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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1631Z May 27, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1231 PM EDT WED MAY 27 2020

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

FORECAST DISCUSSION FROM MAY 27/16UTC: A MID/UPPER LEVEL TROUGH ON
THE NORTHERN STREAM LIES OVER THE EASTERN PACIFIC WITH AXIS NORTH
ALONG 40W TO THE SOUTHEAST STATES OF BRASIL. AT LOW LEVELS...THIS
SUSTAINS A DEEP OCCLUDED LOW AND A SURFACE FRONT TRAILING ACROSS
ESPIRITO SANTO IN BRASIL TO ACRE/RONDONIA TO THE WEST. IT ALSO
FAVORS A PREFRONTAL SHEAR LINE ACROSS AMAZONAS. THE UPPER LEVEL
TROUGH IS TO MOVE EAST ACROSS 30W LATER TODAY...WITH AXIS TO THEN
DAMPEN AS IT ACCELERATES TO THE EAST-SOUTHEAST ACROSS THE SOUTH
ATLANTIC. AS IT LOSES ITS UPPER LEVEL SUPPORT...THE SURFACE FRONT
IS TO THEN FRONTOLIZE ON THURSDAY-FRIDAY AND THE SHEAR LINE WILL
DISSIPATE. MEANWHILE...THESE ARE TO ENHANCE LOW LEVEL MOISTURE
CONVERGENCE ACROSS NORTHERN SOUTH AMERICA. MOST INTENSE IS
EXPECTED OVER NORTHERN AMAZONAS TO SOUTHERN COLOMBIA...WHERE THE
SHEAR LINE WILL SUSTAIN MAXIMA OF 35-70MM OVER THE NEXT COUPLE OF
DAYS. OTHER CONVECTION IS EXPECTED ACROSS PIAUI-TOCANTINS TO
SOUTHERN PARA...WITH MAXIMA OF 20-35MM/DAY THROUGH THURSDAY.
FURTHERMORE...THE MEANDERING FRONT WILL SUSTAIN COASTAL CONVECTION
BETWEEN PERNAMBUCO-EASTERN BAHIA. THIS IS TO GRADUALLY INCREASE
FROM 05-10MM EARLY IN THE CYCLE TO 15-30MM/DAY ON FRIDAY-SATURDAY
AS ENHANCED BY AN EASTERLY LOW LEVEL JET.

OVER THE EASTERN PACIFIC...A TROUGH EXTENDS NORTH ALONG 80W/85W TO
40S...WITH THE LONG WAVE AXIS INTERACTING WITH A SHORT WAVE TROUGH
TO THE NORTH. ON THURSDAY THIS IS TO SLOWLY LIFT ACROSS SOUTHERN
CHILE TO PATAGONIA IN ARGENTINA...EVOLVING INTO A CLOSED LOW AS IT
LIFTS ACROSS LA PAMPA/BUENOS AIRES PROVINCE. IN CONTRAST TO
PREVIOUS RUN...THE MODELS NOW FORECAST A WEAKER AND SLOWER
PERTURBATION TO LIFT ACROSS THE SOUTHERN CONE ON SATURDAY. THE
NORTHERN STREAM PERTURBATION...MEANWHILE...IS TO MAKE LANDFALL
BETWEEN SANTIAGO-LA SERENA LATER ON SATURDAY. THE DEEP CLOSED
LOW/SHORT WAVE TROUGH IS FORECAST TO MEANDER OFF THE NORTH COAST
OF CHILE THROUGH SUNDAY EVENING...WEAKENING ENOUGH ON MONDAY TO
SPILL ACROSS THE ANDES INTO NORTHERN ARGENTINA. AT LOW
LEVELS...THE LONG WAVE TROUGH WILL SUSTAIN A FRONT ACROSS TIERRA
DEL FUEGO-SOUTHERN CHILE LATER TODAY...WHILE AN OLD BOUNDARY TO
THE NORTH EXTENDS ACROSS LA PAMPA-CENTRAL CHILE TO THE EASTERN
PACIFIC. ON THURSDAY-FRIDAY THESE BOUNDARIES ARE TO COMBINE OVER
CENTRAL ARGENTINA...TO SUSTAIN A DEEPENING/OCCLUDING LOW OVER THE
BUENOS AIRES PROVINCE ON FRIDAY. DURING THE WEEKEND THE SURFACE
FRONT IS TO SURGE ACROSS SOUTHERN BRASIL-PARAGUAY AS THE LOW
DEEPENS OVER THE WESTERN ATLANTIC. OVER SOUTHERN CHILE THIS WILL
SUSTAIN MODERATE TO HEAVY CONVECTION WITH MAXIMA OF 15-20MM EARLY
IN THE CYCLE. OVER CENTRAL ARGENTINA THIS IS EXPECTED TO RAPIDLY
INTENSIFY ON SATURDAY...WITH THE OCCLUDING LOW TO SUSTAIN A MOIST
ONSHORE FLOW ACROSS THE BUENOS AIRES/LA PAMPA...TO SUSTAIN MAXIMA
OF 20-40MM. OVER SOUTHERN CUYO...ENVIRONMENTAL CONDITIONS WILL BE
FAVORABLE FOR SNOW TO FALL/ACCUMULATE...TO SUSTAIN HEAVY SNOWFALL
AMOUNTS WITH MAXIMA OF 15-20CM. ON THE CENTRAL ANDES OF CHILE
MODELS NOW FORECAST LESSER AMOUNTS THAN ON PREVIOUS RUNS...WITH
MAXIMA OF 10-15CM ON FRIDAY-SATURDAY. AS THE FRONT SURGES ACROSS
SOUTHERN BRASIL-PARAGUAY/BOLIVIA DURING THE WEEKEND...IT IS TO
SUSTAIN LIGHT CONVECTION WITH ACCUMULATION OF 00-05MM/DAY.

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