208  
FXSA20 KWBC 091731  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1230 PM EST THU NOV 09 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 09 AT 0000 UTC): THE GFS AND  
UKMET MADE PATTERN CORRECTIONS ON THE SOUTHERN STREAM FLOW...NOW  
FAVORING A SLOWER EVOLUTION THAT IS QUITE SIMILAR TO WHAT THE  
ECMWF PREVIOUSLY FORECASTED. ALTHOUGH THE DETERMINISTIC MODELS  
AGREE OVER THE SOUTH AMERICAN DOMAIN...THE VARIABILITY AMONG THE  
ENSEMBLE MEMBERS REMAINS TOO HIGH TO ASCERTAIN CONFIDENCE DURING  
THE MEDIUM RANGE PERIOD.  
 
A MID LEVEL SHORT WAVE TROUGH ON THE SOUTHERN STREAM MOVES ACROSS  
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER TODAY. UNDER  
INFLUENCE OF A RIDGE TO THE EAST...THIS IS TO THEN SHEAR TO THE  
EAST-SOUTHEAST WHILE PULLING ACROSS THE MALVINAS/FALKLAND ISLANDS  
ON FRIDAY. IT WILL THEN ACCELERATE ACROSS THE SOUTH GEORGIA  
ISLANDS ON THURSDAY. AT LOW LEVELS THIS WILL SUSTAIN A PROGRESSIVE  
FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER  
TODAY...TO TRIGGER LIGHT CONVECTION WITH ACCUMULATION OF 05-10MM.  
 
AN ELONGATED MID/UPPER LEVEL TROUGH IS TO FOLLOW...WITH AXIS TO  
EXTEND TO THE NORTHWEST FROM THE DRAKE PASSAGE/TIERRA DEL FUEGO IN  
SOUTHERN CHILE...ALONG 40S 100W TO 27S 115W LATER ON FRIDAY. AS IT  
NEARS THE SOUTHERN CONE...THE TROUGH WILL SUSTAIN A SUBTROPICAL  
CONNECTION. THIS WILL ENHANCE MOISTURE ADVECTION AND CONVERGENCE  
ACROSS SOUTHERN PORTIONS OF CHILE LATER ON FRIDAY/EARLY SATURDAY  
MORNING. AT LOW LEVELS THIS SUSTAINS A FRONTAL WAVE OVER SOUTHERN  
CHILE LATER ON FRIDAY...TO QUICKLY MOVE ACROSS PATAGONIA ON  
SATURDAY. THIS WILL BE ACCOMPANIED BY STRONG BOUNDARY LAYER WINDS  
THAT ARE TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE ACROSS SOUTHERN  
REGIONS OF CHILE. IN THIS AREA EXPECTING MODERATE RAINFALL AMOUNTS  
WITH MAXIMA OF 20-35MM.  
 
REMNANTS OF THE MID LEVEL TROUGH WILL THEN EVOLVE INTO A CLOSED  
LOW NEAR 40S 100W LATER ON SATURDAY. THIS IS TO THEN MIGRATE TO  
THE EAST-SOUTHEAST...ENTERING SOUTHERN CHILE ON MONDAY. AT LOW  
LEVELS THIS WILL SUSTAIN A SURFACE FRONT WITH AN OCCLUDING LOW.  
BETWEEN SATURDAY MORNING AND SUNDAY MORNING THE GFS PROJECTS A  
RAPID RATE OF INTENSIFICATION...WITH THE LOW DEEPENING FROM A 1008  
HPA LOW EARLY ON SATURDAY TO A 988 HPA LOW ON SUNDAY.  
THIS...HOWEVER...IS NOT SUPPORTED BY THE OTHER MODELS...WITH THE  
UKMET...ECMWF AND GLOBAL ENSEMBLES AGREEING ON A WEAKER  
PERTURBATION. SINCE THIS IS NOT AN AREA WHERE MID LATITUDE  
CYCLONES TEND TO RAPIDLY INTENSIFY...WE ARE LEANING IN FAVOR OF  
THE WEAKER EUROPEAN MODELS. AS IT ENTERS SOUTHERN CHILE LATER ON  
SUNDAY THIS WILL SUSTAIN MODERATE RAINFALL AMOUNTS WITH  
ACCUMULATION OF 15-20MM.  
 
OVER THE ATLANTIC...ON THE NORTHERN STREAM FLOW...A 500 HPA LOW IS  
TO MEANDER TO THE EAST-SOUTHEAST OF THE BUENOS AIRES PROVINCE  
EARLY IN THE PERIOD. BUILDING SHORT WAVE RIDGE TO THE WEST IS TO  
THEN SUSTAIN GRADUAL INTENSIFICATION OF MID LEVEL TROUGH ON  
FRIDAY-SATURDAY. AT LOW LEVELS THIS SUSTAINS AN OCCLUDING LOW OFF  
THE COAST OF PATAGONIA. AS IT DEEPENS THE ASSOCIATED FRONT WILL  
SURGE ACROSS SOUTHERN BRASIL-PARAGUAY-SOUTHERN BOLIVIA LATER  
TODAY...MOVING NORTH ACROSS SAO PAULO-MATO GROSSO DO SUL TO SANTA  
CRUZ IN EASTERN BOLIVIA LATER ON FRIDAY. ON SATURDAY-SUNDAY THE  
FRONT IS TO CONTINUE FARTHER NORTH ACROSS RIO DE JANEIRO-NORTHERN  
SAO PAULO TO MATO GROSSO-CENTRAL BOLIVIA. ON THE SOUTHERN AND  
SOUTHEAST STATES OF BRASIL-SOUTHEAST PARAGUAY THIS WILL SUSTAIN  
MODERATE CONVECTION WITH ACCUMULATION OF 20-35MM. HIGHER AMOUNTS  
ARE EXPECTED ACROSS CENTRAL-NORTHERN BOLIVIA-ACRE IN BRASIL AND  
SOUTHEAST PERU...WHERE THE MAXIMA PEAKS AT 25-50MM ON  
FRIDAY-SATURDAY. ON SATURDAY TO SUNDAY MODERATE CONVECTION IS TO  
PERSIST TRIGGERING MAXIMA OF 20-40MM. OVER RIO DE JANEIRO/ESPIRITO  
SANTO THE MEANDERING FRONT IS TO TRIGGER MODERATE TO HEAVY  
RAINFALL AMOUNTS ON SUNDAY-MONDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS  
TO ENVELOP AREA TO THE NORTH OF 20S. THE RIDGE ALOFT IS TO ANCHOR  
ON A CLOSED HIGH OVER AMAZONAS IN BRASIL. THE RIDGE ALOFT IS TO  
VENT ORGANIZED DEEP CONVECTION ACROSS TOCANTINS/GOIAS-BAHIA IN  
BRASIL...WITH DAILY MAXIMA OF 35-70MM EXPECTED OVER THE NEXT TWO  
DAYS. ACROSS NORTHERN AMAZONAS IN BRASIL TO NORTHERN JUNGLE OF  
PERU CONVECTION IS TO GRADUALLY BECOME MORE ACTIVE AND BETTER  
ORGANIZED...PEAKING A 20-45MM. OTHER CONVECTION IS TO CLUSTER ON  
THE CENTRAL AND SOUTHERN SIERRA OF PERU AS ENHANCED BY PERSISTENT  
UPPER LEVEL TROUGH TO THE WEST. THIS IS TO FAVOR MODERATE  
CONVECTION WITH MAXIMA OF 15-20MM/DAY...WITH POTENTIAL FOR LOCALLY  
HIGHER AMOUNTS.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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