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South American Forecast Discussion
 
(Latest Discussion - Issued 1709Z Nov 09, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1209 PM EST FRI NOV 09 2018

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

MODEL DISCUSSION FROM NOVEMBER 09/00 UTC: FLOW OVER THE
DOMAIN...THE MID/UPPER LEVEL FLOW SPLITS BETWEEN A RIDGE ON THE
SOUTHERN STREAM AND A SHORT WAVE TROUGH/CLOSED LOW TO THE NORTH.
THE RIDGE IS TO INITIALLY BOUND BETWEEN 100W-60W AND TO THE SOUTH
OF 50S. LATER DURING THE WEEKEND...AS A POLAR TROUGH ON THE
SOUTHERN STREAM PROGRESSES ACROSS THE SOUTHEAST PACIFIC...THE
RIDGE WILL RELOCATE ACROSS THE ANTARCTIC PENINSULA TO THE
SOUTHWEST ATLANTIC/WEDDELL SEA.

THE MID LEVEL LOW/TROUGH TO THE NORTH REMAINS THE SYSTEM OF
CONCERN. THIS IS FORECAST TO MEANDER OFF THE CENTRAL COAST OF
CHILE DURING THE NEXT THREE DAYS. AS IT MEANDERS OFF THE
COAST...THE TROUGH IS TO FOCUS THE  SUBTROPICAL AND POLAR JETS
ACROSS CENTRAL CHILE TO ARGENTINA. THIS...IN-TURN...IS TO FAVOR AN
UPPER DIVERGENT PATTERN ACROSS CENTRAL/NORTHERN ARGENTINA WHILE
ALSO FAVORING THE GENERATION OF LEESIDE PERTURBATIONS. AS SHORT
WAVE ENERGY SHEARS EASTWARD ACROSS THE CENTRAL ANDES TO CENTRAL
PROVINCES IN ARGENTINA...THIS IS TO SUSTAIN HEIGHT FALLS OF
50-75GPM/DAY...ENHANCING CONVECTIVE INSTABILITY ACROSS
CENTRAL/NORTHERN ARGENTINA. ON MONDAY THE MID LEVEL TROUGH SPILLS
ACROSS THE CENTRAL ANDES...REGENERATING BETWEEN LA PAMPA/BUENOS
AIRES PROVINCE LATER ON MONDAY. THE DEEPENING MID LEVEL LOW IS TO
THEN MEANDER EAST ACROSS THE BUENOS AIRES ON TUESDAY. 

AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS A DEEP OCCLUDED LOW TO
SOUTH-SOUTHWEST OF ARCHIPELAGO DE JUAN FERNANDEZ AND A BROAD
TROUGH OFF THE CENTRAL COAST OF CHILE. THIS IS TO MEANDER EAST AND
CLOSER TO THE COAST LATER THIS EVENING...WITH THE ASSOCIATED
SURFACE FRONT MEANDERING INLAND ACROSS SOUTHERN/CENTRAL CHILE TO
CENTRAL ARGENTINA LATER TODAY. THROUGH SUNDAY MORNING A LOW FORMS
ALONG THIS BOUNDARY OVER THE BUENOS AIRES PROVINCE. THIS IS TO
THEN GRADUALLY OCCLUDE ON MONDAY WHILE LIFTING TO THE
EAST-NORTHEAST ACROSS THE BUENOS AIRES PROVINCE. AS THE LOW
DEEPENS THIS IS TO THEN DRIVE THE FRONT NORTH ACROSS URUGUAY/RIO
DE LA PLATA BASIN TO NORTHWESTERN ARGENTINA LATER ON MONDAY. ALSO
AT LOW LEVELS...BROAD RIDGE OVER THE WESTERN ATLANTIC IS TO FAVOR
A WARM/MOIST NORTHERLY FLOW ACROSS PARAGUAY TO NORTHERN ARGENTINA.
THIS FLOW IS TO STRENGTHEN DURING THE WEEKEND AS THE FRONTAL
TROUGH OVER ARGENTINA DEEPENS. THIS FLOW WILL ENHANCE MOISTURE
TRANSPORT/CONVERGENCE OVER CENTRAL ARGENTINA...WITH PRECIPITABLE
WATER CONTENT TO INCREASE FROM 20-30MM EARLY IN THE CYCLE TO
50-60MM DURING THE WEEKEND. THIS WILL ALSO LEAD TO AN INCREASE IN
CONVECTIVE INSTABILITY ACROSS CENTRAL-NORTHERN  ARGENTINA AND RIO
DE LA PLATA BASIN/URUGUAY. ENVIRONMENTAL CONDITIONS WILL BE
FAVORABLE FOR SEVERE CONVECTION TO DEVELOP DURING THE NEXT FOUR
DAYS...WITH FORECASTED STABILITY INDICES SHOWING A HIGHER RISK ON
SATURDAY...SUNDAY AND MONDAY.  OVER CENTRAL-NORTHERN ARGENTINA THE
 LIFTED INDEX PEAKS AT -6 TO -9 ON SATURDAY...AND -9 TO -11 ON
SUNDAY. CAPE IN THIS AREA WILL RANGE BETWEEN 2800-3400...WHILE
CONVECTIVE INHIBITORS PEAK AT -150 TO -200. THIS TRANSLATES TO
LARGE HAILSTONE AND RISK OF TORNADO PRODUCING SUPERCELLS.

IN ADDITION TO FAVORING SEVERE THUNDERSTORMS...THESE ARE TO
TRIGGER HEAVY RAINFALL AMOUNTS. ACROSS THE BUENOS AIRES
PROVINCE/LA PAMPA-CENTRAL ARGENTINA THIS WILL RESULT IN RAINFALL
MAXIMA OF 40-80MM ON FRIDAY... INCREASING TO 50-100MM ON SATURDAY.
THROUGH SUNDAY HEAVY RAINS ARE TO SPREAD ACROSS MENDOZA/CORDOBA TO
THE NORTHERN PROVINCES IN ARGENTINA-URUGUAY...WITH MAXIMA OF
75-150MM. DUE TO STRONG DYNAMICAL FORCING...LOCALLY HIGHER AMOUNTS
ARE HIGHLY PROBABLE. THE COASTAL LOW IS TO ALSO FAVOR MODERATE TO
HEAVY RAINFALL AMOUNTS OVER CHILE BETWEEN CONCEPCION AND PUERTO
MONTT...WITH MAXIMA OF 20-35MM EXPECTED TODAY...AND 15-20MM ON
SATURDAY TO SUNDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO ANCHOR ON A MEANDERING HIGH OVER EASTERN BOLIVIA-MATO GROSSO IN
BRASIL. THE RIDGE ALOFT IS TO DOMINATE THE FLOW OVER THE CONTINENT
TO THE NORTH OF 30S. AS THE RIDGE HOLDS...IT IS TO GRADUALLY
INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS EASTERN
BRASIL. THROUGH SUNDAY THE TROUGH IS TO AMPLIFY ACROSS ESPIRITO
SANTO/MINAS GERAIS...TO SETTLE OVER NORTHEAST BRASIL EARLY NEXT
WEEK. AT LOW LEVELS MOISTURE CONVERGES ALONG A SURFACE TROUGH
BETWEEN SANTA CRUZ IN EASTERN BOLIVIA AND MINAS GERAIS IN BRASIL.
THIS TROUGH IS EXPECTED TO DISSIPATE DURING THE WEEKEND. AS IT
WEAKENS...MOISTURE IS TO THEN ADVECT ACROSS PARAGUAY TO CENTRAL
ARGENTINA. MEANWHILE...ACROSS MATO GROSSO-MINAS GERAIS/ESPIRITO
SANTO IN BRASIL EXPECTING MAXIMA OF 40-80MM. ON SATURDAY ACTIVITY
SPREADS NORTH ACROSS TOCANTINS/GOIAS WITH MAXIMA OF 35-70MM. ON
SUNDAY-MONDAY THIS DECREASES TO 25-50MM/DAY WHILE SPREADING ACROSS
BAHIA-SOUTHERN PARA IN BRASIL. ON THE SIERRA OF PERU AND THE
ALTIPLANO OF BOLIVIA INITIALLY EXPECTING LIGHT RAINFALL AMOUNTS.
UNDER INFLUENCE OF A SHORT WAVE TROUGH ALOFT THIS IS TO INTENSIFY
DURING THE WEEKEND-EARLY NEXT WEEK...PEAKING AROUND 20-30MM ON
SUNDAY.

SALAZAR...SENAMHI (BOLIVIA)
IZA...INAMHI (ECUADOR)
DAVISON/GALVEZ...WPC (USA)