670  
FXSA20 KWBC 161743  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1242 PM EST TUE JAN 16 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 16 AT 0000 UTC): MODELS ARE IN  
AGREEMENT ON PATTERN EVOLUTION ACROSS THE SOUTH AMERICAN DOMAIN  
THROUGH 72-84 HRS. THEREAFTER THEY THEN DEVELOP AMPLITUDE/SPEED  
DIFFERENCES. ON THE SOUTHERN STREAM FLOW THE GFS FAVORS A FASTER  
PROGRESSION THAN WHAT THE EUROPEAN MODELS SUGGEST...WHILE ON THE  
NORTHERN STREAM FLOW THE UKMET AND ECMWF BOTH FAVOR A DEEPER  
TROUGH ON THE NORTHERN STREAM TO MEANDER OVER NORTHERN ARGENTINA  
BY 96-144 HRS.  
 
ON THE SOUTHERN STREAM FLOW...EXPECTING A PROGRESSIVE MID LEVEL  
TROUGH TO QUICKLY MOVE ACROSS THE DRAKE PASSAGE/SOUTHERN CONE OF  
SOUTH AMERICA LATER TODAY. ON WEDNESDAY...BUILDING RIDGE TO THE  
WEST IS TO THEN INDUCE THE NORTHWARD AMPLIFICATION OF THIS TROUGH  
ALONG 50W TO 40S...TO MEANDER ACROSS 35W/40W LATER ON THURSDAY. AT  
LOW LEVELS...THIS SUSTAINS AN ELONGATED FRONT THAT IS TO MEANDER  
OVER PATAGONIA IN ARGENTINA-SOUTHERN CHILE DURING THE NEXT FEW  
DAYS. AS IT MEANDERS ACROSS SOUTHERN CHILE THIS WILL SUSTAIN A  
SUBTROPICAL CONNECTION...WITH DEEP MOISTURE CONVERGING OVER THE  
CONTINENT TO THE SOUTH OF 40S. IN THIS AREA INITIALLY EXPECTING  
RAINFALL AMOUNTS OF 15-20MM...INCREASING TO 15-30MM ON WEDNESDAY.  
ON THURSDAY THE MAXIMA DECREASES TO 10-15MM IN SCATTERED  
CONVECTION.  
 
AS THE SOUTHERN STREAM TROUGH PULLS ACROSS THE SOUTHERN CONE IT IS  
TO DRAW A SHORT WAVE TROUGH TO THE NORTH. THE MID LEVEL  
PERTURBATION ENTERS CENTRAL-NORTHERN CHILE LATER TODAY...CROSSING  
CENTRAL PROVINCES IN ARGENTINA-RIO DE LA PLATA BASIN ON WEDNESDAY.  
AT LOW LEVELS THIS WILL INTERACT WITH A SURFACE FRONT OVER BUENOS  
AIRES PROVINCE/LA PAMPA-CENTRAL CUYO IN ARGENTINA TO SUSTAIN  
MODERATE TO HEAVY RAINFALL AMOUNTS. THROUGH WEDNESDAY MORNING  
EXPECTING ACCUMULATION OF 25-50MM IN POTENTIALLY SEVERE  
CONVECTION....WHILE ON WEDNESDAY EXPECTING MAXIMA OF 20-35MM TO  
CLUSTER OVER URUGUAY-ENTRE RIOS IN ARGENTINA.  
 
A HIGHER AMPLITUDE TROUGH IS 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 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 WITH  
MAXIMA OF 05-10MM/DAY.  
 
SIMULTANEOUSLY...A SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW  
IS TO REACH CENTRAL CHILE LATER ON FRIDAY...TO MEANDER EAST ACROSS  
CUYO TO CENTRAL ARGENTINA LATER ON SATURDAY. AS PREVIOUSLY  
INDICATED...BOTH EUROPEAN MODELS FORESEE A DEEPER TROUGH THAN WHAT  
THE GFS SUGGESTS. AT LOW LEVELS AN ELONGATED FRONT EXTENDS ACROSS  
THE SOUTH ATLANTIC TO SOUTHERN BRASIL-PARAGUAY/NORTHERN ARGENTINA.  
THIS BOUNDARY IS THE FOCUS OF THE LOW LEVEL MOISTURE....WITH HEAVY  
RAINS TO AFFECT SOUTHERN BRASIL-SOUTHEAST PARAGUAY EARLY IN THE  
CYCLE...WITH RAINFALL MAXIMA OF 40-80MM. ON WEDNESDAY-THURSDAY  
THIS DECREASES TO 15-25MM. ON FRIDAY-TO-SATURDAY...AS THE MID  
LEVEL TROUGH SPILLS ACROSS THE CENTRAL ANDES...ENVIRONMENTAL  
CONDITIONS OVER CENTRAL SOUTH AMERICA ARE TO BECOME FAVORABLE FOR  
GENERATION OF A MESO SCALE CONVECTIVE SYSTEM. IN THIS AREA  
EXPECTING MAXIMA OF 35-70MM.  
 
AT 200 HPA...A RIDGE EXTENDS EAST-TO-WEST ACROSS SOUTHERN  
BRASIL-PARAGUAY-BOLIVIA TO THE EASTERN PACIFIC. AS IT HOLDS...THE  
RIDGE IS TO STEER A SHORT WAVE TROUGH TO THE NORTH. EARLY IN THE  
CYCLE THE TROUGH WILL EXTEND OVER NORTHEAST BRASIL WHILE CENTERING  
ON A CLOSED LOW AT 10S 40W. THIS MEANDERS WEST TO PARA LATER ON  
WEDNESDAY/THURSDAY MORNING. 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 40-80MM. ON  
WEDNESDAY AND THURSDAY THE MAXIMA IS TO PEAK AROUND 25-50MM/DAY.  
HIGHER AMOUNTS ARE EXPECTED ON FRIDAY...WHEN CONVECTION ALONG THE  
NEAR EQUATORIAL TROUGH (NET) OVER NORTHERN PARA-AMAZONAS-RORAIMA  
IS TO PEAK AT 30-60MM.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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