589  
FXSA20 KWBC 031612  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1211 PM EDT FRI NOV 03 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 03 AT 0000 UTC): THE GFS AND  
EUROPEAN MODELS REMAIN IN EXCELLENT AGREEMENT...WITH ENSEMBLE  
MODELS CLUSTERING IN SUPPORT OF THE DETERMINISTIC SOLUTION.  
ENVIRONMENTAL CONDITIONS REMAIN HIGHLY FAVORABLE FOR AN MCS TO  
FORM OVER MIDSECTIONS OF SOUTH AMERICA EARLY IN THE CYCLE. THIS IS  
TO SUSTAIN HEAVY RAINFALL AMOUNTS ACROSS PARAGUAY-MESOPOTAMIA  
VALLEY IN ARGENTINA AND THE SOUTHERN STATES OF BRASIL.  
 
A 500 HPA SHORT WAVE TROUGH IS STREAMING ACROSS CHILE TO  
ARGENTINA...WITH MID LEVEL AXIS TO EXIT THE COAST INTO THE WESTERN  
ATLANTIC LATER TODAY. ON SATURDAY-SUNDAY THIS IS TO THEN MERGE  
WITH A DEEPENING TROUGH TO THE SOUTH. THIS IS TO THEN EVOLVE INTO  
A HIGH AMPLITUDE LONG WAVE TROUGH OVER THE SOUTH ATLANTIC....WITH  
AXIS TO EXTEND BETWEEN 60W-20W AND TO THE SOUTH OF 25S ON  
SUNDAY-MONDAY. AT LOW LEVELS...UNDER INFLUENCE OF A POLAR RIDGE  
OVER PATAGONIA/LA PAMPA IN ARGENTINA...THE ASSOCIATED SURFACE  
FRONT SURGES ACROSS URUGUAY TO SOUTHERN BRASIL-NORTHERN PROVINCES  
IN ARGENTINA/PARAGUAY LATER THIS AFTERNOON. THIS IS TO CONTINUE  
NORTH ACROSS SAO PAULO-PARAGUAY ON SATURDAY...AND ON SUNDAY IT IS  
TO EXTEND ACROSS RIO DE JANEIRO-MATO GROSSO DO SUL TO PARAGUAY.  
OVER SOUTHERN BRASIL-MESOPOTAMIA VALLEY IN ARGENTINA AND  
CENTRAL/SOUTHEAST PARAGUAY THE FRONT WILL TRIGGER A MESO SCALE  
CONVECTIVE SYSTEM EARLY ON SATURDAY MORNING. IN THIS AREA  
EXPECTING RAINFALL AMOUNTS OF 75-150MM IN POTENTIALLY SEVERE  
CONVECTION. ON SATURDAY THE MAXIMA ACROSS PARAGUAY DECREASES TO  
30-60MM...WHILE OVER THE SOUTHERN STATES OF BRASIL IT WILL PEAK AT  
20-30MM. AS THE FRONT MEANDERS NORTH ACROSS SAO PAULO TO RIO DE  
JANEIRO/ESPIRITO SANTO ON SUNDAY...THIS IS TO THEN ENHANCE COASTAL  
CONVERGENCE WHILE FAVORING MODERATE TO HEAVY RAINFALL AMOUNTS. ON  
SUNDAY-TUESDAY THE DAILY MAXIMA IS TO PEAK AT 30-60MM. DUE TO  
STRONG TOPOGRAPHICAL FORCING...LOCALIZED MAXIMA OF 100-125MM IS  
HIGHLY PROBABLE.  
 
THE MODELS THEN FORECAST A LOWER AMPLITUDE MID LEVEL TROUGH TO  
ENTER THE SOUTHERN/CENTRAL REGIONS OF CHILE EARLY ON SATURDAY  
MORNING. THIS IS TO THEN QUICKLY MOVE ACROSS CENTRAL ARGENTINA TO  
THE WESTERN ATLANTIC EARLY ON SUNDAY MORNING. THE TROUGH ALOFT  
SUSTAINS A SURFACE FRONT THAT ENTERS SOUTHERN/CENTRAL CHILE ON  
SATURDAY MORNING...TO TRIGGER MODERATE CONVECTION WITH  
ACCUMULATION OF 15-20MM. ACROSS NORTHERN PATAGONIA/LA PAMPA IN  
ARGENTINA THIS WILL SUSTAIN RAINFALL AMOUNTS OF 05-10MM ON SUNDAY.  
 
A DEEPER/HIGHER AMPLITUDE MID LEVEL TROUGH WILL FOLLOW...TO MOVE  
TO THE SOUTHEAST PACIFIC LATER ON SUNDAY. THE DEEP TROUGH WILL  
SUSTAIN AN INDUCED RIDGE TO THE EAST...TO EXTEND SOUTH FROM  
SOUTHERN CHILE/PATAGONIA IN ARGENTINA TO THE ANTARCTIC PENINSULA.  
AS THE TROUGH PRESSES AGAINST THE RIDGE TO THE EAST...IT IS TO  
SHEAR SHORT WAVE ENERGY TO THE SOUTH-SOUTHEAST. LATER ON MONDAY  
THE RIDGE WILL THEN ALLOW THE WANING TROUGH TO ENTER THE SOUTHERN  
CONE OF SOUTH AMERICA...FOCUSING ITS SHORT WAVE ENERGY ACROSS  
CHILE TO THE SOUTH OF CONCEPCION. AT LOW LEVELS THIS WILL SUSTAIN  
A BROAD TROUGH OVER THE SOUTHEAST PACIFIC LATER ON SUNDAY...WITH  
POLAR FRONT ENTERING SOUTHERN CHILE/PATAGONIA IN ARGENTINA ON  
MONDAY. LACKING STRONG UPPER LEVEL SUPPORT THIS IS TO ONLY TRIGGER  
LIGHT RAINFALL AMOUNTS ACROSS SOUTHERN CHILE WITH MAXIMA OF  
05-10MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...THE FLOW WILL SPLIT  
BETWEEN A RIDGE AND A TROUGH. THE RIDGE IS TO ENVELOP AREA BETWEEN  
20S-30S...WHILE THE TROUGH DOMINATES NORTHEAST BRASIL. THIS  
PATTERN IS TO HOLD DURING THE NEXT FIVE DAYS. THE UPPER LEVEL FLOW  
IS TO DIVERGE BETWEEN THE RIDGE TO THE SOUTH AND THE TROUGH TO THE  
NORTH. THIS...IN-TURN...IS TO VENT DEEP CONVECTION ACROSS  
SOUTHEAST TO NORTHWEST STATES OF BRASIL AND THE PERUVIAN  
JUNGLE/EASTERN ECUADOR. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF  
20-40MM/DAY...INCREASING TO 25-50MM ON SATURDAY. ACROSS  
TOCANTINS-GOIAS-MATO GROSSO EXPECTING RAINFALL AMOUNTS OF 20-30MM.  
THROUGH SATURDAY/SUNDAY THIS INCREASES TO 20-45MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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