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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1832Z Apr 10, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT THU APR 10 2014

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

MODEL DISCUSSION (VALID FROM 10 APRIL 00UTC): THE GLOBAL MODELS
REVERSED TRENDS...WITH THE ECMWF AND UKMET NOW FAVORING A FASTER
EVOLUTION ACROSS THE SOUTH AMERICA DOMAIN...WHILE THE GFS NOW
PROJECTS A SLOWER/DEEPER SOLUTION. THIS IS ADDING TO THE
UNCERTAINTY DURING THE SHORT TO MEDIUM RANGE PERIOD...AND THE
OVERALL LACK OF CONFIDENCE IN THE FORECAST BEYOND 60-72 HRS.
CONSIDERING THE RECENT TRENDS AND THE ENSEMBLE MODEL GUIDANCE...WE
BELIEVE THAT THE GFS OVERCORRECTED...AND THAT THE EUROPEAN MODELS
ARE LIKELY TO MAKE FURTHER CORRECTIONS TO THEIR FORECAST PATTERN.

A MID LEVEL SHORT WAVE TROUGH ON THE SOUTHERN STREAM MOVES ACROSS
THE SOUTH PACIFIC TOWARDS SOUTHERN CHILE THROUGH 30-36
HRS...PULLING ACROSS PATAGONIA THROUGH 48-54 HRS. AS IT NEARS THE
CONTINENT THIS IS TO THEN INTERACT WITH A SHORT WAVE TROUGH TO THE
NORTH...AS THE LATTER MEANDERS OFF THE NORTHERN COAST OF CHILE.
THIS IS TO THEN SPILL ACROSS THE ANDES INTO NORTHWEST ARGENTINA BY
36-42 HRS... CROSSING NORTHERN ARGENTINA TO URUGUAY BY 54-60 HRS.
AS IT EXITS THE COAST AND ENTERS THE WESTERN ATLANTIC THIS VORTEX
IS TO THEN MERGE WITH THE SHORT WAVE TROUGH TO THE SOUTH. THROUGH
72-84 HRS THESE ARE TO THEN COMBINE INTO A FAIRLY INTENSE TROUGH
OVER THE WESTERN ATLANTIC. AT LOW LEVELS A POLAR FRONT ENTERS
SOUTHERN CHILE EARLY IN THE CYCLE...AND THROUGH 48 HRS IT IS TO
PULL ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA. IT IS TO THEN
CONTINUE NORTH ACROSS URUGUAY TO SOUTHERN BRASIL-NORTHERN
ARGENTINA THROUGH 66-72 HRS. AS IT ENTERS SOUTHERN CHILE THIS WILL
SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF 15-20MM...WHILE
ACROSS EASTERN PATAGONIA RAINFALL ACCUMULATION PEAKS AT 05-10MM.

ANOTHER FRONT MEANDERS TO THE NORTH...WITH AXIS ACROSS THE SOUTH
ATLANTIC TO SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA. THE
NORTHERN STREAM TROUGH...AS IT SPILLS ACROSS THE NORTHERN ANDES OF
CHILE TO ARGENTINA...IS TO INTERACT WITH THIS BOUNDARY. THE TROUGH
ALOFT IS TO TRIGGER CYCLOGENESIS ALONG THIS FRONT OVER SOUTHEAST
PARAGUAY/MISIONES IN ARGENTINA EARLY IN THE CYCLE. THE LOW IS TO
THEN DEEPEN/INTENSIFY AS IT MOVES OFF THE COAST OF URUGUAY BY
54-60 HRS. AT 72-84 HRS THE LOW IS TO CONTINUE DEEPENING...WITH
BOTH EUROPEAN MODELS FAVORING A FASTER/DEEPER RATE OF
INTENSIFICATION THAN WHAT THE GFS SUGGESTS...WITH BOTH THESE
MODELS SHOWING POTENTIAL FOR A METEOROLOGICAL BOMB. AS THE LOW
DEEPENS...AND A POLAR RIDGE BUILDS ACROSS ARGENTINA...A SOUTHERLY
WIND SURGE IS TO ESTABLISH. THIS IS TO THEN DRIVE THE FRONT NORTH
ACROSS PARAGUAY TO SOUTHEAST BRASIL BY 72 HRS...INTO NORTHERN
BOLIVIA AT 84-96 HRS. INFLOW OF SHORT WAVE ENERGY...AND FAVORABLE
JET DYNAMICS...WILL RESULT IN ORGANIZED HEAVY CONVECTION BUILDING
ACROSS PARAGUAY-CORRIENTES/MESOPOTAMIA VALLEY IN ARGENTINA TO
SOUTHERN STATES OF BRASIL...WITH RAINFALL MAXIMA OF 50-100MM
EXPECTED THROUGH 36 HRS...AND 25-50MM AT 36-60 HRS. AS THE FRONT
SURGES ACROSS PARANA/SANTA CATARINA TO SAO PAULO IT IS TO THEN
FAVOR MODERATE TO HEAVY CONVECTION ACROSS EASTERN SAO PAULO/RIO DE
JANEIRO...WITH MAXIMA IN THIS AREA LIKELY TO EXCEED FORECAST
GUIDANCE OF 25-50MM. OTHER ACTIVITY TO THE NORTH AND WEST IS TO
THEN BUILD ACROSS BOLIVIA-PERU BY 72-96 HRS...WITH THE SURGING
FRONT AND LOW LEVEL JET ENHANCING MOISTURE CONVERGENCE WHILE
TRIGGERING MODERATE TO HEAVY CONVECTION WITH ACCUMULATION OF
35-70MM. THROUGH 96-108 HRS CONVECTION WILL BUILD NORTH AND WEST
ACROSS ACRE/AMAZONAS IN BRASIL TO CENTRAL-NORTHERN JUNGLE OF
PERU-EASTERN ECUADOR WITH MAXIMA OF 30-60MM. BY 120-132 HRS THE
FOCUS OF THE HEAVY CONVECTION SHIFTS TO SOUTHERN COLOMBIA-EASTERN
ECUADOR WITH MAXIMA OF 25-50MM.

LATER IN THE CYCLE...SHORT WAVE PERTURBATIONS ON THE NORTHERN AND
SOUTHERN STREAMS ARE TO COMBINE IN SUPPORT OF A BROAD TROUGH. THIS
IS TO EXTEND BETWEEN 110W-65W AND TO THE SOUTH OF 30S...WHILE
FOCUSING SHORT WAVE ENERGY ACROSS SOUTHERN CHILE-PATAGONIA IN
ARGENTINA TO THE DRAKE PASSAGE. AT LOW LEVELS THIS WILL SUSTAIN A
BROAD TROUGH WITH A FRONT THAT ENTERS SOUTHERN CHILE/PATAGONIA IN
ARGENTINA BY 96-108HRS...INTO PATAGONIA-SOUTHERN CHILE BY 120 HRS.
THIS IS TO FAVOR STRONG BOUNDARY LAYER WINDS WHILE TRIGGERING
SCATTERED CONVECTION. MOST INTENSE IS EXPECTED BY 108-120 HRS WITH
ACCUMULATION OF 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO CONFINE TO AREA NORTH OF 25S. A MEANDERING HIGH OVER MATO
GROSSO-EASTERN BOLIVIA IS TO ANCHOR THIS RIDGE OVER THE NEXT FEW
DAYS. LATER IN THE CYCLE...AS POLAR FRONT AND DRYER AIR SURGES
ACROSS MID SECTIONS OF SOUTH AMERICA...THE RIDGE ALOFT IS FORECAST
TO WEAKEN. THIS RIDGE...IN INTERACTION WITH THE SUBEQUATORIAL
RIDGE TO THE NORTH...IS FORECAST TO VENT DEEP CONVECTION ACROSS
NORTHEAST BRASIL...WHERE WE EXPECT RAINFALL AMOUNTS OF
20-35MM/DAY. ACROSS NORTHWEST BRASIL EXPECTING ACCUMULATION OF
15-30MM. ON THE SOUTHERN SIERRA OF PERU AND THE ALTIPLANO OF
BOLIVIA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY. THROUGH 72 HRS
FOCUS OF THE ORGANIZED HEAVY CONVECTION SHIFTS TO NORTHERN
BOLIVIA-SOUTHERN PERU AS THE STRONG SOUTHERLY WINDS TRIGGER
ORGANIZED DEEP CONVECTION.

ITA...SENAMHI (PERU)
FERNANDES...INMET (BRASIL)
DAVISON...WPC (USA)