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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1607Z Jun 14, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1207 PM EDT THU JUN 14 2018

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

MODEL DISCUSSION (VALID FROM JUNE 14 AT 0000 UTC): CONFIDENCE IN
THE FORECAST REMAINS HIGH THROUGH 108-120 HRS...WITH GLOBAL MODELS
FOLLOWING A SIMILAR EVOLUTION ACROSS THE SOUTH AMERICAN DOMAIN.

BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW ACROSS THE WESTERN
SOUTH ATLANTIC...WITH AXIS ENVELOPING AREA TO THE WEST OF 20W.
THIS IS TO SLOWLY MOVE TO THE EAST-SOUTHEAST DURING THE NEXT FEW
DAYS. AS IT PULLS AWAY...A SECONDARY MID LEVEL PERTURBATION IS TO
LIFT ALONG THE COAST OF ARGENTINA TO RIO DE LA PLATA BASIN LATER
TODAY. THE SHORT WAVE TROUGH IS TO THEN WEAKEN WHILE SHEARING
SHORT WAVE ENERGY TO THE EAST-SOUTHEAST. AT LOW LEVELS...THESE
SUSTAIN A DEEP TROUGH OVER THE SOUTH ATLANTIC AND AN ELONGATED
FRONT THAT EXTENDS ACROSS NORTHERN SAO PAULO/RIO DE JANEIRO WHILE
TRAILING ACROSS MATO GROSSO TO NORTHERN BOLIVIA/RONDONIA IN
BRASIL.  THE FRONT IS TO THEN REMAIN NEARLY STATIONARY THROUGH THE
WEEKEND...WITH TRAILING END OVER THE CONTINENT FORECAST TO
FRONTOLIZE EARLY NEXT WEEK. OVER SAO PAULO-RIO DE JANEIRO THE
MEANDERING FRONT WILL SUSTAIN LIGHT TO MODERATE RAINFALL AMOUNTS
WITH MAXIMA OF 10-15MM DURING THE NEXT COUPLE OF DAYS...WHILE ON
SATURDAY EXPECTING ACCUMULATION OF 05-10MM/DAY. UNDER INFLUENCE OF
A JET ALOFT...DEEP COASTAL CONVECTION IS POSSIBLE ON SUNDAY TO
MONDAY.

FARTHER WEST...SHORT WAVE TROUGH ON THE NORTHERN STREAM MEANDERS
OFF THE NORTH COAST OF CHILE. THIS IS TO SHEAR EAST ACROSS THE
NORTHERN ANDES TO NORTHWEST ARGENTINA/BOLIVIA EARLY ON FRIDAY
MORNING. REMNANTS OF THIS TROUGH ARE TO THEN CONTINUE ACROSS
PARAGUAY TO SOUTHERN BRASIL EARLY ON SATURDAY MORNING. AS IT
SPILLS ACROSS THE NORTHERN ANDES THE MID LEVEL VORTEX IS TO
TRIGGER SNOW SHOWERS ALONG THE TRI-BORDER AREA BETWEEN
CHILE-ARGENTINA-BOLIVIA...WITH SNOWFALL AMOUNTS OF 15-20CM. OVER
SOUTHEAST BRASIL...IN INTERACTION WITH THE AFOREMENTIONED
FRONT...IT IS TO THEN TRIGGER LIGHT TO MODERATE RAINFALL AMOUNTS.

SIMULTANEOUSLY...A BROAD/LOW AMPLITUDE MID LEVEL RIDGE BUILDS
ACROSS CHILE TO ARGENTINA EARLY IN THE CYCLE. THE RIDGE IS
FORECAST TO HOLD THROUGH SATURDAY...THEN GRADUALLY FLATTEN DURING
THE WEEKEND AS A DEEPENING POLAR TROUGH ENTERS THE DRAKE
PASSAGE/SOUTHERN CONE OF SOUTH AMERICA. THE BROAD TROUGH IS TO
FOCUS ITS SHORT WAVE ENERGY AND A PLUME OF SUBTROPICAL MOISTURE
ACROSS CHILE TO THE SOUTH OF 40S...STARTING EARLY ON FRIDAY
MORNING AND INTENSIFYING DURING THE WEEKEND. ASSOCIATED SURFACE
FRONT ENTERS SOUTHERN CHILE LATER TODAY...WITH BOUNDARY TO THEN
STALL ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA. UNDER
FAVORABLE JET DYNAMICS THIS IS TO RESULT IN SEVERAL DAYS OF
MODERATE TO HEAVY RAINFALL AMOUNTS BETWEEN TEMUCO AND ISLA DE
CHILOE IN SOUTHERN CHILE. ON FRIDAY EXPECTING ACCUMULATION OF
20-30MM...WHILE ON SATURDAY-MONDAY THE DAILY MAXIMA IN THIS AREA
WILL PEAK AT 20-40MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE DOMINATES THE FLOW
TO THE NORTH OF 20S. UNDER INFLUENCE OF MID/UPPER LEVEL TROUGH TO
THE SOUTH THE RIDGE IS EXPECTED TO GRADUALLY WEAKEN THROUGH
MONDAY. MEANWHILE...THIS IS TO VENT DEEP CONVECTION ACROSS
EQUATORIAL SOUTH AMERICA. MOST ACTIVE IS EXPECTED OVER NORTHERN
PERU-EASTERN ECUADOR-SOUTHERN COLOMBIA...WHERE THE MAXIMA OVER THE
NEXT COUPLE OF DAYS IS FORECAST TO PEAK AT 20-40MM. A SURGE IN
ACTIVITY ON SATURDAY IS TO RESULT IN ACCUMULATION OF 35-70MM ALONG
THE ANDES BETWEEN EASTERN ECUADOR AND COLOMBIA. LESSER AMOUNTS ARE
EXPECTED TO THE EAST...WITH ACCUMULATION OF 10-15MM/DAY EXPECTED
ALONG THE NORTH COAST OF BRASIL.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON...WPC (USA)