935  
FXSA20 KWBC 041702  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1201 PM EST MON DEC 04 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 04 AT 0000 UTC): AT MID/UPPER  
LEVELS...A HIGH AMPLITUDE TROUGH EXTENDS NORTH ALONG 40W TO 25S.  
LATER THIS EVENING THE TROUGH IS TO MEANDER EAST ACROSS  
20W...NEARING 10W LATER ON TUESDAY. AT LOW LEVELS...THIS SUSTAIN A  
SURFACE FRONT THAT EXTENDS WEST ACROSS THE SOUTH ATLANTIC TO THE  
SOUTHERN STATES OF BRASIL/NORTHERN PROVINCES IN ARGENTINA. THE  
FRONTAL BOUNDARY IS TO REMAIN NEARLY STATIONARY DURING THE NEXT  
48-72 HRS...WITH BOUNDARY TO WEAKEN OVER THE CONTINENT LATER ON  
THURSDAY. AS IT MEANDERS OVER SOUTHERN BRASIL-NORTHERN  
ARGENTINA...THE FRONT SUSTAINS A DEEP LAYER TROUGH TO THE NORTH.  
AT 850-700 HPA THE TROUGH EXTENDS TO THE SOUTHEAST FROM THE  
BOLIVIAN JUNGLE...ACROSS MATO GROSSO DO SUL TO PARAGUAY/SOUTHERN  
STATES OF BRASIL. THIS BOUNDARY IS TO PERSIST DURING THE NEXT FEW  
DAYS...WITH MOISTURE CLUSTERING ALONG THIS FEATURE. AT 200  
HPA...BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES CONTINENTAL  
AREA TO THE NORTH OF 30S...WITH AXIS ANCHORING ON A CLOSED HIGH  
THAT MEANDERS BETWEEN MATO GROSSO-SANTA CRUZ IN EASTERN BOLIVIA.  
THE RIDGE ALOFT IS VENTING DEEP CONVECTION ALONG THIS BOUNDARY.  
EARLY IN THE CYCLE THE ENVIRONMENTAL CONDITIONS OVER MID SECTIONS  
OF SOUTH AMERICA WILL BECOME FAVORABLE FOR AN MCS TO FORM OVER  
BOLIVIA-MATO GROSSO...WITH MAXIMA OF 50-100MM. ON TUESDAY THE  
MAXIMA DECREASES TO 30-60MM...WHILE ON WEDNESDAY IT PEAKS AT  
20-45MM. FOCUS OF THE HEAVY CONVECTION WILL THEN SHIFT TO THE  
SOUTHEAST STATES OF BRASIL. ACROSS RIO DE JANEIRO-ESPIRITO  
SANTO-MINAS GERAIS INITIALLY EXPECTING MAXIMA OF 20-30MM. ON  
WEDNESDAY-THURSDAY AN MCS IS LIKELY TO FORM...TO TRIGGER MAXIMA OF  
40-80MM/DAY.  
 
ON THE SOUTHERN STRING...IN A TIGHT BELT OF MID LATITUDE  
WESTERLIES...PROGRESSIVE SHORT WAVE PERTURBATIONS ARE STREAMING  
ACROSS THE SOUTHEAST PACIFIC TO THE DRAKE PASSAGE/SOUTHERN CONE OF  
SOUTH AMERICA. AT LOW LEVELS THE ASSOCIATED FRONT IS TO INITIALLY  
LIMIT TO EXTREME SOUTHERN CHILE-PATAGONIA IN ARGENTINA. ON  
WEDNESDAY...AS A RIDGE BUILDS TO THE SOUTH ACROSS PATAGONIA... THE  
FRONT MOVES NORTH ACROSS NORTHERN PATAGONIA-LA PAMPA TO THE BUENOS  
AIRES PROVINCE IN ARGENTINA. OVER SOUTHERN CHILE THIS IS TO FAVOR  
SCATTERED RAINFALL WITH ACCUMULATION OF 00-05MM/DAY.  
 
AS BROAD CELL OF THE SUBTROPICAL RIDGE PERSIST TO THE NORTH...IT  
IS TO ALSO VENT DIURNAL CONVECTION ACROSS MID SECTIONS OF SOUTH  
AMERICA. ACROSS ACRE/RONDONIA TO BAHIA/MINAS GERAIS EXPECTING  
MODERATE RAINFALL AMOUNTS OVER THE NEXT FEW DAYS TO TRIGGER  
RAINFALL AMOUNTS OF 20-35MM. OTHER CONVECTION TO THE NORTH IS TO  
CLUSTER ACROSS NORTHERN PERU-SOUTHERN COLOMBIA-EASTERN  
ECUADOR...WITH MAXIMA OF 20-45MM/DAY. THROUGH WEDNESDAY EVENING  
THE MAXIMA IN THIS AREA DECREASES TO 20-35MM/DAY.  
FURTHERMORE...THE RIDGE ALOFT IS TO ALSO VENT DEEP CONVECTION ON  
THE SOUTHERN SIERRA OF PERU-ALTIPLANO OF BOLIVIA...WITH MAXIMA OF  
20-35MM ON TUESDAY AND 20-40MM ON WEDNESDAY-THURSDAY.  
GE OVER BRASIL.  
 
OVIEDO...SHN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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