889  
FXSA20 KWBC 021741  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1240 PM EST FRI FEB 02 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM FEB 02 AT 0000 UTC): THE GFS AND  
EUROPEAN MODELS FOLLOW SIMILAR EVOLUTION THROUGH 108-120 HRS. THEY  
THEN DISAGREE ON INTENSITY OF LONG WAVE TROUGH ENTERING THE DRAKE  
PASSAGE/SOUTHERN CONE LATER IN THE CYCLE...WITH BOTH EUROPEAN  
MODELS FAVORING A STRONGER/DEEPER TROUGH TO MAKE LANDFALL. NOTE  
THAT THE STRONGER TROUGH IS SUPPORTED BY THE MEAN OF THE GLOBAL  
ENSEMBLE MEMBERS.  
 
A BROAD MID/UPPER LEVEL TROUGH IS INITIALIZED ACROSS THE SOUTHEAST  
PACIFIC/BELLINGSHAUSEN SEA. THIS IS PRESSING AGAINST A RIDGE TO  
THE EAST...WITH RIDGE TO MEANDER OVER CHILE-ARGENTINA TO THE DRAKE  
PASSAGE DURING THE NEXT FEW DAYS. THE TROUGH...AS IT PRESSES  
AGAINST THIS RIDGE...IT IS TO THEN SHEAR SHORT WAVE PERTURBATIONS  
ACROSS EXTREME SOUTHERN PORTIONS OF CHILE-TIERRA DEL FUEGO DURING  
THE NEXT FEW DAYS. THE STRONG RIDGE PATTERN IS TO PERSIST THROUGH  
SATURDAY EVENING. BUT LATER ON SUNDAY...UNDER PRESSURE FROM THE  
TROUGH...IT IS FORECAST TO WEAKEN/NEARLY COLLAPSE TO THE SOUTH OF  
40S. AS IT WEAKENS...SHORT WAVE PERTURBATIONS ARE TO THEN STREAM  
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. AT LOW LEVELS THE  
TROUGH ALOFT SUSTAINS A BROAD TROUGH OVER THE SOUTHEAST  
PACIFIC/BELLINGSHAUSEN SEA...WITH POLAR FRONTS REVOLVING AROUND  
THIS AXIS TO STREAM ACROSS SOUTHERN CHILE/PATAGONIA IN ARGENTINA.  
DURING THE NEXT COUPLE OF DAYS THIS IS TO SUSTAIN LIGHT CONVECTION  
OVER CHILE TO THE SOUTH OF ISLA DE CHILOE...WITH DAILY MAXIMA OF  
05-10MM. ON SUNDAY...AS THE MID LEVEL RIDGE WEAKENS AND THE TROUGH  
ESTABLISHES A SUBTROPICAL CONNECTION...CONVECTION OVER SOUTHERN  
CHILE IS TO INTENSIFY. DURING THIS PERIOD THE MAXIMA INCREASES TO  
15-20MM.  
 
SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM ARE TO PRECEDE THE  
AFOREMENTIONED TROUGH...WITH ONE TO MOVE ACROSS PATAGONIA IN  
ARGENTINA EARLY IN THE CYCLE. ANOTHER IS TO CLOSELY FOLLOW...TO  
STREAM ACROSS THE SOUTHERN CONE ON SATURDAY. AT LOW LEVELS THESE  
ARE TO A SURFACE FRONT THAT FORMS OFF THE COAST OF PATAGONIA TO LA  
PAMPA IN ARGENTINA ON SATURDAY...WHERE IT IS TO MEANDER THROUGH  
SUNDAY. THIS IS TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE TO FAVOR  
SCATTERED CONVECTION. BUT LACKING DEEP MOISTURE THIS IS TO ONLY  
TRIGGER RAINFALL AMOUNTS OF 05-10MM/DAY OVER THE NEXT THREE DAYS.  
 
A STRONGER SHORT WAVE TROUGH IS TO FOLLOW...WITH MID LEVEL VORTEX  
REACHING SOUTHERN CHILE LATER ON MONDAY. THIS IS TO ALSO TRACK  
ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN ATLANTIC ON TUESDAY.  
AT LOW LEVELS...THE MID LEVEL VORTEX WILL SUSTAIN A FRONTAL LOW  
OVER SOUTHERN CHILE LATER ON MONDAY...THAT TRACKS INTO PATAGONIA  
IN ARGENTINA ON TUESDAY MORNING. AS IT ENTERS SOUTHERN CHILE THIS  
WILL TRIGGER LIGHT CONVECTION WITH ACCUMULATION OF 05-10MM...WITH  
SIMILAR AMOUNTS ACROSS NORTHERN PATAGONIA AND LA PAMPA ON TUESDAY.  
 
FARTHER NORTH...BROAD CELL OF THE SUBTROPICAL RIDGE ENVELOPS MOST  
OF SOUTH AMERICA WHILE CENTERING AT 200 HPA ON A CLOSED HIGH OVER  
SOUTHEAST BOLIVIA/CHACO PARAGUAYO. A SHORT WAVE TROUGH LIES TO THE  
EAST-SOUTHEAST OF THIS RIDGE...MEANDERING OFF THE SOUTHEAST COAST  
OF BRASIL. THE UPPER LEVEL HIGH IS FORECAST TO RELOCATE TO  
NORTHERN CHILE LATER ON SATURDAY...WHERE IT IS TO REMAIN THROUGH  
SUNDAY-MONDAY. AS THE HIGH RELOCATES THE UPPER LEVEL RIDGE IS TO  
THEN CONFINE TO CONTINENTAL AREA TO THE WEST OF 55W/60W. AS THE  
RIDGE RELOCATES THIS IS TO THEN INDUCE THE NORTHWARD AMPLIFICATION  
OF THE TROUGH ACROSS SOUTHEAST BRASIL TO TOCANTINS/GOIAS-BAHIA  
LATER ON SATURDAY/SUNDAY. THIS FEATURE IS TO THEN REMAIN OVER THE  
NORTHEAST STATES OF BRASIL THROUGH EARLY NEXT WEEK. AT LOW LEVELS  
THE TROUGH ALOFT INTERACTS WITH A MEANDERING FRONT OVER THE SOUTH  
ATLANTIC...WHILE OVER BRASIL IT SUSTAINS THE SOUTH ATLANTIC  
CONVERGENCE ZONE (SACZ). THE CONVERGENCE ZONE EXTENDS ACROSS  
ESPIRITO SANTO/MINAS GERAIS-MATO GROSSO TO BOLIVIA. LATER DURING  
THE WEEKEND THE CONVERGENCE ZONE DRIFTS OVER RONDONIA TO ACRE IN  
BRASIL. AS MOISTURE CONVERGES ALONG THE SACZ...EXPECTING ORGANIZED  
HEAVY CONVECTION TO CLUSTER ACROSS MINAS GERAIS-ESPIRITO  
SANTO-BAHIA-TOCANTINS-GOIAS. IN THIS AREA EXPECTING DAILY MAXIMA  
OF 75-150MM. LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE DUE TO  
STRONG MESO-SYNOPTIC FORCING...WITH SOME OF THE ENSEMBLE MEMBERS  
SHOWING MAXIMA OF 200-250MM/DAY. THROUGH MONDAY THE CONVECTION  
BUILDS NORTH ACROSS BAHIA TO NORTHEAST STATES OF BRASIL. OTHER  
CONVECTION IS EXPECTED ACROSS MATO GROSSO-NORTHERN BOLIVIA TO PARA  
IN BRASIL...WITH MAXIMA OF 40-80MM/DAY. AS THE UPPER LEVEL TROUGH  
AMPLIFIES ACROSS NORTHEAST BRASIL...THIS WILL GRADUALLY DECREASES  
TO 15-20MM LATER ON MONDAY. OTHER CONVECTION IS TO CLUSTER ACROSS  
ACRE-AMAZONAS IN WESTERN BRASIL TO THE SOUTHERN AND CENTRAL JUNGLE  
OF PERU. IN THIS AREA ALSO EXPECTING MAXIMA OF 40-80MM/DAY OVER  
THE NEXT TWO DAYS...DECREASING TO 20-45MM/DAY ON SUNDAY AND  
MONDAY.  
 
RIDGE ALOFT IS TO ALSO VENT DIURNAL CONVECTION ACROSS THE  
ALTIPLANO OF BOLIVIA-SOUTHERN SIERRA OF PERU...WITH MAXIMA OF  
20-30MM EXPECTED THROUGH SATURDAY MORNING...AND 15-20MM ON  
SATURDAY AND SUNDAY. OVER ECUADOR... MAXIMA PEAKS AT 15-20MM/DAY  
EARLY IN THE CYCLE AS ENHANCED BY A MOIST LOW LEVEL NORTHWESTERLY  
FLOW...DECREASING TO 10-15MM/DAY ON SATURDAY AND ONWARD.  
 
BALBINO...INMET (BRASIL)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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