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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1639Z May 28, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 PM EDT THU MAY 28 2020

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

FORECAST DISCUSSION FROM MAY 28/16UTC: UPPER LEVEL ANALYSIS SHOWS
A CLOSED LOW ENTERING THE SOUTHERN REGIONS OF CHILE. THIS IS
SLOWLY PHASING WITH A BROAD TROUGH TO THE NORTH THAT CENTERS ON A
CLOSED LOW TO THE NORTH-NORTHWEST OF THE ARCHIPELAGO DE JUAN
FERNANDEZ. THESE ARE NOW FORECAST TO GRADUALLY MERGE THROUGH
FRIDAY EVENING/SATURDAY MORNING...WITH THE LOW TO THE SOUTH MOVING
ACROSS TEMUCO CHILE TO SOUTHERN CUYO/LA PAMPA IN ARGENTINA ON
SATURDAY WHILE THE ONE TO THE NORTH FILLS TO AN OPEN TROUGH. IN
THIS CYCLE THE GFS CORRECTED IN FAVOR OF A SLOWER EVOLUTION OF
THIS FEATURE...CLOSELY MATCHING THE UKMET FORECAST THROUGH THE
MEDIUM RANGE PERIOD. THE ECMWF...HOWEVER...CONTINUES TO FORECAST A
FASTER PROGRESSION ACROSS ARGENTINA TO THE WESTERN ATLANTIC. THE
EUROPEAN ENSEMBLES SUPPORT THE FASTER ECMWF...WHILE THE CANADIAN
AND GFS ENSEMBLE MEMBERS SUPPORT THE SLOWER SOLUTION. THIS LEADS
TO LOWER CONFIDENCE IN THE FORECAST BEYOND 72/84 HRS...AS FURTHER
CORRECTIONS ARE LIKELY TO FOLLOW IN FUTURE RUNS OF THE MODELS.

AT LOW LEVELS...THE SOUTHERN STREAM LOW SUSTAINS A FRONTAL WAVE
THAT PULLS ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER
TODAY...WITH AXIS TO THEN PHASE WITH A MEANDERING FRONT TO THE
NORTH ON FRIDAY. ON FRIDAY-SATURDAY...AS ENHANCED BY THE MID LEVEL
TROUGH...THE SURFACE FLOW IS FORECAST TO DEEPEN WHILE GRADUALLY
OCCLUDING. THE DEEPENING/OCCLUDING LOW WILL THEN SUSTAIN A MOIST
EASTERLY FLOW ACROSS THE BUENOS AIRES/LA PAMPA IN ARGENTINA TO
SOUTHERN CUYO IN ARGENTINA. THIS WILL FAVOR ORGANIZED CONVECTION
ACROSS LA PAMPA/BUENOS AIRES PROVINCE...WITH MAXIMA IN THIS AREA
INCREASING FROM 20-45MM ON FRIDAY TO 30-60MM ON SATURDAY. THE
MOIST INFLOW...AS IT CONVERGES/ADIABATICALLY LIFTS ALONG THE
EASTERN SLOPES OF THE ANDES OVER CENTRAL ARGENTINA WILL SUSTAIN
SOLID PRECIPITATION...WITH SCATTERED SNOW SHOWERS TO SUSTAIN
ACCUMULATION OF 20-30CM. ON THE CENTRAL ANDES OF CHILE THIS IS TO
INITIALLY FAVOR ACCUMULATION OF 05-10CM...INCREASING TO 15-20CM ON
FRIDAY-SATURDAY. THE DEEPENING FRONTAL LOW WILL THEN FAVOR A
PAMPERO LOW LEVEL JET ACROSS ARGENTINA THAT DISPLACES THE FRONT
NORTH ACROSS SOUTHERN BRASIL=PARAGUAY TO MATO GROSSO DO
SUL/NORTHERN BOLIVIA EARLY ON MONDAY MORNING. MEANWHILE...ACROSS
URUGUAY THIS WILL SUSTAIN RAINFALL ACCUMULATION OF 15-25MM...WHILE
OVER SANTA CRUZ/CENTRAL BOLIVIA IT WILL INCREASE FROM 05-10MM ON
SUNDAY TO 20-35MM ON MONDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A CELL OF THE SUBTROPICAL
RIDGE IS TO BUILD ACROSS PERU/WESTERN BRASIL ON FRIDAY-SATURDAY.
AS THE UPPER LEVEL RIDGE BUILDS...IT IS TO DISPLACE A SHORT WAVE
TROUGH ACROSS CENTRAL TO NORTHEAST BRASIL EARLY ON SATURDAY. THE
BUILDING RIDGE WILL VENT DEEP CONVECTION ACROSS AMAZONAS-RORA0MA
IN BRASIL TO SOUTHERN COLOMBIA...WITH MAXIMA OF 35-70MM EARLY IN
THE CYCLE. ON FRIDAY THIS DECREASES TO 20-40MM...WHILE ON SATURDAY
THE MAXIMA DWINDLES TO 10-15MM/DAY. ACROSS PARA-AMAZONAS IN
BRASIL...THE TROUGH WILL THEN SUSTAIN AN INCREASE IN DIURNAL
CONVECTION...INCREASING FROM 10-15MM/DAY EARLY IN THE CYCLE TO
20-35MM/DAY LATER DURING THE WEEKEND/EARLY NEXT WEEK. OTHER
CONVECTION IS EXPECTED ON THE NORTHEAST COAST OF BRASIL AS THE
UPPER LEVEL TROUGH INTERACTS WITH A SURFACE FRONT MEANDERING OVER
NORTHERN BAHIA. THIS FAVORS A STRONG EASTERLY FLOW THAT WILL
ENHANCE LOW LEVEL MOISTURE CONVERGENCE. IN THIS AREA INITIALLY
EXPECTING MAXIMA OF 20-30MM...INCREASING TO 25-50MM ON
FRIDAY-SATURDAY. THIS IS TO THEN GRADUALLY WEAKEN LATER ON
SUNDAY-MONDAY.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)