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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1702Z Aug 06, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
102 PM EDT WED AUG 06 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 06 AT 00UTC): THE GLOBAL
MODELS CONTINUE TO AGREE ON LONG WAVE PATTERN EVOLUTION THROUGH
DAY 04. THEREAFTER...HOWEVER...THEY START TO DIVERGE ON THE SPEED
AND AMPLITUDE OF SHORT WAVE PERTURBATIONS ENTERING THE DOMAIN.
THESE DIFFERENCES BECOME MORE PRONOUNCED THROUGH DAY 07.

AT 500 HPA...A LONG WAVE TROUGH IS INITIALIZED OVER THE WESTERN
ATLANTIC...WITH AXIS NORTH TO SOUTHEAST BRASIL.  THE TROUGH IS TO
MOVE EAST ACROSS 20W BY 24 HRS...NEARING 10W BY 48 HRS. THE TROUGH
IS THEN FORECAST TO RAPIDLY DAMPEN WHILE SHORT WAVE ENERGY SHEARS
TO THE EAST SOUTHEAST. AT LOW LEVELS...THE ASSOCIATED FRONT
EXTENDS ACROSS SOUTHEAST BRASIL. UNDER INFLUENCE OF A RIDGE TO THE
SOUTH... STRONG EASTERLY TRADES ARE TO ACCOMPANY THIS FRONT AS IT
MEANDERS NORTH ACROSS ESPIRITO SANTO TO BAHIA IN NORTHEAST BRASIL.
THROUGH 72 HRS THE FRONT IS THEN FORECAST TO FRONTOLIZE.
MEANWHILE...THIS WILL ENHANCE COASTAL CONVERGENCE...WHILE
SUSTAINING SCATTERED CONVECTION WITH RAINFALL AMOUNTS OF 20-35MM.
THE MOST INTENSE IS EXPECTED OVER THE NEXT TWO DAYS...THEN RAPIDLY
WEAKEN AS THE FRONT LOSES UPPER LEVEL SUPPORT.

THE NEXT MID/UPPER LEVEL TROUGH PUSHES EAST ACROSS THE SOUTHERN
CONE OF SOUTH AMERICA THROUGH 24 HRS...EXITING THE COAST OF
ARGENTINA EARLY ON THURSDAY MORNING. THROUGH 48 HRS THIS IS TO
EVOLVE INTO A BROAD TROUGH...WITH AXIS TO EXTEND BETWEEN 60W-30W
AND TO THE SOUTH OF 25S. THE TROUGH CONTINUES EAST ACROSS 20W BY
96 HRS...TO THEN RAPIDLY DAMPEN WHILE MIGRATING ACROSS THE SOUTH
ATLANTIC. AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS AN OCCLUDED
LOW THAT QUICKLY MOVES ACROSS THE MALVINAS/FALKLAND ISLANDS EARLY
IN THE CYCLE. THE ASSOCIATED SURFACE FRONT...UNDER INFLUENCE OF A
BUILDING POLAR RIDGE AND A PAMPERO JET OVER ARGENTINA...IS TO
SURGE NORTH ACROSS THE RIO DE LA PLATA BASIN TO URUGUAY-MENDOZA IN
ARGENTINA BY 24 HRS. AS IT SURGES ACROSS URUGUAY-ENTRE RIOS IN
ARGENTINA THIS IS TO TRIGGER MODERATE CONVECTION WITH ACCUMULATION
OF 20-35MM. BY 48-60 HRS THE FRONT MOVES NORTH ACROSS THE SOUTHERN
STATES OF BRASIL-PARAGUAY-NORTHERN BOLIVIA. THIS IS TO THEN
MEANDER SOUTH ACROSS MISIONES IN ARGENTINA-PARAGUAY LATER IN THE
CYCLE. THE MOST ACTIVE CONVECTION IS EXPECTED AS THE FRONT SURGES
NORTH ACROSS BOLIVIA...TO SUSTAIN SCATTERED CONVECTION OVER
NORTHERN BOLIVIA-CENTRAL/SOUTHERN JUNGLE OF PERU WITH ACCUMULATION
OF 15-25MM. THROUGH 48-72 HRS THE CONVECTION WILL EXPAND FARTHER
NORTH ACROSS NORTHERN PERU-ECUADOR-SOUTHERN COLOMBIA WITH MAXIMA
OF 20-35MM...WHILE OVER SOUTHERN PERU-NORTHERN BOLIVIA IT
DECREASES TO 10-15MM.

UPSTREAM OVER THE PACIFIC...THE GLOBAL MODELS CONTINUE TO FORECAST
INTENSE CYCLOGENESIS DURING THE NEXT FEW DAYS...AS A SHORT WAVE
TROUGH ON THE NORTHERN STREAM COMBINES WITH A DEEPENING TROUGH ON
THE SOUTHERN STREAM. AS THEY INTERACT...THE ONE TO THE SOUTH IS
FORECAST TO RAPIDLY DEEPEN OVER THE BELLINGSHAUSEN SEA/SOUTHEAST
PACIFIC. AT LOW LEVELS THIS IS TO SUSTAIN A RAPIDLY DEEPING
SURFACE LOW...WITH SYSTEM TO DEEPEN FROM A 974 HPA LOW AT 36 HRS
TO A 950 HPA LOW BY 60 HRS. THE FAST RATE OF INTENSIFICATION WILL
LIKELY RESULT IN A METEOROLOGICAL BOMB THAT MOVES ACROSS THE DRAKE
PASSAGE/ BELLINGSHAUSEN SEA BY 60-72 HRS. ASSOCIATED SURFACE FRONT
ENTERS SOUTHERN CHILE BY 54-60 HRS...CROSSING PATAGONIA IN
ARGENTINA BY 72-84 HRS. THROUGH 96 HRS IT IS TO THEN MEANDER NORTH
ACROSS NORTHERN PATAGONIA/LA PAMPA IN ARGENTINA-TEMUCO CHILE TO
THE EASTERN PACIFIC. THE DEEPENING LOW IS TO ALSO SUSTAIN STRONG
LOW LEVEL WINDS ACROSS TIERRA DEL FUEGO-SOUTHERN CHILE...EXPECTED
TO PEAK IN EXCESS OF 50KT. THIS IS TO ALSO FAVOR MODERATE
CONVECTION WITH ACCUMULATION OF 15-30MM...WITH THE MOST INTENSE TO
DEVELOP BETWEEN TEMUCO AND ISLA DE CHILOE.

AT 200 HPA...NORTH OVER THE CONTINENT...SUBEQUATORIAL RIDGE
PATTERN IS TO LIMIT TO EQUATORIAL SOUTH AMERICA...WITH LITTLE TO
NO MODULATION OVER THE NEXT FEW DAYS. MEANWHILE...SHORT WAVE
TROUGHS ARE TO SLIDE UNDER THIS AXIS...WITH ONE TO PULL ACROSS
SOUTHERN PERU/BOLIVIA TO CENTRAL BRASIL THROUGH 48-72 HRS. THIS
CONTINUES TO NORTHEAST BRASIL LATER IN THE CYCLE AS THE RIDGE
PERSISTS TO THE NORTH AND WEST. UNDER INFLUENCE OF THE RIDGE
ALOFT...SCATTERED CONVECTION IS EXPECTED ACROSS AMAZONAS IN BRASIL
TO NORTHERN PERU/SOUTHERN COLOMBIA THROUGH 60 HRS...WITH RAINFALL
AMOUNTS OF 15-25MM/DAY. THIS...HOWEVER...IS TO BRIEFLY INCREASE TO
20-35MM BY 72-84 HRS AS A LOW LEVEL WIND SURGE SPREADS ALONG THE
EASTERN SLOPES OF THE ANDES MOUNTAINS. OVER NORTHERN PARA-RORAIMA
AND AMAPA TO THE EAST THE DAILY MAXIMA IS TO INITIALLY PEAK AT
10-15MM/DAY.

JALFIN...SMN (ARGENTINA)
GALVEZ...WPC (USA)
DAVISON...WPC (USA)