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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1626Z Jul 09, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 PM EDT MON JUL 09 2018

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

MODEL DISCUSSION (VALID FROM JUL 09 AT 0000 UTC): MODELS GENERALLY
AGREE ON HOW THE PATTERN IS GOING TO EVOLVE OVER THE SOUTH
AMERICAN DOMAIN. DIFFERENCES LIMIT TO THE SOUTHEAST
PACIFIC...WHERE MODELS DEVELOP TIMING DIFFERENCES DURING THE
SECOND HALF OF THE FORECAST.

AT MID LEVELS...A LONG WAVE TROUGH IS FORECAST TO MOVE ACROSS THE
SOUTHEAST PACIFIC TO THE ANTARCTIC PENINSULA-SOUTHERN CONE OF
SOUTH AMERICA LATER TODAY/EARLY TUESDAY MORNING. THROUGH WEDNESDAY
MORNING THE TROUGH IS TO MEANDER EAST ACROSS PATAGONIA IN
ARGENTINA. AS IT PULLS AWAY...A BUILDING RIDGE TO THE WEST IS TO
THEN INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS THE
ANTARCTIC PENINSULA TO SOUTHERN PATAGONIA LATER ON WEDNESDAY. THE
SHORT WAVE RIDGE IS TO THEN BECOME THE DOMINANT FEATURE ACROSS THE
SOUTHEAST PACIFIC...WHILE BROAD TROUGH ESTABLISHES BETWEEN THE
WEDDELL SEA AND THE COAST OF ARGENTINA/URUGUAY. UNDER INFLUENCE OF
THE RIDGE TO THE WEST AND THE DEEPENING MID LEVEL TROUGH EXPECTING
COLD ADVECTION ACROSS THE DRAKE PASSAGE TO TIERRA DEL
FUEGO/SOUTHERN PATAGONIA IN ARGENTINA. IN THIS AREA THE
ENVIRONMENTAL CONDITIONS WILL THEN BECOME FAVORABLE FOR SOLID
PRECIPITATION TO DEVELOP.

AT LOW LEVELS...BROAD TROUGH IS TO EXTEND NORTH FROM THE
BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA TO SOUTHERN CHILE/PATAGONIA
IN ARGENTINA LATER TODAY. THIS TROUGH IS TO MEANDER EAST ACROSS
THE SOUTHERN CONE TO THE WESTERN ATLANTIC. ASSOCIATED SURFACE
FRONT MOVES ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA EARLY
IN THE CYCLE...WHERE IT IS TO REMAIN DURING THE NEXT FEW DAYS. THE
MEANDERING FRONT IS TO ENHANCE MOISTURE CONVERGENCE BETWEEN PUERTO
MONTT AND ISLA DE CHILOE...TO FAVOR RAINFALL AMOUNTS OF 15-20MM.
THROUGH THURSDAY THIS INCREASES TO 20-35MM/DAY AS ENHANCED BY A
SUBTROPICAL MOIST PLUME. SIMULTANEOUSLY...A TROUGH ON THE SOUTHERN
STREAM DEEPENS ACROSS THE ANTARCTIC PENINSULA TO SOUTHERN
CHILE/TIERRA DEL FUEGO LATER ON TUESDAY/EARLY ON WEDNESDAY
MORNING. AS IT MEANDERS OVER THE DRAKE PASSAGE THE TROUGH WILL
ADVECT COLD AIR ACROSS THE BELLINGSHAUSEN SEA TO TIERRA DEL FUEGO.
THIS IS TO FAVOR SCATTERED SNOW SHOWERS ON TUESDAY-THURSDAY...WITH
ACCUMULATION OF 05-10CMM/DAY.

ON THE NORTHERN STREAM FLOW...A SHORT WAVE TROUGH IS TO MEANDER
EAST ACROSS PARAGUAY/SOUTHERN STATES OF BRASIL LATER TODAY. ON
TUESDAY-WEDNESDAY THIS EVOLVES INTO A CLOSED NEAR 30S 40W. BUT
LATER ON THURSDAY IT WEAKENS AGAIN TO AN OPEN TROUGH WHILE
SHEARING TO THE EAST-SOUTHEAST. AT LOW LEVELS THIS SUSTAINS AN
OCCLUDING LOW OFF THE SOUTH COAST OF BRASIL...WITH A POLAR FRONT
EXTENDING ACROSS SAO PAULO-MATO GROSSO TO ACRE IN BRASIL/SOUTHERN
JUNGLE OF PERU. AS IT SURGES ACROSS BRASIL THIS IS TO SUSTAIN A
PREFRONTAL SHEAR LINE ACROSS SOUTHERN PARA TO AMAZONAS TO THE
NORTHWEST. LATER ON WEDNESDAY THE FRONT IS TO RETROGRESS TO
NORTHERN BOLIVIA/SOUTHERN PERU...WHERE IT IS TO REMAIN THROUGH THE
END OF THE WEEK. AS THE LOW OCCLUDES OFF THE SOUTH COAST OF BRASIL
THIS WILL TRIGGER SCATTERED DEEP CONVECTION ACROSS RIO GRANDE DO
SUL...WITH MAXIMA OF 20-35MM. ON TUESDAY THIS DECREASES TO 15-20MM
WHILE BUILDING NORTH TO PARANA. OTHER CONVECTION IS EXPECTED ON
THE COAST OF SAO PAULO...WITH ACCUMULATION OF 05-10MM EARLY IN THE
CYCLE. ON TUESDAY THIS INCREASES TO 10-15MM WHILE BUILDING NORTH
ACROSS ESPIRITO SANTO/SOUTHERN MINAS GERAIS. LATER ON WEDNESDAY
CONVECTION IN THIS AREA WILL PEAK AT 05-10MM. PREFRONTAL
CONVECTION OVER CENTRAL/NORTHERN JUNGLE OF PERU IS TO PEAK AT
15-25MM EARLY IN THE CYCLE...INCREASING TO 20-45MM ON TUESDAY
WHILE BUILDING NORTH ACROSS EASTERN ECUADOR TO SOUTHERN COLOMBIA.

NORTH OVER THE CONTINENT...AT 200 HPA...AN ILL ORGANIZED CELL OF
THE SUBTROPICAL RIDGE WILL CONFINE TO EQUATORIAL SOUTH AMERICA.
THIS IS TO VENT CONVECTION ALONG THE NORTH COAST OF BRASIL. MOST
ACTIVE IS EXPECTED OVER RIO GRANDE DO NORTE...WITH MAXIMA OF
15-25MM EXPECTED THROUGH THIS EVENING...INCREASING TO 20-40MM ON
TUESDAY. ON WEDNESDAY EXPECTING ADDITIONAL RAINFALL AMOUNTS OF
15-20MM. ALONG THE NORTH COAST OF BRASIL-AMAPA THE DAILY MAXIMA IS
TO PEAK AT 15-20MM...WITH LESSER AMOUNTS LATER IN THE CYCLE.
HIGHER AMOUNTS ARE EXPECTED OVER NORTHERN PARA-RORAIMA-NORTHERN
AMAZONAS/SOUTHERN COLOMBIA...WITH MAXIMA OF 20-40MM/DAY AS
ENHANCED BY TROPICAL WAVES TO THE NORTH.

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