091  
FXSA20 KWBC 201637  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1236 PM EDT FRI OCT 20 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 20 AT 0000 UTC): CONFIDENCE IN  
THE FORECAST IS HIGH THROUGH 96 HRS TO THE SOUTH OF 45S...AND  
THROUGH 120 HRS IN REGIONS TO THE NORTH. THE ECMWF MODEL IS  
STRUGGLING ON CROSSING A TROUGH ACROSS THE SOUTHERN CONE BY 96  
HRS. THE GFS AND ECMWF ARE IN BETTER AGREEMENT ON THIS SYSTEM.  
 
THE CLIMATE FORECAST SYSTEM MODEL...GFS AND EMPIRICAL WAVE  
PROPAGATION MODEL OF CPC ARE ALL INDICATING THAT THE UPPER  
DIVERGENT PHASE OF THE MADDEN-JULIAN OSCILLATION WILL ESTABLISH  
OVER THE AMERICA DURING THE WEEKEND INTO EARLY NEXT WEEK...AND  
PERSIST THROUGH THE END OF OCTOBER. UNDER THIS FAVORABLE LARGE  
SCALE UPPER DIVERGENT PATTERN...EXPECTING ENHANCEMENT IN  
PRECIPITATION ASSOCIATED WITH THE WEATHER SYSTEMS IN PLACE DURING  
THE REST OF THE MONTH OF OCTOBER.  
 
A ROBUST SHORT WAVE TROUGH IS CROSSING THE ANDES OF NORTHERN  
ARGENTINA ON FRIDAY...AND IS INTERACTING WITH A CONVECTIVELY  
UNSTABLE AIR MASS SITTING IN CENTRAL PARAGUAY...AS WELL AS WITH A  
LOW-LEVEL JET FROM THE NORTH CONVERGING IN THE AREA. THIS WILL  
SUSTAIN STRONG CONVECTION AND LOCALLY HEAVY RAINFALL ON  
FRIDAY-SATURDAY WITH ACCUMULATIONS OF 75-125MM AND THE RISK FOR  
MCS FORMATION. THE CONVECTIVE EVENT IS TO PROLONG INTO LATE  
SATURDAY...WHEN EXPECTING ACCUMULATIONS OF 50-100MM IN EASTERN  
PARAGUAY/SOUTHERN MATO GROSSO DO SUL AND PARANA IN BRASIL. ALSO ON  
SATURDAY...UNDER THE INFLUENCE OF A DEVELOPING SOUTHERLY LOW-LEVEL  
JET ACROSS NORTHERN ARGENTINA/SOUTHERN BOLIVIA...ENHANCED MOISTURE  
CONVERGENCE WILL FAVOR ACCUMULATIONS OF 30-60MM/DAY IN CENTRAL AND  
SOUTHERN BOLIVIA...WHILE A COLD FRONT STARTS PROPAGATING NORTHWARD  
RAPIDLY. BY SUNDAY-MONDAY...THE LOW-LEVEL JET WILL REACH  
CENTRAL/NORTHERN BOLIVIA...WHILE NORTHEASTERLY TRADES ENHANCE  
MOISTURE CONVERGENCE IN AREAS TO THE NORTH. THIS WILL CONTINUE  
SUSTAINING HEAVY RAINFALL...WITH ACCUMULATIONS OF 30-60MM/DAY IN  
SOUTHERN PERU/NORTHERN BOLIVIA/ACRE AND RONDONIA. TO THE  
NORTH...ACROSS THE PERUVIAN AMAZON AND THE ECUADORIAN  
ORIENTE...EXPECTING ACCUMULATIONS OF 20-35MM. ALSO DURING THIS  
PERIOD...ENHANCED FRONTAL CONVERGENCE AND INTERACTIONS WITH THE  
SERRA DO MAR IN SAO PAULO/RIO WILL SUSTAIN ACCUMULATIONS OF  
30-60MM/DAY. INLAND ACROSS MATO GROSSO DO SUL/MATO GROSSO EXPECTED  
MAXIMA OF 15-25MM. BY MONDAY-TUESDAY...THE WANING SOUTHEASTERLY  
SURGE ACROSS NORTHERN PERU/ECUADOR WILL STILL FAVOR MAXIMA OF  
25-50MM/DAY IN THESE REGIONS. ELSEWHERE IN THE WESTERN AMAZON  
EXPECTING MAXIMA OF 20-35MM. IN BRASIL...AS THE FRONT CONTINUES  
INTERACTING WITH THE SERRA DO MAR OF RIO DE JANEIRO...EXPECTING  
ACCUMULATIONS OF 20-40MM.  
 
IN CHILE...A SUBTROPICAL MOISTURE CONNECTION WILL ARRIVE INTO THE  
SOUTHERN CONE ON SATURDAY. THIS WILL SUSTAIN RAINFALL  
ACCUMULATIONS OF 15-20MM/DAY ON SATURDAY THROUGH MONDAY. AFTER  
THIS PERIOD...FRONTAL CONVERGENCE WITH THE SOUTHERN ANDES WILL  
FAVOR ISOLATED AMOUNTS OF 10-15MM/DAY.  
 
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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