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South American Forecast Discussion
 
(Latest Discussion - Issued 1415Z Aug 13, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1014 AM EDT THU AUG 13 2020

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

FORECAST DISCUSSION FROM AUGUST 13/14UTC: THERE IS A STRONG
CONSENSUS AMONG THE GLOBAL MODELS THROUGH 96 HRS...WITH A HIGH
AMPLITUDE RIDGE ON THE SOUTHERN STREAM STEERING SUCCESSIVE MID
LEVEL PERTURBATIONS ACROSS THE SOUTHERN CONE. THE GFS AND ECMWF
THEN FORECAST A FAIRLY DEEP PERTURBATION TO ENTER THE SOUTHERN
CONE EARLY NEXT WEEK...WHILE THE UKMET COMPLETELY OMITS THIS
PERTURBATION. ALTHOUGH THERE IS SOME VARIABILITY AMONG THE GLOBAL
ENSEMBLE MEMBERS...THE MEAN GENERALLY FAVORS THE MORE AGGRESSIVE
GFS AND ECMWF SOLUTIONS...SO THEIR SOLUTION IS FAVORED THIS CYCLE.

THE AFOREMENTIONED MID/UPPER LEVEL RIDGE IS TO REMAIN THE DOMINANT
SYNOPTIC FEATURE OVER THE EASTERN PACIFIC DURING THE NEXT FIVE TO
SEVEN DAYS...WITH RIDGE ENVELOPING AREA BETWEEN 120W-80W AND TO
THE SOUTH OF 35S. THE RIDGE...AS IT HOLDS ITS GROUND...IT IS TO
STEER SUCCESSIVE SHORT WAVE PERTURBATIONS NORTHWARD ACROSS THE
SOUTHEAST PACIFIC INTO THE SOUTHERN CONE. THE MID LEVEL TROUGHS
ARE TO THEN FEED INTO A BROAD TROUGH OVER THE CONTINENT...WITH
AXIS BOTTOMING OUT TO THE SOUTH OF 20S WHILE PRESSING AGAINST A
MID/UPPER LEVEL CELL OF THE SUBEQUATORIAL RIDGE TO THE NORTH. THE
TIGHTENING GRADIENT WILL SIMULTANEOUSLY FAVOR THE RAPID
INTENSIFICATION OF THE SUBTROPICAL JET AS IT MEANDERS EASTWARD
ACROSS THE CONTINENT BETWEEN 20S-30S...WITH THE GLOBAL MODELS
CONSISTENTLY SHOWING A WIND MAXIMA OF 130-140KT AS IT ENTERS
NORTHERN CHILE ON FRIDAY-SATURDAY. THE STRONG JET MAXIMA IN THIS
AREA SEEMS MORE CHARACTERISTIC OF WARM ENSO CONDITIONS RATHER THAN
COLDER LA NINA. AT LOW LEVELS...THE MID LEVEL RIDGE CONTINUES TO
FAVOR AN UNUSUALLY INTENSE/BROAD HIGH PRESSURE RIDGE OVER THE
SOUTHEAST PACIFIC...WITH AXIS ANCHORING ON A MASSIVE 1041-1043 HPA
HIGH. THE BROAD RIDGE WILL CONTINUE DRIVING SUCCESSIVE POLAR
VORTICES NORTHWARD ACROSS THE SOUTHEAST PACIFIC TO THE SOUTHERN
CONE...WITH PERTURBATIONS THEN STREAMING TO THE EAST-SOUTHEAST
INTO THE WESTERN ATLANTIC WHILE ROUNDING THE BROAD CONTINENTAL
TROUGH. AS A RESULT...STRONG BOUNDARY LAYER WINDS ARE EXPECTED
ACROSS THE SOUTHERN REGIONS OF CHILE-TIERRA DEL FUEGO AND
PATAGONIA IN ARGENTINA DURING THE NEXT SIX TO SEVEN DAYS. THIS
WILL HELP SUSTAIN A COLD ADVECTIVE PATTERN ACROSS SOUTHERN CHILE
TO PATAGONIA WHILE ALSO ENHANCING TOPOGRAPHICALLY INDUCED
CONVECTION ACROSS THE SOUTHERN ANDES. IN THIS AREA EXPECTING HEAVY
SNOWFALL AMOUNTS DURING THE NEXT FIVE DAYS TO CLUSTER OVER THE
SOUTHERN ANDES...PEAKING AT 20-40CM TODAY...WHILE ON FRIDAY AND
SATURDAY EXPECTING ADDITIONAL SNOWFALL AMOUNTS OF 20-30CM.

FARTHER NORTH OVER THE CONTINENT...AN ELONGATED FRONT STRETCHES
ACROSS THE WESTERN ATLANTIC TO THE SOUTHERN STATES OF BRASIL-MATO
GROSSO DO SUL TO CENTRAL BOLIVIA. THE BROAD MID/UPPER LEVEL TROUGH
AND STRENGTHENING SUBTROPICAL JET MAXIMA WILL HELP SUSTAIN THE
MEANDERING LOW LEVEL BAROCLINIC BOUNDARY DURING THE NEXT SIX DAYS.
THIS FRONT WILL THEN REMAIN THE FOCUS OF LOW LEVEL MOISTURE
CONVERGENCE ACROSS MID SECTIONS OF SOUTH AMERICA...WITH THE PWAT
CONTENT ALONG THIS BOUNDARY EXPECTED TO PEAK AROUND 30-40MM DURING
THE NEXT FEW DAYS. CONVECTION ACROSS SOUTHEAST PARAGUAY-MISIONES
IN ARGENTINA AND SOUTHERN BRASIL WILL INCREASE FROM 20-35MM EARLY
IN THE CYCLE TO 35-70MM/DAY ON FRIDAY-SATURDAY...WITH ACTIVITY TO
THEN WANE DURING THE WEAKEN TO EARLY NEXT WEEK...WHEN THE MAXIMA
PEAKS AT 20-45MM. STRONG UPPER LEVEL FORCING WOULD LIKELY RESULT
IN SEVERE CONVECTION IN THIS AREA...PARTICULARLY SO ON FRIDAY. THE
MEANDERING FRONT AND UPPER JET MAXIMA ARE TO ALSO ENHANCE
CONVECTIVE DEVELOPMENT ACROSS CENTRAL BOLIVIA...WITH MAXIMA IN
THIS AREA INCREASING FROM 10-15MM EARLY IN THE CYCLE TO 20-40MM ON
SATURDAY. PEAK IN ACTIVITY...HOWEVER...IS EXPECTED ON SUNDAY WHEN
MAXIMA IN THIS AREA INCREASES TO 30-60MM.

NORTH OVER THE CONTINENT...AT 250 HPA...MODELS MAINTAIN GOOD
CONTINUITY WITH PREVIOUS FORECASTS...WITH A CELL OF THE
SUBEQUATORIAL RIDGE TO THE NORTH OF 10S DOMINATING THE EASTERN
TROPICAL PACIFI. CONSISTENT WITH PREVIOUS FORECAST THE UPPER LEVEL
RIDGE IS FORECAST TO GRADUALLY BUILD EAST ACROSS NORTHERN
PERU/ECUADOR TO AMAZONAS IN BRASIL DURING THE WEEKEND. THIS IS TO
THEN STRENGTHEN ITS FOOTHOLD OVER THE CONTINENT EARLY NEXT WEEK.
UNDER THE INFLUENCE OF THE UPPER LEVEL RIDGE...CONVECTION ACROSS
SOUTHERN COLOMBIA TO EASTERN ECUADOR SURGES EARLY IN THE
CYCLE...WITH MAXIMA OF 20-35MM. THIS IS TO THEN SPREAD SOUTH ALONG
THE THE JUNGLE OF PERU/LEE OF THE ANDES ON FRIDAY-SATURDAY. DURING
THE WEEKEND ACTIVITY STARTS TO EBB...WITH FOCUS OF THE ACTIVITY
SHIFTING NORTH OF AMAZONAS IN BRASIL-AMAZONIA IN SOUTHERN
COLOMBIA...WITH MAXIMA OF 15-20MM IN A DIURNAL PATTERN.

DAVISON/GALVEZ...WPC (USA)