371  
FXSA20 KWBC 171730  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1229 PM EST FRI NOV 17 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 17 AT 0000 UTC): THE GLOBAL  
MODELS GENERALLY AGREE ON OVERALL SYNOPTIC PATTERN EVOLUTION  
DURING THE NEXT SIX DAYS. THEY...HOWEVER...CONTINUE TO DIVERGE ON  
THE SPEED AND AMPLITUDE OF SHORT WAVE PERTURBATIONS REVOLVING  
AROUND THE LONG WAVE AXIS. THESE DIFFERENCE GRADUALLY BECOME MORE  
PRONOUNCED BY 84-96 HRS...GRADUALLY BUILDING FROM WEST TO EAST.  
RESULTING IN LOWER CONFIDENCE IN THE FORECAST LATER IN THE CYCLE.  
 
BUILDING MID/UPPER LEVEL RIDGE OVER THE EASTERN PACIFIC WILL  
INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS ARGENTINA TO  
PARAGUAY LATER TODAY. AS IT DEEPENS...THE TROUGH WILL SUSTAIN  
HEIGHT FALLS OF 150-200GPM ACROSS RIO DE LA PLATA BASIN...WHILE  
OVER NORTHERN ARGENTINA HEIGHT FALLS WILL RANGE BETWEEN 35-70GPM.  
ON SATURDAY-SUNDAY THE TROUGH WILL THEN PULL TO THE EAST-SOUTHEAST  
INTO THE WESTERN SOUTH ATLANTIC. AT LOW LEVELS...THIS SUSTAINS A  
POLAR FRONT ACROSS RIO DE LA PLATA BASIN TO MENDOZA IN ARGENTINA  
LATER TODAY. EARLY ON SATURDAY THE FRONT RACES ACROSS URUGUAY TO  
NORTHERN ARGENTINA...DRIVEN BY A 35-40KT PAMPERO LOW LEVEL JET.  
THIS IS TO THEN MERGE WITH A MEANDERING FRONT OVER SOUTHERN  
BRASIL-PARAGUAY...DISPLACING THE FRONT NORTH ACROSS PARANA/SANTA  
CATARINA IN SOUTHERN BRASIL TO NORTHERN PARAGUAY/SANTA CRUZ IN  
EASTERN BOLIVIA LATER ON SATURDAY/SUNDAY MORNING. FRONT IS TO THEN  
REMAIN STATIONARY. ACROSS PARAGUAY-SOUTHERN BRASIL ENVIRONMENTAL  
CONDITIONS REMAIN FAVORABLE FOR AN MCS TO FORM EARLY ON SATURDAY  
MORNING...TO TRIGGER MAXIMA OF 75-150MM. LOCALLY HIGHER AMOUNTS  
ARE HIGHLY PROBABLE...WITH SOME OF THE ENSEMBLE MEMBERS SHOWING  
MAXIMA OF 200MM. ON SATURDAY AFTERNOON THE CONVECTION IS TO SPREAD  
ACROSS SOUTHERN TO SOUTHEAST BRASIL WHERE IT IS TO TRIGGER  
RAINFALL AMOUNTS OF 25-50MM. ON SUNDAY IT MOVES TO NORTHERN SAO  
PAULO/SOUTHERN MINAS GERAIS-RIO DE JANEIRO...WITH MAXIMA OF  
35-70MM. OTHER CONVECTION TO THE WEST IS TO BUILD ALONG THE  
TRAILING END OF THE SURFACE FRONT OVER BOLIVIA...WITH MAXIMA OF  
75-125MM ON SATURDAY TO SUNDAY...WHILE ON SUNDAY-MONDAY THE MAXIMA  
DECREASES TO 20-35MM. OVER SOUTHERN/ CENTRAL PERU TO ACRE IN  
BRASIL MAXIMA WILL PEAK AT 30-60MM ON SATURDAY...WITH AN  
ADDITIONAL RAINFALL AMOUNTS OF 25-50MM ON SUNDAY. ON MONDAY FOCUS  
OF THE CONVECTION SHIFTS TO NORTHERN PERU-EASTERN ECUADOR WITH  
MAXIMA DECREASING TO 20-40MM.  
 
ANOTHER SHORT WAVE TROUGH ON THE SOUTHERN STREAM IS TO THEN LIFT  
ACROSS THE BELLINGSHAUSEN SEA-DRAKE PASSAGE TO TIERRA DEL FUEGO  
LATER TODAY...AND ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN  
ATLANTIC ON SATURDAY. ASSOCIATED SURFACE FRONT REACHES SOUTHERN  
CHILE LATER THIS EVENING...AND ON SATURDAY IT IS TO QUICKLY MOVE  
ACROSS PATAGONIA TO LA PAMPA...REACHING RIO DE LA PLATA BASIN ON  
SUNDAY. OVER SOUTHERN CHILE THIS IS TO FAVOR A COLD ADVECTIVE  
PATTERN...WITH ENVIRONMENTAL CONDITIONS FAVORING SOLID  
PRECIPITATION ACROSS THE SOUTHERN ANDES AND MIXED PRECIPITATION  
ALONG THE COAST TO PUNTA ARENAS CHILE. IN THIS AREA EXPECTING  
ACCUMULATION OF 05-10MM ON BOTH FRIDAY AND SATURDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH OVER ACRE/NORTHERN  
BOLIVIA IS TO ANCHOR A SHORT WAVE RIDGE ACROSS NORTHWEST SOUTH  
AMERICA. A TROUGH TO THE EAST...MEANWHILE...EXTEND OVER THE  
NORTHEAST STATES OF BRASIL. THE LATTER EVOLVES INTO A CLOSED LOW  
NEAR THE CITY OF RECIFE LATER ON SUNDAY. THE RIDGE-TROUGH PATTERN  
ALOFT IS TO VENT CONVECTION ACROSS CENTRAL BRASIL...TO FAVOR  
RAINFALL AMOUNTS OF 20-35MM/DAY. THROUGH MONDAY THIS DECREASES TO  
15-20MM. OTHER CONVECTION IS TO CLUSTER ACROSS SOUTHERN  
COLOMBIA-NORTHERN PERU TO EASTERN ECUADOR...WITH ACCUMULATION OF  
15-20MM. THIS INCREASES TO 20-40MM LATER ON SUNDAY-MONDAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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