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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1535Z Apr 14, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1135 AM EDT MON APR 14 2014

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

MODEL DISCUSSION (VALID FROM 14 APRIL 00UTC): GOOD AGREEMENT AMONG
GLOBAL MODEL GUIDANCE THROUGH 72-84 HRS. MODELS THEN DIVERGE ON
THE SPEED/AMPLITUDE OF SHORT WAVE PERTURBATIONS ENTERING THE SOUTH
AMERICAN DOMAIN. AS A RESULT...OUR CONFIDENCE IN THE FORECAST
BEYOND 84/96 HRS IS LOW.

BROAD MID LEVEL TROUGH IS INITIALIZED OVER THE WESTERN ATLANTIC.
THROUGH 48-60 HRS THE TROUGH WILL PULL TO THE EAST-SOUTHEAST. AS
IT PULLS AWAY...THE ASSOCIATED SURFACE FRONT IS TO GRADUALLY LOSE
UPPER LEVEL SUPPORT AND START TO FRONTOLIZE. EARLY IN THE CYCLE
THE FRONT IS TO EXTEND ACROSS SAO PAULO-MATO GROSSO-RONDONIA IN
BRASIL TO NORTHERN BOLIVIA. THROUGH 48-60 HRS IT IS TO THEN
FRONTOLIZE OVER THE CONTINENT...WHILE REMNANTS OVER THE ATLANTIC
MEANDER OFF THE COAST OF SAO PAULO/RIO DE JANEIRO. MOISTURE IS
CONVERGING ALONG AND NORTH OF THE WANING FRONT...TO CLUSTER ALONG
A LINE FROM AMAZONAS/ ACRE IN WESTERN BRASIL TO SAO PAULO/RIO DE
JANEIRO. IN THIS AREA EXPECTING RAINFALL MAXIMA OF 20-35MM THROUGH
36 HRS. AS THE FRONT WEAKENS...MOST ACTIVE IS EXPECTED ACROSS SAO
PAULO AND RIO DE JANEIRO WITH MAXIMA OF 15-25MM. FURTHERMORE...A
POLAR RIDGE LIES TO THE SOUTH OVER ARGENTINA.
THIS...IN-TURN...FAVORS A BRISK SOUTHEASTERLY FLOW ACROSS
PARAGUAY-BOLIVIA TO WESTERN BRASIL/ PERUVIAN JUNGLE. THE SOUTHERLY
JET IS ENHANCING MOISTURE CONVERGENCE ACROSS CENTRAL/WESTERN PERU
AND PORTIONS OF AMAZONAS IN BRASIL. IN THIS AREA EXPECTING
RAINFALL MAXIMA OF 25-50MM THROUGH 36 HRS. THROUGH 72-96 HRS THIS
WILL DECREASE TO 20-35MM IN SCATTERED CONVECTION.

BROAD TROUGH OVER THE EASTERN PACIFIC IS TO FOLLOW...WITH MID
LEVEL VORTEX MAKING LANDFALL OVER SOUTHERN CHILE BY 24 HRS.
THROUGH 60-72 HRS THIS IS TO SLOWLY PUSH ACROSS CHILE TO PATAGONIA
IN ARGENTINA... WITH AXIS NORTH ALONG 60W TO ENTRE RIOS IN
ARGENTINA. THIS IS TO THEN START TO WEAKEN AS IT PULLS TO THE
EAST-SOUTHEAST THROUGH 132 HRS.AT LOW LEVELS THIS SI TO SUSTAIN A
BROAD TROUGH ACROSS THE BELLINGSHAUSEN SEA TO SOUTHERN
CHILE/PATAGONIA IN ARGENTINA. POLAR FRONTS ARE TO REVOLVE AROUND
THIS AXIS...WITH ONE THAT PULLS ACROSS SOUTHERN CHILE TO PATAGONIA
BY 24 HRS...THEN WEAKENING AS IT MOVES NORTH ACROSS LA PAMPA IN
ARGENTINA. AS IT ENTERS SOUTHERN CHILE THIS IS TO TRIGGER
SCATTERED CONVECTION WITH RAINFALL AMOUNTS OF 15-20MM...WHILE OVER
PATAGONIA/LA PAMPA IT IS TO RESULT IN WIDELY ISOLATED COASTAL
CONVECTION.

A MORE RESILIENT FRONT FOLLOWS...ENTERING SOUTHERN CHILE BY 48
HRS...THEN NORTH ACROSS LA PAMPA TO THE BUENOS AIRES
PROVINCE/CORDOBA IN ARGENTINA. ACROSS SOUTHERN CHILE THIS IS TO
ALSO FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF 10-15MM. AS
IT PRESSES NORTH ACROSS ARGENTINA BY 72 HRS...AND AS A MOIST
NORTHERLY JET ESTABLISHES ACROSS BOLIVIA/PARAGUAY THIS IS LIKELY
TO TRIGGER ORGANIZED DEEP CONVECTION ACROSS THE NORTHERN PROVINCES
IN ARGENTINA/PARAGUAY-MESOPOTAMIA VALLEY AND OVER URUGUAY/RIO
GRANDE DO SUL IN BRASIL. IN THIS AREA THE RAINFALL MAXIMA WILL
PEAK AT 25-50MM BY 96-108 HRS.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE
CONTINUES TO WEAKEN AS COOLER/DRYER AIR ADVECTS ACROSS
PARAGUAY-BOLIVIA TO NORTHERN PORTIONS OF SOUTH AMERICA. THROUGH
48-72 HRS THE ILL ORGANIZED RIDGE IS EXPECTED TO WEAKEN INTO AN
OPEN RIDGE OVER NORTHERN BRASIL. DIURNAL CONVECTION ACROSS BRASIL
IS TO ALSO WEAKEN...WITH MOST ACTIVE ALONG AND SOUTH OF THE
EQUATOR TO RESULT IN ACCUMULATION OF 15-20MM. HIGHER AMOUNTS ARE
EXPECTED TO THE NORTH...ACROSS VENEZUELA-COLOMBIA TO NORTHERN
PORTIONS OF AMAZONAS IN BRASIL WITH ACCUMULATION OF 20-35MM/DAY.

ITA...SENAMHI (PERU)
FERNANDES...INMET (BRASIL)
DAVISON...WPC (USA)