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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1609Z Aug 13, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1209 PM EDT WED AUG 13 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 13 AT 00UTC): MODELS GENERALLY
AGREE ON LONG WAVE PATTERN EVOLUTION...WITH BUILDING RIDGE OVER
THE CONTINENT TO DOMINATE THE MEDIUM-LONG RANGE PERIOD. THIS
PATTERN IS WELL SUPPORTED BY THE GLOBAL ENSEMBLE MEMBERS...WHICH
SHOW RIDGE PATTERN PERSISTING THROUGH DAY 10. THIS IS TO BRING
UNSEASONABLY WARM TEMPERATURES ACROSS CENTRAL/SOUTHERN PORTIONS OF
SOUTH AMERICA.

SOUTH OVER THE CONTINENT...HIGHLY AMPLIFIED SINUSOIDAL WAVE
PATTERN DOMINATES THE MID/UPPER LEVELS. UNDER INFLUENCE OF A LONG
WAVE RIDGE OVER THE EASTERN PACIFIC/CHILE A HIGH AMPLITUDE TROUGH
EXTENDS ACROSS THE WESTERN ATLANTIC TO MID SECTIONS OF SOUTH
AMERICA. THROUGH 48-60 HRS PATTERN IS TO EVOLVE...WITH THE RIDGE
FORECAST TO PULL ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC.
AS IT RELOCATES ACROSS THE SOUTHERN CONE...THE RIDGE IS TO
DISPLACE THE TROUGH FARTHER TO THE EAST...WITH AXIS TO RELOCATE TO
THE CENTRAL ATLANTIC BETWEEN 50W-10W AND TO THE SOUTH OF 20S. THIS
IS TO THEN SLOWLY WEAKEN THROUGH 96-120 HRS AS SHORT WAVE ENERGY
SHEARS TO THE EAST-SOUTHEAST. AT LOW LEVELS...BUILDING POLAR RIDGE
OVER ARGENTINA WILL SUSTAIN THE NORTHWARD MIGRATION OF A POLAR
FRONT ACROSS SOUTHEAST BRASIL-BOLIVIA...WITH BOUNDARY TO MOVE
NORTH ACROSS SAO PAULO TO RIO DE JANEIRO-MATO GROSSO-NORTHERN
BOLIVIA/SOUTHERN PERU BY 24 HRS...WHERE IT IS TO REMAIN NEARLY
STATIONARY THROUGH 48-54 HRS. BY 72-84 HRS...AS IT LOSES UPPER
LEVEL SUPPORT...FRONT IS TO THEN RETROGRESS ACROSS SOUTHEAST
BRASIL TO PARAGUAY BY 72-96 HRS. PREFRONTAL CONVECTION ACROSS
CENTRAL/SOUTHERN PERU IS TO RESULT IN MAXIMA OF 20-45MM THROUGH 36
HRS...WHILE OVER THE ALTIPLANO OF BOLIVIA IT IS TO PEAK AT
15-20MM. POST FRONTAL CONVECTION ACROSS EASTERN SAO PAULO AND RIO
DE JANEIRO PEAKS AT 20-35MM EARLY IN THE CYCLE. PREFRONTAL
CONVECTION ACROSS ESPIRITO SANTO/EASTERN BAHIA IS TO PEAK AT
15-25MM/DAY BY 36-108 HRS. AS THE FRONT RETROGRESSES ACROSS
SOUTHEAST TO SOUTHERN BRASIL/PARAGUAY IT IS TO SUSTAIN STRATIFIED
CLOUD COVER AND LIGHT TO MODERATE CONVECTION. BY 72-84 HRS THIS IS
TO PEAK AT 05-10MM...AND BY 84-120 HRS IT WILL INCREASE TO 10-15MM.

MEANWHILE...OVER THE EASTERN PACIFIC...A DEEP TROUGH ON THE
SOUTHERN STREAM IS TO MOVE TO THE BELLINGSHAUSEN SEA/SOUTHEAST
PACIFIC BY 42-48 HRS. BUILDING RIDGE TO THE WEST IS TO GRADUALLY
UNDERCUT THIS TROUGH...INDUCING THE NORTHWESTWARD AMPLIFICATION OF
THE TROUGH ALONG 50S 100W TO 30S 120W BY 72 HRS. THE TROUGH IS TO
THEN SHEAR...WITH SOUTHERN HALF TO MIGRATE ACROSS THE ANTARCTIC
PENINSULA/WEDDELL SEA WHILE NORTHERN HALF TRAILS OVER THE EASTERN
PACIFIC. THE LATTER IS TO THEN ENVELOP AREA BETWEEN 120W-90W AND
TO THE SOUTH 18S. AS THE TROUGH DEEPENS TO THE WEST...THIS IS TO
THEN INDUCE THE SOUTHWARD AMPLIFICATION OF A RIDGE ACROSS THE FAR
EASTERN PACIFIC/CHILE TO ARGENTINA. THROUGH 144-168 HRS MODEL
GUIDANCE SHOWS FURTHER INTENSIFICATION OF THIS RIDGE. EVOLVING
TROUGH/RIDGE PATTERN OVER THE EASTERN PACIFIC-SOUTH AMERICA WILL
THEN FOCUS SUBTROPICAL MOISTURE AND SHORT WAVE ENERGY ACROSS
SOUTHERN REGIONS OF CHILE TO PATAGONIA ARGENTINA. BEST INFLOW OF
ENERGY...HOWEVER...IS EXPECTED BETWEEN 36-108 HRS. AT LOW LEVELS
THIS IS TO SUSTAIN A DEEP TROUGH ACROSS THE BELLINGSHAUSEN
SEA-SOUTHERN CONE OF SOUTH AMERICA THROUGH 108-120 HRS...WITH
POLAR FRONTS TO CONFINE TO EXTREME SOUTHERN CHILE/PATAGONIA AS
THEY REVOLVE AROUND THE BROAD TROUGH. INFLOW OF MOISTURE AND
ENERGY WILL FAVOR SCATTERED CONVECTION ACROSS CHILE SOUTH OF
PUERTO MONTT. THROUGH 36 HRS THIS INCREASES TO 15-20MM... AND BY
36-108 HRS IT IS TO PEAK AT 20-35MM. LESSER AMOUNTS ARE EXPECTED
TO THE SOUTH...TO AFFECT TIERRA DEL FUEGO/EXTREME SOUTHERN CHILE
WITH ACCUMULATION OF 05-10MM IN MIXED PRECIPITATION.

NORTH OVER THE CONTINENT...AT 500 HPA...AN EAST-TO-WEST RIDGE IS
TO EXTEND WEST ACROSS THE TROPICAL ATLANTIC TO NORTHERN SOUTH
AMERICA. CONSISTENT WITH PREVIOUS FORECASTS THE MID LEVEL RIDGE
PATTERN IS TO HOLD THROUGH DAY 05. AS THE RIDGE HOLDS IT IS TO
SUSTAIN A TRADE WINDS CAP ACROSS EASTERN-CENTRAL BRASIL. THE CAP
INVERSION... HOWEVER...WEAKENS TO THE NORTH...WITH ENVIRONMENTAL
CONDITIONS ACROSS NORTHERN AMAZONAS-NORTHERN JUNGLE OF PERU AND
COLOMBIA TO REMAIN CONDUCIVE AND FAVORABLE FOR DEEP CONVECTION. IN
THIS AREA EXPECTING RAINFALL AMOUNTS OF 20-40MM/DAY THROUGH 36
HRS...AND 15-20MM AT 36-60 HRS. THIS IS TO GRADUALLY DECREASE TO
10-15MM/DAY BY 60-120 HRS.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
GALVEZ...WPC (USA)
DAVISON...WPC (USA)