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South American Forecast Discussion
 
(Latest Discussion - Issued 1552Z Apr 24, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 AM EDT THU APR 24 2014

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

MODEL DISCUSSION (VALID FROM 24 APRIL 00UTC): GLOBAL MODELS AND
ENSEMBLE MEMBERS CONTINUE AGREEING QUITE WELL ON FORECAST
EVOLUTION. FORECAST CONFIDENCE IS HIGH. SOME DIFFERENCES ARISE
AFTER 91-108 HRS ESPECIALLY ON THE SOUTHERN CONE.

LARGE TROUGH IN THE SOUTHERN STREAM IS SLOWLY APPROACHING THE
CONTINENT. THIS TROUGH WILL START AFFECTING SOUTHERN CHILE ON DAY
02. SURFACE FRONTS WILL INTERACT WITH UPPER DYNAMICS TO PRODUCE
ACCUMULATIONS OT 10-15MM/DAY NEAR AND TO THE SOUTH OF PUERTO
MONTT. ON DAY 03...EXPECTING CONVECTIVE INSTABILITY TO INCREASE.
THIS WILL LEAD TO A LOCALIZED INCREASE IN MAXIMA TO 15-20MM/DAY.
FURTHER NORTH...STILL EXPECTING 10-15MM/DAY TO EXTEND AS FAR NORTH
AS CONCEPCION. AMOUNTS ARE TO START DECREASING AFTERWARDS. ONCE
TROUGH CROSSES INTO ARGENTINA...IT WILL LEAD TO SOME
DESTABILIZATION AND ASSOCIATED PRECIPITATION. YET...MOISTURE WILL
BE LIMITED. THIS SHOULD LIMIT MAXIMA TO 05-10MM/DAY WITH ISOLATED
HIGHER AMOUNTS IN STRONGEST THUNDERSTORMS.

LATER IN THE CYCLE...MODELS ARE VERY CONFIDENT ON UNDULATING A
SHORT WAVE TROUGH OFF THE COAST OF CENTRAL CHILE. THE TROUGH WILL
APPROACH CENTRAL/NORTHERN CHILE ON DAY 05. MOISTURE WILL BE
LIMITED IN CHILE ONCE AGAIN...YET THIS SYSTEM WILL LIKELY INCREASE
THE CHANCE FOR WIND AND SNOW IN THE CENTRAL/NORTHERN ANDES OF
CHILE. ONCE IT STARTS SPILLING ACROSS THE ANDES...THE SYSTEM WILL
INTERACT WITH BUILDING MOISTURE POOL ACROSS PARAGUAY AND SOUTHERN
BRASIL. THIS WILL LIKELY PRODUCE MODERATE RAIN ON DAYS 06 INTO
07...BUT IT IS TOO EARLY FOR DETAILS.

NORTH OVER THE CONTINENT...MOISTURE REMAINS BLOCKED TO THE NORTH
OF 15-20S. BEST VENTILATION CONTINUES TO LINGER OVER NORTHWESTERN
AMAZONIA STRETCHING FROM NORTHWESTERN/NORTHCENTRAL BRASIL INTO
ECUADOR AND COLOMBIA. THIS IS IN RESPONSE TO A WELL ESTABLISHED
SUBEQUATORIAL UPPER RIDGE OVER THE GUIANAS/NORTHERN BRASIL...AND A
RE-ESTABLISHING SUBTROPICAL HIGH ACROSS RONDONIA/ACRA/SOUTHERN
AMAZONAS IN BRASIL. EXPECTING SCATTERED DIURNAL SHOWERS AND A FEW
STRONG STORMS TO CONTINUE THROUGH THE CYCLE WITH A SLIGHT
DECREASING TREND IN ACCUMULATIONS. INITIALLY...EXPECTING STRONGEST
STORMS TO PRODUCE MAXIMA OF 25-50MM/DAY. THIS WILL DECREASE TO
20-40MM/DAY BY MID TO LATE CYCLE. MODERATE TO LOCALLY HEAVY
AMOUNTS ARE ALSO EXPECTED IN AMAPA/NORTHERN PARA ASSOCIATED WITH
AN ACTIVE ITCZ/NET AND GOOD UPPER VENTILATION.

IN BRASIL...CONVECTION IS CLUSTERING IN THE SOUTHEAST IN THE TAIL
OF TWO SURFACE FRONTS MOVING NORTHEASTWARD NEAR RIO DE
JANEIRO/SOUTHERN ESPIRITO SANTO. FURTHERMORE...THE REGION LIES IN
THE DIVERGENT ENTRANCE OF AN UPPER JET...AND ON THE DIVERGENT TIER
OF AN UPPER TROUGH. THESE FACTORS WILL ENHANCE ACCUMULATIONS
ESPECIALLY ACROSS THE SERRA DO MAR. ON DAY O1 EXPECTING LARGEST
AMOUNTS TO AFFECT MOST OF RIO DO JANEIRO INTO SOUTHERN ESPIRITO
SANTO REACHING MAXIMA OF 20-40MM/DAY. INLAND ACROSS MOST OF MINAS
GERAIS EXPECTING 15-25MM/DAY. ON DAY 02 THROUGH 04...EXPECTING
LARGEST AMOUNTS IN COASTAL LOCATIONS MOVING GRADUALLY FROM
ESPIRITO SANTO INTO MOST OF BAHIA AND ALAGOAS/SERGIPE. COASTAL
AMOUNTS WILL BE IN THE 20-45MM/DAY RANGE WHILE EXPECTING LIGHTER
AMOUNTS INLAND. A DECREASING TREND IN ACCUMULATIONS IS EXPECTED BY
LATE CYCLE...WHEREAS BY THIS TIME ACTIVITY WILL STRENGTHEN ALONG
THE NORTHERN COAST OF BRASIL. THIS WILL LEAD TO NEW ROUNDS OF
MODERATE RAINS OVER CEARA/MARANHAO INTO PARTS OF PARA.

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