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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1544Z Jun 08, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 AM EDT FRI JUN 08 2018

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

MODEL DISCUSSION (VALID FROM JUNE 08 AT 0000 UTC): OVER THE
CONTINENT AND WESTERN ATLANTIC THE MODELS REMAIN IN GENERAL
AGREEMENT THROUGH 108-120 HRS...WHILE OVER THE EASTERN PACIFIC
THEY START TO DIVERGE BY 96 HRS. THROUGH 144 HRS THESE DIFFERENCES
BECOME MORE PRONOUNCED AS THE MODELS FAIL TO AGREE ON THE
INTENSITY/SPEED OF SHORT WAVE VORTICES ENTERING THE DOMAIN.

ON THE NORTHERN STREAM...A MID LEVEL TROUGH EXTENDS NORTH ALONG
50W TO 20S. THIS IS FORECAST TO ACCELERATE ACROSS 30W LATER
TODAY...NEARING 15W/20W LATER ON SATURDAY. AT LOW LEVELS...THE
TROUGH ALOFT SUSTAINS AN ELONGATED FRONT THAT EXTENDS ACROSS RIO
DE JANEIRO/SOUTHERN SAO PAULO IN BRASIL TO SANTA CRUZ IN EASTERN
BOLIVIA. UNDER INFLUENCE OF A NORTHERLY LOW LEVEL JET THE TRAILING
END OF THE FRONT IS TO RETROGRESS TO SOUTHERN BRASIL-PARAGUAY ON
SATURDAY...INTO URUGUAY/SOUTHERN BRASIL-NORTHERN ARGENTINA LATER
ON SUNDAY. OVER THE ATLANTIC...THE FRONT IS TO INDUCE A PREFRONTAL
SHEAR LINE INTO THE NORTHEAST STATES OF BRASIL. THIS IS EXPECTED
TO MEANDER ACROSS THE STATE OF BAHIA ON SATURDAY-MONDAY. THE SHEAR
LINE WILL ENHANCE LOW LEVEL COASTAL CONVERGENCE TO SUSTAIN
ACCUMULATION OF 10-15MM ON SATURDAY...WHILE ON SUNDAY/MONDAY THE
MAXIMA IS TO PEAK AT 15-25MM/DAY. FRONTAL CONVERGENCE OVER RIO DE
JANEIRO/SOUTHERN MINAS GERAIS IS TO FAVOR RAINFALL AMOUNTS OF
05-10MM EARLY IN THE CYCLE. ON SATURDAY...AS THE FRONT
RETROGRESSES TO THE SOUTHERN STATES OF BRASIL-MISIONES IN
ARGENTINA IT IS TO SUSTAIN SIMILAR RAINFALL AMOUNTS.

A BROAD MID LEVEL TROUGH FOLLOWS...MOVING ACROSS THE SOUTHERN CONE
TO THE WESTERN ATLANTIC EARLY IN THE CYCLE. UNDER INFLUENCE OF
THIS TROUGH AND A RIDGE TO THE WEST...A SHORT WAVE TROUGH IS TO
THEN LIFT ACROSS THE EASTERN PACIFIC LATER TODAY...MEANWHILE
FOCUSING ITS SHORT WAVE ENERGY AND SUBTROPICAL MOISTURE ACROSS
CENTRAL CHILE. THIS IS TO THEN EVOLVE INTO A BROAD TROUGH OVER THE
CONTINENT TO THE SOUTH OF 20S LATER ON SATURDAY/EARLY SUNDAY
MORNING. ACROSS CENTRAL ARGENTINA-RIO DE LA PLATA BASIN THIS IS TO
THEN INDUCE HEIGHT FALLS OF 75-150GPM ON SATURDAY AND SUNDAY. AT
250 HPA...A SUBTROPICAL JET ROUNDING THE BASE OF THE TROUGH WILL
PHASE WITH A NORTHERN POLAR JET MAXIMA TO THE SOUTH...FAVORING A
BROAD AREA OF DIVERGENCE AS IT ENTERS CENTRAL CHILE ON SATURDAY.
ON SUNDAY THIS SHIFTS TO PARAGUAY-MESOPOTAMIA VALLEY IN ARGENTINA
AND NORTHERN URUGUAY/SOUTHERN STATES OF BRASIL. ON MONDAY-TUESDAY
THE JET IS TO THEN DRAW THE TROUGH EAST TO THE WESTERN ATLANTIC
WHERE IT IS FORECAST TO DEEPEN. AT LOW LEVELS THE ASSOCIATED FRONT
WILL EXTEND LATER TODAY FROM A BROAD TROUGH OVER THE WESTERN
ATLANTIC...ACROSS THE BUENOS AIRES PROVINCE-CONCEPCION CHILE TO AN
OCCLUDING LOW TO THE WEST. THE DEEPENING LOW IS TO THEN MEANDER
EAST ACROSS THE SOUTHERN CONE LATER ON SATURDAY/ EARLY ON SUNDAY
MORNING...DRIVING THE FRONT NORTH ACROSS LA PAMPA IN
ARGENTINA/CENTRAL REGIONS OF CHILE. ON SUNDAY THE BOUNDARY MOVES
NORTH ACROSS THE BUENOS AIRES PROVINCE-MENDOZA IN ARGENTINA. A
BUILDING POLAR RIDGE AND A STRONG PAMPERO JET...WILL THEN DRIVE
THIS FRONT FARTHER NORTH ACROSS SOUTHERN BRASIL-PARAGUAY TO
SOUTHEAST BOLIVIA LATER ON MONDAY/EARLY ON TUESDAY MORNING. NOTE
THAT LATER IN THE CYCLE THE MODELS AGREE ON THE RAPID
INTENSIFICATION OF THE ASSOCIATED SURFACE LOW...SUGGESTING THE
POSSIBILITY OF A METEOROLOGICAL BOMB.

ON THE CENTRAL COAST OF CHILE THIS IS TO SUSTAIN MODERATE TO HEAVY
RAINFALL AMOUNTS...WITH ACCUMULATION OF 20-40MM TODAY AND 20-30MM
ON SATURDAY. ON SUNDAY EXPECTING ADDITIONAL RAINFALL AMOUNTS OF
15-20MM. ON THE CENTRAL ANDES THIS IS TO SUSTAIN HEAVY SNOWFALL
AMOUNTS...WITH MAXIMA OF 25-50MM/DAY TODAY AND SATURDAY...WHILE ON
SUNDAY IT IS TO FAVOR ADDITIONAL SNOWFALL ACCUMULATION OF 15-20CM.
STORM TOTAL AMOUNTS IN EXCESS OF ONE METER ARE HIGHLY PROBABLE. AS
THE FRONT SURGES ACROSS URUGUAY-SOUTHERN
BRASIL-CORRIENTES/MISIONES IN ARGENTINA TO SOUTHEAST PARAGUAY THE
ENVIRONMENTAL CONDITIONS ARE TO BECOME FAVORABLE FOR SEVERE
CONVECTION TO DEVELOP ON SUNDAY...TRIGGERING MAXIMA OF 35-70MM. ON
MONDAY...AS IT SPREADS ACROSS SOUTHERN BRASIL...MAXIMA IS TO THEN
PEAK AT 25-50MM. OVER CENTRAL BOLIVIA...PREFRONTAL CONVECTION ON
SATURDAY-SUNDAY WILL SUSTAIN ACCUMULATION OF 15-20MM ON
SUNDAY...INCREASING TO 20-30MM ON MONDAY. PEAK IN
ACTIVITY...HOWEVER...IS EXPECTED ON TUESDAY WHEN UNDER FAVORABLE
JET DYNAMICS THE MAXIMA INCREASES TO 20-45MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A BROAD/OPEN RIDGE IS TO
CONFINE TO AREA TO THE NORTH OF 10S. LATER IN THE CYCLE THE RIDGE
GRADUALLY BECOMES BETTER ORGANIZED WHILE SLOWLY BUILDING SOUTH
ACROSS BOLIVIA. AS IT MEANDER TO THE NORTH...THE RIDGE ALOFT WILL
VENT DEEP CONVECTION ACROSS EQUATORIAL SOUTH AMERICA. MOST ACTIVE
IS TO INITIALLY CLUSTER ACROSS AMAZONAS IN BRASIL TO SOUTHERN
COLOMBIA/NORTHERN PERU...WITH MAXIMA OF 20-40MM/DAY OVER THE NEXT
TWO DAYS. LATER DURING THE WEEKEND IT DECREASES TO
15-30MM/DAY...WITH MOST ACTIVE AFFECTING EASTERN ECUADOR-NORTHERN
PERU-SOUTHERN COLOMBIA. ACROSS PARA-AMAPA TO THE EAST THE DAILY
MAXIMA IS TO INITIALLY PEAK AROUND 15-20MM. LATER DURING THE
WEEKEND THIS DECREASES TO 05-10MM/DAY IN MOSTLY ISOLATED
CONVECTION.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON...WPC (USA)