310  
FXSA20 KWBC 081723  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1222 PM EST WED NOV 08 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 08 AT 0000 UTC): THE GLOBAL  
MODELS FOLLOW A SIMILAR EVOLUTION THROUGH 84-96 HRS...THEN DIVERGE  
ON THE SPEED/AMPLITUDE OF SHORT WAVE PERTURBATIONS STREAMING TO  
THE SOUTH. DURING THIS PERIOD THE UKMET FORESEES A FASTER  
EVOLUTION...WHILE THE ECMWF FAVORS A MUCH SLOWER PROGRESSION. THE  
GFS IS THE COMPROMISE SOLUTION...FAVORING A FASTER EVOLUTION THAN  
THE ECMWF BUT SLOWER THAN THE UKMET. THE GFS SOLUTION IS CLOSER TO  
THE MEAN OF THE GLOBAL ENSEMBLE...BUT VARIABILITY AMONG THE  
MEMBERS IS TOO HIGH TO ESTABLISH CONFIDENCE IN THE MEDIUM RANGE  
FORECAST.  
 
A MID LEVEL TROUGH ON THE SOUTHERN STREAM DOMINATES THE SOUTHEAST  
PACIFIC. AS IT PRESSES AGAINST A RIDGE TO THE EAST THE TROUGH IS  
FORECAST TO SHEAR TO THE SOUTHEAST ACROSS THE DRAKE PASSAGE/  
ANTARCTIC PENINSULA. REMNANTS OF THIS TROUGH WILL THEN STREAM  
ACROSS EXTREME SOUTHERN CHILE/TIERRA DEL FUEGO ON  
THURSDAY...QUICKLY MOVING TO THE EAST-SOUTHEAST OF THE  
MALVINAS/FALKLAND ISLANDS ON FRIDAY. AT LOW LEVELS THIS SUSTAINS  
AN ELONGATED FRONT THAT MOVES TO THE DRAKE PASSAGE-TIERRA DEL  
FUEGO LATER TODAY...THEN EAST ACROSS PATAGONIA IN ARGENTINA ON  
THURSDAY. EARLY IN THE CYCLE THIS IS TO SUSTAIN LIGHT CONVECTION  
WITH ACCUMULATION OF 00-05MM. ON THURSDAY IT INCREASES TO 05-10MM.  
 
NORTH OF THIS AXIS...A MID LEVEL TROUGH MEANDERS OFF THE COAST OF  
ARGENTINA WHILE CENTERING ON A CLOSED LOW NEAR 40S 60W. BUILDING  
SHORT WAVE RIDGE TO THE WEST WILL THEN INDUCE THE NORTHWARD  
AMPLIFICATION OF THIS TROUGH ON THURSDAY-FRIDAY...WITH BROAD  
MID/UPPER LEVEL TROUGH TO THEN MEANDER ACROSS  
SOUTHERN/SOUTHEASTERN BRASIL THROUGH THE WEEKEND. AT LOW LEVELS  
THIS SUSTAINS A SURFACE FRONT THAT SURGES ACROSS LA PAMPA TO  
CENTRAL ARGENTINA LATER TODAY...MOVING TO SOUTHERN BRASIL-PARAGUAY  
ON THURSDAY. ON FRIDAY TO SATURDAY THE FRONT IS TO CONTINUE ACROSS  
PARANA/SAO PAULO IN SOUTHEAST BRASIL TO MATO GROSSO DO SUL/SANTA  
CRUZ IN EASTERN BOLIVIA. OVER THE BUENOS AIRES PROVINCE-URUGUAY  
THIS IS TO INITIALLY TRIGGER LIGHT TO MODERATE CONVECTION WITH  
ACCUMULATION OF 05-10MM... WHILE OVER NORTHWEST ARGENTINA  
EXPECTING ACCUMULATION OF 20-35MM. AS IT SURGES ACROSS PARAGUAY TO  
THE SOUTHERN STATES OF BRASIL ON THURSDAY-FRIDAY THIS WILL TRIGGER  
MAXIMA OF 20-30MM. HIGHER AMOUNTS ARE EXPECTED OVER NORTHERN  
BOLIVIA-ACRE IN BRASIL AND SOUTHERN JUNGLE OF PERU ON  
FRIDAY-SATURDAY. DURING THIS PERIOD A SOUTHEASTERLY JET ACROSS  
PARAGUAY IS TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE TO TRIGGER  
MAXIMA OF 25-50MM. ON SATURDAY THIS DECREASES TO 20-40MM.  
 
A HIGHER AMPLITUDE MID/UPPER LEVEL TROUGH EXTENDS OVER THE SOUTH  
ATLANTIC...WITH AXIS NORTH BETWEEN 40W-10W TO 20S. THIS IS TO  
SLOWLY MEANDER TO THE EAST-SOUTHEAST AS THE CYCLE PROGRESSES. AT  
LOW LEVELS THE UPPER LEVEL TROUGH SUSTAINS AN ELONGATED FRONT THAT  
EXTENDS TO THE NORTHWEST ACROSS THE SOUTH ATLANTIC TO RIO DE  
JANEIRO/ESPIRITO SANTO...THEN TO THE SOUTHWEST TO PARAGUAY. THIS  
BOUNDARY IS TO FRONTOLIZE ON THURSDAY. MEANWHILE...ACROSS  
PARAGUAY-MATO GROSSO DO SUL-PARANA/SAO PAULO IN BRASIL IT WILL  
FAVOR MODERATE CONVECTION WITH MAXIMA OF 20-35MM.  
 
FARTHER UPSTREAM...A POSITIVELY TILTED MID/UPPER LEVEL TROUGH IS  
TO MOVE TO THE SOUTHEAST PACIFIC LATER ON SATURDAY. AS IT PRESSES  
AGAINST A SHORT WAVE RIDGE OVER ARGENTINA...THE LONG WAVE AXIS IS  
TO THEN SHEAR A SHORT WAVE TROUGH THAT EJECTS ACROSS SOUTHERN  
CHILE/PATAGONIA IN ARGENTINA ON SUNDAY AFTERNOON. FURTHERMORE...AS  
IT NEARS THE SOUTHERN CONE...THE LONG WAVE TROUGH WILL SUSTAIN A  
SUBTROPICAL CONNECTION...ENHANCING MOISTURE TRANSPORT/CONVERGENCE  
ACROSS SOUTHERN PORTIONS OF CHILE. AT LOW LEVELS THIS WILL SUSTAIN  
AN ELONGATED FRONT THAT IS TO EXTEND TO THE NORTHWEST ACROSS  
PATAGONIA IN ARGENTINA-SOUTHERN CHILE TO THE EASTERN PACIFIC.  
ACROSS SOUTHERN CHILE THIS IS TO SUSTAIN MODERATE RAINFALL AMOUNTS  
ON SATURDAY WITH MAXIMA OF 10-15MM...INCREASING TO 15-20MM ON  
SUNDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A NARROW CELL OF THE  
SUBTROPICAL RIDGE EXTENDS WEST-TO-EAST ACROSS THE CONTINENT  
BETWEEN 05S-20S. A WANING SHORT WAVE TROUGH TO THE NORTH MEANDERS  
OVER AMAPA IN BRASIL/AMAZON RIVER DELTA REGIONS. THE RIDGE ALOFT  
PROVIDES THE VENTILATION ALOFT TO DEEP CONVECTION ON THE CENTRAL  
AND EASTERN STATES OF BRASIL. OVER THE NEXT FEW DAYS...CONVECTION  
ON THE STATES OF TOCANTINS-GOIAS-BAHIA IS TO BECOME BETTER  
ORGANIZED....WITH HEAVY CONVECTION TO SUSTAIN MAXIMA OF 40-80MM  
THROUGH THURSDAY MORNING. ON THURSDAY AND FRIDAY EXPECTING  
ADDITIONAL RAINFALL AMOUNTS OF 30-60MM/DAY...WHILE ON SATURDAY THE  
MAXIMA DECREASES TO 20-40MM. OTHER CONVECTION IS EXPECTED ACROSS  
NORTHERN AMAZONAS IN BRASIL TO SOUTHERN COLOMBIA...WITH MAXIMA TO  
PEAK AT 20-35MM. THIS SPREADS WEST ACROSS NORTHERN PERU TO EASTERN  
ECUADOR ON THURSDAY-SATURDAY TO SUSTAIN MAXIMA OF 20-30MM/DAY.  
OTHER CONVECTION TO THE SOUTH IS EXPECTED ON THE CENTRAL AND  
SOUTHERN SIERRA OF PERU. A SHORT WAVE TROUGH MEANDERING ACROSS THE  
EASTERN PACIFIC IS TO STALL OFF THE COAST OF PERU EARLY IN THE  
CYCLE. THIS IS TO THEN FAVOR AN UPPER DIVERGENT PATTERN THAT IS TO  
VENT DEEP CONVECTION. EARLY IN THE CYCLE EXPECTING MAXIMA OF  
05-10MM. THROUGH FRIDAY THIS INCREASES TO 15-20MM.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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