740  
FXSA20 KWBC 261726  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1226 PM EST TUE DEC 26 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 26 AT 0000 UTC): CONFIDENCE IN  
THE FORECAST IS HIGH...WITH GLOBAL MODELS FOLLOWING A SIMILAR  
EVOLUTION OVER THE CONTINENT-SOUTH ATLANTIC THROUGH 132-144 HRS.  
DIFFERENCES OVER THE SOUTH PACIFIC LIMIT TO SPEED OF A SHORT WAVE  
TROUGH ENTERING THE DOMAIN LATER ON DAY 06...WITH GFS FAVORING A  
FASTER PROGRESSION THAN WHAT THE EUROPEAN MEMBERS SUGGEST.  
 
A BROAD/LOW AMPLITUDE TROUGH ON THE SOUTHERN STREAM DOMINATES THE  
MID/UPPER LEVEL FLOW ACROSS THE SOUTHEAST PACIFIC-SOUTHERN CONE OF  
SOUTH AMERICA...FAVORING A TIGHT BELT OF MID LATITUDE WESTERLIES  
ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA. THE BROAD TROUGH  
PATTERN IS TO PERSIST NEARLY UNCHANGED DURING THE NEXT TWO DAYS.  
ON THURSDAY...AS A RIDGE BUILDS TO THE WEST...THE TROUGH IS TO  
AMPLIFY BETWEEN 105W-70W TO 30S. IT IS TO THEN SLOWLY PUSH ACROSS  
SOUTHERN CHILE-PATAGONIA IN ARGENTINA ON  
FRIDAY-SATURDAY...MEANWHILE FAVORING HEIGHT FALLS OF 75-125GPM  
OVER THE CONTINENT TO THE SOUTH OF 30S. THE DEEPENING TROUGH IS TO  
THEN ESTABLISH A SUBTROPICAL CONNECTION...ADVECTING WARM/MOIST AIR  
ACROSS THE EASTERN PACIFIC TO SOUTHERN PORTIONS OF CHILE. AT LOW  
LEVELS THIS IS TO INITIALLY FAVOR A BROAD TROUGH ACROSS THE  
SOUTHEAST PACIFIC...THAT FOCUSES A POLAR FRONT ACROSS THE DRAKE  
PASSAGE/TIERRA DEL FUEGO. ON WEDNESDAY THE FRONT MOVES NORTH OVER  
SOUTHERN CHILE...WHILE ON THURSDAY IT EXPANDS ACROSS PATAGONIA IN  
ARGENTINA TO LA PAMPA. IT THEN PUSHES FARTHER NORTH ACROSS RIO DE  
LA PLATA BASIN-NORTHERN ARGENTINA LATER IN THE PERIOD. EARLY IN  
THE CYCLE THIS IS TO TRIGGER LIGHT CONVECTION OVER SOUTHERN  
CHILE...WITH MAXIMA OF 05-10MM. ON WEDNESDAY THIS INCREASES TO  
10-15MM WHILE FOCUSING BETWEEN ISLA DE CHILOE AND TEMUCO. ON  
THURSDAY AND FRIDAY...AS PLUME OF SUBTROPICAL MOISTURE ENTERS  
CHILE...THE DAILY MAXIMA WILL PEAK AT 20-40MM. IN THIS AREA  
EXPECTING STORM TOTAL AMOUNTS IN EXCESS OF 100MM. AS THE FRONT  
PUSHES NORTH ACROSS LA PAMPA ON SATURDAY IT IS TO SUSTAIN LIGHT  
CONVECTION WITH MAXIMA OF 10-15MM...INCREASING TO 15-25MM ON  
SUNDAY WHILE BUILDING NORTH ACROSS THE BUENOS AIRES PROVINCE-ENTRE  
RIOS-CORDOBA IN ARGENTINA.  
 
OVER THE SOUTH ATLANTIC...MEANWHILE...BROAD/LOW AMPLITUDE MID  
LEVEL TROUGH IS TO MEANDER OFF THE COAST OF PATAGONIA LATER  
TODAY...TO MOVE ACROSS 30W ON WEDNESDAY...AND NEARING 10W LATER ON  
FRIDAY. AT LOW LEVELS THIS WILL SUSTAIN A SURFACE FRONT THAT  
EXTENDS ACROSS THE SOUTH ATLANTIC TO SOUTHERN BRASIL-NORTHERN  
ARGENTINA LATER TODAY. THE FRONT REMAINS NEARLY STATIONARY OVER  
NORTHERN ARGENTINA WHILE GRADUALLY FRONTOLIZING LATER ON  
THURSDAY...WHILE THE REMNANTS OVER THE ATLANTIC MEANDER NORTH  
ALONG THE COAST OF SAO PAULO TO RIO DE JANEIRO. THE FRONT IS TO  
THEN WEAKEN INTO A LOW/MID LEVEL TROUGH OVER SOUTHEAST BRASIL.  
THIS FEATURE WILL BE THE FOCUS OF LOW LEVEL MOISTURE CONVERGENCE.  
EARLY IN THE PERIOD THE FRONT IS TO FAVOR MODERATE TO HEAVY  
CONVECTION ACROSS PARAGUAY-MATO GROSSO DO SUL-SAO PAULO...WITH  
MAXIMA OF 25-50MM. AS THE FRONT WEAKENS THIS DECREASES TO 20-30MM  
THROUGH THURSDAY. BUT AS THE LOW/MID LEVEL TROUGH ESTABLISHES OVER  
SOUTHEAST BRASIL EXPECTING CONVECTION TO BECOME MORE ACTIVE/BETTER  
ORGANIZED...WITH MAXIMA ON SATURDAY INCREASING TO 30-60MM. ON  
SUNDAY EXPECTING A PEAK IN CONVECTION WITH MAXIMA OF 40-80MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH OVER BOLIVIA  
ANCHORS A RIDGE OVER MID SECTIONS OF SOUTH AMERICA...WITH AXIS  
UNDERCUTTING A TROUGH TO THE NORTH. THE TROUGH EXTENDS OVER THE  
NORTHEAST STATES OF BRASIL. UPPER RIDGE IS TO GENERALLY HOLD  
DURING THE NEXT 96-108 HRS. THE CLOSED HIGH...UNDER INFLUENCE OF  
AN ANOMALOUSLY WARM AREA OF SEA SURFACE TEMPERATURES OFF THE NORTH  
COAST OF CHILE...IS TO MEANDER WEST ACROSS BOLIVIA-NORTHERN  
CHILE/SOUTHERN PERU TO THE EASTERN PACIFIC LATER ON THURSDAY.  
EARLY IN THE CYCLE...AS THE HIGH MEANDERS OVER BOLIVIA...IT IS TO  
VENT ORGANIZED DEEP CONVECTION ACROSS SOUTHERN PERU-NORTHERN  
BOLIVIA-ACRE/RONDONIA-MATO GROSSO IN BRASIL...WITH MAXIMA OF  
30-60MM/DAY. OVER PARA-AMAZONAS TO THE NORTHERN THE DAILY MAXIMA  
IS TO PEAK AT 20-45MM. THROUGH THURSDAY-FRIDAY...AS THE HIGH  
RELOCATES... THIS DECREASES TO 20-35MM/DAY IN SCATTERED CONVECTION.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page