021  
FXSA20 KWBC 161548  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1047 AM EST THU NOV 16 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 16 AT 0000 UTC): GLOBAL MODELS  
AGREE ON PATTERN EVOLUTION ACROSS THE CONTINENT AND WESTERN SOUTH  
ATLANTIC THROUGH 144-168 HRS. OVER THE SOUTH PACIFIC THEY  
GENERALLY AGREE THROUGH 84-96 HRS...THEN DIVERGE ON INTENSITY OF  
MID LEVEL RIDGE MEANDERING OFF THE COAST OF CHILE AND SHORT WAVE  
PERTURBATIONS STREAMING TO THE SOUTH. IN THIS AREA CYCLE-TO-CYCLE  
INCONSISTENCIES ABOUND...LEADING TO LOWER CONFIDENCE IN THE  
FORECAST DURING THE MEDIUM RANGE PERIOD. THE HIGH VARIABILITY  
AMONG THE DETERMINISTIC MODELS IS ALSO EVIDENT AMONG THE ENSEMBLE  
MEMBERS.  
 
CONSISTENT WITH PREVIOUS FORECAST...A MID LEVEL TROUGH OVER THE  
WESTERN ATLANTIC IS TO RAPIDLY PULL TO THE EAST-SOUTHEAST AS A  
DEEPER PERTURBATION ENTERS THE SOUTHERN CONE. UNDER INFLUENCE OF A  
BUILDING RIDGE OVER THE EASTERN SOUTH PACIFIC THE LATTER IS  
FORECAST TO RAPIDLY AMPLIFY ACROSS ARGENTINA TO MID SECTIONS OF  
SOUTH AMERICA ON FRIDAY. THIS IS TO FOCUS SHORT WAVE ENERGY ACROSS  
THE SOUTHERN CONE OF SOUTH AMERICA...WITH 24 HRS HEIGHT FALLS OVER  
ARGENTINA EXPECTED TO PEAK BETWEEN 150-200GPM. ON SATURDAY-SUNDAY  
THE TROUGH WILL THEN PULL TO THE EAST-SOUTHEAST. AT LOW  
LEVELS...POLAR FRONT MOVES TO SOUTHERN BRASIL-PARAGUAY LATER TODAY  
AS A STRONGER BOUNDARY RACES ACROSS PATAGONIA IN ARGENTINA TO THE  
RIO DE LA PLATA BASIN. THIS WILL BE DRIVEN NORTH BY A PAMPERO LOW  
LEVEL JET OF 35-40KT. THROUGH SATURDAY MORNING THE LATTER FRONT  
THEN CATCHES UP WITH THE FORMER BOUNDARY MEANDERING OVER SOUTHERN  
BRASIL-PARAGUAY. ENVIRONMENTAL CONDITION WILL THEN BECOME HIGHLY  
FAVORABLE FOR GENERATION OF ORGANIZED DEEP CONVECTION ACROSS MID  
SECTIONS TO NORTHERN PORTIONS OF SOUTH AMERICA. ACROSS SOUTHERN  
BRASIL TO PARAGUAY INITIALLY EXPECTING RAINFALL AMOUNTS OF 25-50MM  
IN SCATTERED DEEP CONVECTION. ON FRIDAY TO SATURDAY MORNING AN MCS  
IS LIKELY TO FORM OVER PARAGUAY-MATO GROSSO DO SUL-MISIONES IN  
ARGENTINA...WITH MAXIMA OF 75-150MM. NOTE THAT IN THIS AREA SOME  
OF THE ENSEMBLE MEMBERS SHOW MAXIMA OF NEARLY 200MM. THE  
LIKELIHOOD OF SEVERE CONVECTION IS HIGH. ON SATURDAY  
AFTERNOON...UNDER INFLUENCE OF A SOUTHERLY LOW LEVEL JET ACROSS  
NORTHERN ARGENTINA/PARAGUAY... THE CONVECTION IS TO SPREAD ACROSS  
SOUTHERN TO SOUTHEAST BRASIL WHERE IT IS TO TRIGGER RAINFALL  
AMOUNTS OF 25-50MM. OVER CENTRAL/NORTHERN BOLIVIA EXPECTING MAXIMA  
OF 75-125MM...WHILE ON THE SOUTHERN JUNGLE OF PERU THE MAXIMA WILL  
THEN PEAK AT 30-60MM. AS IT SPREADS NORTH ACROSS CENTRAL PERU THIS  
DECREASES TO 25-50MM ON SUNDAY.  
 
ANOTHER MID LEVEL TROUGH ON THE SOUTHERN STREAM IS TO RACE ACROSS  
THE SOUTHEAST PACIFIC LATER TODAY...LIFTING ACROSS THE  
BELLINGSHAUSEN SEA TO THE DRAKE PASSAGE/SOUTHERN CHILE ON FRIDAY  
AFTERNOON...AND INTO PATAGONIA IN ARGENTINA ON SATURDAY. AT LOW  
LEVELS THIS WILL SUSTAIN A DEEP OCCLUDED LOW OVER THE ANTARCTIC  
PENINSULA LATER ON SATURDAY...WHILE THE ASSOCIATED FRONT STREAMS  
ACROSS TIERRA DEL FUEGO TO PATAGONIA IN ARGENTINA. THIS WILL  
SUSTAIN A COLD ADVECTIVE PATTERN...WITH ENVIRONMENTAL CONDITIONS  
TO FAVOR MIXED PRECIPITATION ON SATURDAY...WITH LIGHT TO MODERATE  
CONVECTION IN RAIN/SNOW SHOWERS TO AFFECT THE SOUTHERN ANDES OF  
CHILE/TIERRA DEL FUEGO WITH ACCUMULATION OF 05-10MM.  
 
PATTERN ACROSS NORTHERN SOUTH AMERICA WILL REMAIN UNDER THE  
INFLUENCE OF A 200 HPA HIGH/RIDGE OVER WESTERN BRASIL/PERU AND A  
SHORT WAVE TROUGH TO THE EAST. THE TROUGH IS TO MEANDER ACROSS THE  
NORTHEAST STATES OF BRASIL DURING THE NEXT FEW DAYS. THE RIDGE  
ALOFT IS TO VENT DEEP CONVECTION ACROSS NORTHWEST SOUTH  
AMERICA...WITH MAXIMA OF 20-35MM TO AFFECT SOUTHERN  
COLOMBIA-CENTRAL/NORTHERN JUNGLE OF PERU AND AMAZONAS IN BRASIL  
DURING THE NEXT FEW DAYS. OVER PARA-TOCANTINS/GOIAS TO THE  
EAST...THE DAILY MAXIMA WILL PEAK AT 20-45MM THROUGH THURSDAY  
EVENING...DECREASING TO 15-20MM ON FRIDAY-SATURDAY. OTHER  
CONVECTION IS TO BUILD ACROSS THE SOUTHERN SIERRA OF PERU TO THE  
ALTIPLANO OF BOLIVIA. IN THIS AREA THE MAXIMA OVER THE NEXT COUPLE  
OF DAYS IS TO PEAK AT 15-20MM...WITH LOCALLY HIGHER AMOUNTS  
POSSIBLE DUE TO STRONG TOPOGRAPHICAL FORCING.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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