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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1606Z Apr 16, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1206 PM EDT WED APR 16 2014

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

MODEL DISCUSSION (VALID FROM 16 APRIL 00UTC): GLOBAL MODELS AND
ENSEMBLE ARE IN EXCELLENT AGREEMENT THROUGH 72/84 HRS. FORECAST
CONFIDENCE DECREASES AFTERWARDS AS LARGE WAVE TROUGHS ORGANIZE IN
THE SOUTHERN CONE.

BROAD LONG WAVE TROUGH CENTERS OVER THE SOUTHERN CONE. MODELS
CONTINUE FORECASTING THE MAIN TROUGH MOVING VERY LITTLE WHILE
SHORT WAVE TROUGHS EVOLVE IN ITS PERIPHERY. A SURFACE FRONT IS
MOVING ACROSS CENTRAL ARGENTINA AND WILL REACH THE CENTRAL BUENOS
AIRES PROVINCE BY 24 HRS...NORTHERN URUGUAY-TUCUMAN BY 48 HRS TO
THEN DECREASE IN SPEED ACROSS RIO GRANDE DO SUL-CHACO IN
ARGENTINA. INITIALLY...THE FRONT WILL HAVE VERY LITTLE EFFECTS ON
PRECIPITATION. BY 36-48 HRS...MOISTURE RETURN AIDED BY A LOW-LEVEL
JET ACROSS PARAGUAY WILL LEAD TO AN INCREASE IN INSTABILITY. A
SHORT WAVE TROUGH ARRIVING FROM THE SOUTHWEST WILL ALSO INCREASE
CYCLONIC VORTICITY ADVECTION AND HEIGHT FALLS ACROSS NORTHEASTERN
ARGENTINA...AIDING CONVECTIVE DEVELOPMENT. EXPECTING THUNDERSTORMS
TO PRODUCE ACCUMULATIONS OF 25-50MM/DAY FROM THE CHACO
PARAGUAYO/FORMOSA IN ARGENTINA INTO NORTHERN URUGUAY AND RIO
GRANDE DO SUL IN BRASIL. MAXIMA WILL DECREASE TO 20-40MM/DAY BY
60-84 HRS WITH ACCUMULATIONS CONCENTRATING OVER MOST OF PARAGUAY
INTO SOUTHERN BRASIL. ON DAY 04 EXPECTING ACCUMULATIONS DECREASING
TO 20-30MM/DAY AS THEY CONCENTRATE IN PARTS OF SOUTHERN AND
SOUTHEASTERN BRASIL.

AFOREMENTIONED SHORT WAVE UPPER TROUGH APPROACHING ON DAYS 02 AND
03 WILL ENHANCE ACCUMULATIONS ACROSS SOUTHERN CHILE. SHOWERS WILL
BECOME MORE NUMEROUS AND HEAVY ON DAY 02 LEADING TO DAILY MAXIMA
OF 15-20MM/DAY FROM OSORNO/VALDIVIA TO PARTS OF THE MAGALLANES
REGION. AMOUNTS ARE TO RAPIDLY DECREASE AFTERWARDS.

DIURNAL CONVECTION IN SOUTHEASTERN BRASIL IS DECREASING IN
INTENSITY TO THE NORTH OF A WEAKENING COLD FRONT OFF THE COAST OF
RIO DO JANEIRO. DIURNAL SHOWERS AND THUNDERSTORMS WILL STILL
PRODUCE ISOLATED MAXIMA APPROACHING 10-15MM/DAY ON DAY 01 TO
DECREASE AFTERWARDS.

NORTH OVER THE CONTINENT MOST ACTIVE CONVECTION CONCENTRATES NOW
TO THE NORTH OF THE EQUATOR COVERING MOST OF THE CONTINENT...FROM
THE AMAZON DELTA INTO COLOMBIA AND SOUTHERN VENEZUELA. EXPECTING
THIS REGION TO PERSIST SEASONALLY ACTIVE THROUGH THE CYCLE WITH
DIURNAL ACCUMULATIONS OF 20-35MM/DAY. ISOLATED HIGHER AMOUNTS ARE
ALWAYS POSSIBLE IN STRONGEST THUNDERSTORMS. ISOLATED TO SCATTERED
SEASONAL CONVECTION WILL ALSO AFFECT NORTHEASTERN BRASIL WITH
ACCUMULATIONS GENERALLY IN THE 15-20MM/DAY RANGE.

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