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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1557Z May 29, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT FRI MAY 29 2020

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

FORECAST DISCUSSION FROM MAY 29/16UTC: A MID LEVEL LOW/SHORT WAVE
TROUGH ON THE SOUTHERN STREAM ENTERED THE SOUTHERN CONE. UNDER
INFLUENCE OF A RIDGE TO THE WEST AND SOUTH OF THIS AXIS...THE MID
LEVEL LOW IS TO LIFT ACROSS PATAGONIA/LA PAMPA IN ARGENTINA TO THE
BUENOS AIRES PROVINCE LATER ON SATURDAY. NOTE THAT THIS IS
CONSIDERABLY FASTER THAN WHAT THE GFS AND UKMET PREVIOUSLY
SUGGESTED...AND CLOSER TO WHAT THE ECMWF PREDICTED. THIS MOVES
ACROSS THE BUENOS AIRES PROVINCE TO THE WESTERN ATLANTIC EARLY ON
WEDNESDAY MORNING...WHILE SIMULTANEOUSLY A TRAILING SHORT WAVE
TROUGH ON THE NORTHERN STREAM REACHES THE NORTHERN REGIONS OF
CHILE. THE LATTER IS TO SLOWLY SPILL ACROSS THE ANDES INTO
NORTHWEST ARGENTINA EARLY ON MONDAY MORNING. IT IS TO THEN TRACK
ACROSS MID SECTIONS OF SOUTH AMERICA TO THE SOUTHERN STATES OF
BRASIL. AT LOW LEVELS...THESE WILL COMBINE IN SUPPORT OF A SURFACE
FRONT ACROSS THE BUENOS AIRES PROVINCE-MENDOZA IN ARGENTINA LATER
THIS AFTERNOON. AS THE MID TROUGH INTERACTS WITH THE SURFACE
FRONT...IT WILL SUSTAIN A FRONTAL LOW OVER CENTRAL ARGENTINA. THIS
IS TO RAPIDLY DEEPEN AS IT MOVES ACROSS THE BUENOS AIRES PROVINCE
TO THE WESTERN ATLANTIC ON SATURDAY-SUNDAY. THIS WILL THEN DRAW
THE SURFACE FRONT NORTH ACROSS NORTHERN ARGENTINA TO SOUTHERN
BRASIL-PARAGUAY/MATO GROSSO DO SUL-NORTHERN ARGENTINA LATER ON
SUNDAY/EARLY MONDAY MORNING. OVER LA PAMPA/SOUTHERN BUENOS AIRES
PROVINCE THE OCCLUDING SURFACE LOW WILL TRIGGER HEAVY CONVECTION
WITH MAXIMA OF 20-40MM. OVER SOUTHERN CUYO IT IS TO SUSTAIN HEAVY
SNOWFALL AMOUNTS AS THE FLOW CONVERGES ALONG THE LEE OF THE
ANDES...WITH SNOWFALL MAXIMA OF 20-30CM EARLY IN THE CYCLE. ON THE
CENTRAL ANDES OF CHILE IT IS TO TRIGGER MODERATE SNOWFALL AMOUNTS
BETWEEN LA SERENA AND SANTIAGO...WITH MAXIMA OF 05-10CM EARLY IN
THE CYCLE...INCREASING TO 10-15CM ON SATURDAY. AS THE FRONT SURGES
ACROSS ACROSS PARAGUAY TO MATO GROSSO-BOLIVIA IT IS TO INITIALLY
TRIGGER LIGHT CONVECTION WITH ACCUMULATION OF 05-10MM. ON
MONDAY-TUESDAY THE ACTIVITY SURGES WHILE BUILDING NORTH AND WEST
ACROSS NORTHERN BOLIVIA TO SOUTHERN JUNGLE OF PERU...WITH MAXIMA
OF 20-45MM.

MID LEVEL RIDGE IS TO BECOME THE DOMINANT FEATURE ACROSS THE
SOUTHERN CONE EARLY ON SATURDAY...WITH AXIS EXPECTED TO HOLD
THROUGH MONDAY MORNING. UNDER PRESSURE FROM POLAR PERTURBATIONS
STREAMING TO THE SOUTH...THE RIDGE WILL THEN WEAKEN ENOUGH TO
ALLOW A FAIRLY STRONG MID LEVEL TROUGH TO MAKE LANDFALL OVER
SOUTHERN CHILE/TIERRA DEL FUEGO LATER ON MONDAY. AT LOW LEVELS...A
MID LATITUDE RIDGE IS TO EXTEND TO THE THE EAST-SOUTHEAST ACROSS
THE EASTERN PACIFIC TO THE SOUTHERN CONE LATER TODAY. POLAR
PERTURBATIONS STREAMING UNDER THIS AXIS ARE TO CONFINE TO SOUTH
COAST OF CHILE/TIERRA DEL FUEGO DURING THE NEXT THREE DAYS. EARLY
NEXT WEEK...THE SURFACE RIDGE WILL YIELD TO A POLAR TROUGH
ENTERING SOUTHERN CHILE ON MONDAY...WITH BOUNDARY TO THEN QUICKLY
PUSH ACROSS LA PAMPA TO CENTRAL ARGENTINA/CUYO ON TUESDAY. OVER
SOUTHERN CHILE THESE ARE TO FAVOR LIGHT CONVECTION WITH MAXIMA OF
10-15MM/DAY ON SATURDAY THROUGH TUESDAY...WHILE OVER CENTRAL
ARGENTINA ONLY EXPECTING LIGHT RAINFALL EARLY NEXT WEEK.

NORTH OVER THE CONTINENT...AT 200 HPA...THE MODELS CONTINUE TO
FORECAST A CELL OF THE SUBTROPICAL TO BUILD ACROSS PERU/WESTERN
BRASIL ON FRIDAY-SATURDAY...WITH AXIS TO ANCHOR ON A CLOSED HIGH
OVER MATO GROSSO IN BRASIL. AS THE UPPER LEVEL RIDGE BUILDS...IT
IS TO DISPLACE A SHORT WAVE TROUGH ACROSS CENTRAL TO NORTHEAST
BRASIL EARLY ON SATURDAY. THE BUILDING UPPER LEVEL RIDGE WILL VENT
DEEP CONVECTION ACROSS AMAZONAS-RORAIMA IN BRASIL TO SOUTHERN
COLOMBIA...WITH MAXIMA OF 20-40MM EARLY IN THE CYCLE. ON SATURDAY
THE CONVECTION WEAKENS 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 25-50MM AS ENHANCED BY A PREFRONTAL SHEAR
LINE. THROUGH SUNDAY THIS IS TO GRADUALLY WEAKEN...DECREASING TO
MAXIMA OF 10-15MM IN SCATTERED CONVECTION.

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