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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2021Z Aug 08, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
421 PM EDT FRI AUG 08 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 08 AT 00UTC): GLOBAL MODELS
CONTINUE TO DIVERGE DURING THE MEDIUM RANGE PERIOD...FAILING TO
REACH A CONSENSUS ON HOW SHORT WAVE PERTURBATIONS STREAMING ACROSS
THE SOUTH ATLANTIC ARE TO EVOLVE. THE GLOBAL ENSEMBLE MEMBERS
DEPICT HIGH VARIABILITY DURING THAT PERIOD...LEADING TO LOW
CONFIDENCE ON THE FORECAST BEYOND 96/108 HRS.

AT 500 HPA...A BROAD TROUGH EXTENDS ACROSS THE WESTERN ATLANTIC
BETWEEN 60W-30W AND TO THE SOUTH OF 30S. AS PREVIOUSLY
FORECASTED...THIS IS TO PULL ACROSS 20W BY 48 HRS...NEARING 10W BY
72 HRS. IT IS TO THEN RAPIDLY WEAKEN AS SHORT WAVE ENERGY SHEAR TO
THE SOUTH-SOUTHEAST. AT LOW LEVELS THIS WILL SUSTAIN AN ELONGATED
FRONT THAT MEANDERS NORTH ACROSS SAO PAULO-MATO GROSSO DO SUL IN
BRASIL TO CENTRAL BOLIVIA EARLY IN THE CYCLE. BUT AS THE TROUGH
ALOFT MIGRATES ACROSS THE SOUTH ATLANTIC...THE SURFACE FRONT IS TO
RETROGRESS ACROSS THE SOUTHERN STATES OF BRASIL-PARAGUAY TO
NORTHERN ARGENTINA. AS THE FRONT MEANDERS NORTH TO SAO PAULO...IT
IS TO TRIGGER SCATTERED COASTAL CONVECTION WITH ACCUMULATION OF
05-10MM. OTHER ACTIVITY IS EXPECTED ALONG THE TRAILING END OF THIS
FRONT OVER BOLIVIA/SOUTHERN PERU...WITH ACCUMULATION OF 10-15MM
EXPECTED THROUGH 36 HRS.

ALSO AT MID LEVELS...A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS
TO NEAR NORTHERN CHILE EARLY IN THE CYCLE. THE SHORT WAVE TROUGH
IS THEN FORECAST TO SLOWLY SPILL ACROSS THE ANDES TO THE NORTHWEST
PROVINCES IN ARGENTINA BY 42-48 HRS. THIS IS TO THEN TRACK
EAST-SOUTHEAST ACROSS PARAGUAY/CORRIENTES IN ARGENTINA TO SOUTHERN
BRASIL/URUGUAY BY 60-66 HRS. AS IT ENTERS NORTHERN CHILE THIS IS
TO INTERACT WITH A MOIST PLUME OVER PERU/BOLIVIA...TRIGGERING
SCATTERED SNOW SHOWERS ON THE SOUTHERN SIERRA OF PERU AND THE
ALTIPLANO OF BOLIVIA. IN THIS AREA EXPECTING SNOWFALL AMOUNTS OF
04-06CM THROUGH 36 HRS...AND 02-04CM AT 36-60 HRS. THE TROUGH
ALOFT IS TO THEN INTERACT WITH AFOREMENTIONED FRONT OVER SOUTHERN
BRASIL-NORTHERN ARGENTINA...TRIGGERING SCATTERED CONVECTION ALONG
THIS BOUNDARY. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM
BY 48-60 HRS AND 10-15MM AT 60-84 HRS.

SIMULTANEOUSLY...A DEEP TROUGH MOVES ACROSS THE BELLINGSHAUSEN SEA
TO THE DRAKE PASSAGE/SOUTHERN CONE OF SOUTH AMERICA BY 24 HRS.
THROUGH 48 HRS THIS EVOLVES INTO A BROAD TROUGH ACROSS CHILE/
ARGENTINA TO THE WESTERN ATLANTIC. THROUGH 96 HRS THIS IS TO THEN
PULL ACROSS 30W/35W AS ANOTHER SHORT WAVE PERTURBATION ENTERS
CHILE/ARGENTINA. AT LOW LEVELS THIS SUSTAINS A DEEP OCCLUDED 940
HPA LOW OVER THE BELLINGSHAUSEN SEA EARLY IN THE CYCLE...WITH A
POLAR FRONT OT EXTEND ACROSS PATAGONIA IN ARGENTINA/SOUTHERN
CHILE. IT IS TO ALSO SUSTAIN A TIGHT PRESSURE GRADIENT ACROSS THE
SOUTHERN CONE...FAVORING BOUNDARY LAYER WINDS OF 40-50KT ACROSS
TIERRA DEL FUEGO/EXTREME SOUTHERN CHILE AND PATAGONIA IN ARGENTINA
THROUGH 30-36 HRS. AS THE LOW/TROUGH RELOCATES TO THE WESTERN
SOUTH ATLANTIC... THE SURFACE FRONT IS TO MOVE NORTH ACROSS
PATAGONIA TO AL PAMPA IN ARGENTINA/CENTRAL CHILE. THROUGH 72 HRS
THE FRONT REACHES RIO DE LA PLATA BASIN-MENDOZA IN
ARGENTINA...LIFTING ACROSS URUGUAY/ENTRE RIOS IN ARGENTINA BY 96
HRS. OVER SOUTHERN CHILE THIS IS TO FAVOR SCATTERED CONVECTION
WITH ACCUMULATION OF 20-35MM EXPECTED BETWEEN ISLA DE CHILOE AND
TEMUCO...WHILE OVER TIERRA DEL FUEGO IT IS TO SUSTAIN RAINFALL
AMOUNTS OF 10-15MM IN MIXED CONVECTION (SNOW/RAIN SHOWERS). AS THE
FRONT MEANDERS NORTH ACROSS CENTRAL CHILE...IT IS TO TRIGGER
SCATTERED SNOW SHOWERS WITH ACCUMULATION OF 02-04CM BY 72-84 HRS.
AS THE FRONT MEANDERS NORTH TO SOUTHERN BRASIL-NORTHERN
ARGENTINA...IT IS TO SUSTAIN SCATTERED CONVECTION WITH
ACCUMULATION OF 15-25MM BY 96-108 HRS.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBEQUATORIAL RIDGE IS
TO REMAIN CONFINED TO EQUATORIAL SOUTH AMERICA. THIS IS TO PERSIST
NEARLY UNCHANGED OVER THE NEXT FEW DAYS. SHORT WAVE PERTURBATIONS
TO THE SOUTH OF 10S ARE TO MEANDER EAST ACROSS CENTRAL-EASTERN
BRASIL OVER THE NEXT FEW DAYS. BUT UNDER INFLUENCE OF A PERSISTENT
MID LEVEL RIDGE PATTERN THESE ARE TO HAVE LITTLE TO NO IMPACT ON
LOCAL/DIURNAL CONVECTION IN BRASIL. MOST ACTIVE CONVECTION IS
EXPECTED ACROSS ECUADOR-CENTRAL/NORTHERN PERU AND SOUTHERN
COLOMBIA THROUGH 30-36 HRS...WITH RAINFALL AMOUNTS OF 20-35MM.
THROUGH 48-72 HRS THIS DECREASES TO 10-15MM/DAY IN ISOLATED TO
SCATTERED CONVECTION. OVER NORTHEAST BRASIL...MEANWHILE...SHALLOW
COASTAL CONVECTION IS EXPECTED BETWEEN BAHIA AND PERNAMBUCO TO THE
NORTH...WITH ACCUMULATION OF 05-10MM/DAY.

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