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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1705Z Nov 30, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EST THU NOV 30 2017

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

MODEL DISCUSSION (VALID FROM NOV 30 AT 0000 UTC): MODELS ONCE
AGAIN MAKE PATTERN CORRECTIONS TO THE SOUTHERN STREAM FLOW DURING
THE MEDIUM RANGE PERIOD...WITH THE GFS NOW FAVORING A
SLOWER/HIGHER AMPLITUDE TROUGH TO ENTER THE SOUTHERN CONE LATER
DURING THE WEEKEND. IN CONTRAST...THE EUROPEAN MODELS NOW FORECAST
A SLIGHTLY FASTER/LOWER AMPLITUDE PERTURBATION. IN THIS PERIOD THE
VARIABILITY AMONG THE ENSEMBLE MEMBERS IS TOO HIGH TO ESTABLISH
CONFIDENCE ON EITHER SOLUTION. SO FURTHER CORRECTIONS ARE EXPECTED.

FLOW OVER THE WESTERN ATLANTIC SPLITS BETWEEN A RIDGE ON THE
SOUTHERN STREAM AND A SHORT WAVE TROUGH TO THE NORTH. THE RIDGE
EXTENDS SOUTH OF 40S AND ALONG 30W/35W TO 75S. UNDER INFLUENCE OF
SHORT WAVE PERTURBATIONS STREAMING ACROSS THE DRAKE
PASSAGE/SOUTHERN CONE...THE RIDGE IS FORECAST TO GRADUALLY FLATTEN
EARLY ON SATURDAY MORNING. THE TROUGH TO THE
NORTH...MEANWHILE...IS TO EXTEND BETWEEN 55W-25W...WHILE CENTERING
ON A CLOSED LOW AT 33S 42W. THROUGH SUNDAY EVENING THE SHORT WAVE
TROUGH IS TO WEAKEN WHILE SHEARING SHORT WAVE ENERGY TO THE
SOUTH-SOUTHEAST. MEANWHILE...THIS IS TO INTERACT WITH MEANDERING
FRONT OVER THE WESTERN ATLANTIC. THE SURFACE FRONT EXTENDS TO THE
NORTHWEST ACROSS RIO DE JANEIRO/SOUTHERN MINAS GERAIS TO MATO
GROSSO DO SUL-CHACO PARAGUAYO. THE MID LEVEL TROUGH IS TO INTERACT
WITH THIS BOUNDARY...TRIGGERING AN MCS ACROSS CHACO
PARAGUAYO-SANTA CRUZ IN EASTERN BOLIVIA-MATO GROSSO DO SUL EARLY
ON FRIDAY MORNING. IN THIS AREA THIS IS TO FAVOR RAINFALL MAXIMA
OF 75-125MM LATER ON FRIDAY/EARLY ON SATURDAY MORNING. OVER MINAS
GERAIS-NORTHERN SAO PAULO THE MAXIMA IS TO INITIALLY PEAK AT
30-60MM. ON FRIDAY-SATURDAY THIS INCREASES TO 40-80MM...WHILE ON
SATURDAY-MONDAY IT IS TO PEAK AT 30-60MM/DAY.

ANOTHER MID LEVEL SHORT WAVE TROUGH ON THE NORTHERN STREAM EXTENDS
OVER THE FAR EASTERN PACIFIC WITH AXIS NORTH ALONG 80W TO 30S.
THIS IS TO REMAIN STATIONARY WHILE SHEARING SHORT WAVE ENERGY
ACROSS CENTRAL-NORTHERN CHILE TO ARGENTINA. AT LOW LEVELS THE
TROUGH SUSTAINS A SURFACE FRONT ACROSS LA PAMPA IN ARGENTINA TO
CENTRAL REGIONS OF CHILE. THIS MEANDERS NORTH TO THE BUENOS AIRES
PROVINCE/ MENDOZA IN ARGENTINA LATER ON THURSDAY. LATER ON SUNDAY
IT IS TO THEN UNDULATE NORTH ACROSS PARAGUAY. THE TROUGH ALOFT IS
INTERACTING WITH A SURFACE FRONT THAT MEANDERS OVER CENTRAL
ARGENTINA. LATER ON SATURDAY THE WEAK BAROCLINIC BOUNDARY MOVES
NORTH ACROSS CENTRAL ARGENTINA...REACHING SOUTHERN BRASIL-URUGUAY
ON SUNDAY. OVER LA PAMPA-NORTHERN CUYO THIS IS TO FAVOR MAXIMA OF
20-40MM/DAY. ON FRIDAY-SATURDAY THIS INCREASES TO 25-50MM WHILE
BUILDING NORTH ACROSS ARGENTINA TO PARAGUAY AND CORRIENTES IN
ARGENTINA

MID/UPPER LEVEL SHORT WAVE RIDGE IS TO THEN ESTABLISH ACROSS THE
EASTERN PACIFIC. AS THE RIDGE HOLDS...IT IS TO FOCUS SHORT WAVE
ENERGY ACROSS CENTRAL CHILE TO ARGENTINA. THIS WILL COMBINE WITH A
MOIST NORTHERLY FLOW TO LIKELY FAVOR SCATTERED DEEP CONVECTION
ACROSS CENTRAL/INTERIOR PORTIONS OF PUERTO RICO ON FRIDAY AND
SATURDAY.

BROAD CELL OF THE SUBTROPICAL RIDGE EXTENDS AT 200 HPA OVER
NORTHERN SOUTH AMERICA WHILE CENTERING ON A CLOSED HIGH OVER
NORTHERN BOLIVIA. THIS IS TO PERSIST DURING THE NEXT FEW DAYS. AS
THE RIDGE HOLDS...IT IS TO VENT DIURNAL CONVECTION ACROSS
BRASIL-PERU-ECUADOR/SOUTHERN COLOMBIA. THE MOST ACTIVE IS TO
CLUSTER ALONG AND NORTH OF THE AFOREMENTIONED SURFACE FRONT OVER
BRASIL-PARAGUAY/BOLIVIA. OTHER CONVECTION IS EXPECTED ACROSS PARA
IN BRASIL TO FAVOR MAXIMA OF 20-30MM/DAY IN SCATTERED DEEP
CONVECTION. OVER ACRE-AMAZONAS IN WESTERN BRASIL TO THE NORTHERN
JUNGLE OF PERU/EASTERN ECUADOR EXPECTING MAXIMA OF 10-15MM/DAY.
THROUGH SATURDAY THIS IS TO INTENSIFY...WITH MAXIMA OVER
AMAZONAS-SOUTHERN COLOMBIA-NORTHERN JUNGLE OF PERU TO PEAK AT
20-40MM. ON THE HIGH JUNGLE OF PERU...MEANWHILE...THE DAILY MAXIMA
IS TO PEAK AT 20-30MM ON SATURDAY.

OVIEDO...SHN (ARGENTINA)
VANNUCCI...SMN (ARGENTINA)
RIVAS...SENAMHI (PERU)
DAVISON...WPC (USA)