE THROUGH DAY 04...MEANWHILE
SHEARING SHORT WAVE ENERGY EASTWARD ACROSS THE CENTRAL ANDES INTO
THE CENTRAL PROVINCES IN ARGENTINA. BEST INFLOW OF ENERGY...
HOWEVER...IS EXPECTED EARLY IN THE CYCLE WHEN A STRONG VORTEX
SPILLS ACROSS THE ANDES AND THEN LIFTS ACROSS THE CENTRAL
PROVINCES TO URUGUAY/SOUTHERN STATES OF BRASIL. A SUBTROPICAL JET
MAXIMA ACCOMPANIES THIS PERTURBATION...SUSTAINING AN UPPER
DIVERGENT PATTERN. AT LOW LEVELS...A MOIST NORTHERLY FLOW ACROSS
PARAGUAY WILL HELP SUSTAIN PRECIPITABLE WATER CONTENT VALUES IN
EXCESS OF 50MM. THIS IS TO THEN FEED ORGANIZED DEEP
CONVECTION...WITH RISK OF HEAVY/ EXCESSIVE RAINFALL AMOUNTS
EXPECTED THROUGH 36 HRS AS AN MCS IS TO DEVELOP OVER ARGENTINA.
DURING THAT PERIOD EXPECTING RAINFALL MAXIMA OF 75-150MM...WITH
LOCALLY HIGHER AMOUNTS POSSIBLE. FURTHERMORE.... THERE IS ALSO A
MODERATE TO HIGH RISK OF SEVERE CONVECTION DURING THE DAY TODAY
THROUGH THURSDAY MORNING. BY 36-60 HRS...AS THE MCS
WEAKENS...FOCUS OF THE CONVECTION SHIFTS TO URUGUAY-ENTRE RIOS IN
ARGENTINA WHERE THE MAXIMA IS TO PEAK AT 30-60MM...AND BY 60-108
HRS THE DAILY MAXIMA DECREASES TO 15-30MM. BUT LATER IN THE
CYCLE...AS THE REMNANTS OF THE MID LEVEL TROUGH MOVES ACROSS
CENTRAL CHILE TO ARGENTINA...EXPECTING A SURGE IN CONVECTION OVER
ARGENTINA...WITH MAXIMA ACROSS THE NORTHERN PROVINCES EXPECTED TO
PEAK AT 20-45MM IN A SLIGHT RISK OF SEVERE CONVECTION.

BUILDING MID/UPPER LEVEL RIDGE IS TO THEN DOMINATE THE NORTHERN/
SOUTHERN STREAM FLOW ACROSS THE EASTERN PACIFIC TO THE
BELLINGSHAUSEN SEA. AS THE RIDGE BUILDS...A HIGH AMPLITUDE LONG
WAVE TROUGH TO THE EAST IS TO ESTABLISH ACROSS THE WESTERN
ATLANTIC. THE TROUGH IS TO GRADUALLY AMPLIFY THROUGH 60-72
HRS...WHEN IT IS TO EXTEND BETWEEN 55W-20W TO 25S. IT IS TO THEN
GRADUALLY WEAKEN WHILE MIGRATING FARTHER EAST INTO THE SOUTH
ATLANTIC. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH AND A
PROGRESSIVE POLAR FRONT. THIS IS TO MOVE NORTH ACROSS PATAGONIA IN
ARGENTINA TO URUGUAY/RIO DE LA PLATA BASIN IN ARGENTINA BY 60-72
HRS...STALLING OVER THE NORTHERN PROVINCES IN ARGENTINA LATER IN
THE CYCLE. AS IT SURGES ACROSS ARGENTINA MOST ACTIVE CONVECTION IS
EXPECTED TO THE NORTH...BETWEEN JUJUY/SALTA IN ARGENTINA AND RIO
GRANDE DO SUL IN BRASIL. IN THIS AREA THE DAILY MAXIMA IS TO PEAK
AT 20-45MM LATER ON DAY 05.

NEXT LONG WAVE TROUGH MOVES ACROSS THE EASTERN PACIFIC THROUGH
48-72 HRS...TO SLOWLY REACH THE SOUTHERN CONE BY 108-120 HRS WHILE
PRESSING AGAINST THE RIDGE TO THE EAST. THE HIGH AMPLITUDE/LONG
WAVE TROUGH IS TO EXTEND BETWEEN 110W-65W TO 30S. THIS IS TO THEN
FOCUS SUBTROPICAL MOISTURE INTO THE SOUTHERN REGIONS IN CHILE. AT
LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH ON THE SOUTHERN
STREAM FLOW ACROSS THE BELLINGSHAUSEN SEA/SOUTHEAST PACIFIC TO THE
SOUTHERN CONE OF SOUTH AMERICA. ASSOCIATED SURFACE FRONT IS TO
STRETCH ACROSS THE DRAKE PASSAGE/TIERRA DEL FUEGO BY 72-96
HRS...THEN NORTH INTO PATAGONIA-SOUTHERN CHILE BY 96-120 HRS.
STRONG BOUNDARY LAYER WINDS ARE TO ACCOMPANY THIS BOUNDARY...WITH
WINDS TO PEAK AT 35-45KT. THE INFLOW OF SUBTROPICAL MOISTURE IS TO
SUSTAIN MODERATE...LOCALLY HEAVY CONVECTION...WITH MAXIMA TO PEAK
AT 15-20MM.

UPPER FLOW PATTERN NORTH OVER THE CONTINENT IS FORECAST TO
GRADUALLY EVOLVE DURING THE NEXT FEW DAYS...WITH A CELL OF THE
SUBTROPICAL RIDGE OVER NORTHWEST SOUTH AMERICA/EASTERN TROPICAL
PACIFIC TO RAPIDLY WEAKENING AS IT MEANDERS OFF THE COAST OF PERU
EARLY IN THE CYCLE. AS THE RIDGE WEAKENS...AN UPPER LEVEL TROUGH
OVER BRASIL IS ALSO FORECAST TO GRADUALLY FILL. BY 96-120 HRS A
WEST-TO-EAST RIDGE IS TO THEN EXTEND OVER NORTHERN SOUTH AMERICA.
IN THIS PATTERN...MOST ACTIVE CONVECTION IS EXPECTED ALONG THE
NEAR EQUATORIAL TROUGH OVER NORTHERN BRASIL TO NORTHERN JUNGLE OF
PERU...WITH MAXIMA OF 20-40MM/DAY. ON THE NORTH COAST OF
BRASIL-AMAZON RIVER DELTA SEA BREEZE CONVERGENCE IS TO INITIALLY
FAVOR MAXIMA OF 20-30MM. BUT THROUGH 48-72 HRS THIS DECREASES TO
15-20MM/DAY. SCATTERED DIURNAL CONVECTION IS TO THEN BUILD BETWEEN
ACRE IN BRASIL/SOUTHERN JUNGLE OF PERU AND MINAS GERAIS...WITH
MAXIMA IN THIS AREA TO PEAK AT 15-20MM/DAY. HIGHER
AMOUNTS...HOWEVER...ARE EXPECTED ACROSS RIO DE JANEIRO/SOUTHERN
MINAS GERAIS AND ESPIRITO SANTO IN BRASIL...WHERE DEEPENING TROUGH
OVER THE WESTERN SOUTH ATLANTIC IS TO FAVOR AN INCREASE IN COASTAL
CONVECTION...WITH MAXIMA OF 20-35MM/DAY EXPECTED BY 84-132 HRS.

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