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South American Forecast Discussion
 
(Latest Discussion - Issued 1635Z Jun 11, 2021)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1235 PM EDT FRI JUN 11 2021

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

FORECAST DISCUSSION FROM JUN 11/17UTC: A LONG WAVE TROUGH CROSSING
THE SOUTHERN CONE NOW EXTENDS NORTH FROM THE WEDDELL SEA TO
PARAGUAY/SOUTHERN STATES OF BRASIL. OVER THE NEXT DAY OR
SO...WHILE PRESSING AGAINST A RIDGE TO THE EAST...THE TROUGH WILL
SPLIT IN TWO. A MID LEVEL SHORT WAVE TROUGH ON THE NORTHERN STREAM
IS TO THEN MEANDER OFF THE SOUTH COAST OF BRASIL WHILE ITS
SOUTHERN HALF RAPIDLY WEAKENS AS IT SHEARS UNDER THE RIDGE TO THE
EAST. LATER DURING THE WEEKEND...THE REMNANTS ON THE NORTHERN
STREAM TROUGH MOVE FARTHER OFFSHORE AS A DEEPENING TROUGH TO THE
SOUTH MOVES ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC. AS
IT PROPAGATES ACROSS THE CONTINENT...A SUBTROPICAL JET MAXIMA WILL
ROUND THE APEX OF THIS TROUGH...WITH AXIS WEST-TO-EAST ACROSS
SOUTHERN BOLIVIA-PARAGUAY-SOUTHERN BRASIL TO THE TROPICAL
ATLANTIC. THIS IS TO SLOWLY PULL ACROSS MIDSECTIONS OF SOUTH
AMERICA DURING THE NEXT FEW DAYS...TO INITIALLY FAVOR AN AREA OF
UPPER DIVERGENCE ACROSS BOLIVIA/PERU THAT IS TO VENT DEEP
CONVECTION. AT LOW LEVELS...DRIVEN BY A POLAR RIDGE TO THE
SOUTH...THE SURFACE FRONT SURGES ACROSS SOUTHEAST BRASIL-SANTA
CRUZ IN EASTERN BOLIVIA LATER TODAY... MOVING FARTHER NORTH ACROSS
RIO DE JANEIRO TO ESPIRITO SANTO/MINAS GERAIS-MATO GROSSO TO
CENTRAL BOLIVIA ON SATURDAY. THROUGH THE WEEKEND THIS IS TO THEN
WEAKEN AS IT LOSES ITS UPPER LEVEL SUPPORT. OVER CENTRAL/SOUTHERN
PERU...UNDER THE INFLUENCE OF A SOUTHERLY LOW LEVEL
JET...EXPECTING MODERATE TO HEAVY RAINFALL AMOUNTS WITH MAXIMA OF
20-45MM. THROUGH SATURDAY MORNING FOCUS OF THE ORGANIZED
CONVECTION SHIFTS TO NORTHERN PERU/EASTERN ECUADOR-SOUTHERN
COLOMBIA...WHERE IT IS TO ALSO TRIGGER SIMILAR RAINFALL AMOUNTS.
OVER SAO PAULO/RIO DE JANEIRO...EXPECTING LIGHT CONVECTION WITH
ACCUMULATION OF 05-10MM/DAY EARLY IN THE CYCLE...INCREASING TO
10-15MM/DAY AS IT BUILDS NORTH ACROSS ESPIRITO SANTO TO BAHIA ON
SATURDAY TO MONDAY.

A DEEPENING MID/UPPER LEVEL TROUGH IS TO CLOSELY FOLLOW...WITH ITS
LEADING EDGE TO ENTER EXTREME SOUTHERN REGIONS OF CHILE LATER
TODAY. ON SATURDAY THIS MOVES TO THE WESTERN ATLANTIC AS A
SECONDARY/DEEPER PERTURBATION LIFTS ACROSS THE SOUTHEAST PACIFIC
TO THE SOUTHERN CONE. THE LATTER IS TO THEN EVOLVE INTO A SLOW TO
EVOLVE BROAD TROUGH OVER THE WESTERN ATLANTIC EARLY NEXT WEEK.
THIS WILL THEN BECOME THE DOMINANT FEATURE THROUGH THE MIDDLE OF
THE WEEK. AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS A BROAD TROUGH
ACROSS THE DRAKE PASSAGE/SOUTHERN CONE LATER TODAY...WITH AXIS TO
SUSTAIN A SUBTROPICAL CONNECTION AS IT STREAMS ACROSS SOUTHERN
CHILE TO PATAGONIA. THIS WILL FEED ORGANIZED CONVECTION BETWEEN
TEMUCO-ISLA DE CHILOE...WITH HEAVY RAINFALL AMOUNTS EXPECTED
THROUGH SATURDAY...WITH MAXIMA OF 50-100MM. ON SATURDAY EXPECTING
ADDITIONAL RAINFALL AMOUNTS OF 20-35MM AS THE FRONT EXTENDS ACROSS
NORTHERN PATAGONIA-SOUTHERN CHILE TO THE EASTERN PACIFIC. ACROSS
TIERRA DEL FUEGO AND THE SOUTHERN ANDES...SOLID PRECIPITATION IS
EXPECTED ON SATURDAY AND SUNDAY...WITH MAXIMA OF 10-15CM ON
SATURDAY AND 03-06CM ON SUNDAY. EARLY NEXT WEEK...AS THE FRONTAL
TROUGH DEEPENS OVER THE WESTERN ATLANTIC AND A RIDGE BUILDS TO THE
WEST...THE ASSOCIATED FRONT SURGES ACROSS THE BUENOS AIRES
PROVINCE/CENTRAL ARGENTINA. THROUGH TUESDAY IT WILL MOVE NORTH TO
SOUTHERN BRASIL-PARAGUAY.

THIS SETS THE STAGE FOR A MID/UPPER LEVEL LOW ON THE NORTHERN
STREAM TO PROPAGATE ACROSS THE EASTERN PACIFIC...WITH THE CLOSED
LOW NEARING LA SERENA CHILE EARLY ON TUESDAY MORNING. AT LOW
LEVELS THIS WILL SUSTAIN A WEAK BAROCLINIC BOUNDARY AS IT NEARS
NORTHERN CHILE ON TUESDAY...WITH BOUNDARY TO WEAKEN AS IT SPILLS
ACROSS THE CENTRAL ANDES TO CUYO IN ARGENTINA ON WEDNESDAY. ON THE
CENTRAL ANDES THIS WILL SUSTAIN MODERATE SNOWFALL AMOUNTS...WITH
ACCUMULATION OF 05-10CM ON TUESDAY TO WEDNESDAY. OVER NORTHWEST
ARGENTINA THIS WILL TRIGGER LIGHT TO MODERATE CONVECTION WITH
MAXIMA OF 10-15MM ON TUESDAY AND WEDNESDAY.

NORTH OVER THE CONTINENT...AT 250 HPA...A BROAD RIDGE WILL
DOMINATE THE FLOW TO THE NORTH OF 12S DURING THE NEXT FEW
DAYS...WITH AXIS FORECAST TO GRADUALLY STRENGTHEN ITS FOOTHOLD
EARLY NEXT WEEK. ON TUESDAY IS TO THEN AMPLIFY SOUTH ACROSS
BOLIVIA TO PARAGUAY/NORTHERN ARGENTINA...DRIVING THE SUBTROPICAL
JET SOUTH OF ITS CLIMATOLOGICAL POSITION. THE RIDGE ALOFT WILL
VENT DIURNAL CONVECTION ACROSS NORTHERN BRASIL TO THE WEST OF ILHA
DE MARAJO...WITH ACCUMULATION OF 15-25MM OVER THE NEXT FEW
DAYS...DECREASING TO 10-15MM/DAY EARLY NEXT WEEK. HIGHER AMOUNTS
ARE EXPECTED TO THE WEST...CLUSTERING OVER SOUTHERN
COLOMBIA/NORTHERN PERU TO EASTERN BOLIVIA...WITH MAXIMA OF
20-45MM/DAY EXPECTED OVER THE NEXT TWO DAYS. EARLY NEXT WEEK IT
WILL DECREASES TO MAXIMA OF 20-35MM/DAY.

DAVISON...WPC (USA)