259  
FXSA20 KWBC 151721  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1221 PM EST WED NOV 15 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 15 AT 0000 UTC): EXCEPT FOR MINOR  
CORRECTIONS DURING THE MEDIUM RANGE PERIOD...THE GLOBAL MODELS  
MAINTAIN GOOD CONTINUITY WITH PREVIOUS RUNS...LEADING TO A HIGH  
CONFIDENCE IN THE FORECAST THROUGH AT LEAST 108 HRS. AS PREVIOUSLY  
NOTED...THE ENVIRONMENTAL CONDITIONS OVER MID SECTIONS OF SOUTH  
AMERICA ARE TO BECOME HIGHLY FAVORABLE AND CONDUCIVE FOR ORGANIZED  
DEEP CONVECTION TO DEVELOP ON FRIDAY-SATURDAY. THIS IS TO TRIGGER  
HEAVY RAINFALL AMOUNTS AND POTENTIALLY SEVERE CONVECTION.  
 
A MID/UPPER LEVEL TROUGH MOVES ACROSS THE SOUTHERN CONE TO THE  
WESTERN ATLANTIC LATER TODAY. THIS IS TO QUICKLY PULL ACROSS  
30W/40W WHILE CONFINING TO THE SOUTH OF 30S ON THURSDAY. THE  
TROUGH SUSTAINS A SURFACE FRONT THAT MOVES NORTH ACROSS URUGUAY TO  
RIO GRANDE DO SUL IN BRASIL-NORTHERN PROVINCES IN ARGENTINA LATER  
TODAY...MOVING TO PARAGUAY ON THURSDAY. ACROSS URUGUAY-ENTRE RIOS  
IN ARGENTINA THIS IS TO SUSTAIN SCATTERED CONVECTION WITH MAXIMA  
OF 15-25MM THROUGH THURSDAY MORING. OVER PARAGUAY-MISIONES IN  
ARGENTINA AND RIO GRANDE DO SUL THE MAXIMA ON THURSDAY IS TO PEAK  
BETWEEN 25-50MM...WITH FORECAST STABILITY INDICES SHOWING SLIGHT  
RISK OF SEVERE CONVECTION OVER PARAGUAY.  
 
THIS IS FOLLOWED BY A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN  
STREAM FLOW. CONSISTENT WITH PREVIOUS FORECASTS THE MID LEVEL  
VORTEX REACHES SOUTHERN CHILE LATER TODAY. ON THURSDAY-FRIDAY...AS  
A RIDGE BUILDS TO THE WEST BETWEEN 85W-105W...THE TROUGH IS TO  
AMPLIFY ACROSS ARGENTINA...TO EXTEND ACROSS PARAGUAY TO 20S LATER  
ON FRIDAY. ON SATURDAY THE TROUGH IS TO SLOWLY LIFT ACROSS URUGUAY  
TO SOUTHERN BRASIL...AND SUNDAY IT ACCELERATES ACROSS 30W/35W.  
ALSO ON THURSDAY... AS THE TROUGH DEEPENS ACROSS PATAGONIA IN  
ARGENTINA...IT IS TO SUSTAIN HEIGHT FALLS OF 150-200GPM. ON FRIDAY  
THE FOCUS OF THE ENERGY WILL BE ACROSS RIO DE LA PLATA BASIN/RIO  
GRANDE DO SUL... WHERE IT IS TO FAVOR HEIGHT FALLS OF 150-180GPM.  
AT LOW LEVELS THE ASSOCIATED FRONT SURGES ACROSS SOUTHERN CHILE TO  
PATAGONIA IN ARGENTINA ON THURSDAY MORNING...AND THROUGH FRIDAY  
EVENING IT RACES ACROSS URUGUAY TO NORTHERN ARGENTINA. ON  
SATURDAY...THIS WILL THEN MERGE WITH THE OLD BOUNDARY TO THE  
NORTH. AS IT ENTERS SOUTHERN CHILE THIS WILL TRIGGER SCATTERED  
CONVECTION TO THE SOUTH OF ISLA DE CHILOE...WITH MAXIMA OF  
15-20MM. ON THURSDAY THE CONVECTION WILL BUILD NORTH ACROSS TEMUCO  
TO CONCEPCION WHERE IT IS TO SUSTAIN RAINFALL MAXIMA OF 05-10MM.  
LATER ON FRIDAY TO EARLY MORNING HOURS ON SATURDAY...AS THE FRONT  
SURGES ACROSS NORTHERN ARGENTINA...IT IS TO TRIGGER AN MCS ACROSS  
PARAGUAY-CORRIENTES/MISIONES IN ARGENTINA TO THE SOUTHERN STATES  
OF BRASIL. IN THIS AREA EXPECTING MAXIMA OF 75-150MM...WITH  
LOCALLY HIGHER HIGHLY PROBABLE. THIS IS TO ALSO FAVOR SEVERE  
CONVECTION...WITH POTENTIAL FOR SMALL HAIL. ON SATURDAY...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 ON THURSDAY...LIFTING ACROSS THE  
BELLINGSHAUSEN SEA TO THE DRAKE PASSAGE/SOUTHERN CONE OF SOUTH  
AMERICA 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.  
 
AT 200 HPA...OVER NORTHERN SOUTH AMERICA...A HIGH OVER NORTHERN  
BOLIVIA/RONDONIA IN BRASIL IS TO ANCHOR A CELL OF THE SUBTROPICAL  
RIDGE ACROSS NORTHWEST SOUTH AMERICA DURING THE NEXT FEW DAYS. THE  
RIDGE ALOFT IS INDUCING THE NORTHWARD AMPLIFICATION OF A SHORT  
WAVE TROUGH ACROSS THE NORTHEAST STATES OF BRASIL. THE TROUGH  
REACHES MAXIMUM AMPLITUDE ON THURSDAY-FRIDAY. 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. ON THE SOUTHERN SIERRA  
OF PERU EXPECTING MAXIMA OF 10-15MM/DAY EARLY IN THE  
CYCLE...INCREASING TO 15-20MM ON FRIDAY-SATURDAY. HIGHER AMOUNTS  
TO THE EAST ARE EXPECTED ON THE ALTIPLANO OF BOLIVIA...WHERE GDI  
SHOWS POTENTIAL FOR DEEP CONVECTION. IN THIS AREA EXPECTING MAXIMA  
OF 15-30MM DURING THE DAY TODAY...WHILE ON FRIDAY THE MAXIMA WILL  
PEAK AT 15-20MM.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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