703  
FXSA20 KWBC 061706  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1206 PM EST MON NOV 06 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 06 AT 0000 UTC): THE GFS AND  
ECMWF FOLLOW A SIMILAR EVOLUTION THROUGH 132-144 HRS...A SOLUTION  
THAT IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS.  
OVERALL CONFIDENCE IN THE FORECAST IS HIGH.  
 
A BLOCKING RIDGE ON THE SOUTHERN STREAM EXTENDS SOUTH FROM  
PATAGONIA IN ARGENTINA...ACROSS THE DRAKE PASSAGE TO THE ANTARCTIC  
PENINSULA. POLAR TROUGH TO THE WEST IS TO PRESS AGAINST THIS AXIS.  
AS THE RIDGE HOLDS...THE TROUGH IS TO GRADUALLY WEAKEN WHILE  
SHEARING SHORT WAVE ENERGY TO THE SOUTH-SOUTHEAST.  
THIS...HOWEVER...SETS THE STAGE FOR A DEEPER/HIGHER AMPLITUDE  
TROUGH TO MAKE LANDFALL LATER IN THE WEEK.  
 
SIMULTANEOUSLY...SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM  
ARE FORECAST TO PROPAGATE ACROSS THE EASTERN PACIFIC TO CENTRAL  
REGIONS OF CHILE...WITH ONE TO ENTER CENTRAL CHILE LATER  
TODAY/EARLY ON TUESDAY MORNING. THIS IS TO SLOWLY PULL ACROSS  
CENTRAL ARGENTINA TO THE WESTERN ATLANTIC...AS ANOTHER SHORT WAVE  
TROUGH REACHES THE CENTRAL REGIONS OF CHILE. THESE WILL THEN  
COMBINE INTO A BROAD TROUGH OFF THE COAST OF BUENOS AIRES LATER ON  
WEDNESDAY. AS ADDITIONAL SHORT WAVE PERTURBATIONS STREAM ACROSS  
THE SOUTHERN CONE THIS IS TO THEN BECOME BETTER  
ORGANIZED/STRENGTHEN. AT LOW LEVELS THIS SUSTAINS A MEANDERING  
FRONT OVER NORTHERN PATAGONIA/LA PAMPA IN ARGENTINA. INFLOW OF  
SHORT WAVE ENERGY WILL TRIGGER MODERATE CONVECTION ACROSS LA  
PAMPA/BUENOS AIRES PROVINCE EARLY ON TUESDAY MORNING...TO TRIGGER  
MAXIMA OF 20-45MM. ON TUESDAY TO WEDNESDAY THIS DECREASES TO  
15-25MM...WITH LESSER AMOUNTS ALONG THE COAST ON  
WEDNESDAY-THURSDAY. LATER IN THE WEEK...AS THE MID LEVEL LOW  
DEEPENS...THIS WILL SUSTAIN A SOUTHERLY LOW LEVEL JET THAT  
DISPLACES THE FRONT NORTH ACROSS SOUTHERN BRASIL-NORTHERN  
ARGENTINA ON THURSDAY...TO SAO PAULO-PARAGUAY ON FRIDAY. ACROSS  
PARAGUAY-SOUTHERN BRASIL THIS IS TO SUSTAIN MODERATE CONVECTION  
WITH MAXIMA OF 20-35MM. HIGHER AMOUNTS ARE EXPECTED ACROSS  
NORTHERN BOLIVIA-ACRE/RONDONIA IN BRASIL TO THE SOUTHERN JUNGLE OF  
PERU...WHERE THIS IS TO TRIGGER MAXIMA OF 30-60MM.  
 
A BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW OVER THE SOUTH  
ATLANTIC...AS IT EXTENDS BETWEEN 50W-10W AND TO THE SOUTH OF 20S.  
THIS IS A SLOW TO EVOLVE SYSTEM...TO REMAIN NEARLY UNCHANGED  
THROUGH MIDDAY ON WEDNESDAY. LATER IN THE DAY/EARLY THURSDAY THE  
TROUGH BEGINS TO WEAKEN WHILE PULLING TO THE EAST-SOUTHEAST. AT  
LOW LEVELS THIS SUSTAINS AN ELONGATED FRONT THAT EXTENDS TO THE  
NORTHWEST ACROSS THE SOUTH ATLANTIC TO RIO DE JANEIRO/NORTHERN SAO  
PAULO...THEN TO THE WEST-SOUTHWEST TO PARAGUAY. THIS BOUNDARY IS  
TO PERSIST DURING THE NEXT FEW DAYS. ACROSS ESPIRITO SANTO/RIO DE  
JANEIRO THIS IS TO FAVOR LIGHT TO MODERATE CONVECTION WITH MAXIMA  
OF 15-30MM/DAY. ON WEDNESDAY-THURSDAY THIS DECREASES TO  
15-20MM/DAY. ON THE TRAILING END OF THE FRONT OVER PARAGUAY/MATO  
GROSSO DO SUL EXPECTING MAXIMA OF 20-45MM ON TUESDAY...DECREASING  
TO 20-35MM/DAY ON WEDNESDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A NARROW CELL OF THE  
SUBTROPICAL RIDGE IS TO EXTEND WEST-TO-EAST BETWEEN PERU AND THE  
SOUTHEAST STATES OF BRASIL...CENTERING ON A CLOSED HIGH OVER  
NORTHERN BOLIVIA. THE RIDGE ALOFT UNDERCUTS A SHORT WAVE TROUGH TO  
THE NORTH...WITH TROUGH CENTERING ON A CLOSED LOW OVER NORTHERN  
PARA-AMAPA IN BRASIL. THE RIDGE ALOFT IS VENTING CONVECTIVE  
DEVELOPMENT ACROSS CENTRAL AND EASTERN STATES OF BRASIL. OVER THE  
NEXT FEW DAYS...CONVECTION ON THE STATES OF TOCANTINS-GOIAS-BAHIA  
IS TO BECOME BETTER ORGANIZED. IN THIS AREA INITIALLY EXPECTING  
RAINFALL MAXIMA OF 20-45MM. THROUGH WEDNESDAY THIS INCREASES TO  
40-80MM. IN RESPONSE TO THE LATENT HEAT RELEASED BY THE ORGANIZED  
CONVECTION...THE SUBTROPICAL RIDGE PATTERN WILL STRENGTHEN. THIS  
IS TO BUILD TO ENVELOP CONTINENTAL AREA TO THE NORTH OF 20N.  
OTHER CONVECTION TO THE WEST IS EXPECTED ACROSS THE NORTHERN  
JUNGLE OF PERU-EASTERN ECUADOR/SOUTHERN COLOMBIA...WITH MAXIMA OF  
20-45MM...WHILE ACROSS AMAZONAS-ACRE-RONDONIA TO NORTHERN BOLIVIA  
EXPECTING MAXIMA OF 15-25MM/DAY. AS THE RIDGE PATTERN ALOFT BUILDS  
ACROSS BRASIL...CONVECTION OVER NORTHWEST SOUTH AMERICA IS TO  
WANE. ON THE PERUVIAN JUNGLE/NORTHERN BOLIVIA THE MAXIMA WILL PEAK  
AT 15-25MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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