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South American Forecast Discussion
 
(Latest Discussion - Issued 1732Z Feb 22, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 PM EST THU FEB 22 2018

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

MODEL DISCUSSION (VALID FROM FEB 22 AT 0000 UTC): MID/UPPER LEVEL
SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM FLOW COMBINE IN
SUPPORT OF A TROUGH THAT MEANDERS OVER THE WESTERN ATLANTIC TO THE
SOUTHERN STATES OF BRASIL. IN A SLOW TO EVOLVE PATTERN THIS TROUGH
IS TO MEANDER EAST ACROSS35W LATER ON FRIDAY...TO THEN DAMPEN
WHILE SHEARING UNDER A BROAD RIDGE TO THE EAST. A SECONDARY VORTEX
FOLLOWS...TO CROSS CENTRAL CHILE LATER THIS EVENING/EARLY ON
FRIDAY MORNING...THEN ACROSS RIO DE LA PLATA BASIN/URUGUAY LATER
IN THE DAY. DURING THE WEEKEND THIS IS TO EVOLVE INTO A BROAD
TROUGH OFF THE SOUTH COAST OF BRASIL/URUGUAY. AT LOW LEVELS THESE
COMBINE IN SUPPORT OF A FRONTAL BOUNDARY OVER THE WESTERN ATLANTIC
THAT EXTENDS TO THE NORTHWEST ACROSS RIO DE JANEIRO/NORTHERN SAO
PAULO-MATO GROSSO/NORTHERN BOLIVIA. BOUNDARY OVER THE CONTINENT
WEAKENS TO AN OPEN TROUGH EARLY IN THE CYCLE...WHILE REMNANTS OVER
THE ATLANTIC TEND TO PERSIST THROUGH THE MEDIUM RANGE PERIOD. THE
MEANDERING FRONT/TROUGH WILL BE THE FOCUS OF LOW LEVEL MOISTURE
CONVERGENCE. ACROSS MINAS GERAIS/RIO DE JANEIRO TO
RONDONIA/SOUTHERN PARA AND AMAZONAS THIS IS TO INITIALLY FAVOR
MODERATE TO HEAVY RAINFALL AMOUNTS WITH ACCUMULATION OF 35-70MM.
ON FRIDAY-SATURDAY THIS DECREASES TO 30-60MM...WHILE ON SATURDAY
AN ONWARD EXPECTING MAXIMA OF 20-30MM TO CLUSTER OVER
PARA-AMAZONAS-RONDONIA. HIGHER AMOUNTS ARE EXPECTED OVER MATO
GROSSO-TOCANTINS/GOIAS-MINAS GERAIS WITH MAXIMA OF
25-50MM/DAY...WHILE OVER BAHIA-EASTERN MINAS GERAIS/ESPIRITO SANTO
THE MAXIMA WILL PEAK AT 20-30MM. ALSO...EARLY IN THE CYCLE...AN
MCS FORMS OVER ACRE/SOUTHERN AMAZONAS IN BRASIL-SOUTHERN/CENTRAL
JUNGLE IN PERU...WITH MAXIMA OF 40-80MM. THIS SPREADS NORTH ACROSS
CENTRAL-NORTHERN PERU TO EASTERN ECUADOR ON
FRIDAY-SATURDAY...WHERE THE MAXIMA PEAKS AT 30-60MM/DAY.

ON THE SOUTHERN STREAM FLOW...MEANWHILE...DEEPENING MID LEVEL
TROUGH WILL DOMINATE THE FLOW OVER THE SOUTHEAST PACIFIC. ON
FRIDAY IT IS TO EXTEND NORTH BETWEEN 110W-80W TO 30S...MEANWHILE
FOCUSING ITS SHORT WAVE ENERGY ACROSS THE DRAKE PASSAGE-EXTREME
SOUTHERN PORTIONS OF CHILE. THE TROUGH IS TO SLOWLY PULL ACROSS
THE SOUTHERN CONE TO THE WESTERN ATLANTIC LATER IN THE CYCLE. AT
LOW LEVELS THIS IS TO SUSTAINS A BROAD TROUGH OVER THE
BELLINGSHAUSEN SEA-SOUTHEAST PACIFIC EARLY ON FRIDAY
MORNING...WITH ASSOCIATED FRONT MOVING OVER TIERRA DEL
FUEGO/SOUTHERN PATAGONIA ON SATURDAY. ON SUNDAY-MONDAY THIS IS TO
MEANDER NORTH ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA-CENTRAL
REGIONS OF CHILE. AS IT ENTERS SOUTHERN CHILE THIS IS TO TRIGGER
LIGHT CONVECTION ON SATURDAY WITH ACCUMULATION OF 05-10MM. ON
SUNDAY THE MAXIMA DECREASES TO 00-05MM. OTHER CONVECTION IS TO
THEN CLUSTER AHEAD OF THIS FRONT OVER NORTHERN PATAGONIA-LA PAMPA
ON MONDAY-TUESDAY...WHEN IT IS TO SUSTAIN RAINFALL AMOUNTS OF
10-15MM IN SCATTERED DEEP CONVECTION.

NORTH OF 30S...AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE
REMAINS THE DOMINANT FEATURE...WITH AXIS ANCHORING ON A MEANDERING
HIGH OVER MATO GROSSO IN BRASIL. THE RIDGE ALOFT FAVORS AN UPPER
DIVERGENT PATTERN THAT IS VENTING DEEP CONVECTION ALONG THE NEAR
EQUATORIAL TROUGH OVER BRASIL. PERSISTENT UPPER RIDGE PATTERN IS
TO FAVOR REGENERATION OF DIURNAL CONVECTION ACROSS THE NORTHEAST
STATES OF BRASIL...WHERE THE DAILY MAXIMA WILL RANGE BETWEEN
20-45MM. OTHER CONVECTION IS EXPECTED TO THE WEST ACROSS NORTHERN
PARA AND AMAZONAS IN BRASIL...WHERE THE DAILY MAXIMA PEAKS AROUND
20-30MM. THIS...HOWEVER...DECREASES TO 15-20MM EARLY NEXT WEEK.
OVER WESTERN ECUADOR...UNDER INFLUENCE OF THE PANAMANIAN
TROUGH...MODERATE CONVECTION IS EXPECTED OVER THE NEXT DAY OR SO
TO TRIGGER RAINFALL MAXIMA OF 20-35MM. THIS DECREASES TO
15-20MM/DAY ON SATURDAY-MONDAY. ON THE SOUTHERN SIERRA OF PERU
ALSO EXPECTING MODERATE RAINFALL AMOUNTS...WITH ACCUMULATION OF
15-20MM/DAY. HIGHER AMOUNTS... HOWEVER...ARE EXPECTED ON
FRIDAY-SATURDAY WHEN THE MAXIMA IS TO PEAK AT 20-40MM/DAY.
LIKEWISE...OVER THE ALTIPLANO OF BOLIVIA INITIALLY EXPECTING
MAXIMA OF 15-20MM...INCREASING TO 20-30MM ON FRIDAY-SATURDAY.

BALBINO...INMET (BRASIL)
POMIER...SENAMHI (BOLIVIA)
GALVEZ...WPC (USA)