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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1920Z Sep 11, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 PM EDT TUE SEP 11 2018

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM SEP 11 AT 0000 UTC): MODELS CONTINUE
IN GOOD AGREEMENT ON THE EVOLUTION OF THE FORECAST THROUGH 72-96
HRS. FROM 96 HRS AND ON THE SOLUTIONS START TO DIVERGE TO THE
SOUTH OF 50S. CONFIDENCE AFTER 96 HRS IS LOWER THAN YESTERDAY OVER
ALL THE DOMAIN. ANOTHER REGION WHERE MODELS ARE STRUGGLING...IS
WITH THE CROSSING OF TWO TROUGHS INTO ARGENTINA FROM 96 HRS AND
ON. THE GFS WAS THE SLOWEST OF ALL MODELS...AND HAS NOW CORRECTED
TO THE UKMET AND ECMWF SOLUTION...CROSSING THE TROUGH LATE ON DAY
4.

SOUTH OF 50S...A MID-UPPER LEVEL TROUGH IS SLOWLY CROSSING THE
SOUTHERN CONE OF THE CONTINENT. SEVERAL SURFACE FRONTS WILL CROSS
OVER THE ANDES FROM CHILE TO SOUTHERN PATAGONIA LEAVING LIGHT
RAINFALL AMOUNTS AS THERE WILL BE LITTLE MOISTURE AVAILABLE
THROUGH MOST OF THE CYCLE. OVER SOUTHERN CHILE...RAIN AND SNOW IS
EXPECTED FOR TUESDAY...SUSTAINING 05-10MM. BY WEDNESDAY/THURSDAY A
WEAK SUBTROPICAL MOISTURE CONNECTION WILL ARRIVE FROM THE
PACIFIC...AND ENHANCED BY VERY STRONG 60 KT WINDS AT 850
HPA...WILL SUSTAIN 15-20MM/DAY FROM WEDNESDAY THROUGH FRIDAY.
AMOUNTS WILL THEN DECREASE TO 05-10MM ON FRIDAY/SATURDAY.

OVER THE ATLANTIC...A 1032 HPA HIGH IS HELPING TO GRADUALLY
REBUILD A MOISTURE POOL OF OVER 38MM OF PRECIPITABLE WATER OVER
CENTRAL AND NORTH ARGENTINA...AS IT ENHANCES A NORTHERLY LOW LEVEL
FLOW OVER THE CENTER OF THE CONTINENT. THIS WILL INTERACT WITH A
COLD FRONT CROSSING THE ANDES ON TUESDAY. ALSO...A MID LEVEL
TROUGH WITH A NEGATIVE AXIS WILL CROSS OVER THE SAME REGION ON
WEDNESDAY/THURSDAY...ENHANCING UPPER LEVEL DIVERGENCE...THAT WILL
SUSTAIN MODERATE TO HEAVY RAINFALL AMOUNTS AND SEVERE WEATHER. FOR
TUESDAY...INITIALLY...AMOUNTS OF 20-30MM/DAY ARE EXPECTED OVER
SOUTHERN BUENOS AIRES PROVINCE...AND 10-15MM OVER SAN LUIS/LA
PAMPA/BUENOS AIRES IN ARGENTINA. ON WEDNESDAY...AS THE SURFACE
FRONT MEANDERS NORTH...AMOUNTS OF 15-20MM ARE EXPECTED OVER
CENTRAL ARGENTINA AND 20-30MM OVER NORTHERN ARGENTINA. BY
THURSDAY...AS THE UPPER LEVEL TROUGH SPILLS OVER THE
ANDES...AMOUNTS OF 20-40MM ARE EXPECTED OVER PARAGUAY AND MISIONES
IN ARGENTINA...AND 15-25MM WITH POSSIBLE SMALL HAIL OVER SOUTHERN
BRASIL. CHANCE OF SEVERE WEATHER WILL ALSO BE PRESENT BY FRIDAY
WITH LOWER RAINFALL AMOUNTS OF 05-10MM OVER EASTERN
PARAGUAY/MISIONES/SOUTHERN BRASIL. FURTHER NORTH...AMOUNTS WILL
PEAK AT 20-30MM OVER THE SOUTHEASTERN BRASIL AND 10-15MM OVER
BOLIVIA AND SOUTHWESTERN BRASIL. LATER ON THE CYCLE...RAINFALL
AMOUNTS WILL INCREASE AGAIN OVER CENTRAL AND NORTHERN ARGENTINA.

TO THE NORTH...OVER THE ATLANTIC COAST OF BRASIL TWO WEAK SURFACE
FRONTS WILL SUSTAIN LIGHT RAINFALL AMOUNTS AS THEY MEANDER
NORTHWARD...TO FINALLY EXIT TO THE ATLANTIC. THROUGH EARLY
WEDNESDAY EXPECTING MAXIMA OF 10-15MM/DAY IN RIO DE JANEIRO AND
MAXIMA OF 00-05MM IN THE NORDESTE. THIS WILL DECREASE TO MAXIMA OF
05-10MM/DAY IN ESPIRITO SANTO ON THURSDAY AND AFTER...WHILE
EXPECTING ISOLATED AMOUNTS TO THE NORTH.


OVER THE ANDES OF PERU AND BOLIVIA...ISOLATED DIURNAL STORMS ARE
EXPECTED TO SUSTAIN LIGHT RAINFALL ACCUMULATIONS THROUGH FRIDAY.
BY SATURDAY...AS A MID-UPPER LEVEL TROUGH CROSSES OVER THE
ANDES...AND LOW LEVEL MOISTURE CONVERGENCE IS ENHANCED FROM THE
AMAZON...AN INCREASE IN RAINFALL AMOUNTS IS EXPECTED TO PRODUCE
20-40MM/DAY BY SATURDAY-SUNDAY.

ALSO OVER TROPICAL SOUTH AMERICA...A BROAD UPPER LEVEL RIDGE IS
EXPECTED TO PERSIST OVER THE ENTIRE CYCLE...SUSTAINING VENTILATION
FOR CONVECTION. OVER THIS PERIOD RAINFALL AMOUNTS OF 15-20MM ARE
EXPECTED OVER NORTHERN PERU/AMAZONAS/COLOMBIA/PARA IN BRASIL. ON
TUESDAY...THE TROUGH/TROPICAL WAVE ASSOCIATED WITH TROPICAL
CYCLONE ISAAC TO THE NORTH WILL PROPAGATE ACROSS SURINAME ON
TUESDAY...TO REACH THE ANDES ON SATURDAY...AND WILL ENHANCE
RAINFALL AMOUNTS AS IT MEANDERS WEST. 20-30MM ARE EXPECTED OVER
GUYANAS/VENEZUELA ON TUESDAY/WEDNESDAY...20-40MM OVER
VENEZUELA/COLOMBIA ON THURSDAY...AND INCREASING TO 25-50MM...AS
THE WAVE FINALLY EXISTS TO THE PACIFIC OCEAN OFF THE COASTS OF
COLOMBIA.

SANCHEZ...SMN (ARGENTINA)
SALAZAR...SENAMHI (BOLIVIA)
GALVEZ...WPC (USA)