Prognostic Meteorological Discussion
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000
FXSA20 KWBC 261619
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1219 PM EDT MON SEP 26 2016

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 26 AT 0000 UTC): CONFIDENCE
IN THE FORECAST THROUGH DAY 06 IS HIGH...WITH GLOBAL MODEL
GUIDANCE FOLLOWING A SIMILAR EVOLUTION ACROSS THE SOUTH AMERICAN
DOMAIN.

DEEPENING SHORT WAVE TROUGH ON THE SOUTHERN STREAM FLOW IS TO MOVE
ACROSS THE DRAKE PASSAGE/SOUTHERN CONE EARLY IN THE CYCLE. THROUGH
TUESDAY EVENING IT WILL PULL ACROSS 50W...WHERE IT IS FORECAST TO
DEEPEN AS A RIDGE BUILDS TO THE WEST. THROUGH THURSDAY MORNING
THIS IS TO AMPLIFY BETWEEN 50W-20W TO 20S...WHILE ANCHORING ON A
CLOSED LOW NEAR 45S 30W LATER IN THE DAY. THE DEEPENING TROUGH
DRIVES A PROGRESSIVE FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN
ARGENTINA LATER TODAY...WHERE IT IS TO TRIGGER LIGHT CONVECTION
WITH ACCUMULATION OF 00-05MM. ON TUESDAY THE FRONT MOVES NORTH
ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA. ON WEDNESDAY TO
THURSDAY MORNING A BUILDING 1031-1033 HPA HIGH OFF THE COAST OF
ARGENTINA WILL DISPLACE THIS BOUNDARY NORTH TO SOUTHERN
BRASIL-NORTHERN ARGENTINA/PARAGUAY LATER ON THURSDAY. AS THE FRONT
SURGES ACROSS SOUTHERN TO SOUTHEAST BRASIL...AND UNDER INFLUENCE
OF A SOUTHERLY JET OVER THE WESTERN ATLANTIC...EXPECTING SCATTERED
COASTAL CONVECTION BETWEEN NORTHERN SAO PAULO AND RIO DE JANEIRO
LATER IN THE CYCLE.

AS THE MID LEVEL TROUGH DEEPENS OVER THE WESTERN ATLANTIC IT IS TO
INTERACT WITH A BROAD TROUGH TO THE NORTH. THE TROUGH IS TO EXTEND
BETWEEN 60W-20W AND TO THE SOUTH OF 20S THROUGH TUESDAY EVENING.
ON WEDNESDAY IT IS TO THEN RAPIDLY WEAKEN WHILE SHEARING EAST
ACROSS 20W. AT LOW LEVELS THIS SUSTAINS A BROAD TROUGH OVER THE
WESTERN SOUTH ATLANTIC...AND A MEANDERING FRONT ACROSS ESPIRITO
SANTO/SOUTHERN MINAS GERAIS. THROUGH WEDNESDAY EVENING/THURSDAY
MORNING THE FRONT IS THEN FORECAST TO FRONTOLIZE. MEANWHILE...THIS
WILL ENHANCE MOISTURE CONVERGENCE BETWEEN SOUTHERN PARA-BAHIA IN
BRASIL...TO FAVOR MODERATE CONVECTION WITH ACCUMULATION OF 20-35MM
THROUGH TUESDAY MORNING...AND 15-20MM ON TUESDAY TO WEDNESDAY.

SHORT WAVE TROUGH ON THE NORTHERN STREAM WILL FOLLOW...WITH MID
LEVEL PERTURBATION EXPECTED TO MOVE ACROSS 90W LATER ON TUESDAY.
AS IT NEARS CENTRAL CHILE THIS WILL SUSTAIN AN INDUCED RIDGE TO
THE EAST...THAT IS TO EXTEND OVER ARGENTINA TO THE DRAKE PASSAGE.
AS IT PRESSES AGAINST THE RIDGE TO THE EAST THE TROUGH IS FORECAST
TO WEAKEN AS SHORT WAVE ENERGY SHEARS SOUTH. THE RIDGE IS TO THEN
STEER THE REMNANTS OF THE WANING SHORT WAVE TROUGH ACROSS
SOUTHERN/CENTRAL CHILE TO PATAGONIA IN ARGENTINA ON THURSDAY TO
FRIDAY. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH OFF THE
CENTRAL COAST OF CHILE LATER ON WEDNESDAY...WITH AXIS TO MOVE
INLAND EARLY ON THURSDAY. ACROSS CENTRAL CHILE THIS WILL FAVOR
MODERATE RAINFALL AMOUNTS WITH ACCUMULATION OF 10-15MM...WHILE
ACROSS THE CENTRAL PROVINCES IN ARGENTINA EXPECTING MAXIMA OF
15-25MM. THIS IS TO INCREASE/BECOME BETTER ORGANIZED ON FRIDAY TO
SATURDAY AS THE TROUGH MEANDERS EAST AND ASSOCIATED FRONT PUSHES
ACROSS CENTRAL PROVINCES IN ARGENTINA.

NORTH OVER THE CONTINENT...AT 200 HPA...A LOW AMPLITUDE RIDGE WILL
ENVELOP CONTINENTAL AREA TO THE NORTH OF 10S WHILE EXTENDING WEST
ACROSS THE TROPICAL ATLANTIC TO NORTHERN SOUTH AMERICA. THE RIDGE
PATTERN ALOFT WILL REMAIN NEARLY UNCHANGED OVER THE NEXT FEW DAYS.
A TROUGH TO THE SOUTH...MEANWHILE...IS TO INITIALLY EXTEND ACROSS
SOUTHEAST BRASIL TO MATO GROSSO. THIS IS FORECAST TO MEANDER EAST
ACROSS MINAS GERAIS/RIO DE JANEIRO THROUGH THURSDAY AFTERNOON. THE
RIDGE ALOFT WILL VENT CONVECTION ACROSS NORTHWEST SOUTH
AMERICA...WITH MAXIMA OF 15-20MM EXPECTED ACROSS
RONDONIA-ACRE-AMAZONAS IN BRASIL. LOCALLY HIGHER AMOUNTS ARE TO
CLUSTER ON THE CENTRAL JUNGLE OF PERU OVER THE NEXT COUPLE OF
DAYS...WITH MAXIMA IN THIS AREA TO PEAK AT 20-35MM. BUT THROUGH
WEDNESDAY IT IS TO ALSO DECREASE TO 15-20MM. OVER ECUADOR MOST
ACTIVE IS EXPECTED ON THE JUNGLE...WITH DAILY RAINFALL AMOUNTS OF
10-15MM. MODERATE RAINFALL AMOUNTS ARE EXPECTED BETWEEN PARA-MINAS
GERAIS IN BRASIL...WITH MAXIMA IN THIS AREA TO PEAK AT 20-35MM AS
ENHANCED BY UPPER TROUGH PATTERN.

OSORIO...DMC (CHILE)
ALVA...SENAMHI (PERU)
DAVISON...WPC (USA)
$$




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