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South American Forecast Discussion
 
(Latest Discussion - Issued 1636Z Jun 27, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1236 PM EDT TUE JUN 27 2017

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

MODEL DISCUSSION (VALID FROM JUNE 27 AT 0000 UTC): MINOR CHANGES
TO PREVIOUS FORECAST...WITH MODELS FOLLOWING A SIMILAR EVOLUTION
THROUGHOUT THE MEDIUM RANGE PERIOD. CONFIDENCE IN THE FORECAST IS
HIGH.

AT 500 HPA...A SHORT WAVE TROUGH ON THE NORTHERN STREAM MEANDERS
OFF THE CENTRAL COAST OF CHILE. THIS IS TO GRADUALLY WEAKEN WHILE
SHEARING SHORT WAVE ENERGY ACROSS CENTRAL CHILE TO ARGENTINA. ON
WEDNESDAY...THE WANING TROUGH WILL MOVE TO CENTRAL
CHILE...SPILLING ACROSS THE ANDES INTO CUYO IN ARGENTINA LATER ON
THURSDAY. DURING THE DAY ON FRIDAY THIS IS TO THEN CONTINUE ACROSS
URUGUAY/RIO DE LA PLATA BASIN. AS IT SPILLS ACROSS THE ANDES THIS
WILL INTERACT WITH MEANDERING FRONT OVER URUGUAY/NORTHERN
PROVINCES IN ARGENTINA. THE FRONT IS TO REMAIN NEARLY STATIONARY
DURING THE NEXT THREE DAYS. ON FRIDAY IT IS TO THEN MOVE NORTH
ACROSS PARANA/SANTA CATARINA-MATO GROSSO DO SUL TO
PARAGUAY-SOUTHEAST BOLIVIA AS A POLAR RIDGE BUILDS TO THE SOUTH.
EARLY ON WEDNESDAY THE FRONT WILL FAVOR SCATTERED CONVECTION WITH
ACCUMULATION OF 05-10MM/DAY. ON WEDNESDAY AND THURSDAY THIS IS TO
BECOME BETTER ORGANIZED...WITH MAXIMA OF 20-35MM ACROSS
URUGUAY/RIO GRANDE DO SUL-CORRIENTES IN ARGENTINA. ACROSS SOUTHERN
SAO PAULO THIS IS TO THEN FAVOR SCATTERED CONVECTION ON
SATURDAY...WITH ACCUMULATION OF 15-25MM. ACROSS CENTRAL
BOLIVIA-SOUTHERN JUNGLE OF PERU THIS IS TO THEN FAVOR PREFRONTAL
CONVECTION...WITH ACCUMULATION OF 10-15MM ON FRIDAY AND 20-30MM ON
SATURDAY.

PROGRESSIVE MID LEVEL PERTURBATIONS ARE TO POPULATE THE SOUTHERN
STREAM FLOW...WITH ONE ENTERING THE DRAKE PASSAGE/TIERRA DEL FUEGO
EARLY ON WEDNESDAY. ON THURSDAY THIS IS TO THEN PULL ACROSS THE
SOUTHERN CONE TO THE WESTERN ATLANTIC. ON FRIDAY TO SATURDAY...AS
A LONG WAVE RIDGE BUILDS TO THE WEST...THE TROUGH IS TO THEN
AMPLIFY ACROSS THE WESTERN ATLANTIC BETWEEN 65W-30W AND TO THE
SOUTH OF 20S. AT LOW LEVELS THIS IST O SUSTAIN A BROAD TROUGH
ACROSS THE SOUTHERN CONE...WITH ASSOCIATED FRONT TO INITIALLY
LIMIT TO SOUTHERN CHILE-PATAGONIA IN ARGENTINA. ON THURSDAY THE
FRONT SURGES ACROSS LA PAMPA/BUENOS AIRES PROVINCE...CROSSING RIO
DE LA PLATA BASIN-URUGUAY LATER ON FRIDAY. THIS IS TO THEN MERGE
WITH AFOREMENTIONED FRONT AS THE LATTER MEANDERS OVER THE
SOUTHEAST STATES OF BRASIL LATER IN THE WEEK. MEANWHILE...AS IT
MEANDERS OVER THE SOUTHERN CONE THIS FRONT WILL SUSTAIN SCATTERED
CONVECTION BETWEEN PUERTO MONTT-ISLA DE CHILOE IN SOUTHERN CHILE.
THROUGH WEDNESDAY MORNING THIS IS TO RESULT IN RAINFALL AMOUNTS OF
15-20MM...WHILE ON WEDNESDAY IT INCREASES TO 20-30MM. ON THURSDAY
THE FOCUS OF THE CONVECTION SHIFTS TO PUERTO MONTT-TEMUCO...WITH
MAXIMA OF 15-20MM.

AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE REMAIN THE
DOMINANT FEATURE ACROSS NORTHERN SOUTH AMERICA. EARLY IN THE CYCLE
THE RIDGE IS TO ENVELOP CONTINENTAL AREA TO THE NORTH OF 30S. BUT
AS POLAR TROUGH PATTERN TO THE SOUTH DEEPENS...THE RIDGE IS TO
THEN CONFINE TO AREA NORTH OF 20S LATER IN THE WEEK. EAST OF THIS
RIDGE...A TROUGH EXTENDS ACROSS THE SOUTH ATLANTIC TO
BAHIA/NORTHEAST STATES OF BRASIL. THE TROUGH IS TO GRADUALLY
WEAKEN AS THE RIDGE TO THE WEST FLATTEN. MEANWHILE...THIS IS TO
ENHANCE CONVECTION ALONG THE NORTHEAST COAST OF BRASIL...TO
SUSTAIN MAXIMA OF 20-40MM EARLY IN THE CYCLE AND 20-30MM/DAY
THEREAFTER THROUGH THE END OF THE WEEK. OVER NORTHERN
BRASIL-SOUTHERN COLOMBIA EXPECTING ACCUMULATION OF
15-25MM/DAY...INCREASING TO 20-30MM ON WEDNESDAY TO THURSDAY. OVER
SOUTHERN COLOMBIA-NORTHERN PERU-EASTERN ECUADOR INITIALLY
EXPECTING MAXIMA OF 20-40MM IN SCATTERED CONVECTION. THROUGH
THURSDAY THIS DECREASES TO 10-15MM/DAY.

ESPINOLA...DNM (PARAGUAY)
GONZALEZ...DMC (CHILE)
DAVISON...WPC (USA)