180  
FXSA20 KWBC 301735  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1235 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 20S.  
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. THIS REMAINS  
NEARLY STATIONARY DURING THE NEXT THREE DAYS...BUT EARLY ON SUNDAY  
MORNING IT IS TO UNDULATE NORTH ACROSS SOUTHERN BRASIL TO  
PARAGUAY. EARLY IN THE CYCLE THIS IS TO SUSTAIN RAINFALL MAXIMA OF  
15-20MM. ON FRIDAY-SATURDAY THIS INCREASES TO 20-45MM IN SCATTERED  
DEEP CONVECTION. ON SUNDAY IT IS TO THEN FOCUS CONVECTION ACROSS  
PARAGUAY-SOUTHERN BRASIL AND PORTIONS OF BOLIVIA WHERE THE MAXIMA  
PEAKS AT 25-50MM.  
 
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)  

 
 
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