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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1642Z Jun 04, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EDT THU JUN 04 2020

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

FORECAST DISCUSSION FROM JUNE 03/16UTC: A DEEPENING MID/UPPER
LEVEL TROUGH IS TO RAPIDLY BECOME THE DOMINANT SYNOPTIC SCALE
FEATURE OVER THE EASTERN PACIFIC LATER THIS EVENING...WITH AXIS TO
SPAN BETWEEN 70W-106W AND TO THE SOUTH OF 25S BY DAYBREAK ON
FRIDAY. UNDER THE INFLUENCE OF A RIDGE TO THE WEST...THE HIGHLY
AMPLIFIED TROUGH IS TO PERSIST THROUGH THE WEEKEND TO EARLY NEXT
WEEK. MEANWHILE...THE MID LEVEL TROUGH IS TO FOCUS SHORT WAVE
PERTURBATIONS AND DEEP SUBTROPICAL MOISTURE ACROSS THE SOUTHERN
REGIONS OF CHILE. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH
THAT IS TO EXTEND BETWEEN THE BELLINGSHAUSEN-WEDDELL SEAS TO THE
THE SOUTHERN CONE OF SOUTH AMERICA...FAVORING A TIGHT PRESSURE
GRADIENT AND STRONG BOUNDARY LAYER WINDS ACROSS SOUTHERN CHILE AND
PATAGONIA IN ARGENTINA. IN THIS AREA THE WINDS ARE FORECAST TO
PEAK AT 35-50KT DURING THE NEXT SEVERAL DAYS. THIS WILL ENHANCE
LOW LEVEL MOISTURE TRANSPORT AND CONVERGENCE ON THE SOUTHERN
REGIONS OF CHILE...WHILE ADIABATICALLY LIFTING ACROSS THE SOUTHERN
ANDES. THE MOST ACTIVE CONVECTION WITH THIS FEATURE IS EXPECTED
BETWEEN PUERTO MONTT AND ISLA DE CHILOE IN SOUTHERN CHILE...WITH
MAXIMA OF 20-45MM/DAY EXPECTED OVER THE NEXT TWO DAYS AND
20-30MM/DAY DURING THE WEEKEND TO EARLY NEXT WEEK. DUE TO STRONG
TOPOGRAPHICAL FORCING AND ABOVE NORMAL MOISTURE CONTENT...LOCALLY
HIGHER AMOUNTS ARE HIGHLY LIKELY. FURTHERMORE...THE INFLOW OF COLD
AIR ALOFT WOULD LIKELY FAVOR ISOLATED THUNDERSTORMS OVER SOUTHERN
CHILE DURING THE DAY ON SUNDAY THROUGH MONDAY MORNING.

ALSO OVER THE EASTERN PACIFIC...A MID/UPPER LEVEL LOW ON THE
NORTHERN STREAM MEANDERS OFF THE NORTH COAST OF CHILE. AS THE
AFOREMENTIONED TROUGH AMPLIFIES...IT IS TO DISPLACE THE NORTHERN
STREAM VORTEX EAST ACROSS THE ANDES OF CHILE TO THE NORTHWEST
PROVINCES IN ARGENTINA LATER THIS EVENING/EARLY FRIDAY MORNING.
UNDER FAVORABLE JET DYNAMICS...THE CLOSED LOW IS TO GRADUALLY
INTENSIFY/DEEPEN AS IT THEN TRACK TO THE EAST-SOUTHEAST ACROSS
NORTHERN ARGENTINA TO SOUTHERN BRASIL/URUGUAY LATER ON FRIDAY. AS
A SHORT WAVE RIDGE BUILDS TO THE EAST...THE CLOSED LOW IS TO
BRIEFLY STALL OVER URUGUAY/RIO GRANDE DO SUL THROUGH MIDAFTERNOON
ON SUNDAY...THEN WEAKEN AS IT MEANDERS EAST INTO THE WESTERN
ATLANTIC ON SUNDAY-MONDAY. AT 250 HPA...A POLAR JET MAXIMA...IN
ADDITION TO FAVOR THE RAPID INTENSIFICATION OF THE MID LEVEL LOW
ON FRIDAY...IT IS TO ALSO FAVOR AN UPPER DIVERGENT PATTERN ACROSS
URUGUAY-CORRIENTES/MISIONES IN NORTHERN ARGENTINA TO SOUTHERN
BRASIL-PARAGUAY...VENTING ORGANIZED/POTENTIALLY SEVERE CONVECTION.
AT LOW LEVELS...THE MID LEVEL VORTEX WILL SUSTAIN CYCLOGENESIS
ALONG A MEANDERING FRONT OVER CENTRAL SOUTH AMERICA...WITH CLOSED
LOW FORMING OVER CORRIENTES ARGENTINA/SOUTHEAST PARAGUAY EARLY IN
THE CYCLE. THE FRONTAL LOW IS THEN FORECAST TO DEEPEN AS IT
GRADUALLY OCCLUDES ACROSS URUGUAY TO ENTRE RIOS/CORRIENTES IN
ARGENTINA. THE DEEPENING LOW WILL THEN DRIVE THE FRONT NORTH
ACROSS SOUTHEASTERN BRASIL-MATO GROSSO TO CENTRAL BOLIVIA ON
SATURDAY-SUNDAY. OVER PARAGUAY-MISIONES IN ARGENTINA-SOUTHERN
BRASIL THIS WILL TRIGGER ORGANIZED/POTENTIALLY SEVERE CONVECTION
EARLY IN THE CYCLE...WITH MAXIMA OF 40-80MM. ON FRIDAY...AS THE
CONVECTION BUILDS EAST ACROSS PARANA/SANTA CATARINA IN BRASIL TO
SAO PAULO-MATO GROSSO DO SUL THE MAXIMA DECREASES TO
20-40MM...WHILE OVER URUGUAY-ENTRE RIOS IN ARGENTINA IT WILL SURGE
TO 30-60MM AS MOISTURE WRAPS AROUND THE OCCLUDING LOW IN SUPPORT
OF AN ECHO TRAINING PATTERN. ACROSS CENTRAL BOLIVIA...AS THE FRONT
SURGES ACROSS MID SECTIONS OF SOUTH AMERICA...IT WILL SUSTAIN
MODERATE TO HEAVY RAINFALL AMOUNTS DURING THE NEXT TWO DAYS...WITH
MAXIMA OF 20-40MM/DAY.

AT 200 HPA...A CLOSED HIGH OVER NORTHEAST BRASIL ANCHORS A RIDGE
OVER NORTHERN SOUTH AMERICA...WITH AXIS DOMINATING THE UPPER FLOW
TO THE NORTH OF 20S. CONSISTENT WITH PREVIOUS FORECASTS...THE HIGH
IS TO MEANDER TO THE WEST-SOUTHWEST DURING THE NEXT FEW
DAYS...REACHING ACRE IN WESTERN BRASIL/NORTHERN BOLIVIA LATER
DURING THE WEEKEND. AS THE RIDGE HOLDS TO THE NORTH...A
SUBTROPICAL JET IS TO BOUND THE SOUTHERN FRINGES OF THIS RIDGE
DURING THE NEXT COUPLE OF DAYS...MEANWHILE FAVORING A DIVERGENT
PATTERN ALOFT THAT IS TO VENT THE AFOREMENTIONED CONVECTION OVER
PARAGUAY-SOUTHERN BRASIL. THE RIDGE ALOFT IS TO ALSO VENT
CONVECTION ACROSS EQUATORIAL SOUTH AMERICA...WITH MOST INTENSE AS
TROPICAL WAVE STREAMING TO THE NORTH INTERACT WITH THE NEAR
EQUATORIAL TROUGH. ACROSS AMAZONAS IN BRASIL-SOUTHERN
COLOMBIA/NORTHERN PERU-EASTERN ECUADOR THIS IS TO FAVOR SEVERAL
DAYS OF SCATTERED DEEP CONVECTION WITH MAXIMA IN THIS AREA PEAKING
AROUND 30-60MM EARLY IN THE CYCLE. SCATTERED CONVECTION IS TO THEN
PERSIST THROUGH THE WEEKEND...WITH DAILY MAXIMA SETTLING AROUND
20-40MM/DAY. OTHER CONVECTION IS TO CLUSTER ACROSS AMAPA IN
BRASIL/NORTHERN PARA TO THE SOUTHERN GUIANAS...WITH MAXIMA OF
15-30MM EXPECTED OVER THE NEXT FEW DAYS.

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