535  
FXSA20 KWBC 121753  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1252 PM EST TUE DEC 12 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 12 AT 0000 UTC): CONFIDENCE IN  
THE FORECAST IS HIGH...WITH MODELS FOLLOWING A SIMILAR EVOLUTION  
THROUGH DAY 06. THE DETERMINISTIC SOLUTION IS WELL SUPPORTED BY  
THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS.  
 
A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN STREAM IS TO ENTER  
THE SOUTHERN REGIONS OF CHILE EARLY ON WEDNESDAY  
MORNING...CROSSING PATAGONIA IN ARGENTINA LATER IN THE DAY. AT LOW  
LEVELS THIS SUSTAINS A BROAD TROUGH OVER THE SOUTHEAST PACIFIC  
LATER THIS AFTERNOON...WITH ASSOCIATED FRONT MOVING ACROSS  
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA ON WEDNESDAY  
MORNING...WHILE TRAILING ACROSS THE SOUTHERN REGIONS OF CHILE. AS  
IT MEANDERS OVER THE SOUTHERN CONE THIS IS TO SUSTAIN A  
SUBTROPICAL CONNECTION. THIS IS TO THEN FEED CONVECTIVE  
DEVELOPMENT OVER CHILE BETWEEN ISLA DE CHILOE AND TEMUCO TO THE  
NORTH. ON WEDNESDAY THIS IS TO FAVOR MODERATE CONVECTION WITH  
ACCUMULATION OF 20-30MM.  
 
AN ELONGATED FRONT TO THE NORTH...MEANWHILE...IS TO EXTEND FROM  
THE SOUTH GEORGIA ISLANDS TO LA PAMPA IN ARGENTINA. THE FRONT IS  
TO REMAIN NEARLY STATIONARY THROUGH WEDNESDAY EVENING...SURGING  
ACROSS RIO DE LA PLATA BASIN/URUGUAY TO SOUTHERN BRASIL-NORTHERN  
PROVINCES IN ARGENTINA ON THURSDAY. AS IT MEANDERS OVER THE  
SOUTHERN CONE...A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO  
ENTER CENTRAL CHILE EARLY ON WEDNESDAY MORNING...TO MOVE ACROSS LA  
PAMPA/CENTRAL ARGENTINA LATER ON WEDNESDAY. AS IT STREAMS ACROSS  
CENTRAL ARGENTINA THIS WILL INTERACT WITH MEANDERING FRONT OT THE  
NORTH. EARLY IN THE CYCLE THE FRONT IS TO TRIGGER LIGHT TO  
MODERATE CONVECTION OVER CENTRAL ARGENTINA WITH ACCUMULATION OF  
15-20MM ON TUESDAY-WEDNESDAY. ON WEDNESDAY TO THURSDAY THIS  
INCREASES TO 10-15MM. OTHER CONVECTION TO THE NORTH IS TO AFFECT  
RIO GRANDE DO SUL IN BRASIL-CORRIENTES/MISIONES IN  
ARGENTINA...WITH RAINFALL AMOUNTS OF 05-10MM ON FRIDAY TO  
SATURDAY. ON SATURDAY TO SUNDAY EXPECTING AN INCREASE IN ACTIVITY  
ACROSS URUGUAY-ENTRE RIOS IN ARGENTINA...WITH MAXIMA OF 25-50MM IN  
POTENTIALLY SEVERE CONVECTION. OVER NORTHWEST  
ARGENTINA...MEANWHILE... THE MAXIMA PEAKS AT 15-20MM.  
 
THE NEXT MID LEVEL PERTURBATION ENTERS SOUTHERN CHILE EARLY ON  
FRIDAY MORNING. BUILDING RIDGE TO THE WEST IS TO THEN INDUCE THE  
NORTHWARD AMPLIFICATION OF THIS TROUGH ACROSS PATAGONIA IN  
ARGENTINA TO LA PAMPA/SOUTHERN BUENOS AIRES PROVINCE ON FRIDAY. AS  
IT SPILLS ACROSS THE ANDES TO CENTRAL PROVINCES IN ARGENTINA THIS  
WILL SUSTAIN SURFACE CYCLOGENESIS. ON FRIDAY TO SATURDAY THE  
TROUGH MOVES ACROSS THE SOUTHERN CONE TO CENTRAL ARGENTINA...WHILE  
LATER ON MONDAY IT WILL EXTEND ALONG 60W TO ENTRE RIOS IN  
ARGENTINA. AS IT AMPLIFIES TO MID SECTION OF ARGENTINA THIS TROUGH  
IS TO TRIGGER MODERATE TO HEAVY CONVECTION...WITH POTENTIAL FOR  
SEVERE THUNDERSTORMS. AT LOW LEVELS THIS IS TO SUSTAIN AN  
ELONGATED FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA.  
THIS MOVES NORTH TO THE MESOPOTAMIA VALLEY IN ARGENTINA LATER ON  
FRIDAY/EARLY SATURDAY MORNING. OVER SOUTHERN CHILE THIS IS TO  
FAVOR MODERATE RAINFALL AMOUNTS...WITH MAXIMA OF 05-10MM/DAY.  
THROUGH FRIDAY THIS INCREASES TO 10-15MM/DAY...WHILE ON SATURDAY  
THE MAXIMA PEAKS AT 15-20MM. OVER CENTRAL ARGENTINA THE MAXIMA ON  
SATURDAY WILL PEAK AT 15-20MM/DAY...WITH HIGHER AMOUNTS TO THE  
NORTH AS THE MID/UPPER LEVEL TROUGH INTERACTS WITH A SURFACE FRONT  
OVER SOUTHERN BRASIL-NORTHERN ARGENTINA.  
 
AT 200 HPA...AN ILL ORGANIZED CELL OF THE SUBTROPICAL RIDGE  
CONFINES TO CONTINENTAL AREA TO THE NORTH OF 12S/14S. THROUGH  
THURSDAY THIS CELL OF THE SUBTROPICAL RIDGE IS TO BECOME BETTER  
ORGANIZED WHILE CENTERING ON A CLOSED HIGH OVER NORTHERN BOLIVIA.  
THIS...IN-TURN...WILL SUSTAIN THE NORTHWARD AMPLIFICATION OF A  
TROUGH ACROSS THE SOUTHEAST STATES OF BRASIL. THE TROUGH REACHES  
MAXIMUM AMPLITUDE LATER DURING THE WEEKEND. EARLY IN THE CYCLE  
SCATTERED DEEP CONVECTION IS TO CLUSTER ALONG THE SOUTH ATLANTIC  
CONVERGENCE ZONE...AS IT EXTENDS FROM ESPIRITO SANTO/MINAS GERAIS  
TO RONDONIA/SOUTHERN AMAZONAS IN BRASIL. THE SACZ IS TO WEAKEN TO  
AN OPEN TROUGH LATER ON TUESDAY...TO THEN REMAIN ILL ORGANIZED  
WHILE CONFINING TO MATO GROSSO-RONDONIA. EARLY IN THE CYCLE  
MODERATE TO HEAVY CONVECTION IS TO BUILD FROM BAHIA/MINAS GERAIS  
IN BRASIL TO PARA...WITH MAXIMA OF 40-80MM. AS THE UPPER PATTERN  
EVOLVES...AND THE SACZ WEAKENS TO AN OPEN TROUGH...MOST ACTIVE IS  
TO CLUSTERS ACROSS BAHIA-TOCANTINS AND GOIAS...WITH MAXIMA IN THIS  
AREA PEAKING AT 35-70MM/DAY. ON SATURDAY THIS DECREASES TO  
30-60MM...WHILE ON SUNDAY A MAXIMA OF 40-80MM IS TO CLUSTER OVER  
EASTERN PARA-GOIAS IN BRASIL. ON THE NORTHERN JUNGLE OF PERU TO  
EASTERN ECUADOR THE DAILY MAXIMA WILL PEAK AT 15-20MM IN DIURNAL  
CONVECTION.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  

 
 
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