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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1555Z Apr 11, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EDT FRI APR 11 2014

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

MODEL DISCUSSION (VALID FROM 11 APRIL 00UTC): THE GLOBAL MODELS
CONTINUE TO MAKE PATTERN CORRECTIONS ACROSS THE SOUTH AMERICAN
DOMAIN. AS THE SOLUTIONS CHANGE...THE MODELS ARE SLOWLY REACHING A
CONSENSUS. THE DETERMINISTIC SOLUTION IS WELL SUPPORTED BY THE
MEAN OF THE GLOBAL ENSEMBLES. CONFIDENCE IN THE FORECAST IS HIGH.

A DEEP MID LEVEL SHORT WAVE TROUGH ON THE SOUTHERN STREAM IS TO
MOVE ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA EARLY IN THE
CYCLE. AS IT ENTERS THE CONTINENT...THIS IS INTERACTING WITH A
SHORT WAVE TROUGH TO THE NORTH...AS THE LATTER MEANDERS OFF THE
NORTHERN COAST OF CHILE. UNDER INFLUENCE OF THE PERTURBATION TO
THE SOUTH...THE SHORT WAVE TROUGH SPILLS ACROSS THE ANDES INTO
NORTHWEST ARGENTINA EARLY IN THE CYCLE...CROSSING NORTHERN
ARGENTINA TO URUGUAY BY 30-36 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 48-60 HRS THESE ARE TO
THEN COMBINE INTO A FAIRLY INTENSE TROUGH OVER THE WESTERN
ATLANTIC. THE DEEP PERTURBATION IS TO THEN TRACK TO THE SOUTHEAST
INTO THE SOUTH ATLANTIC...SLOWLY PULLING AWAY FROM THE CONTINENT.
AT LOW LEVELS...ASSOCIATED POLAR FRONT MOVES ACROSS PATAGONIA TO
LA PAMPA IN ARGENTINA THROUGH 24-30 HRS. IT IS TO THEN CONTINUE
NORTH ACROSS URUGUAY TO SOUTHERN BRASIL-NORTHERN ARGENTINA THROUGH
42-48 HRS. POST FRONTAL CONVECTION OVER SOUTHERN CHILE WILL RESULT
IN RAINFALL AMOUNTS OF 05-10MM...WHILE OVER NORTHEAST PATAGONIA/LA
PAMPA EXPECTING ACCUMULATION OF 05-10MM IN SCATTERED CONVECTION.

THE SHORT WAVE TROUGH...AS IT SPILLS ACROSS THE ANDES TO NORTHWEST
ARGENTINA IS TO ALSO INTERACT WITH A SURFACE FRONT THAT EXTENDS
ACROSS SOUTHERN BRASIL-NORTHERN ARGENTINA. THE TROUGH ALOFT
SUPPORTS A SURFACE LOW OVER SOUTHEAST PARAGUAY/MISIONES IN
ARGENTINA. THE LOW IS TO THEN DEEPEN/INTENSIFY AS IT MOVES OFF THE
COAST OF URUGUAY BY 30-36 HRS. MODELS THEN PROJECT A NEAR
EXPLOSIVE RATE OF INTENSIFICATION...WITH LOW DEEPENING TO A 988
HPA LOW BY 48 HRS. AS THE LOW DEEPENS...AND A POLAR RIDGE BUILDS
ACROSS ARGENTINA...A SOUTHERLY JET/WIND SURGE IS TO ESTABLISH.
THIS IS TO THEN DRIVE THE FRONT NORTH ACROSS PARAGUAY TO SOUTHEAST
BRASIL BY 48 HRS...INTO NORTHERN BOLIVIA AT 60-72 HRS. THE 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 35-70MM EXPECTED
THROUGH 36 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 48-72
HRS...WITH THE SURGING FRONT AND LOW LEVEL JET ENHANCING MOISTURE
CONVERGENCE WHILE TRIGGERING MODERATE TO HEAVY CONVECTION WITH
ACCUMULATION OF 35-70MM. THROUGH 72-84 HRS THE 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 96-132 HRS THE FOCUS OF THE HEAVY CONVECTION SHIFTS TO
SOUTHERN COLOMBIA-EASTERN ECUADOR WITH MAXIMA OF 25-50MM/DAY.

LATER IN THE CYCLE...SHORT WAVE PERTURBATIONS ON THE NORTHERN AND
SOUTHERN STREAMS ARE TO COMBINE IN SUPPORT OF A BROAD TROUGH. BY
96-120 HRS THIS IS TO EXTEND BETWEEN 90W-45W 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 72-84HRS...INTO PATAGONIA-SOUTHERN
CHILE BY 102-108 HRS. THIS IS TO FAVOR STRONG BOUNDARY LAYER WINDS
WHILE TRIGGERING SCATTERED CONVECTION. MOST INTENSE IS EXPECTED BY
84-96 HRS WITH ACCUMULATION OF 15-20MM.

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 THREE
DAYS...RELOCATING TO ACRE/SOUTHERN AMAZONAS IN BRASIL LATER IN THE
CYCLE. BUT AS THE POLAR FRONT AND DRYER AIR SURGES ACROSS MID
SECTIONS OF SOUTH AMERICA...THE RIDGE ALOFT IS FORECAST TO
GRADUALLY WEAKEN AS THE CYCLE PROGRESSES. 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. MOST INTENSE IS
EXPECTED OVER THE NEXT COUPLE OF DAYS...THEN DECREASING TO 15-20MM
DURING THE SECOND HALF OF THE FORECAST. ACROSS NORTHWEST BRASIL
EXPECTING ACCUMULATION OF 15-30MM. THROUGH 72-96 HRS THIS WILL
INCREASE TO 25-50MM AS THE AFOREMENTIONED SOUTHERLY WIND SURGE
SUSTAINS AN INCREASE IN ACTIVITY.

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