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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1617Z Sep 15, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 PM EDT MON SEP 15 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 15 AT 00UTC): THE GLOBAL
MODELS FOLLOW A SIMILAR EVOLUTION THROUGH DAY 06...WITH SHORT WAVE
PERTURBATIONS EXPECTED TO POPULATE THE SOUTH AMERICAN DOMAIN
THROUGH DAY 04. LATER IN THE CYCLE A HIGHER AMPLITUDE SINUSOIDAL
WAVE PATTERN IS TO ESTABLISH. CONFIDENCE IN THE FORECAST IS HIGH.

IN A TIGHT BELT OF MID LATITUDE WESTERLIES...PROGRESSING SHORT
WAVE TROUGHS ON THE SOUTHERN STREAM ARE TO RACE ACROSS THE SOUTH
PACIFIC INTO THE SOUTHERN CONE OF SOUTH AMERICA/DRAKE PASSAGE OVER
THE NEXT FEW DAYS...WITH ONE TO ENTER THE SOUTHERN CONE EARLY IN
THE CYCLE. ANOTHER FOLLOWS...MAKING LANDFALL BY 78-84 HRS. AT LOW
LEVELS THIS IS TO SUSTAIN A BROAD OCCLUDED TROUGH ACROSS THE
BELLINGSHAUSEN SEA/DRAKE PASSAGE TO THE SOUTHERN CONE OF SOUTH
AMERICA. THE ENSUING PRESSURE GRADIENT WILL RESULT IN BOUNDARY
LAYER WINDS OF 25-40KT. THIS WILL COMBINE WITH PROGRESSIVE FRONTS
TO SUSTAIN SCATTERED RAINFALL ACROSS CHILE SOUTH OF ISLA DE
CHILOE. ON DAY 01 THE MAXIMA IS TO PEAK AT 15-20MM...WHILE ON DAY
03 THE MAXIMA PEAKS AT 10-15MM.

SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW MOVES OFF THE SOUTH
COAST OF BRASIL EARLY IN THE CYCLE...WITH MID LEVEL AXIS TO SLOWLY
PULL ACROSS 38W/40W BY 48 HRS...AND ACROSS 20W BY 96 HRS. AT LOW
LEVELS IT SUSTAINS AN OCCLUDING LOW OFF THE SOUTH COAST OF
BRASIL... FORECAST TO MEANDER TO THE EAST-SOUTHEAST AS THE CYCLE
PROGRESSES. ASSOCIATED FRONT MOVES NORTH ACROSS SAO PAULO-MATO
GROSSO IN BRASIL TO CENTRAL BOLIVIA EARLY IN THE CYCLE...WHERE IT
IS TO MEANDER THROUGH 48-54 HRS. BUT AS THE MID LEVEL LOW PULLS
AWAY...AND FRONT LOSES UPPER LEVEL SUPPORT...IT IS TO THEN
RETROGRESS TO MATO GROSSO DO SUL-PARAGUAY BY 60-72 HRS.
MEANWHILE...THIS IS TO TRIGGER SCATTERED RAINS ACROSS SOUTHEAST
STATES OF BRASIL WITH ACCUMULATION OF 05-10MM. HIGHER AMOUNTS ARE
EXPECTED FROM SOUTHERN PERU TO CENTRAL BOLIVIA...WHERE
FRONTAL/PREFRONTAL CONVECTION IS TO RESULT IN RAINFALL AMOUNTS OF
20-35MM.

NEXT MID LEVEL PERTURBATION REACHES CENTRAL CHILE EARLY IN THE
CYCLE. THE TROUGH IS TO MEANDER OFF THE CENTRAL/NORTHERN COAST OF
CHILE THROUGH AT LEAST 66-72 HRS. IT IS TO THEN SPILL ACROSS THE
ANDES INTO NORTHERN ARGENTINA...WITH AXIS TO MOVE ACROSS
URUGUAY/MESOPOTAMIA VALLEY IN ARGENTINA TO SOUTHERN BRASIL BY
96-108 HRS. AS IT SPILLS ACROSS THE ANDES THIS IS TO INTERACT WITH
SURFACE FRONT OVER SOUTHERN BRASIL/PARAGUAY...INDUCING
CYCLOGENESIS OVER MISIONES IN ARGENTINA/SOUTHEAST PARAGUAY BY 96
HRS. THROUGH 120 HRS THIS IS TO ALSO OCCLUDE AS IT MOVES OFF THE
COAST OF BRASIL INTO THE SOUTH ATLANTIC. THE DEEPENING LOW WILL
REINFORCE THE BAROCLINIC BOUNDARY AS IT MEANDERS NORTH INTO SAO
PAULO-SANTA CRUZ IN EASTERN BOLIVIA. UNDER FAVORABLE JET DYNAMICS
THIS IS TO SUSTAIN ORGANIZED HEAVY CONVECTION....WITH MODELS
SHOWING RISK OF AN MCS FORMING BETWEEN SOUTHERN BRASIL AND
SOUTHEAST PARAGUAY BY 72-96 HRS...WITH MAXIMA TO PEAK AT 35-70MM.
OVER CENTRAL/NORTHWEST PARAGUAY TO SOUTHERN BOLIVIA EXPECTING
ACCUMULATION OF 10-15MM. AS THE FRONT MEANDERS NORTH ACROSS
SOUTHEAST BRASIL IT IS TO SUSTAIN SCATTERED CONVECTION WITH
ACCUMULATION OF 20-30MM...WHILE OVER BOLIVIA/SOUTHERN JUNGLE OF
PERU IT IS TO RESULT IN RAINFALL AMOUNTS OF 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO REMAIN ILL ORGANIZED...WITH AXIS TO CONFINE TO NORTHWEST SOUTH
AMERICA AND THE EASTERN TROPICAL PACIFIC. AS THE RIDGE HOLDS TO
THE WEST...THIS WILL SUSTAIN AND INDUCED TROUGH ACROSS THE
NORTHEAST STATES OF BRASIL. THE RIDGE ALOFT IS TO VENT DEEP
CONVECTION ALONG THE SIERRA/JUNGLE OF PERU TO ECUADOR AND NORTHERN
BOLIVIA. MOST ACTIVE IS EXPECTED OVER THE NEXT COUPLE OF
DAYS...WHEN MAXIMA IN THIS AREA IS TO PEAK AT 20-35MM. THROUGH
72-96 HRS THIS DECREASES TO 15-25MM.

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