502  
FXSA20 KWBC 171723  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1222 PM EST WED JAN 17 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 17 AT 0000 UTC): THE GFS AND  
EUROPEAN MODELS CONTINUE TO FORECAST A SIMILAR EVOLUTION ACROSS  
THE SOUTH AMERICAN DOMAIN...WITH GLOBAL ENSEMBLE MEMBERS PROVIDING  
STRONG SUPPORT TO THE DETERMINISTIC SOLUTION.  
 
AT 500 HPA...A TROUGH EXTENDS FROM THE ANTARCTIC PENINSULA TO THE  
SOUTHERN CONE OF SOUTH AMERICA...WITH THE MID LEVEL TROUGH TO  
MEANDER EAST ACROSS 60W LATER TODAY. ON THURSDAY THE TROUGH IS TO  
EXTEND ALONG 40W/45W TO 38S...TO CONTINUE ACROSS 30W ON FRIDAY. AS  
IT PULLS ACROSS THE SOUTHERN CONE THIS IS TO INTERACT WITH A SHORT  
WAVE TROUGH TO THE NORTH... DRAWING THE LATTER ACROSS CENTRAL  
CHILE TO ARGENTINA EARLY IN THE CYCLE. ON THURSDAY IT IS TO THEN  
MOVE OFF THE COAST OF URUGUAY/ SOUTHERN BRASIL...TO THEN MERGE  
WITH THE HIGHER AMPLITUDE TROUGH TO THE SOUTH. AT LOW LEVELS THIS  
SUSTAINS A SURFACE FRONT THAT MOVES NORTH ACROSS THE BUENOS AIRES  
PROVINCE-CUYO IN ARGENTINA LATER THIS EVENING...TO MEANDER NORTH  
OVER RIO DE LA PLATA BASIN ON THURSDAY-FRIDAY. ANOTHER FRONT LIES  
TO THE NORTH...EXTENDING ACROSS THE SOUTH ATLANTIC TO SOUTHERN  
BRASIL-NORTHERN ARGENTINA. THIS BOUNDARY IS TO PERSIST DURING THE  
NEXT FEW DAYS. OVER THE BUENOS AIRES PROVINCE AND THE RIO DE LA  
PLATA BASIN THIS IS TO TRIGGER SCATTERED DEEP CONVECTION WITH  
MAXIMA OF 20-35MM THROUGH THURSDAY MORNING. SIMILAR AMOUNTS ARE  
EXPECTED ACROSS SOUTHERN BRASIL-SAO PAULO THROUGH THURSDAY  
EVENING.  
 
SIMULTANEOUSLY...ANOTHER SHORT WAVE TROUGH ON THE NORTHERN STREAM  
FLOW IS TO EXPECTED OVER CENTRAL CHILE LATER ON FRIDAY...TO  
MEANDER EAST ACROSS CUYO TO CENTRAL ARGENTINA LATER ON SATURDAY.  
IN THIS RUN THE GFS IS TRENDING IN FAVOR OF A DEEPER MID LEVEL  
TROUGH TO PULL ACROSS CENTRAL ARGENTINA...PROVIDING MORE SUPPORT  
TO THE UKMET AND ECMWF SOLUTIONS. AS IT NEARS THE CENTRAL ANDES  
THIS WILL FAVOR SCATTERED CONVECTION ACROSS CUYO IN  
ARGENTINA...WITH MAXIMA OF 10-15MM/DAY ON THURSDAY-FRIDAY...AND  
05-10MM/DAY ON SATURDAY-SUNDAY. ACROSS NORTHERN ARGENTINA-PARAGUAY  
TO SOUTHERN BRASIL THIS IS TO THEN SUSTAIN AN MCS ALONG THE  
MEANDERING FRONT LATER ON FRIDAY/EARLY SATURDAY MORNING...WITH  
MAXIMA OF 35-70MM IN ORGANIZED CONVECTION. HIGHER AMOUNTS ARE  
EXPECTED ON SATURDAY...WHEN MAXIMA ALONG THIS FRONT IS TO PEAK AT  
50-100MM.  
 
THE MODELS FORECAST A HIGHER AMPLITUDE TROUGH TO FOLLOW...TO  
EXTEND NORTH BETWEEN 120W-90W TO SOUTH OF 45S LATER ON THURSDAY.  
THE DEEPENING TROUGH IS TO THEN INDUCE A NORTH-TO-SOUTH RIDGE  
ALONG THE COAST OF CHILE TO THE BELLINGSHAUSEN SEA/ANTARCTIC  
PENINSULA. AS THE TROUGH PUSHES EAST IT IS TO SLOWLY DISPLACE THE  
RIDGE TO THE EAST ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC  
LATER ON FRIDAY. AS IT YIELDS...THE POLAR TROUGH IS TO THEN FOCUS  
ITS SHORT WAVE ENERGY ACROSS SOUTHERN REGIONS OF CHILE AND  
PATAGONIA IN ARGENTINA LATER IN THE CYCLE. AT LOW LEVELS THIS IS  
TO SUSTAIN A BROAD TROUGH ACROSS THE SOUTHEAST PACIFIC LATER ON  
WEDNESDAY...THAT SLOWLY MOVES ACROSS THE ANTARCTIC PENINSULA-DRAKE  
PASSAGE LATER ON THURSDAY/EARLY FRIDAY MORNING. ASSOCIATED FRONT  
IS TO MEANDER EAST ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA ON  
THURSDAY-SATURDAY...MEANWHILE FAVORING SCATTERED CONVECTION OVER  
TIERRA DEL FUEGO/EXTREME SOUTHERN CHILE WITH MAXIMA OF  
05-10MM/DAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE EXTENDS  
EAST-TO-WEST ACROSS SOUTHERN BRASIL-PARAGUAY-BOLIVIA TO THE  
EASTERN PACIFIC. A SHORT WAVE TROUGH TO THE NORTH EXTENDS OVER THE  
NORTHEAST STATES OF BRASIL. UNDER INFLUENCE OF THE RIDGE TO THE  
SOUTH THE TROUGH WILL RETROGRESS ACROSS PARA IN BRASIL ON  
THURSDAY. BUT AS IT MOVES FARTHER WEST TO AMAZONAS ON  
FRIDAY-SATURDAY THE LOW/TROUGH IS TO RAPIDLY WEAKEN. EARLY IN THE  
CYCLE THIS IS TO ENHANCE CONVECTION ACROSS NORTHERN PARA-NORTHEAST  
COAST OF BRASIL TO SUSTAIN MAXIMA OF 15-25MM/DAY. HIGHER AMOUNTS  
ARE EXPECTED TO THE WEST ACROSS AMAZONAS-RONDONIA-ACRE IN  
BRASIL...WITH MAXIMA OF 25-50MM.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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